If a 24V system with battery buffer is desired then it is common practice to wire two commercially available 12 volt batteries in series.
With this technique, the batteries must be paired and have the same load and ageing state. If this is not the case overloading, destruction or premature ageing of one of the batteries could occur.
To prevent this happening PULS has developed the one battery concept. Only one 12V battery is used for UPS up to 10A. In the case of a buffer a switching regulator converts the battery supply to a constant output voltage (22.5V, for example). More powerful UPS use two batteries in series. Each battery is loaded and monitored individually so that none of the described problems can arise.
In practice, a 50% longer battery service life can usually be achieved. The method avoids having to use paired batteries and reduces potential dangers.
The 19-inch-rack system is a modular construction system in accordance with the DIN 41494. The system is comprised of plug-ins circuit cards, a card carrier and 19-inch-rack cabinets, all of which can be matched and combined.
The most important system dimensions in the 19-inch-rack system are:
- 1 HP: unit width 5.08mm
- 1 U unit height 44.45mm
- Circuit board standard:
European format 3 HE: 100x160mm
Double European format 6 HE: 233x160mm
- Circuit board depth:
European format 3 HE depth: 100x160mm
Double European format 6 HE depth: 233x160mm
The 19-inch-rack system was a common mounting system from the 1970s up to the 90s and was often used in the field of measuring technology, computer technology, and industrial electronics.
With the AP and APD series PULS offers various power supply options for 19-inch-rack systems.
3-D data are tridimensional mechanical designs of power supplies and devices in electronic format.
In the product section of our website the 3D data formats ".stp" and ".dwf" of many PULS devices are available for download.
The adjustment range commonly is the guaranteed output voltage trim range. This enables compensation of voltage drops on long supply lines.
The ambient temperature is defined as the air inlet temperature 2cm below the device.
PULS differentiate between the working temperature and the storage and transport temperature.
AP devices are PULS power supplies and DC/DC converters using 19-inch technology.
AS-Interface® (actuator-sensor interface) is a bus system in which energy and data are transmitted on a common two-wire line. One identifying feature of the bus system is the yellow profiled cable.
The AS-Interface® Power Supply Systems supply AS-Interface ®bus devices such as actuators and sensors. The nominal voltage of the bus is 30.5V. An AS-Interface®power supply is equipped with data decoupling which prevents the modulated signals on the DC line from being impaired. The output of this power supply is inductive and may not be used for other consumers.
The specification and certification of this bus system is overseen by the AS-Interface® association (www.as-interface.org). The association publishes the specification and assumes the task of certification of AS-Interface® approved components.
ATEX (French: “Atmosphère Explosible”)
PULS is offering ATEX power supplies and accessories which are tested according to EN 60079-0 and EN 60079-15 and comply with the ATEX Directive. These devices may be used in systems in potentially explosive atmospheres of zone 2, category 3G.
Auto select input
1-phase power supplies with an auto-select or auto-range input detect the input voltage and automatically select the correct input voltage range.
Autotransformers are matching transformers without galvanic isolation. A portion of the winding is jointly used by both the input and output side.
AWG (American Wire Gauge) specifies the diameter of the wire and the cross section of wires. The AWG system is mainly used in North America.
Decelerating motors and inductors can feed voltage back to the power supply output. The output
can absorb a certain amount of energy in the output capacitors and thereby increase the output voltage. The back EMF is the maximum voltage that may occur at the output of the power supply.
24V PULS power supplies tolerate a maximum of 35V at the output terminals. During electrical feedback the power supply does not switch off and when the feedback ends the power supply provides power immediately with no drop in the output voltage.
The base load is the minimum load required at one or more of the outputs of a multi voltage power supply unit which is necessary for proper function If the minimum base load value is not maintained, the power supply will not suffer damage but it may lead to significant deviations in the output voltage or an interruption of the power supply.
The BonusPower® property describes the permitted short time overload factor by which a power supply may be overloaded. Typically this is 50% more power for a period of 4 seconds.
Almost all DIMENSION Q Series devices have the BonusPower® property.
Fast transient electrical disturbances (e.g. on the power line) are referred to as burst.
Burst frequencies are in the range of a few kilohertz up the megahertz range and the impulse voltages in between the range from 100V to several 1000V.
The minimum requirements for immunity to fast transients (burst) are laid down in EN 61000-6-2. Test conditions can be found in EN 61000-4-4.
The CB Scheme is an international agreement on the mutual recognition of test results currently endorsed by approximately 60 national testing organizations in more than 40 countries.
The harmonized IEC standards in conjunction with the national deviations of each country are used as the basis for the scheme.
A unified report form and a review of test laboratories according to set standards ensure that the testing methods in all test laboratories are the same and the quality of the test results is guaranteed. All participating countries must recognize the CB Scheme report and award a national test mark on this basis.
PULS offers a CB Scheme according to IEC 60950-1 for numerous devices.
The chassis ground is a port on a device to which a metallic casing with a protective conductor system or the machine ground can be connected.
Even if it is not necessary to connect the protective conductor system for personnel safety reasons, some applications (such as ATEX) may require that metal parts of a particular mass are grounded to prevent sparks resulting from electrostatic discharge.
Common mode disturbances
Common mode disturbances are interference voltages on the power supply line or load lines which spread with the same phase positions with regard to the earth or ground on both the supply and return lines.
Remedial measures for common mode disturbances are current compensated chokes, Y-capacitors or capacitors between the lines and the ground or earth.
With the conformal coating option the circuit boards in the device are provided with an acrylic resin based protective coating.
PULS is offering a selection of devices from the standard power supply range with the option of "protective coating" from stock.
Convection cooling is a passive cooling without forced cooling with fans. The heat flow is based on natural convection. Heated air particles have lower density, they therefore rise as a result of gravity and thereby cause movement of the air.
The crest factor describes the ratio between peak and RMS of an alternating quantity.
For a sinusoidal alternating voltage with an RMS of 230V and a peak of 325V the crest factor is 1.41.
The crest factor is of practical importance in AC UPS systems. These set a maximum crest factor or the maximum peak of the output stream. Crest factor values can be found in the PULS product data sheets.
''Cross regulation'' refers to the change of the output voltage of a multi-voltage power supply which is caused by a load change on other outputs.
A crowbar is a method used to limit the maximum output voltage of a power supply.
In the event of overvoltage the output is short circuited by an electronic switch, (a thyristor or suppressor diode, for example), which protects connected consumers from damage. Crowbar circuits are not self-resetting. To reset the circuit the power supply must be switched off.
For limiting the maximum output voltage PULS uses a second, redundant designed control loop (overvoltage protection OVP) and only rarely a crowbar.
"Daisy Chaining" refers to connecting devices by cascading, which means they are not star-wired but linked through a single line to ground.
With "Daisy Chaining" it makes sense if the devices are equipped with double terminals (as is mostly the case with PULS).
Be careful with the terminal clamp load: The maximum specified terminal current to the clamp must not be exceeded even at the last device. Values for this purpose can be found in the product data sheets.
The DC-OK signal (also called ''power good signal'') monitors the output voltage that is generated from the power supply and is independent of whether an external voltage is fed into the system or not (e.g. from a parallel power supply).
This signal can be used to monitor the power supply with redundant applications. In most cases the DC-OK signal is performed via a relay contact (NO contact).
With PULS devices the contact is closed if the generated voltage is greater than 90% of the preset output voltage. If the voltage is less, the contact opens. Short interruptions up to 1ms are ignored; longer interruptions are extended to a minimum time of 100ms.
Derating describes a necessary reduction of the maximum output power under specific operating conditions.
Derating may be necessary for example with:
- low input voltages
- high temperatures
- extremely low temperatures
- mounting positions which deviate from standard
- installation altitudes above 2000m
In many cases, a reduction of the maximum permitted ambient temperature or the use of forced ventilation (fan) offer a possible alternative to derating.
The user is responsible for observing the derating. The devices have no automatic derating control. Brief periods of exceeding the permitted power usually do not cause any problems; longer periods may trigger thermal shutdown.
DeviceNet™ is an open sensor actuator bus system with worldwide coverage. The power supply of this fieldbus is via two wires of a multi-pin cable.
Special features of the DeviceNet™-power supplies are:
- The nominal currents are adapted to the DeviceNet™-cables.
- Large bus device capacities can be provided at an allotted time.
- During the ramp-up of the output voltage the predetermined DeviceNet™- timing is held.
- The output is adapted exactly to the DeviceNet™-voltage.
PULS offer two power units for this bus system, the QS5.DNET and the QS10.DNET.
Both devices are tested by the independent user group Open DeviceNet™ Vendor Association (ODVA) and bear the approval mark "DeviceNet™ Conformance Tested".
Differential mode disturbances
Differential mode disturbances are interference voltages in the power supply line or in the load lines which spread out in opposing directions.
Remedial measures for differential mode disturbances are X-capacitors or capacitors between the lines.
DIMENSION devices are the modern DIN rail devices with a metal-casing from PULS for intermediate and high performance.
DIMENSION devices distinguish themselves from all previous equipment through the implementation of new leaps in technology and many other improvements to detail.
The outstanding features of this family of equipment are:
- offering high functionality
- ease of use
The DIN rail is a 35mm mounting rail also known as a top hat rail, support or carrier rail.
DP devices are the first generation DIN rail devices from PULS.
EDLC (Electrochemical Double Layer Capacitor) are double layer capacitors that are also known as super capacitors or ultra-capacitors.
No chemical reaction takes place within these capacitors. The charge is stored in an electrochemical double layer (known as the Helmholtz double layer), where positive and negative ions of electrolyte shift through the electric field to the corresponding electrode. As a consequence these are more age resistant than lead-acid batteries, in regard to both service life and temperature.
Although this technology can achieve very high capacitance values it is, however, limited to a nominal voltage of 2.7V, and as a result a series circuit of multiple capacitors is necessary. EDLC have approximately 40 times the energy density of electrolytic capacitors and are suitable as an energy store in buffer modules. In contrast to lead-acid batteries they have a service life expectancy similar to power supplies and need not be replaced during the period of operation.
EDLC can operate without any difficulty at temperatures of up to -40°C and are therefore ideal for outdoor applications. The upper temperature range is typically limited to +65°C due to the very low boiling point.
''Efficiency'' describes the ratio between the output power and the input power of a power supply. The difference between input and output power is converted into heat as loss.
Latest technology in power supply design enables an economical realization of efficiencies up to 96%. At PULS, these technologies are consistently followed, improved and offered to users in various device families. High efficiency values ensure low warming, long service life and high reliability of all components in the control cabinet. It also enables devices to be designed and built as small as possible.
The EMC (Electromagnetic Compatibility) is defined by the EMC Directive 2004/108/EC and is the capability of an electrical device to operate satisfactorily in its electromagnetic environment, without itself causing electromagnetic interference which would be unacceptable for other devices installed in this environment.
The limits for electromagnetic radiation and the severity level for electromagnetic immunity depend on the site of operation and are given in the generic standards or the product standards.
The EMI emission is a generic term for electromagnetic interference caused by a power supply.
The propagation of faults is either conductor-bound (conducted emission) or field-bound through radiation (radiated emission).
The limits for the emission depend on the location and are specified in the generic standards or product standards.
The EMI immunity is a generic term for electromagnetic interference that a power supply must be able to withstand.
The faults can either be conductor-bound (conducted immunity) or field-bound (radiated immunity) from an external source having an impact on the power supply.
The severity level of the required immunity depends on the location and is specified in the generic standards or product standards.
ePLAN is a high-end CAD/CAE software in the field of electrical engineering.
The software offers many possibilities for design, documentation, and management of automation projects. ePLAN is a member of the Friedhelm LOH Group and one of the leading software houses in this field. The ePlan macros of most PULS devices are available both on the online ePlan data portal as well as in the product area of the PULS website.
ESD (Electrostatic Discharge) is a spark or flashover created by a major potential difference in an electrically isolated material, which causes a very short but, highly charged electrical impulse.
The electrostatic charge of bodies is caused by the triboelectric effect of different materials. A discharge can destroy sensitive electronic components. For example, a risk to electronic devices can arise if a person wearing well-insulated shoes walks across a well-insulated floor covering. As a result, comprehensive measures are required to avoid ESD during electronics manufacturing.
The minimum ESD requirements for a device are laid down in EN 61000-6-2. Test conditions can be found in EN 61000-4-2.
Following two test methods are used:
With this method the ESD voltage is discharged by means of high voltage relays and test stylus making direct contact with a metallic surface (device housing).
With this method a test stylus charged with ESD is brought in close proximity with the test object until breakthrough occurs. For devices with non-conductive surfaces (e.g. plastic housing or metal housing with insulating membrane) the air discharge is applied to electrical connection contacts.
During the ESD test, the test object is in operation.
EUROBAT (Association of European Storage Battery Manufacturers, www.eurobat.org) is engaged in the development of standards for manufacturers of lead-acid batteries, in particular for the predetermination of the expected service lifetime.
EUROBAT has defined three classes of batteries:
- 3 to 5-year batteries
- 6 to 9-year batteries
- 10-12 year batteries
Flicker is the low-frequency influence of the mains voltage by consumers.
Flicker effects cause disturbances such as the fluctuation in brightness of lighting devices or monitors. Possible sources of flicker are the inrush current surge or periodic loading of the power supply. The limit values are defined in the "Flicker standard" IEC/EN 61000-3-3 for both one-time and recurring operation.
PULS guarantees compliance with the limit values for power supply switch-on process, but not for extreme pulse loads at the output of a power supply unit.
The flyback converter can be recognized due to the fact that it needs only one winding goods. With a closed switching transistor the transformer is magnetically charged.
When the switch opens the energy is transferred to the output.
The flyback converter is a very simple converter concept but has the disadvantage that it results in a high load on the capacitors. Usually it is only used for smaller capacities up to 200W. Multiple output voltage can be generated at low cost.
In a forward converter, the energy flow between the primary and secondary circuit takes place in a closed switching transistor.
In comparison to the flyback converter, the flow transducer can be recognized by its two coiled wire products. The transformer is used for galvanic separation and to adjust the voltage. The storage choke is part of the downstream buck converter and, in conjunction with the free-wheeling diode, ensures a continuous flow in the output capacitor. The forward converter is typically used where a performance greater than 200W is required. The forward converter is available as a push-pull converter with half-and full-bridge circuits.
Functional safety is the part of the overall system safety, both of which depend on the correct function of a device.
Components responsible for functional safety must meet the requirements of IEC 61508 (VDE 0803). This standard provides general guidelines for the prevention and control of outages in devices. It sets organisational and technical requirements for the development and operation of the device. Four equipment safety levels are defined: SIL1 for low risk and extent of potential damage and progressing up to SIL4 for very high risk. The higher the risk, the more reliable the measures to risk reduction must be. The requirements on the components used increase accordingly. SIL is the abbreviation for "Safety Integration Level".
PULS power supplies are not considered safety-related components within the context of IEC 61508 and therefore are not classified according to SIL. However, in the overall equipment FMEA assessment it is possible to achieve a SIL2 level rating (equivalent to performance level PFH and PFD in equipment and plant engineering or performance level D category 3 in mechanical engineering).
Risks associated with a power supply which could affect functional safety are:
- Low voltage
- Oscillation (e.g. in the case of overload or overvoltage protection mode)
The probability of such a risk can be identified by the MTBF rating. For this purpose, PULS provides values that can be used for assessing the functional safety of a plant, system or piece of equipment. With simple machines and equipment (up to SIL2) a zero-current condition represents a minimum "fail safe" mode. In these cases if the power supply can be safely disconnected it is sufficient to reach this rating level.
The FUSE Mode® describes the property of a power supply to switch off after a predetermined time if an overload occurs at the output. Reconnection is possible by using the reset button or by disconnecting the mains voltage.
The outputs of PULS power supplies are galvanically separated from the input voltage and comply with the requirements of safe isolation according to EN 50178, IEC 60204-1, IEC 60950-1 and IEC 62103.
The design of transformers used in PULS power supplies correspond to EN 61558-2-17, which is a follow-on standard to DIN VDE 0551. EN 61558-2-17 deals with the safe isolation of transformers as they are applied in switching power supplies. There is no need for the use of expensive isolation transformers to comply with DIN VDE 0551.
In addition to the transformers, all other components between input and output must meet minimum requirements for a galvanic isolation in the form of clearance and creepage distances and insulation thickness.
Galvanic isolation between the input and the output (B):
Reinforced, double isolation or basic isolation with additional supplementary isolation is used for this purpose. This ensures that safety is maintained even in the event of a first isolation fault.
Galvanic isolation between the input and the protective ground (A):
Basic isolation is used.
Galvanic isolation between the output and the protective ground (C):
Function insulation is used for this purpose. The output has no galvanic association with the protective ground. It is possible to ground the (+) pole as well as the (-) pole.
The harmonics is an integral multiple of the fundamental wave. For example, the 3rd harmonic at
50Hz is an oscillation with 150Hz.
HART (Highway Addressable Remote Transducer Protocol) is a standardized, widely used communication system for the assembly of industrial fieldbuses. It enables digital communication between multiple field devices using a common data bus. HART uses the 4-20mA standards for the transmission of analog sensor signals.
The hi-pot test is a safety test for power supplies.
The hi-pot test is a safety test for power supplies. It is performed between the input and output, between the input and ground and between the output and ground. Distinction is made between:
- Type tests that are performed during the approval process
- Component tests, carried out on each device during manufacture and
- Re-tests, that are performed by the user on the machine or plant.
Type and component tests are carried out by PULS or the licensing authorities. Re-tests must only be carried out using a suitable tester with slow voltage ramps (2s rising and falling 2s) in the application. At faster ramps, resonance effects may occur with the filters in the power supply. This can lead to excessive voltage and may cause irreparable damage to the power supply.
Before performing the tests, all of the input and output signal terminals as well as all contacts are to be connected with each other. During the tests, the current cut-off threshold may not be too low, as an improper shutdown can also damage the power supply.
Hi-pot tests always stress the power supply and should not be performed too often on the same device. Values for the hi-pot test (voltage and duration) as well as for the minimum cut-off threshold can be found in the device data sheets.
With a power supply or DC/DC converter the hold-up time is the time between the collapse of the input voltage below the minimum permitted value and the fall in output voltage by 5%.
Hot Plug or Hot Swap refers to the ability to exchange components whilst in running mode.
Inhibit input is a signal input with which a buffering can be interrupted or prevented in a DC-UPS or buffer module by means of an external input voltage.
The inrush current is the power surge at the input to a power supply which occurs when the input voltage is connected after charging the input capacitors.
For power supplies with NTC inrush current limitation, this current impulse can reach very high values and trigger fuses or circuit breakers.
Inrush current limitation
A power supply nominal voltage is rectified and smoothed with a large electrolytic capacitor, which is also responsible for the buffer time. The capacitor charging current causes a high inrush current which must be limited. Here the devices vary in the different concepts employed.
Inrush current limitation using NTC:
This is undoubtedly the easiest and most cost effective way of inrush current limitation. Upon switching on, the resistance is cold with high impedance which effectively limits the charging current. After a relatively short time the resistance warms up due to its own losses and impedance drops. Consequently, the losses remain within limits during operation. Depending on the particular component, the effect of the inrush current limitation strongly depends on the ambient temperature. If the temperature is too cold, (within the negative range), then start-up problems can occur; if the temperature is too high, the inrush current limitation is insufficient. Another serious disadvantage is the inadequate inrush current limitation following short power supply interruptions: The electrolytic capacitor discharges itself; the NTC has already stored the heat due to losses, remains of low impedance and is practically ineffectual when the power supply is restored.
Inrush current limitation using a fixed resistance:
This method uses a fixed resistance which is bridged after charging the electrolytic capacitor. Relays, triacs, IGBTs can be used as a bridge. This method is significantly more complex than the inrush current with NTC's and is ordinarily only used for a power class from 250W. The advantages are a temperature-independent limit of load current and significantly less power losses.
Pulsed charging of the input capacitor:
This method "gently" recharges the capacitor. A mini-switching power supply is used as a charging circuit which enables low-loss charging of the capacitor. Parameters such as peak power and loading delay can be accurately calculated and incorporated accordingly. This method renders the undesired switch-on current surge insignificantly small. The automatic mains fuse can be dimensioned according to the input power. This technique is used in many DIMENSION Q-series devices.
Trailing edge phase dimming for inrush current limitation:
With this method the limiting path is bridged with a relay after charging the capacitor, similar to the fixed resistance method. The trick here lies in the limiting part itself. An electronic system measures the instantaneous value of the AC voltage and compares it with the value of the partly charged capacitor. If the difference is less than a set threshold of, for instance, 30V, a MOSFET closes. If the voltage difference is greater than 30, the MOSFET reopens. The on-resistance of MOSFET thereby limits the peak charging current. For example, if this has a value of 4 ohms, the power is limited to 7.5A (30V /4 ohms). A gentle start for all input voltages is therefore guaranteed. This technique is used in many DIMENSION C-series devices. To prevent power losses, the inrush current limiting circuit is bridged if the capacitor is fully charged.
Up to 2000m:
PULS devices are designed to be operated at up to 2000m above sea level without any restrictions.
Typically a derating of 7%/1000m or a reduction of the permitted temperature range by 5°C / 1000m is required at altitudes between 2000m and 6000m. Forced ventilation is a possible alternative solution. Overvoltage protection is reduced from category 3 to overvoltage category 2.
Operation at above 6000m is not recommended because of increased exposure to cosmic radiation.
An inverter converts DC voltage (e.g. from a solar system or a battery) into an alternating voltage. Usually the AC voltage generated by the inverter is fed into the power supply grid.
IP rating (IP Code = International Protection Marking)
The IP rating defines the degree of protection of electrical equipment against contact, foreign bodies and water. The ratings of IP protection are defined in IEC / EN 60529 and consist of two digits.
Common IP codes are IP00, IP20, IP40, IP44, IP54, IP65, IP67, IP68. PULS devices usually are classified class IP20 protection.
IT networks, IT systems
IT system is a definition from IEC 60364-1 for AC power systems. With IT systems, the feeding device is not grounded or only grounded via relatively high impedance or via a voltage limiter.
Linear regulators use a transistor connected in series with the load circuit to keep voltages which are too high away from the load.
Current DIN rail power supplies in a robust plastic housing for low and medium power range from 15W to 120W.
A MOV (metal oxide varistor) is a voltage-dependent resistor for surge suppression. MOVs are also referred to as VDRs (Voltage Dependent Resistor). MOVs are often used at the input between the individual phases or between the phase and neutral conductors.
MTBF (Mean Time Between Failure) is the probability of a "random equipment failure".
Various standards are available to calculate the MTBF values; for instance SN 29500, IEC 61709, MIL HDBK 217F and Belcore amongst others. The calculation is always made in the same way.
The standard provides a database where base failure rates are available for individual components which are then adjusted with the stress factor for the actual application. The calculated failure rates of all components are added up and result in the failure rate for the overall unit.
The MTBF number indicates the statistical probability of failure. An MTBF figure of 1,000,000 means if there are 1,000 units in service then statistically one unit will fail every 1,000 hours. However, it is not possible to state whether a failed device was already in service for 50,000 or only 100 hours.
MTBF hours must not be confused with service life hours. PULS gives detailed values for both properties in the product data sheets.
NAMUR (Standardization association for measurement and control technology in the chemical industry) is an international association of users of automation technology for the process industry.
NAMUR supports the exchange of experiences among members and between other organisations and associations. The results are published in the form of NAMUR recommendations and NAMUR worksheets.
The network stabilisation is the static voltage fluctuation of the output voltage as a result of different input voltage under otherwise constant conditions such as output load or temperature.
The typical nominal frequency range of PULS AC power supplies is 50-60Hz ± 10%. Different frequencies are often possible (e.g. 16 2/3Hz or 400Hz), however, prior consultation with PULS is required.
Unless otherwise specified, for the nominal voltages AC 100V, AC 220V, AC 230V, 3AC 380V and 3AC 400V 50Hz; and for nominal voltages AC 120V and 3AC 480V 60Hz are assumed as the typical rated frequency.
The nominal voltage is the specified system voltage of the supply circuit to which the device may be connected.
For 3-phase systems the nominal voltage is the voltage between the external lines.
In this catalogue the following standard notation will be used for this purpose:
- If the term AC or DC precedes a number, then this is a nominal voltage or a nominal voltage range. (e.g: AC 230V, AC 100-240V, 3AC 380-480V, DC 12V).
- The nominal voltage or nominal voltage range may be supplemented with information on tolerances. (e.g: AC 230V ±10%, AC 100-240V -15%/+10%, DC 12V ±25%). The resulting total range then specifies the device's operating range.
- If the term Vac or Vdc follows the number then this indicates an instantaneous voltage value without additional tolerances.
Example: DC 12V describes a 12V battery, regardless of whether it is fully charged (13.7 Vdc) or discharged (10Vdc).
An NTC resistor (Negative Temperature Coefficient) is a resistor which has a relatively high resistance value in the cold state and at high temperatures has virtually no resistance.
NTCs can be used for inrush current limiting. Upon switching on, the resistance is high and limits the charging current of the electrolytic capacitors. The flow of current through the NTC heats the NTC, the resistance value is reduced and the losses in the NTC in practice reduce to <1W.
Open Frame power supplies
Open Frame power supplies have no housing and are designed to IP00. Open frame power supplies are usually integrated into machines or systems in which a total overall housing meets the necessary protection against fire, mechanical hazards and electrical shock.
An optocoupler is a component which consists of a photo diode (LED) and an electrically isolated phototransistor. It serves for signal transmission and is often used for electrical isolation of power supplies in the control circuit.
The output characteristic is one of the most important features of a power supply. From this characteristic it is possible to read the overload reserve and overload behaviour.
The output current is applied to the x-axis and the output voltage to the y-axis. In the event of an overload the power supply automatically switches from the voltage regulation mode to the current regulation mode and protects the power supply from damage.
The output ripple is the AC voltage superimposed on the output voltage and is specified in mVpp (ripple and noise voltage) in a switch mode power supply. ...
- Ripple voltage with frequency
- Residual ripple with the switching frequency of the converter Glitches (spikes) in the MHz range caused by the shifting of the internal switching transistors and diodes
The peak-to-peak specified in the data sheet includes all three components' values.
Notes on the measurement of output ripple:
The measurement must be performed immediately at the power supply output with a short twisted ground lead (no loops) and a series capacitor (e.g. parallel connection of a 100nF capacitor and a 560µF electrolytic capacitor). The scope must be set to 50ohm AC measurement. A bandwidth limit of 20MHz must be enabled.
All PULS power supplies are overload, short-circuit and open-circuit-proof on the output side. No external backup is required at the output to protect the power supply.
Switched-mode power supplies electronically limit the output current during overload. If the maximum current is reached, the power supply automatically switches from voltage regulation mode to the current regulation mode.
The following functions can be identified in the current regulation mode:
- "Fold-back" characteristic
Here the current is reduced depending on the level of the overload. This behaviour is inappropriate to start-up heavy loads and it is mainly used for linear regulated power supplies.
- Constant current or U/I characteristics
Here the current remains almost constant at overload.
- "Fold-forward" characteristics
Deemed to be the most non-problematic overload behaviour, but carries the risk of a high short circuit current.
- Hiccup mode
Switches off power in cases of overload or short circuit and carries out periodic attempted restarts until the fault is eliminated.
See also "Hiccup Mode".
- HiccupPLUS mod
A combination of the "fold-forward characteristics" and hiccup mode, which was developed by PULS and which does not overload the lines in the event of a short circuit.
See also "HiccupPLUS Mode".
An overshoot is the amount by which the output voltage exceeds the set static value in response to a rapid change in load or input voltage or when connecting power to the input voltage.
The overtemperature protection is an emergency shut-down and prevents the thermal destruction of the power supply or failure of safety isolation due to high temperatures.
The response threshold for overtemperature protection typically is significantly higher than the specified operating temperature range. The temperature sensor/sensors is/are fitted in critical safety points such as the transformer.
On triggering the overtemperature protection, the power supply switches off, cools down, and makes an automatic re-start attempt once it falls below a set temperature.
The overvoltage categories classify positions in the mains supply based on the highest transient overvoltage which can be expected to occur at the junction of devices.
The transient overvoltage of the mains supply is the basis for the minimum clearance of the isolation in primary circuits.
- Overvoltage category I:
Equipment to connect to a specific network connection in which measures are taken to reduce transient overvoltage (e.g. a computer which is connected via a filtered socket).
- Overvoltage category II:
Equipment with plug and socket connector or fixed connection supplied from the electrical system of a building (e.g. household appliances and tools which are connected directly to the power outlet).
- Overvoltage category III:
Equipment which is part of the electrical system of a building (such as sockets, protection and control panels, equipment for monitoring electrical values).
- Overvoltage category IV:
Equipment which is connected at the site where the power supply enters the building (e.g. electricity meters).
The requirements (e.g. values of dielectric strength, minimum clearance) on the serviceability of a product in a certain overvoltage category is individually set in the product standards.
PULS power supplies typically meet the requirements of overvoltage category II according to IEC\/EN 60950-1 and overvoltage category III according to IEC 62103/
The abbreviation OVP (Over Voltage Protection) refers to a protection circuit which limits the output voltage to a predetermined maximum value.
OVP voltage must be higher than the output voltage. The circuit used must be designed as a redundant circuit to the main control circuit, so that in the event of a main control circuit failure the output voltage is limited and sufficient personnel and equipment protection is provided.
"Parallel Mode" is a feature for uniform current distribution between power supplies connected in parallel. In "Parallel Mode'', the output voltage is regulated so that it is about 5% higher in the no-load state than at nominal load.
For an uniform distribution of the load current it is required that all devices are precisely set for the no load state at less than ± 100mV or remain at the factory setting.
In many PULS power supplies "Parallel Mode" can be activated using a "Single Use / Parallel Use" jumper on the front of the unit. If a jumper is not inserted then "Single Use" is activated. The factory setting is "Single Use".
PELV (Protective Extra Low Voltage, formerly known as extra low voltage) describes a voltage that is set so low that in the event of indirect contact and small area direct contact there is no risk of electric shock. In the event of an insulation failure adequate protection must still be provided.
For power supplies this is achieved through a galvanic separation with double or reinforced insulation between the primary and secondary side.
Since the term PELV is not uniformly specified across the various standards, it is necessary to specify here that PULS only use the term PELV in the context of EN 60204-1. The nominal voltage of a PELV voltage source may not be greater than 25V AC effective or 60V harmonic-free DC voltage. One side of the PELV circuit must be connected to the protective grounding system. But this must not necessarily occur at the power supply.
All PULS power supplies with an output voltage <60Vdc meet the requirements for a PELV power source.
See Functional Safety
PFC (Power Factor Correction)
Determined by the circuit, input current of power supplies is often not sinusoidal but pulsed. The harmonic currents thereby produced may, in certain applications, exceed the limits of EN 61000-3-2 or the product standards.
The harmonic currents can either be reduced by an additional converter stage (active PFC) or by means of a throttle (passive PFC). PULS often provides a range of different power supplies for this purpose.
Compliance with EN 61000-3-2 can often bring technical drawbacks such effecting efficiency, warming and reliability. Higher component and circuit costs can also result in commercial disadvantages. As the reduction of harmonic currents often brings no benefit to the user it is useful to understand whether measures are really necessary in the particular case or if they can be dispensed with.
Compliance with EN 61000-3-2 is not required if:
- the harmonic requirements are included in the applicable end equipment standard and there are no additional requirements,
- the input power of the power supply is less than 75W; (the measurement of the harmonics may be averaged over a typical load cycle, including pauses),
- the measurement of power above 1,000W is carried out using professional quality equipment
- the supply voltage is < 220V,
- the terminal equipment is operated outside the EU,
- the machine or system is supplied from a network with its own transformer, for instance from a non-public network
If several self-contained consumers (e.g. power supplies, power amplifiers) are installed in a rack or housing they may either be considered individually or as a group. The term "Power Factor Correction" (PFC) in the context of EN 61000-3-2 can be misleading, since the purpose is mainly reducing the harmonic content of the input current and not to improve the power factor. EN 61000-3-2 only specifies requirements and limit values for special applications (e.g. lighting equipment).
EN 61000-3-2: (Limits for harmonic current emissions) applie to equipment with rated input current up to 16A per phase, EN 61000-3-12: (Limits for harmonic current emissions) applie to equipment with rated input current higher than 16A and lower than 75A per phase.
PISA devices are protection modules (electronic fuse) from PULS for the protection of 24V DC circuits.
The pollution degree describes the environmental influences such as dust, moisture and aggressive substances that can affect a device and its insulation. IEC/EN 60664-1 and VDE 0110-1 define four pollution degrees.
- Pollution degree 1:
There is no contamination or only dry, non-conductive contamination.
- Pollution degree 2:
Only non-conductive pollution or occasional temporary conductivity due to condensation.
- Pollution degree 3:
Conductive pollution occurs or dry non-conductive pollution occurs which becomes conductive due to condensation.
- Pollution degree 4:
The pollution generates persistent conductivity caused by conductive dust or by rain or moisture.
Power supplies proven in industrial use comply with Class 2. PULS power supplies are designed for this class.
The Power Boost Feature describes the permitted short-term overload with which a power supply may be overloaded.
At ambient temperatures of lower than +45°C it is common for up to 25% more power to be permanently pulled from the system. Above +45°C the short-term performance should not exceed 10% (<1 minute per 10 minutes).
Almost all DIMENSION Q Series devices have the Power Boost Feature.
The power factor or cosine phi factor is the ratio between active power and apparent power.
A purely resistive load (e.g. a heating coil) has a maximum power factor of 1. The power factor can be reduced either by a phase shift between voltage and current (inductive or capacitive loads) or a non-sinusoidal waveform of the current (e.g. power supply). The apparent input power (VA) can be measured with a voltmeter and ammeter on the input lines. The product of current and voltage is the apparent power.
To measure the input power (W) a wattmeter with sufficient bandwidth is required. The input current of a power supply can be calculated using the power factor and efficiency if the output power and the input voltage are known.
The characteristics for the power factor as a function of input voltage and load can be found in the PULS data sheets.
Power supply for intermediate bus voltages
Power supplies for intermediate bus voltages are power supplies which are suitable for the connection of frequency converters and servo amplifiers to the internal intermediate circuit (usually DC 600V).
In practice it is advantageous to connect the power supply to the DC and not to the AC voltage. In the event of power failure, the rotating motors act as generators and feed back power to the intermediate circuit. This ensures that controls and brakes are supplied with power even without a DC UPS until the motor is at rest.
Intermediate circuits are often only slightly filtered and burdened with high interference and leakage currents. 3-phase power supplies, even if they are designed for supply with DC voltage, are when used in intermediate circuits often overstrained and can be destroyed.
For this application, PULS has developed special power supplies (the QTD series).
The Power-Fail Signal indicates that the minimum value of the input voltage is not met.
IEC/EN 61140 classifies electrical equipment in terms of safety against hazardous touch current and electric shock.
The design features of devices are assigned the following protection classes:
- Protection class 0:
No protection, the use of such devices is not permitted in the European Union.
- Protection class I:
Device with protective ground connection and basic insulation between accessible parts and the protective earth. A proper protective ground connection is compulsory.
- Protection class II:
Device with double or reinforced insulation between touchable parts and hazardous-live-parts. With these devices it is not possible to connect a protective ground.
- Protection class III:
A device which is supplied by SELV or PELV circuits and which do not generate higher voltages than those permitted with SELV or PELV.
PULS Network devices are usually built to protection class I.
The push-pull converter is a flow converter which magnetically controls the transformer in both directions.
Push-pull converters achieve high levels of efficiency but are very expensive due to the number of components and are used only for high performance systems.
The reliability and availability of the DC voltage can be increased by a redundant system. To achieve redundancy, a supplementary device is installed to act as a "reserve". This device then continues to provide the necessary load current if a system device fails.
The individual devices must be decoupled from the modules with redundancy to prevent a defective device (e.g. short-circuit in the output diode) generating load on the working devices and preventing the guaranteed output voltage.
Usually two identical power supplies are connected together in a 1+1 configuration. For powerful systems an N +1 configuration is also possible. For example, if a current of 100A is required, six devices can be connected redundantly, each with 20A. If one device fails, there are still five units in operation with a total current of 100A.
Each power supply must be equipped with a separate input fuse. Redundant systems must be monitored in order to trigger a service call in the event of failure of a device. The DC-OK signal of the power supplies is used for this purpose.
The term regional versions refers to power supplies that are designed for an input voltage range (e.g. AC 100-120V or AC 220-240V). The design of power supplies can significantly reduce costs and the number of components which, in turn, improves the reliability of the power supplies.
Resonant converters are variants of basic circuits which reduce switching losses by taking advantage of resonance effects. Resonant converters achieve the very highest efficiencies and often work with very high switching frequencies. The half-bridge resonant converter is in widespread use.
Due to the nature of the system, resonant converters are very difficult to control, so that power supplies which use a resonant converter are usually built-up in several stages. A switching regulator conditions the input voltage for the resonant converter which then takes over the role of energy transfer, galvanic isolation and voltage matching.
The shut-down input is a signal input with which a power supply can be brought to the off mode by an externally supplied voltage or a simple switch. The shut-down input is galvanically isolated from the input voltage and can be supplied by SELV circuits.
In the off mode the power occasionally switches on for a short period to supply the electronic monitoring system. During the off mode or at very low output currents, low voltages (< 4V) and currents (< 2mA) can be seen at the output.
The shut-down input does not meet any safety requirements.
SELV (Safety Extra Low Voltage) describes a voltage that is set so low that in the event of direct touch either during proper operation or in the event of a single fault there is no danger of electric shock due to touch current.
In the event of an insulation failure, adequate protection must still be provided. For power supplies this is achieved through a galvanic separation with double or reinforced insulation between the primary and secondary side. No additional protection against direct touch is required.
Since the term SELV is not uniformly specified across the various standards, it is necessary to state here that PULS only uses the term SELV in the context of EN 60950-1.
The voltage of a SELV power supply in a dry location during proper operation must not exceed a peak value of 42.4V for an AC voltage or superimposed AC voltage and 60Vdc for a DC voltage.
For an individual fault the specified voltage limits may not be exceeded for longer than 200ms. Moreover, the peak value of 71V for alternating current and direct current voltage value of 120Vdc may not be exceeded. Grounding of the secondary side is not required, but permitted.
All PULS power supplies with an output voltage <60Vdc meet the requirements for a SELV power source.
SEMI F47 compatibility is a quality characteristic of the semiconductor industry which ensures compatibility of devices with poor mains power supply.
With a drop in the nominal mains voltage to 50%, power supplies must not show a drop in the output voltage for 200ms. Such voltage drops can occur when heavy loads are switched on or power supply grids are switched.
Many PULS devices comply with the SEMI F47 requirements and are accordingly tested and certified. These devices display the SEMI F47 test mark.
Semi-regulated power supply
Transformer power supplies usually are unregulated. This means that if the input voltage varies then the output voltage also varies proportionally.
With semi-regulated power supplies (e.g. the DIMENSION X series) the core range of the input voltage (360 to 440Vac or 432 to 528Vac) is regulated to give a constant output voltage.
A proportional drop or raise in the output voltage only occurs outside of this range.
The expected service life of a device indicates the useful life in operating hours. This is the time during operation of the device until the first signs of wear (e.g. dried capacitors) occur. The component with the shortest service life expectancy in a device determines the service life of the overall device.
Components which determine the service life of a power supply unit:
- Electrolytic capacitors - due to drying out
- Microcontrollers - due to data loss
- Optocouplers - due to reduction in transparency
The service life expectancy of electrolytic capacitors can be accurately calculated using the specified basic service life (in the data sheet mostly stated for +105°C) and the correction formulas for the actual operating conditions. High temperature will shorten the service life. As a rule of thumb the service life doubles for each reduction in temperature of 10° C.
For an electrolytic capacitor which has a specified basic service life of 2,000h at +105°C a reduction
in temperature of 10°C to +95°C will extend the expected service life to 4,000h. At +85°C the expected service life is then 8,000h, at +75°C 16,000h and so on. To achieve a long service life the design of the power supply unit, the quality of the components used, and the conditions of use are of crucial importance:
- Place critical components in a cool spot
- Do not impede air flow
- Ensure good venting of the heat generated to the outside
- Place the power supply unit in a cool location within the electrical cabinet
An important design policy at PULS is a minimum service life expectancy of 50,000h. This is defined at the rated output current, +40°C ambient temperature and nominal input voltage.
Service life hours must not be confused with MTBF hours. PULS gives detailed values for both properties in the product data sheets.
The shelf life of power supplies and auxiliary equipment is mainly dependent on the properties of the electrolytic capacitors, the preservation of data in the flash memory of microcontrollers and the storage temperature.
In general a shelf life of 15 years can be expected if an average storage temperature of +25°C is maintained and the electrolytic capacitors are used at regular intervals to a specified voltage and are reformatted. For this purpose it is sufficient to supply power to the input side for approximately 10 minutes at this voltage. With an average storage temperature of +25°C this procedure should be performed at least every five years, and at higher temperatures every three years. The elapsed storage time has an influence on the service life of a device. After 15 years in storage the expected service life is reduced by half, approximately.
Shock and vibration resistance
Shock and vibration resistance gives information concerning the robustness of the mechanical design of a device. The methods for evaluating the shock resistance are defined in IEC 60068-2-27.
The shock resistance is important for the permissible device operating and transport conditions. PULS devices in metal housings can typically withstand shock loads of 30g 6ms and 20g 11ms. Devices in plastic housings are specified and tested with 15g 6sm and 10g 11ms. Three strikes are applied in all six degrees of movement.
Therefore it is possible to transport a fully assembled electrical cabinet to the site of installation without the devices slipping on the DIN rail. The methods for evaluating the vibration resistance are defined in IEC 60068-2-6 and IEC 60068- 2-64. PULS devices are typically tested with a sinusoidal vibration load according to IEC 60068-2-6 in the frequency range of 2Hz to 500Hz at 2g and a broadband noise according to IEC 60068-2-64 at 0.5 m2 (s3).
These values should be sufficient for general industrial applications. All shock and vibration tests are performed on operating devices. More information about shock and vibration resistance can be found in the PULS data sheets or in the individual shock and vibration test reports.
The shut-down input is a signal input with which a power supply can be brought to the off mode by an externally supplied voltage or a simple switch. The shut-down input is galvanically isolated from the input voltage and can be supplied by SELV circuits.
In the passive state the power supply occasionally switches on for a short period to supply the electronic monitoring system. During the passive state or at very low output currents, low voltages (< 4V) and currents (< 2mA) can be seen at the output.
The shut-down input does not meet any safety requirements.
Second-generation PULS DIN rail device.
In single-mode the output voltage is virtually independent of the output current.
See also parallel mode.
Spring clamp terminal
Spring clamp terminals are terminal clamps which use a spring to clamp the wire to the contact bracket.
This type of connection is vibration-proof and eliminates the need for periodic tightening of terminal screws. Operating errors (e.g. tightening torque too low or too high) are excluded with this 'digital' connecting system. Another advantage is the shorter installation time compared to screw terminals. Thanks to the integrated actuating lever in PULS spring terminals the wires can be connected without using tools.
Star and Delta systems
In a conventional star system (in English also known as the wye system), the voltage between the individual phases higher by √3 than between the phases and neutral. Delta systems have no neutral line.
Surge or surge voltage (for example on the power supply line) can occur from adjacent lightning strikes or as inductive voltage rises after the triggering of fuses due to short circuits.
The minimum requirements for immunity to surges (surge voltage) are laid down in EN 61000-6-2. Test conditions can be found in EN 61000-4-5.
Switching regulators are DC-DC converters without electrical isolation consisting of an inductor, a switching transistor, a diode and capacitors.
Depending on the arrangement of these components the output voltage may be higher or lower than the input voltage.
Negative inverse converters with negative output voltages are also possible.
TN networks, TN system
''TN system'' is a definition from IEC 60364-1 for AC power systems.
In a TN system one pole of the supplying equipment has a direct electrical connection with the protective ground. This is usually the neutral point or, if no neutral point is present, an exterior conductor.
Parts which require grounding in the consumer device are electrically connected to the ground of the power-supplying equipment.
TT networks, TT system
''TT system'' is a definition from IEC 60364-1 for AC power systems.
In TN system one pole of the supplying equipment has a direct electrical connection with the protective ground. This is usually the neutral point or, if no neutral point is present, an exterior conductor.
Parts which require grounding in the consumer device are electrically connected to their own ground which is electrically independent of the power supply system ground.
A UPS (Uninterruptible Power Supply) is a power supply with battery which can provide the connected consumers with power for a certain period of time after a mains power failure.
An AC-UPS supplies AC voltage at the output to buffer the AC power supply
A DC-UPS supplies direct current (mostly 24Vdc) at the output.
A DC-UPS can be simply a control unit to charge and monitor the battery. It can also be a control unit with built-in battery or it can be completely integrated in an AC power supply and include a battery.
VDE 0160 Pulse
The VDE 0160 Pulse is a high-energy voltage pulse which may occur on mains voltages of industrial networks (e.g. when switching off large loads or due to the decay of short circuit currents).
Although the VDE 0160 standard is no longer up to date, the impulse is still a quality feature of power supplies. The pulse is superimposed on the sinusoidal voltage at the peak value with an excess of 2.3 times the peak value. The duration of the pulse is either 0.3ms (class 1) or 1.3ms (class 2).
A VDE 0160 Pulse can not be sufficiently attenuated with conventional filters. Active filters (fade circuits) or an over sizing of the power units are necessary.
All PULS power supplies are protected against these high-energy input transients.
VRLA batteries (Valve Regulated Lead Acid) are sealed, valve-controlled lead acid batteries, in which the gas resulting from overloading or a cell error is vented through a safety valve.
VRLA batteries have excellent leak security and can be used in any orientation. They are absolutely maintenance-free. VRLA batteries are also known as SLA (Sealed Lead Acid) batteries.
There are two types of VRLA batteries:
- AGM batteries:
AGM stands for Absorbent Glass Mat. In this type of battery the electrolyte is absorbed by capillary action into a non-woven material of fine glass fibres. AGM batteries are the most commonly used VRLA batteries and can also be loaded with high discharge currents for a short period.
- Gel batteries:
With this type of battery the electrolyte is bound in a silicate gel. Gel batteries have a longer service life, lower self-discharge and are better suited for cyclic loads. Disadvantages are a higher sensitivity to mechanical loads (shock, vibration) and unfavourable response to high discharge currents.
In addition to the sealed VRLA there are the closed lead acid batteries such as those used as starter batteries in vehicles.
Wide range input
At 1 phase power supplies, a wide range input is an input which covers the AC voltage range from 100-240V without automatic or manual switching.
Approved capacitor which serves to suppress radio frequency interference and which is switched between the phase and the neutral conductor or between phases to short-circuit differential-mode interference.
Approved capacitor which serves to suppress radio frequency interference and which is switched between the phase(s) and the housing or the PE, or between the neutral conductor and the housing or the PE to short-circuit differential-mode interference.