Quality assurance of pulse load power supply
Practical solutions
Author: Oleg Negreba (Head of R&D, AEDON, LLC)
There is a number of application areas of modern electronics that are featured by clear pulse nature of power consumption. For instance, power consumption of contemporary high-performance processor devices directly depends on dynamic load of the processor and can alter in a very wide range within short time.
Apart from this transceiver equipment consumes the most power in transmitting mode, while in receiving mode it tends to no-load condition. Such dynamics of load sets quite strict requirements to the quality of output power of power supplies with step change nature of output current. Limited voltage feedback speed of power supply units requires capacitive accumulators to be installed between them and the dynamic load. At the same time you can see an unambiguous dependence between dynamic characteristics of a source and the value of a necessary capacitance accumulator.
It is evident, that slow feedback requires a larger capacitance accumulator and increases weight and dimensions of the complete power supply system. Miniaturization tendency in electronics makes it necessary to increase operating speed of power supplies to reduce the size of capacitance accumulator with the same quality of power supply of the load.
To resolve these tasks AEDON, LLC has introduced modular isolated power supply units of MDA series. Thanks to very quick voltage feedback these PSU's allow to reduce the number of capacitance accumulators, and sometimes eliminate them completely, and reduce the size and weight of the power supply system. In the Figure 1 you can see the exterior of MDA unit.
Figure 1. Exterior of MDA unit
● Basic MDA specifications:
● 2 year warranty
● Output power 170 W, 340 W, 500 W
● Output voltage 8 to 68 VDC
● Output current up to 30A
● Input voltage 10.5…13.5 VDC, 22…33 VDC, 44…66 VDC, 99...121 VDC, 270…330 VDC, 342...418 VDC;
● Switching frequency 470 ... 530 kHz, external synchronization
● Typical efficiency 90...92%
● Case operating temperature -60…+125°С;
● Overall dimensions 105.1 × 38.0 × 12.85 mm (without flanges and contacts)
The quality of output voltage of MDA units with pulse load operation can be evaluated by oscillogram chart of transient output voltage deviation at step change of load power. Figure 2 shows oscillogram charts of output power of a conventional PSU (a) compared to a similar MDA340F50 (b) during load power transients within the range from zero to max (Scale: vertical 5V/div, horizontal - 10 ms/div) Output voltage transient deviation of the conventional unit: +5% / –35%. Output voltage transient deviation of MDA340F50: ±2,4%).
Figure 2. Oscillogram charts of output voltage of a conventional unit (a) and MDA unit (b) with 50V output voltage with step transients of load power from zero to 100%.
These oscillogram charts show that in the same conditions at load power drop and surge the output voltage transition deviation is approximately 15 times less for MDA340F50 comparing to similar conventional PSU. That become possible thanks to very quick voltage feedback time of MDA units wich makes less than 100ms (see Figure 3) (Scale on Figure 3: vertical - 0.5 V/div, horizontal - 100ms/div).
Figure 3. Oscillogram chart of output voltage transition deviation of MDA340F50 unit during load power surge between 0 and 340W.
Initially MDA units were created to power supply of transceiver modules of active phased array radars. But the final specifications made them a demanded product for other systems with pulse nature of load. MDA PSU is optimized for application in fully decentralized power supply systems. Figure 4 shows an example of structure of such system.
Figure 4. Example of a decentralized power supply system with galvanically connected output voltages.
Decentralized power supply is a system where each consumer is supplied by its own relatively low-power supply unit which in its turn is supplied directly from the on-board mains, power generator or any other input power supply, and ensure the max reliability of the system as a whole. If we put a fuse at the input of each MDA unit, then in case of fail the broken cell will be automatically disconnected from the input mains. Thus the failure of one of the cells or its power supply will not influence the operation of other consumers and will not break the complete system.
Thanks to such decentralization communication electronics becomes invulnerable comparing to centralized system, reliability of which depends on reliability of one powerful source supplying power to all consumers. Apart from this centralization of power supply usually leads to higher voltage drop at connection circuits.
That is a result of supplying larger power at input and further remoteness of the consumers at output which makes is necessary to use wires of larger cross-section. Decentralized power supply system has lower powers transferred inside, while the power supply units can be located close to their consumers and thus minimize dynamic instabilities of voltage.
Another advantage of power supply units for decentralized systems is their unified character, i.e. they can be used in power supply systems of different devices unlike high power systems which are usually unique and can be used for one type of equipment only.
Development of MDA units consider that their output current will increase the pulse current of the supplied load and will ensure its proper power supply during the complete operating pulse. In this case the specific drop of output voltage in the end of the operating pulse is fully eliminated.
First, this feature allows to avoid using large capacitance accumulators for power supply of the load during the complete power consumption pulse, retaining the minimum capacitance to ensure the required quality of voltage during the transition process in the front and rise of load pulse.
Second, due to the fact that the mode of nominal power of the converter corresponds to its max efficiency, thermal losses of the complete power supply system are minimized.
Third, in case of using these units for power supply of AESA transceivers, who's typical off duty factor of pulse is usually less then 5, the comfortable thermal mode of the unit itself is supported.
Galvanically isolated differential synchronization input allows to sync the frequency of several simultaneously operating units and ensure reliable hardware and software filtration of electromagnetic interference of converters. MDA units are able to operate at frequency 470-530 kHz. High conversion frequency does not only positively impact the weight and dimensions of the units, but allows to isolate in different ranges the operating frequency area of the equipment of AESA transceivers and unit's switching noise.
Despite small dimensions the output power of the units can reach up to 500W, they are able to operate within case temperature range from -60 to +125°С. Additional functions include remote on/off, a set of protections from overcurrent, short circuit, and overvoltage, as well as output voltage PGOOD diagnostics. Polymer sealing potting ensures strong protection from harsh environments and excludes damage of the units caused by vibration, dirt, moisture or salt mist. These units can be equipped with different input, output and service contacts, for example, with axial or radial arrangement of pins, blade contacts, flexible mounting outputs, or terminal blocks.
Unified MDA modules can be customized on a single PCB alongside with PGOOD diagnostic and control circuits in the housing required by the customer. Figure 5 shows such multi-channel power supply system of total power of almost 1500W.
Figure 5. Power supply system based on MDA units.
High reliability of MDA units within adverse impacts is ensured by components with high values of MTBF and effective patented heat removal system. Due to the fact the MDA units ensure proper power supply of the load during the complete operating pulse and do not require significant power accumulators for their operation, the current they consume from the mains is clearly of pulse nature, which is not acceptable in all applications.
Figure 6 shows an example where the mains should be designed for at least 1.5 kW power, while the average consumed power is about 300W.
Figure 6. Type of power consumed by MDA units from the mains.
If the mains has such specification, you will not have any problems. But if its power is limited and does not allow to feed the load by proper pulse power, in this case you have to take special measures to turn the consumed pulse current to direct current with some allowable ripple. During load pulse such device should limit the current consumed from the mains but at the same time feed the load with the requires pulse power; and during the space pulse it should compensate from the mains the difference between fed and consumed power.
It evident that such device being a current filter at the same time should be a power accumulator. Application of passive induction or capacitance power accumulators almost always makes the product over-sized and expensive, so the best way is to use high frequency voltage converter without galvanic isolation and with a filtering capacitor at the output as a current filter. It is recommended to use step-up converters instead of step-down ones, as usually it is more effective to accumulate the power with higher voltage as the power accumulated in capacitor is proportional to the voltage squared (E = CU2/2). Thus the requirement to bring pulse power of the load to the average power consumed from the mains turns into the power supply system shown in the figure 7.
Figure 7. Active filtration of the pulse current
In this type of power supply it is suggested to use 200W and 400W active current filter of ATF series [6].
These filters are implemented in the same housing as MDA units and can be seamlessly used with them.
Brief spec of ATF active current filters:
- Power range: 200W, 400W;
- Input voltage range 9…18 VDC, 18…36 VDC, 36…72 VDC, 200…340 VDC;
- Output voltage: 24 VDC, 60 VDC, 96 VDC, 380 VDC;
- Temperature range: –60…+125°С;
- Switching frequency: 470…530 kHz;
- Overall dimensions without flanges and contacts 105.1 × 38.0 × 12.85 mm
ATF filters have the function of external synchronization with frequency from 470kHz to 530 kHz which allows to sync the operating frequency of all voltage converters of the power supply system. As the input voltage of ATF can vary in a wide range, it can also be used as the mains' normalizer. Figures 8 and 9 show two more examples of MDA and ATF application and in DC power supply mains.
Figure 8. 12 VDC pulse load consumer supplied by on-board 27 VDC main without significant input current impacts on the on-board main
Figure 9. ATF application as a common step-up converter without galvanic isolation.
If you need to use MDA unit in AC power supply mains, you can apply KAD500 filter-rectifier and modular PFC of KKM series with power 200W and 400W. Figures 10-13 show some examples of AC/DC power supply systems of communication electronics based on unified units.
Figure 10. Power supply system of 8 transceivers of AESA from AC mains without pulse load to the input mains
Figure 11. Power supply of a 12-volt consumer from 220 VAC mains with power factor correction
Figure 12. AC/DC converter without power factor correction
Fugire 13. Low profile (h = 16.5 mm) AC/DC power supply system of 340 W built on unified units.
The products described in this document are designed for building pulse load power supply systems based on modular units. Electric, weight and dimension specification of MDA units allow to implement compact decentralized power supply systems without significant capacitance power accumulators. ATF active current filters are used to smoothen pulses of current, consumed by the power supply system when feeding the pulse load. Power supply systems fed with power from AC mains are built using filter rectifiers and power factor correctors.