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 100 ms/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 lowpower 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 mai
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 correctio
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.