COVER STORY
Power averaging for counter-UAS systems delivers speed and reliability
DC-DC converters provide high-power pulses for size- and weight-constrained platforms explains Dave Berry, sr. principal applications engineer, Vicor
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hether detecting or disabling enemy drones or drone swarms, counter-UAS (unmanned aircraft system) platforms rely on power delivery networks (PDNs) that can deliver short, high-power
pulses to their load. The challenge, however, is optimizing the source of power to ensure speed and reliability. In most cases, supporting sustained peak loads requires PDNs with extremely bulky supplies adding size and weight. Unfortunately, Counter-Unmanned Aircraft Systems (C-UAS) are often mobile and battery- or generator-powered, inherently limiting their PDN’s peak power capabilities. While a platform’s pulsed emitter may demand tens of kilowatts for a few hundred microseconds, most C-UAS systems can only provide a small fraction of that. Power averaging offers an efficient solution. With power averaging, rather than sizing the entire supply for the peak power condition that occurs only for brief periods, a power- averaging circuit pairs a current-limiting converter with a bulk capacitor to deliver far more power than the converter alone could supply. With high power density, fast capacitor recharge and safe operation into large bulk capacitance, high-density modular DC-DC converters can make power averaging a reality for C-UAS systems.
Using power averaging to deliver C-UAS speed and performance
One solution for applications where the load is only on for a short duration and is repetitive, is to use a current- limiting converter and a capacitor to supply peak power needs. When configuring such a power system, the designer must take into account the current limit, power limit and stability of the power supply as well as sizing the capacitor properly to keep the voltage drop at the load within its tolerances. Pulsed emitters, radar and LIDAR arrays, and similar pulsed C-UAS loads can take advantage of power averaging to reduce cost, space and weight within the system.
Power averaging configurations are very effective when the load can tolerate a wide input voltage range. This is typically the case where the load is another regulating
10 September 2026 Components in Electronics
Figure 1: C is the hold-up capacitor value, P is the power needed during each pulse. T1 –T2 is the pulse duration. V1 is the starting voltage before the pulse and V2 is the final voltage at the end of the load pulse.
device — typically a point-of-load converter — or several of these regulating devices.
When the point-of-load (PoL) or load demands power, the capacitor will deliver a greater portion of the load current because the DC converter will go into current limit feeding the capacitor and the load. As the capacitor delivers the PoL or load current, its voltage will begin to fall. The capacitor must be sized so that the voltage across the capacitor stays within the input voltage range of the PoL converter (Figure 1).
To minimize the capacitance needed the designer can charge the capacitor to the PoL’s maximum input voltage and allow the power draw over the power duration to operate the capacitor down to the PoL’s minimum input voltage.
Safeguard against power system failure by setting current limiters
DC-DC converters are typically designed to regulate voltage up to a maximum power level and therefore have a maximum current and power rating. If the load, such as the radar load in a C-UAS emitter, tries to draw more than the rated current from the supply, the supply typically goes into a current-limiting mode that either folds back the output voltage or shuts down and restarts.
The current limit is typically set just above the maximum rated current so that full power delivery is possible at the voltage set point of the converter. A converter rated for 500W at 48VDC
rating of 500W/48VDC however, may not start until the output current is at 13A.
Current limiting is typically designed for load faults where the converter will see current limit only a few times in its life. If the converter isn’t designed to go into current limit as a normal mode of operation, doing so too frequently can stress components within the converter and shorten the life of the power system.
If the load draws more than the maximum current but below the current limit at the voltage set point, then eventual power system failure can result from chronic overpowering of the supply. Thus, a 500W converter at 48VDC with a current limit set at 13A will be overpowered up to 624W before current limiting starts.
Dealing with complications of large bulk capacitance
The large bulk capacitance used in power-averaging applications can cause many complications for the DC power system. Upon power-up the larger capacitor, which in many cases can be in the thousands of microfarads, can draw the DC supply into current limit. With the potential problems associated with built-in current limiter, frequently an external current-limiting circuit is required to limit the supply within its maximum current and maximum power ratings.
Counter-UAS power designers can pre-charge the capacitor or add series resistance that limits the current
will have a maximum continuous current or 10.4A. The current-limiting feature
Figure 2: 10mF cap is the capacitor needed for DCM operation. The 100mF capacitor is the pulse hold-up capacitor. U1 is the capacitor introduction circuit.
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