Energizing Output Filter Inductor Enables Instantaneous PSU Activation

Focus:

Using a cold redundancy technique to wake up a battery backup module allows for accelerated power supply wake-up. It is based on precharging output capacitors to their steady-state voltage levels. In this case, a soft start is not required, as only the output filter inductor needs to be charged to the current matching the current consumed by the load. Although a full power stage activation in this case typically lasts only a few hundred microseconds, the usage of this technique still requires much larger dc bus capacitor values than would be needed in the “ideal” instantaneous wakeup case. To overcome this limitation, this article discusses the opportunity to “precharge” the output filter inductor along with the output capacitor, to further accelerate the backup module activation process. After quantifying the reduced capacitance requirement with instantaneous power supply activation, a circuit is presented for energizing the output filter inductor’s core. Then, its operation is explained and verified through simulation. Some design considerations for implementing the proposed circuit are also discussed.

What you’ll learn:

• How to speed activation of a battery backup power supply by pre-energizing its output filter inductor
• How to reduce dc bus capacitor requirements through instantaneous activation of backup power supplies

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Author & Publication:

Viktor Vogman, Olympia, Wash., How2Power Today, Sep 15 2025

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