Hold-Up Modules Reduce Capacitance Requirements For High-Rel Power Supplies

by Christophe Massenet, Gaia Converter, Summit, N.J., How2Power Today, Oct 15 2013

Focus:
The transparency or hold-up requirement in military applications is the minimum amount of time during which input power can go away but the equipment remains operational. This power interruption may last from 50 ms to 1000 ms. The simplest way to achieve the hold up function is to install a huge tank capacitor on the input bus. But with typical hold-up circuitry, the capacitors required to achieve the specified hold-up time can be quite large. However, an integrated hold-up module offers a space-saving alternative. By increasing the voltage to which the hold-up capacitor is charged, the module increases the stored energy for a given capacitance value, reducing the capacitance needed for a given hold-up time. This article assesses the impact of hold-up modules on mil/aerospace applications employing 28-V input dc-dc converters operating at different power levels, comparing capacitance requirements and design size with and without the modules. Article begins by presenting the equation for hold-up capacitance, discusses converter hold-up capability as a function of input voltage level, and explains operation of the holdup module. The article concludes with a diagram showing the placement of a hold-up module in a typical 28-V input distributed power architecture for mil/aerospace applications.

What you’ll learn:

• How to reduce hold-up capacitance requirements in 28-V input distributed power architectures by using integrated hold-up modules
• How to calculate a power supply’s hold-up capacitance required for a given hold-up time

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