Skip to content
sergimon edited this page Sep 14, 2010 · 7 revisions

Capacitor Calculations

We are having one of these un-regulated underpowered (500mA) power sources, so we needed a big enough capacitor to the 1.5A regulator output so our regulator circuit could offer 2A ~500us bursts. The capacitor value can be calculated using following formulas.

First calculate the energy reguired (the consumption is assumed to be the same for the time window):

Then the formula for calculating capacitor energy:

Combine these:


We got 500uF capacitor from these formulas.

Zener Calculations

Short note how to calculate the zener protection circuit resistor value. The series resistor is required to ensure that zener does break for over current.

In following figure is shown a simple circuit where zener is used for over voltage protection.

In the worst case when there is no load at all (R_LOAD) all current goes through R_IN and zener. To calculate R_IN:

This protection circuit should only be used for small currents.