Transformer Design for Charging Defibrillator Capacitors

Generating high voltage by means of flyback topology is a common approach. Using the generated voltage to charge a capacitor for a high energy pulse are used in defibrillators, photoflashs, strobes and ignition circuits to name a few. The procedure outlined in this article is useful in the initial transformer design phase for charging a capacitor in a stated time. The procedure presented eliminates "cut and try" or over-design approaches. Selection of critical values can be made with confidence using the guidance provided. First a little background in flyback topology. Flyback topology has several advantages - 1) Simple circuit. 2) High voltage output is not dependent on large turns ratios. 3) Circuit is self limiting. Output can be shorted without damage. 4) Output can be regulated over a large range. 5) Transformer can provide voltage isolation. 6) Multiple isolated outputs are possible. One output can be used for a low ratio feedback voltage. 7) Smoothing choke not required.