Transformer Design For Charging Defibrillator CapacitorsSource: Datatronic
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 -
- Simple circuit.
- High voltage output is not dependent on large turns ratios.
- Circuit is self limiting. Output can be shorted without damage.
- Output can be regulated over a large range.
- Transformer can provide voltage isolation.
- Multiple isolated outputs are possible. One output can be used for a low ratio feedback voltage.
- Smoothing choke not required.
Some disadvantages -
- Requires a transformer.
- Fast switching can generate EMI problems.
- Leakage inductance must be kept low for good efficiency.
- Without a feedback loop, circuit may be damaged if the load is removed.
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