Allowing an inductor to ring while still protecting the rest of the circuit.

Thread Starter

MagicSmokeMaker

Joined Jan 22, 2018
2
Good afternoon all, I need to ask a bit of a newish question involving driving transformers using solid state electronics. That is, how would one go about allowing inductive spiking to occur (AKA no clamping diode in parallel with the coil) while protecting the transistors of the driving circuit so that you can achieve a higher primary voltage and thus a higher secondary voltage?
 

crutschow

Joined Mar 14, 2008
25,267
Are you referring to using transformers in a flyback design?
In that case the spikes are typically clamped with a zener with a voltage rating of 50-75% of the transistor maximum voltage rating.
 

MrAl

Joined Jun 17, 2014
7,758
Good afternoon all, I need to ask a bit of a newish question involving driving transformers using solid state electronics. That is, how would one go about allowing inductive spiking to occur (AKA no clamping diode in parallel with the coil) while protecting the transistors of the driving circuit so that you can achieve a higher primary voltage and thus a higher secondary voltage?
Hello,

The way it is done in H bridge converters is the outputs of the bridge are clamped to the DC buss and ground, NOT across the winding. Many transistors like MOSFETs already have an internal diode that does this, but external Schottkeys work better.

Despite the clamping diodes, there is also a high speed spike that the diode can not catch due to the inevitable lead inductance. To kill that a snubber is employed, wired as close in to the collector and emitter of the transistor as possible.

Zeners typically are not used because the power dissipation would be too high and the efficiency would be worse.
 
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