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Re: Choke Snubber Circuits Questions

I can't really speak to Morgan Jones' book, but you don't need a snubber on CLC circuits. The whole point is to give an out for the current when the circuit is broken; that is to say when the unit is turned off. With an LCL filter, where critical inductance is reached with the first choke, all the current which is 'stored' in the first choke. When the line is broken, all the current appears on the line as a reflection of the various impedances at both ends of the choke. Now that's not a problem on the CL side of the choke where the impedance is relatively low. However, on the rectifier end of the choke, the impedance can be very high, but the current appears never-the-less. So, by Ohm's law the resultant voltages can become staggeringly high; high enough to tear right through the PIV of silicon diodes, for instance.

The fix is the snubber which offers the circuit a low impedance drain to the instantaneous pulse which appears. I am not sure but the 256R in your circuit is probably the DC resistance of the specific choke used. And with that value as a guide, the specific capacitors would be chosen to be low enough impedance to dissipate the current for the single fast pulse but have high enough impedance at the 60-120hz of the power supply to be invisible.


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  • Re: Choke Snubber Circuits Questions - corerosin 10:45:31 03/02/07 (0)


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