Andy said:
>My current power supply project has been built with a tuned filter on the
>negative rail of the DC, tuned to 100hz (i.e. 2xmains hz)
Have you checked the actual resonant frequency? My understanding of the
tuned choke filter is that it should be tuned slightly higher in frequency.
This makes the circuit look like a very much bigger inductance, so that a
smaller bleed resistor is needed to keep the inductance above the critical
value. Actually hitting resonance can give some very nasty voltages, as
Tom, W8JI, can tell you. From your nominal values, the resonant frequency
(nominal)is 102.7Hz. This means the effective inductance is 38.08 Henries,
which should be OK, but if the tolerances are such that the resonance is
far off, you could be seeing problems. Typically, the choke will probably
be around 10% and the cap is probably no better than 5%. I'd suggest you
start by measuring the real resonant frequency.
73
Peter G3RZP
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