Re: undervoltage lockout for flyback powersupply input

Eeyore wrote:

Jamie wrote:

Jamie Morken wrote:
I have a flyback powersupply that operates from about 20V to 450V+ (AC
or DC input) and I would like to reduce the operation to 75V to 450V,
what is a possible circuit to use on its input to keep it from starting
up until this threshold is reached?

For simplicity reasons, Get your self a DIAC rated around 75 volts
connect one end to the cathode of D34 and the other end will be
the V+ supply for R5 instead of connecting R5 directly to V+.

Neat idea actually Jamie. 30-40V diacs are more commonly available though
(I've never met a 75V diac) so perhaps 2 of those in series.

http://uk.farnell.com/jsp/search/browse.jsp?N=500004+1000013&Ntk=gensearch_001&Ntt=diac&Ntx=

Graham


Thanks for the ideas guys, also is there a way to shut off the circuit
when the voltage drops below 75V? I think the DIAC and comparator circuits will only prevent startup until 75V, but won't disable the
circuit if the voltage drops below 75V.

cheers,
Jamie
.

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