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Re: De-Q-ing diodes



Original poster: "Malcolm Watts" <m.j.watts-at-massey.ac.nz> 

On 30 Nov 2003, at 9:29, Tesla list wrote:

 > Original poster: Rob Maas <robm-at-nikhef.nl>
 >
 > Hi All,
 >
 > Recently Daniel Barrett wrote:
 >
 >
 >  >Original poster: "Daniel Barrett" <dbarrett1-at-austin.rr-dot-com>
 >  >
 >  >	Gee, I feel like an advertisement for these things, but the 1N4007,
 >  though >cheap, is a little slow for the 200uS-ish pulse from the
 >  coil. I >experimented with this a year ago and they are inefficient,
 >  get hot and die >fast when used with anything but a 60Hz sine wave
 >  due to a very slow reverse >recovery time. Better to use then UF4007
 >  (A string of 50 for your >application). More expensive but will work
 >  as expected for higher frequency >stuff like ignition coil rectifiers
 >  and DC Tesla coil "De-Q-ing" diodes. Get >these from Mouser or
 >  similar. Digikey does not carry them. >db
 >
 >
 > I was just planning to construct a de-Q-ing diode from a string of
 > 1N4007's. Now I am worried. I thought a de-Q-ing diode basically
 > 'sees' only as highest frequency BPS_max, say 400-600 Hz ? Has anybody
 > experience (good or bad) with using 1N4007's in such applications. The
 > UF4007 certainly is 'better' than the common 1N4007, but also MUCH
 > more expensive (I need at least 40...).
 >
 > Any reaction greatly appreciated,    Rob Maas

Diodes with "normal" recovery times (in the uS range) behave more and
more like resistors than diodes when frequencies climb beyond a few
kHz. The breakrate is irrelevant save for multiplying the losses when
much higher frequencies are really what's being rectified.

Malcolm