[Amps] Using HV rectifiers from microwave ovens

[Manfred Mornhinweg]

Hi Angel,

> I was thinking of using about 1 ohm. This would produce a voltage drop 
> of about 0.5 volts at 500 mA. Ten times more than the mismatch between 
> two individual rectifiers. Does this seem right?

No, it's not enough. The problem is thermal runaway. If one diode gets 
warmer, it will reduce its voltage drop, take a larger current share, 
get even hotter, etc. You would end up with most current in one diode.

To be safe against this problem, you need about 0.5V drop in the 
resistor for EACH silicon junction. Since your rectifiers seem to have 
six diodes in series, you would need about 3V drop in the resistors. 
With 0.5A total, that's 0.25A in each resistsor, thus about 12 Ohm. A 2 
Watt rating should provide enough safety margin.

But all this is rather academic. I agree with Carl. 1N5408 diodes are 
cheap, rugged and plentiful. Use strings of them in series, and you 
probaly don't even need any resistors nor capacitors with them. In my 
amp I have strings of 5 of these diodes in series, in each leg, for 
2800V, which is still really cheap and gives ample safety margin. I'm 
using just the bare diodes, with no resistors nor capacitors. So far it 
works, and has worked for years.

Manfred.

========================
Visit my hobby homepage!
http://ludens.cl
========================