[AMPS] PIN stuff

[Peter Chadwick]

George says;

>Does anybody know what the downsides would be
>of placing a pair of PIN diodes in parallel to increase
>power handling capability of the circuit. 


Unless you increase the current, it won't help the power handling. I don't
have the 2001 data to hand, but my feeling is that you don't have enough
bias current. Incidentally, with PINs, it's the low frequency end that gets
readily compromised, because you need enough stored charge in the junction
that during the reverse half RF cycle, the diode doesn't stop conducting. So
2 PINs in parallel will need effectively the same current in each one that
you have at the moment to handle twice the RF current.

I'd suggest that you go for the maximum DC through the diode that you can
handle without exceeding the diode ratings. That will quite probably reduce
the dissipation. If you need more, then parallel diodes for RF, but keep
them separate for DC - you could get one diode hogging most of the current,
otherwise. Or put a  few ohms (less than 10 if you're running 500mA) in
series with each diode, with a good low loss high current capacitor across
the resistor. For 160, that means a something like a 0.5 microfarad ceramic.
So you're better off with separate DC feeds to each diode, and parallel them
for RF.

I'm a bit dubious about the reverse volts - it seems a bit low for the power
level you're talking about, and you might do better increasing that.

Hope this helps

73

Peter G3RZP



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