[R-390] OT: Diode Matching

[Bob Camp]

Hi

Normally what this cryptic little note means is "buy the over priced 
ones from us".

Depending on what the circuit is actually doing there are a number of 
ways to match the diodes. The first question to ask is "how many diodes 
do you have?". The answer is usually a limited number so the whole 
exercise comes down to getting things close enough rather than perfect.

I would take a low current forward voltage reading and use that to pick 
the two diodes that are the closest to each other.

	Enjoy!

		Bob Camp
		KB8TQ



On Apr 20, 2005, at 3:49 PM, Jim Temple wrote:

> I am trying to match a set of diodes for a tube tester.  They are 
> 1n540's.
> The schematic says "matched for equal forward resistance".
>
> I have a Fluke 87 meter that has a diode test position.  I get similar
> forward voltage indications of about .510 volts.  I get similar 
> resistance
> measurements of about 1.7meg.
>
> What confuses me is when I measure the forward voltage in the diode 
> mode,
> then without disconnecting the leads switch to resistance mode, I get 
> either
> approx 40K resistance, or approx 380K resistance, randomly.
>
> When attempting to match for equal forward resistance, which procedure 
> seems
> correct?
>
> 1. Simply measure the resistance.
> 2. Measure the diode voltage, then switch to resistance mode and 
> measure the
> resistance, which gives me either approx 40K or 380K?
> 3. Measure the diode voltage, then switch to resistance mode, 
> disconnect and
> reconnect the leads, which gives me approx 1.7meg?
>
> Thanks for any help on this matter.
>
> Sincerely,
>
> Jim Temple
> Louisville, KY,
>
>
>
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