[sdiy] Diode Matching

[John Marshall]

Take a bunch of diodes (24) and tack solder them in series add a 10k ohm
resistor in series. Then connect the series string to an adjustable power
supply. Measure the voltage drop across the 10k ohm resistor and set the
power supply so that the resistor drops 2.0 Volts. 200 microvolts is a good
place on the curve to match diodes. Measure the voltage drop of each diode.
CAUTION. Glass diode are light sensitive. It is best to measure the diodes
in dim light. Diodes are heat sensitive.

In some circuits matched diodes are important.

John

On Fri, Apr 10, 2020 at 5:03 PM TERRY SHULTZ <thx1138 at earthlink.net> wrote:

> Hi,
>
> I use tweezers/pinchettas to pick up parts so my body temp will not
> influence the measurement.
>
> I match transistors all the time and we super match resistors for building
> my own DACs and I use a piece of styrofoam to hold the measured devices.
>
> I keep a few extra from each category so I can replace one if it goes
> defective.
>
> We bake the resistors at a low temperature in the oven to drive out
> moisture .
>
> Best regards,
>
> Terry
>
> Shultz Products LLC.
> thx1138 at earthlink.net
>
>
>
> On Apr 10, 2020, at 4:12 PM, Didier Leplae via Synth-diy <
> synth-diy at synth-diy.org> wrote:
>
> Gordon,
>
> I tried your suggestion. Over 5 minutes the reading changed from about
> 350mV to about 365mV. When I grab the diode with my fingers, it actually
> goes down a bit, just about 2mV. I tested this repeatedly with exactly the
> same result.
>
> Incidentally, if I change the multimeter to read another diode, the
> reading stays at the elevated reading, 365mV. So that suggests to me that
> the meter is what's heating up, or causing the change, rather than the
> diode.
>
> Throughout all this testing, I've been quite careful not to subject the
> diodes to temperature changes. I've got them taped to a notebook. The
> notebook is sitting by itself on a chair, not in my lap or anything. I've
> been working in a basement, so no big temperature changes or sunlight
> coming in to heat them up.
>
>
> On Friday, April 10, 2020, 05:14:22 PM EDT, Gordonjcp <gordonjcp at gjcp.net>
> wrote:
>
>
> On Fri, Apr 10, 2020 at 08:44:28PM +0000, Didier Leplae via Synth-diy
> wrote:
>
> > So far I have tried three different methods of testing and find the
> results to be confusing and unreliable.
>
>
> Get a single 1N4148 diode.  Stick it in your meter in diode check mode.
> Observe the reading.  Leave it for five minutes.  Observe that the reading
> has changed.  Squeeze the diode between your finger and thumb.  Notice that
> the reading changes wildly with the temperature.
>
> --
> Gordonjcp
>
>
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