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Matching Stuff

Posted 27th November 2011 at 12:24 AM by Michael Rothacher

The topic of JFET and MOSFET matching comes up often in the forums, so I thought I'd show you the jigs I use.

First up, is my trusty old JFET IDSS matcher.

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There's a 9V battery inside, and the meter probes are conneted across a 10 Ohm resistor which is connected to the JFET drain. I included a polarity switch for convenience when testing P channel parts.

It's pretty easy to connect the microclips, count to five, and take a reading.

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And here's what I use for the big stuff. This is my MOSFET Vgs matcher.

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First, I install a sample part and let it warm up for about an hour. There's a thermistor hot-glued to the heat sink, and it's attached to an outdoor thermometer so I can monitor the heat sink temperature as I measure parts to ensure things stay within range. Things tend to stay within a degree or two without a lot of fuss.

Click the image to open in full size.

I use a couple of TO-220 sockets for the sample, and it's very easy to slide the part in and clamp it down to the heat sink for measurement.

You could probably come up with something much fancier if you like, but these simple jigs have served me well for years.
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