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derekyu 28th April 2007 11:15 AM

transistor matching
 
I am looking for the ways to match pairs of transistors. I only have a multimeter but do not have any osc. Can somebody show me the ways to match a pair of npn with a pnp or a pair of pnp with a pnp?

jackinnj 28th April 2007 02:20 PM

You can use your sound card as a curve tracer -- go to the ARRL (American Radio Relay League) - experimenteer site and download the file under author name Steber -- this article appeared in 2006:

http://www.arrl.org/qexfiles/

EUVL 28th April 2007 02:24 PM

Derek,

if you only want to match bipolar transistors (as opposed to FETs) and not at high current (i.e. TO92 devices), most multimeters today offer hfe measurements. This is the easiest (though perhaps not necessarily the best) way, depending on your application.


Patrick

Nordic 28th April 2007 03:35 PM

Hi Jack, thanks for the project idea.... might come in handy now that I have given up my chip pacifiers....

derekyu 28th April 2007 03:43 PM

thank you very much for your help. In searching Passlab, i got some information for matching a mosfet by using resistor. Can some device like this for matching a npn tr?

I know some multimeter can check the hfe; but i wannta to find a way to obtain more (maybe a little) precise result than by using multimeter.

jackinnj 28th April 2007 04:15 PM

Quote:

Originally posted by derekyu
thank you very much for your help. In searching Passlab, i got some information for matching a mosfet by using resistor. Can some device like this for matching a npn tr?

I know some multimeter can check the hfe; but i wannta to find a way to obtain more (maybe a little) precise result than by using multimeter.

My radio shack multimeter matches HFE +/- 1 digit -- regrettably it eats 9V batteries :( --

You don\'t really need a specialized meter -- if you connect a resistor from Collector to power source, of say 470 ohms, and a resistor from Base to power source of, say 10k ohms, measure the voltage drop across each resistor, calculate the current and voila by dividing you have the HFE - choose the resistor values for current that is appropriate.

AKSA 29th April 2007 03:52 AM

Try this one:

Matching Devices

See #13.

Cheers,

Hugh

smithy666 29th April 2007 08:48 AM

Elektor published a power MOSFET tester circuit in Nov 93, developed by Ton Giesberts. It matched 2 n-channel and 2 p-channel at a time, under load (peak drain currents of up to 13A), and relied on a scope to display Ugs and Id (x and y) for each device. I am building this as the moment, so I'll report back on how well it works.

AndrewT 29th April 2007 09:46 AM

Hi Aksa,
can a lab supply be substituted for the battery.
It's what I use at present, but you've got me wondering if the regulation interferes with the DUT measurement.

john_ellis 29th April 2007 10:51 AM

One simple way to match devices is to use a fixed voltage supply (lab or battery), connect an ammeter between collector and supply, and use a series of resistors between the base and supply. For NPN supply is +, PNP, -.

For high currents it is best to put the transistors onto a heatsink, but it also depends how quickly you make the measurements.

Compare currents measured between two transistors you'd hope are matched.

More accurately you can then connect your meter to measure the base voltage for the same resistors, to calculate base current and therefore gain. Assumes that the collector voltage drop in your meter is low (say < 0.5V at max amps).

So long as you restrict the power supply to e.g. 5V ( I use an old computer SM-PSU for this!) dissipation is not too bad.

For MOSFETS, you need to alter the gate voltage rather than current, so use a low resistance pot. so that your meter does not load it too much (e.g. 1kohm) but you may want to insure against oscillation by including a 100 ohm series resistor.

cheers

John


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