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Author Topic: Measuring Transistor HFE  (Read 6901 times)
KA5IPF
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« on: April 27, 2012, 08:34:08 AM »

What is your method?

I saw a note somewhere that a ham used his DMM to measure HFE. Now I can't find it to see how he did it.

Clif
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K8AXW
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« Reply #1 on: April 27, 2012, 08:51:57 AM »

As far as I know..... transistor HFE can be checked only with a transistor checker or a DMM with a transistor checking socket..... which means a special DMM.
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KB3HG
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« Reply #2 on: April 27, 2012, 09:09:50 AM »

A start:
smaller transistors
http://www.harborfreight.com/7-function-multimeter-98025.html

One could setup a test jig, but with some meters having them built in there is the learning experience.

I have some monster transistors Motorola's 800v 50a Pd was 500w with a real large heat sink, doubt if that meter would be of any help.

from memory, very loose terms beta x ib (base current) =+/- hfe common emitter circuit a handbook would give you a better idea

Tom Kb3hg



Heathkit sold semiconductor curve tracers back in the 70s, might find one on ebay. Just one note. hfe is nice but it is the surrounding circuit to the semiconductor that will determine the circuit gains.
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AC5UP
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« Reply #3 on: April 27, 2012, 10:03:02 AM »

Check out the simple transistor tester shown here: http://sound.westhost.com/project31.htm

There are scads of schematics on the web for Hfe testers and this only one example. The "Full Monty" version looks simple enough that even N4NYY could build one, although it would require starting a new thread to discuss the temperature coefficient of a chicken salad sandwich...

Grin
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M6GOM
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« Reply #4 on: April 27, 2012, 10:13:34 AM »

HFE of a transistor is easy to work out and can be done with a multimeter and a bit of maths.

HFE is the ratio of Ic to Ib.

There are formulas to work out Ic and Ib without measuring the current.
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KA5IPF
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« Reply #5 on: April 27, 2012, 11:06:35 AM »

It didn't take me long to figure out I don't have the time to build one. So I looked around and ordered one.

http://www.anatekcorp.com/atlasdca55.htm

Any thoughts or comments, looks nice.

Clif
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KA4POL
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« Reply #6 on: April 27, 2012, 11:45:54 AM »

I'd like it better in pink  Grin So much for looking nice.

It seems to suit your needs. Many DMMs do have the function built in.
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KA1MDA
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« Reply #7 on: April 27, 2012, 12:54:48 PM »

My Beckman DMM has a diagram for building a test fixture to measure trasistor DC beta using the diode test function. Collector connects to one lead of the meter, and Emitter connects to the other meter lead. The meter leads need to be reversed for NPN vs PNP, or you can put in a DPDT switch in the jig to swap lead polarity easily.

Two 2K ohm resistors are connected in series between the transistor's Collector and Base. A SPST switch is wired across (in parallel to) one of the 2K ohm resistors, so that the resistor is shorted out of the circuit when the switch is closed. Thus, the resistance between the Collector and Base terminals is 4K ohms with switch open, and 2K ohms with switch closed.

To calculate beta, place the meter in diode check mode. Ignoring the decimal point in the display, beta = 2000 / (reading with switch open) - (reading with switch closed). So if you read .800 with the switch open, and .700 with the switch closed,

Beta = 2000 / (800-700) or 2000/100 = 20

I  built a jig like this in a small project box,with a few transistor sockets and 3 clip leads, with a pair of banana plugs that connect to the meter. An DPDT switch makes it easy to go from NPN to PNP. It seems to work quite well.

Tom, KA1MDA
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