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TomT 12th January 2002 09:48 PM

Matching IRF610's
Here's a simple method I use for matching IRF610's used in the balzen preamp.
The link is:
Hopefully the tl431 isn't to exotic. The data sheets can be found on the web at on-semi, TI and Zetex.
The tl431 part has always been a favorite part of mine over the years.


rtirion 12th January 2002 11:56 PM

Sorry to say the link isn't working
Reply I get is "This page is not available"


AudioFreak 13th January 2002 03:53 AM

try this.........

goto then click on the link to tl431matching.jpg

TomT 13th January 2002 05:10 AM

Thank-you Audio Freak.

Sorry about the link. Just joined DIYaudio.
Trying to these web things working.


promitheus 14th January 2002 06:46 PM

itīs a very good idea. Does this zener always have 2.5 V reference voltage ?

TomT 15th January 2002 09:57 AM

The Zetex part numbers are:
ZR431 is the 2.5V
ZR243 is the 1.24V

The On-Semi and T.I. part numbers are:
TL431 is the 2.5V
TLV431 is the 1.24V

See the web sites for the data sheets.
I believe the voltage references are band-gap types.

I have also used the circuit to match npn transistors and n-channel jfets. When using the circuit with n-channel jfets a resistor or diodes must be placed between the source of the jfet and the reference pin to keep the voltage greater than zero between the cathode and reference pins on the 431 part.
Also have used the circuit as a current source in amplifiers.

promitheus 15th January 2002 02:01 PM

This means the ref voltage is always constant. so we can measure the Vgs of the fets. how can someone hook up a irf9610 to measure? And how can someone measure bigger FETS like IRFP240 at 1 amp?

GRollins 15th January 2002 03:02 PM

National Semiconductor has similar parts; the LM-336 series.
Bear in mind that the voltage will drift with temperature, but there's a fairly simple circuit you can build with some 1N914s (or other small diodes) to counteract the drift. Also, the adjust pin means just that--the voltage is approximately 2.5V, but may be slightly off due to manufacturing tolerances. You can include a compensation pot in the temperature correction circuit. Check the Nat. Semi. datasheets for details of the compensation circuit.


TomT 16th January 2002 03:49 AM

Sorry the tl431 circuit does not work with p-channel mosfets like the IRF9610. Here is and idea for matching the IRF9610 mosfet. Go to
then click on the link to lm337match.jpg
I have not tried the tl431 circuit at large currents on power mosfets.

promitheus 16th January 2002 06:30 AM

also a very good idea.

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