Can TL431 be used as a bias transistor??

Leolabs · 15th January 2009, 01:41 PM

Since that TL431 does have low impedance characteristics,wonder can it be used as a bias transistor in a power amp???

Ouroboros · 15th January 2009, 01:47 PM

I use a TL431 (with a capacitor to bypass it) as the bias voltage source in my MOSFET-output current-dumping amplifier.

Don't forget that the minimum voltage produced is 2.5V, so it may not be useful in a bipolar-output amp, and also that the voltage doesn't vary with temperature, so it might not be appropriate for use in many cases.

Corax · 15th January 2009, 02:01 PM

I've done it with success at my "Alexander current feedback amplifier" with IGBTs (of type GT20D101 and GT20D201). The application can be found here:
http://www.analog.com/static/importe...17334AN211.pdf

I finally replaced Q14/Q15 and Q16/Q17 also with a TL431, but had to increase the values of C1 and C2 to 47µF - otherwise the TL431 tends to oscillate.

After all it works just fine.

lumanauw · 15th January 2009, 03:05 PM

Nelson Pass use it in one of his Firstwatt amplifier

jaycee · 15th January 2009, 05:57 PM

It's used in Giovanni Stochino's fast MOSFET power amp, with 4 diode connected BD139's for temperature sensing.

lineup · 15th January 2009, 08:51 PM

Quote:

Originally posted by lumanauw
Nelson Pass use it in one of his Firstwatt amplifier

In Firstwatt F4.
TL431 is used as a precision VBE multiplier.
As F4 works in Class A the insensitiveness to temp. is not a problem.
In Class A temperarture compensation can be less of a problem.
Usually after warm up for some time, the bias will stay very constant.

15th January 2009, 01:41 PM	#1
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Can TL431 be used as a bias transistor?? Since that TL431 does have low impedance characteristics,wonder can it be used as a bias transistor in a power amp???

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15th January 2009, 01:47 PM	#2
Ouroboros diyAudio Member Join Date: Dec 2003 Location: Nottingham UK	I use a TL431 (with a capacitor to bypass it) as the bias voltage source in my MOSFET-output current-dumping amplifier. Don't forget that the minimum voltage produced is 2.5V, so it may not be useful in a bipolar-output amp, and also that the voltage doesn't vary with temperature, so it might not be appropriate for use in many cases.

15th January 2009, 02:01 PM	#3
Corax diyAudio Member Join Date: Feb 2005 Location: south of lower saxon	I've done it with success at my "Alexander current feedback amplifier" with IGBTs (of type GT20D101 and GT20D201). The application can be found here: http://www.analog.com/static/importe...17334AN211.pdf I finally replaced Q14/Q15 and Q16/Q17 also with a TL431, but had to increase the values of C1 and C2 to 47µF - otherwise the TL431 tends to oscillate. After all it works just fine.

15th January 2009, 03:05 PM	#4
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	Nelson Pass use it in one of his Firstwatt amplifier

15th January 2009, 05:57 PM	#5
jaycee diyAudio Member Join Date: Apr 2004 Location: Norwich, UK	It's used in Giovanni Stochino's fast MOSFET power amp, with 4 diode connected BD139's for temperature sensing.

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