Can TL431 be used as a bias transistor?? - diyAudio
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Old 15th January 2009, 01:41 PM   #1
Leolabs is offline Leolabs  Malaysia
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Default 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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Old 15th January 2009, 01:47 PM   #2
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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.
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Old 15th January 2009, 02:01 PM   #3
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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:

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

After all it works just fine.
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Old 15th January 2009, 03:05 PM   #4
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Nelson Pass use it in one of his Firstwatt amplifier
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Old 15th January 2009, 05:57 PM   #5
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It's used in Giovanni Stochino's fast MOSFET power amp, with 4 diode connected BD139's for temperature sensing.
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Old 15th January 2009, 08:51 PM   #6
lineup is offline lineup  Sweden
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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.
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