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jackinnj 25th September 2004 04:08 PM

The "not so lowly" TL431
Interesting, in the current issue of "SwitchingPower" magazine, Dr. Riddley has a lengthy article on the popular and cheap (not inexpensive, cheap !!!) TL431 adjustable reference. The conclusion is that it will work quite well as an error amplifier cum reference (and a good low noise reference at that.) Riddley suggests several compensation methods which will result in very good performance.

These parts cost about a dime apiece !

wrenchone 25th September 2004 05:44 PM

This is no great secret - the TL431 (and its earlier incarnation, the TL430) have been used as error amp/references by the power supply industry for over 20 years. Hardly anyone uses them for their original intended application.

jcarr 25th September 2004 08:36 PM

Older thread along similar lines:

regards, jonathan carr

peranders 25th September 2004 08:44 PM

jackinnj, what was your point?

BTW: I have it in a fairly new design with power factor correction and all. It (the LM431) works pretty good as a comparator/voltage level sensing element. Switching frequency 100-200 kHz (don't know exactly).

jackinnj 25th September 2004 09:12 PM

the point -- Ridley goes on to describe the compensation scheme for optimal performance when using optical isolation.

paulb 26th September 2004 01:02 AM

There is an elegant design for a soft-start circuit using the TL431 as the only active element in the latest AudioXpress magazine. When the input voltage via an RC exceeds the reference voltage, the output pulls down a relay to ground.
It's also in the TL431 datasheet, Fig. 27.

jaycee 27th September 2004 02:15 AM

I've also seen the TL431 used as a bias servo, look up the Stochino amplifier. He uses it to set bias along with 4 BD139's in diode configuration as a thermal sensor.

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