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Tl431 based filter

Has anyone ever pressed a TL431 into service as an active filter? I'm looking to use one of the TO-92 types as a single-stage MFB bandpass filter around 1 kHz. It simulates OK, but any gotchas to be aware of?

Reply to
bitrex
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Nope. It's a convenient one-input (2.5V above ground) OpAmp. I used it a lot in the 1977-87 time frame when I was at GenRad, in opto-isolated feedback loops. Worked great! ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Interesting, I wonder how that would work out as a notch filter?

I use a TL431 in a cascode configuration and set the input from a remote part of the circuit, sort of like a modulator circuit. It works very good and is compact but this circuit operates in a line power noisy environment and it would be nice if I could fit it to notch the 60hz.

We'll have to investigate further to see if that would actually work.

Nice idea btw.. I've always like doing a lot with minimum part count.

Jamie

Reply to
Jamie

The only possible "gotcha" I can see, if it could be called that, is that the "Ref" pin draws significantly higher current than the input of an ordinary bipolar opamp; uA vs. nA. The filter design software I use often chooses very large values for the feedback resistor going to the inverting input in the MFB configuration to keep the capacitances small, so a compromise will have to be made here.

Reply to
bitrex

So use your software, then realize, in ANY active filter: R*C=constant, so scale trivially ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     | 
| Analog Innovations, Inc.                         |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| Phoenix, Arizona  85048    Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

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