Simple precision constant current LDR controller

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The TL431 and BC550 form a precision constant current sink, the maximum current is set by the presets RV1 & RV2.

RV3 is the 'volume control', the value should be chosen to set the input impedance of the attenuator.
 

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In a word, yes.

I can't comment on performance as I haven't built other peoples designs to compare it to, other than say I prefer it to my Alps and Noble pots.

My volume control stays in pretty much the same position, so the non logarithmic/audio taper function doesn't bother me.

I do recommend multi turn presets and a reasonable quality device for the volume control.

I haven't tried this, but it might be possible to get away with a cheaper pot if a couple of small value caps are added between the presets and either end of the pot to ground for decoupling, reversed biased diodes across the caps will also be needed.

The power supply I use is probably a little over kill, but I had it laying around, it's a series reg/current limit/shunt reg combination based around TL431's & IRF510's, the design is nothing new under the sun.

If you build it, post your results/impressions.
 
Dr.H

PSU as requested, drawn from memory so may not be totally accurate.

I don't recommend building it as it is very inefficient, a LM317 or 7809 would be more than good enough.

I originally built this PSU for another project, and out of curiosity, as I had the parts in my junk box.
 

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