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Old 10th June 2012, 11:05 AM   #1
Itsmee is offline Itsmee  England
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Default Simple precision constant current LDR controller

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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Old 4th July 2012, 02:15 PM   #2
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HI Itsmee, have you built this and listened?
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Old 4th July 2012, 07:19 PM   #3
Itsmee is offline Itsmee  England
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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.
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Old 5th July 2012, 09:21 PM   #4
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Thanks for the info. Do you have a schematic of the power supply you refer to?
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Old 6th July 2012, 08:10 AM   #5
Itsmee is offline Itsmee  England
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No, but I will put one together and try to post it over the weekend - if I get time.

As I said, nothing new, all the modules (series reg/constant current/shunt reg) used in the PSU can be found in the TL431 data sheet.
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Old 7th July 2012, 01:20 PM   #6
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What part number are the LDRs? Thanks.
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Old 7th July 2012, 01:51 PM   #7
Itsmee is offline Itsmee  England
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I'm not entirely sure what they are, they are the ones used in the lighter note kit.

You can get a matched set from here FEBRUARY LDRS
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Old 8th July 2012, 07:40 PM   #8
Itsmee is offline Itsmee  England
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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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Old 8th July 2012, 09:31 PM   #9
gootee is offline gootee  United States
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For the current source:

How did you do the layout/routing?

Also, do you have any information about the temperature stability?

Last edited by gootee; 8th July 2012 at 09:34 PM.
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Old 8th July 2012, 10:38 PM   #10
Itsmee is offline Itsmee  England
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The current source is point to point wiring and laid out pretty much as it is on the schematic.

Thermal stability measurements, haven't got any.

Have a look at the TL431 data sheet for more info on temperature stability.
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