[sdiy] current sink idea

[Roman Sowa]

Thank you.

Aparently this is old news anyway. Someone found Analog Devices article 
from 2006 where such current sources are discussed:
https://www.analog.com/en/resources/technical-articles/variations-among-currentsinksource-circuits-with-a-single-op-amp.html

Roman

W dniu 2024-11-30 o 17:33, Jean-Pierre Desrochers pisze:
> To me it's a very good idea and a very different way to solve this design problem..
> I've always liked and promoted the 'weird' ways to solve problems
> that are too often analyzed and cured with 'mostly' available solutions.
> Easy problems can be solved by easy solutions though..
> But sometimes you need to use your 'grey matter'.
>
> Good job Roman !
> JP
>
>> -----Message d'origine-----
>> De : Synth-diy <synth-diy-bounces at synth-diy.org> De la part de Roman Sowa
>> via Synth-diy
>> Envoyé : 30 novembre 2024 03:32
>> À : synth-diy at synth-diy.org
>> Objet : Re: [sdiy] current sink idea
>>
>> well, the pictures haven't went through, so here's the schemo in attachment
>>
>> Roman
>>
>> W dniu 2024-11-30 o 09:17, Roman Sowa via Synth-diy pisze:
>>> Since criticizing circuit ideas is a new trend, here's something I
>>> came up with 2 days ago.
>>> Special needs require special solutions - I needed to control
>>> display's backlit intensity from internal DAC of the microcontroller,
>>> which unfortunately is unbuffered and rather high impedance. Obvious
>>> simplest solution with emitter follower works, but even high beta
>>> transistor loads the DAC too much. I could replace it with Darlington,
>>> but then there's even more of DAC range lost and possibly even worse
>>> repeatability between units.
>>> Next step was well known current source/sink using opamp driving
>>> transistor with current sensing resistor. But that's 2 active parts
>>> and space is limited. So I made this (hoping ithis shows up in the
>>> email body or attachment):
>>> Current sink schematics
>>> I moved the sensing resistor to opamp's power input thus eliminating
>>> the need of external transistor. Quiescent current is 60uA so it
>>> doesn't affect performance. It works up to 23mA of LED current, which
>>> is all I needed. It can also be controlled by PWM with 1st order
>>> very-low pass RC filter, like 1M+100nF adding free fade in/out effects.
>>>
>>> And here's how it looks:
>>> assembled prototype
>>>
>>> Roman
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