[sdiy] current sink idea

[Jean-Pierre Desrochers]

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
> > ________________________________________________________
> > This is the Synth-diy mailing list
> > Submit email to: Synth-diy at synth-diy.org View archive at:
> > https://synth-diy.org/pipermail/synth-diy/
> > Check your settings at:
> > https://synth-diy.org/mailman/listinfo/synth-diy
> > Selling or trading? Use marketplace at synth-diy.org