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previous: kg if you want a current source, then ... -- 4/23/2003 5:00 PM View Thread

Re: CF for ~constant current?

4/24/2003 7:19 PM
Jack Koochin
Re: CF for ~constant current?
Haven't had any time to really think about this, and not sure if this is a 2 or 3-terminal display device, but here is something to consider anyways:  
It may be much easier to adapt these devices using a solid state interface. One device I've used in the past is an opto-coupler that has a purely resistive 2-terminal output that you could hook up to anything. The output resistance varies in accordance with the level of drive to the LED. Does that give you any ideas ?  
So, here's one possible scenario..... buffer and rectify the signal (using filter caps or maybe not) you want to sample, feed it to the LED. Have the opto-coupler resistance vary a "current source" device that is in series with the display tube and the 140V power supply. The current source can be a 3-terminal IC.... you might even be able to enlist a voltage regulator in this role.  
Anyhow, there's an idea for you to kick around. Been some time since I've played with this stuff. Lots of ideas in OP AMP / IC applications manuals.  
Good luck,  

Mark Lavelle Thanks, Jack – lots to chew o... -- 4/24/2003 8:06 PM