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Driver Circuit Thread

rhd

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Here's an interesting update. I solved the problem with this board, though I did it without actually figuring out what exactly the problem was - or at least what the root of it was.

The problem, somehow, arose from using the 5V regulator for the LED power source. In fact, the actual split rail circuit worked just fine, but when I introduced the regulated 5V into the equation by connecting the LED panel, problems materialize.

What's interesting, is that the LED panel I'm using supposedly has isolated grounds. IE, a GND for the 5V power supply, and a separate GND for the measurement signal.

Well - that can't be true, because it sure didn't like the 5V regulator using a ground different from the split rail's ground.

The solution was simple - to take the 5V regulator and move it to the positive rail side. I'm hoping that having the additional drain on the + side and not the - side won't create any troubles, because it appears to work great now :)
 

rhd

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Here is an easy dual rail driver based on a LM358N Op-Amp and a NPN/PNP Transistor pair. Useful for things that requires a + and - voltage like OPHIR Thermopile heads.


Sorry for the necropost.

My LPM uses this circuit. I had one made through Oshpark (Laen at the time) years ago.

Back then it was irrelevant, but now I'm wondering what determines max reading range? My setup clips at about 3800 mW (mV) of reading, and I'm trying to figure out whether this circuit is the culprit, or the LED digital display I'm feeding the reading to.

Any thoughts?
 

Atomicrox

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What voltage are you feeding the circuit with and what voltage does it output to the Ophir? The Ophir needs a couple Volts above the power you want to measure. I drive mine with 10V and it's fine up to 5W (my bottleneck is the ADC).
 




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