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Disclaimer: I have little to no background in electronics / electrical engineering.

I believe this circuit is to provide a steady and accurate current source, which can be altered with a potentiometer. I would like to know why 4 op amps have been used, and what the benefit of this configuration is?

Unfortunately, I don't have the exact spec of the chip at this moment in time, merely the hand drawn diagram attached.

circuit diagram

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Most likely, this is intended to provide variable brightness in the LED without dissipating much power. It cannot be a current source, since there is no current sense resistor, which would normally be inserted between the FET source and ground. The amp using pins 12-14 is clearly set up as a comparator, and if it were fed a triangle or sawtooth wave to pin 12 would produce a PWM signal at the gate of the FET, modifying its brightness by turning the pot.

However, the rest of the circuit is incomprehensible, and should not produce anything useful. At the very least, tieing pin 3 to +12 ensures that the output will not change, and neither will the output on pin 7. I also doubt the two resistors in series between pins 9 and 12.

I suspect you need to go back and have another go at tracing your connections.

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  • \$\begingroup\$ I have inherited this from a previous owner. I couldn't make any sense out of it either... Someone has actually built this circuit on prototyping board. I will attempt to follow what has been done, but its been poorly made. I suspect I may be better off scrapping this and building my own! \$\endgroup\$ – CaptainConundrum Oct 15 '15 at 20:08
  • \$\begingroup\$ I suspect the idea is to first produce a square wave using 1 op amp as a relation amplifier, then an integrator stage to produce a triangle wave, and finally comparator stage to drive the FET. But this will take at least one more capacitor, and maybe two, than you show. \$\endgroup\$ – WhatRoughBeast Oct 15 '15 at 20:12
  • \$\begingroup\$ I am sure I have seen a circuit diagram like this as a PWM motor control. IIRC it was a kitsrus kit, but I can find the link. \$\endgroup\$ – Wouter van Ooijen Oct 15 '15 at 21:13
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It's been drawn incorrectly - it's meant to be a switching (PWM) controller but pin 3 connects to pin 4 and this invalidates it. The op-amp at pins 1, 2 and 3 should be a relaxation oscillator but it is not. The op-amp around pins 4, 5 and 6 should be a linear buffer amp but it's missing a resistor.

The major clue that drives me down this train of thought is the final op-amp on pins 12, 13 and 14 - it connects to a pot and it makes total sense that the other input to this op-amp is a triangle waveform from a relaxation oscillator of some sort.

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