OpAmp eventually burns/malfunctions

operational-amplifier

I try to drive a galvo-mirror with a dual OpAmp AD8532. No spec sheet for the mirror, but it is about 16 Ohm and takes about 50mA at 2Vp-p, if I measured correctly. The OpAmp starts malfunctioning after a while. I could not determine when/what causes it to malfunction, but it stops to provide all the required power. It seems like it gets fried up a little. The only thing I could think of right now, are the reversed currents caused by induction. I will try to add reversed diode to each of the outputs, but I am not sure if the problem will go away. Do not want to burn more OpAmps. Any suggestions what else should be added to the circuit below, to make it right?

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Best Answer

I would try adding Schottky diodes (eg. 1N5819) from the output of each op amp to ground and +5 (four diodes total).

Also put a resistor (something like 1K) in series with the inverting inputs (two resistors total).

You should also make sure there is good bypassing on the 5V supply. Perhaps 10uF ceramic in parallel with 1000uF/6.3V low impedance electrolytic.

The total power dissipation with the output railed could be as much as ~400mW in each amplifier so if you're using anything other than the SOIC package with a nice copper pour around it (and maybe a stick-on heatsink), you could just be overheating the chip. The SC-70 package would die quickly if railed. Maybe put a resistor from the input (if it can be disconnected) to your 2.5V reference so that if the input is disconnected the current drops to about zero.

Ah, I missed that you're using the dual op-amp, as Andy notes, so the power dissipation is doubled. If you switch to two singles in SOIC you might be okay.