OPA551: Op Amp getting hot

Adolfo Russo

Part Number: OPA551
Other Parts Discussed in Thread: LM7321,

Hi,

I'm trying to drive primary winding of an isolation transformer (10uH inductance) with 2 high current op amps (following schematic). A zero-centered sinusoidal waveform is injected in R26, max 10V amplitude.

I'm not sure why op amps get hot at frequencies lower than 3kHz, especially the inverting one, I also tried LM7321 but with same result. Any help is really appreciated.

Thanks,

over 3 years ago

0 Adolfo Russo over 3 years ago

Prodigy 140 points

0 Raymond Zhang1 over 3 years ago in reply to Adolfo Russo

TI__Guru 51481 points

Hi Adolfo,

Can you place a current probe and measure the current at the output of U11 or U12 (return line)? I have a feeling that the output current exceeds +/-200mA rating of OPA551 part.

At 3kHz, the impedance of 10uf is 5.3Ohm and 10uH is low impedance at 0.188Ohm + ESL in XmOhm. Replace C49 from 10uf to 1uf and place another one at the output of U11. which the impedance will be approx 106Ohm or so. Or replace C49 with ~0.5uf low leakage ceramic capacitor instead. Please let me know if it will help the over heating issues in OPA551.

Best,

Raymond

0 Adolfo Russo over 3 years ago in reply to Raymond Zhang1

Prodigy 140 points

Hi Raymond,

you're absolutely correct, tested with resistive load down to 10hz and it's ok, I'm gonna use a different trafo for low frequencies.

thanks,

Adolfo

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OPA551: Op Amp getting hot