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LM2904 issue

Madhuri Akkenepalli
Expert 1215 points

I have a general application question regarding the LM2904N. We are currently using the LM2904N Op-Amp in one of our products (schematics are attached as CDR-6406 – Vista Voltage Output Card). Each Op-Amp is being powered by 5 VAC. The output of the Op-Amp is then connected to another board (schematics are attached as CDR-7027 – 5/70 Step transformer board). At this PCB, the 5 VAC output from the Op-Amp goes through a step-up transformer where the voltage is raised to 70 VAC to help power a relay. We’ve been using this Op-Amp for quite some time, but recently, we have been receiving returned units with voltage losses occurring at the Vista Voltage Output Card. We have conducted tests and we were able to confirm the loss of voltage issue. In order to understand the root cause within the Op-Amp, we sent some units for analysis. we have the FA report that can be sent. Please review this and advise on your feedback.

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    TI__Prodigy 500 points

    Madhuri,

    How long has this op amp been used in this product? Has there been a change to the board that is being driven?

    Because you are driving a step up transformer, there could be severe inductive kickback. We recommend that power Schottky diodes be added from the output to the supply rails. You could have as much as 7A flowing back into the output.

     

    Jim