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Boost Converter Problem with Vibration Motor

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eepty

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I have a AC/DC boost converter circuit which is implemented on a massager with the main loading is a 3.6V vibration motor.

When I switch on the massager the first time it has no problem. Then I switch it off (this will also switch off the boost IC), the weight on the vibration motor will still rotate for a few cycles. Then if I switch it on again during this period, the boost converter IC stop working. This problem is repeatable.

If I switch it on again a few seconds after switching it on the first time, it will not have problem.

Then I found that if I change the C3 capacitor from 220uF to 22uF, the problem gone.

I have used oscilloscope to check the current through D1 but I did not found there is any difference for using 220uF and 22uF.

Attached the boost converter schematics and the boost IC datasheet.

Anyone has idea about what is the problem?

Thank you very much
 

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Hi,

some (possible) issues:
* R3 (datasheet) is missing.
* C1 is not as close (low impedance) to the IN pin as multiple times recommended in the datasheet.
* layout considerations can´t be checked without your PCB layout. (This is one major cause of mistakes with SMPS circuits)
* part parameters (like ESR of C1 and saturation current of L1...) can´t be checked without your information.
* what´s the input voltage and how stable is it?
* What are the voltage levels on the EN pin?
* what´s the peak load current?

Klaus
 

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