All,
I have a circuit which is essentially is a 12V to 8V Buck regulator that is providing power to an LED which is turned on and off
fast using a voltage controlled current source. See picture attached. The current pulses are 5A with a duty cycle of 20%.
I find in operation at full current (5A), the ceramic caps start to sing due to Piezo effect. Most probably because the frequency of this pulsed load is hitting the acoustic frequency band. I can mitigate this on my board by the usual methods e.g. changing the caps to metal standoff ones or to Tants. This is fine to deal with the audible noise on my board but ceramic caps further back in the chain (in the benchtop supply) are still singing. I know that I could put a two stage LC filter on the input to the regulator to try and reduce the noise going back to the supply (I already have a common mode filter on the input supply to my board) but my question is this:
1) Is there anyway I could reduce the noise on the input to the regulator to stop the ceramics singing? If I put an LC filter after the input decoupling caps I would starve my regulator. If I put it before the decoupling then I likely think it would stop noise following back of my board but not stop the noise on the decoupling caps.
2) There isn't a lot of noise on the output of the buck regulator as is typical. Would it be worth trying to filter this more?
Your advice would be gratefully received
AH
I have a circuit which is essentially is a 12V to 8V Buck regulator that is providing power to an LED which is turned on and off
fast using a voltage controlled current source. See picture attached. The current pulses are 5A with a duty cycle of 20%.
I find in operation at full current (5A), the ceramic caps start to sing due to Piezo effect. Most probably because the frequency of this pulsed load is hitting the acoustic frequency band. I can mitigate this on my board by the usual methods e.g. changing the caps to metal standoff ones or to Tants. This is fine to deal with the audible noise on my board but ceramic caps further back in the chain (in the benchtop supply) are still singing. I know that I could put a two stage LC filter on the input to the regulator to try and reduce the noise going back to the supply (I already have a common mode filter on the input supply to my board) but my question is this:
1) Is there anyway I could reduce the noise on the input to the regulator to stop the ceramics singing? If I put an LC filter after the input decoupling caps I would starve my regulator. If I put it before the decoupling then I likely think it would stop noise following back of my board but not stop the noise on the decoupling caps.
2) There isn't a lot of noise on the output of the buck regulator as is typical. Would it be worth trying to filter this more?
Your advice would be gratefully received
AH
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