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5V 200A Lambda power supply generates strong audible at 10A load

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i200yrs

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Hello mates...good day..I has been troubleshooting this lambda power supply (5V, 200A) for about 60days. So this could be the right time to call for help. The failure is the power supply generates a strong audible sound at only 10A load. We have good unit here but it never create a sound at any point of load. I replaced all high frequency transformers, all power mosfets, all capacitors, all op-amps, all transistors, and all IC including the PWM. We are using UC3524 PWM. Without load the voltage is correct 5V and no sounds. Really appreciates any inputs from you guys....thanks a lot.
 

Well in SMPS major source of auditable noise is magnetic components, output ceramic capacitors also make noise. Another source is snubber circuit.

We understand that your power supply(5V@200A) making audible noise only when operating at 10A load. It means at 10A your SMPS switching at audible range of frequency.
Burst Switching Operation will cause audible noise, better to change the switching frequency so this audible noise at 10A will go off
 

10A is likely where the power stage goes from dis-continuous to continuous mode of operation, the change in characteristic is enough to make the total delay in the control loop enough to enter a partially unstable region - difficult to fix, put the old lossy o/p caps back in the output, or if you have the schematics - try and fix the control loop - by putting speed up (phase lead) R-C components in the volt sensing ckt ...
 

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