Other Parts Discussed in Thread: TIDA-00702, UCC28740,
Tool/software:
Hi,
We has a new design for the auxiliary power supply, and our spec. for below:
1. We need to auxiliary power supply output is 24V/3.3A(fully loaded);
2. The output use the synchronous rectification UCC24612-1DBVR solution, the QR Flyback solution use the UCC28740DR+CS6N120( 6A1200V MOSFET);
Our issue is the below:
1. The switch frequecy is still work on 43K-55KHz when the fully loaded(3.0A+0.3A), and the MOSFET will be enabled at several waveform valleys, we can not increase the switch frequency,
2. Half Load/ Light load, the switch frequency will be 20K-30KHz, we can hear the Inductive whistling sound;
3. The efficiency is about 87%, and the EVM is more than 90%;
Our support need:
1. We need to Increase the switch frequency to 50K~55KHz and the MOSFET will be enable on the first waveform valleys;
2. How to modify our design that we can limit the switch frequency more than 30KHz if it is on different load;
3. We test design based on the TIDA-00702 EVM: R28 to 200K, R30 to 10-20K and there are no improve:
We test the waveform for your evaluated:
1. Vds waveform:
2. Vin=250VDC, output current=3.3A:
3. Vin=310VDC
The transformer file and schematic diagram please refer to below
