Original question:
Dears:
Pls. refer the before post, the customer has debugged the board and have an issue.
12V output, the load power consumption exceeds 21W will burn MOS; when 20W, MOS will be very hot, it will burn out after a long time.
1. What should be the normal level of GATE?
2, Kindly help to look at the diagram, the current maximum frequency of transformer support is 200K, FRS resistance is 69.8K, the switching frequency is about 250K, is it OK?
Dears：
There are other issues as follows:
1. If TPS23754's frequency is configured 250K and the Transformer's frequency is only 200KHz, is it OK?
If change the resistance of the control frequency to 100K, is there any adjust about the other design?
2. From datasheet the normal range of the Gate voltage level is -0.3v ~ Vc+0.3V. If it is too low, how can make it higher?
3. Sometimes during the power turns on we can see the output is not met 12V with a multimeter. And when detect PD device then the Power output is not met 12V too.
The output is unstable in the power on's process. Is it normal?
4.Does the output have minimum load power requirements? It is found that the idling sometimes loses power, and nothing is idling.
Dears:
Pls. refer the below information:
1. I don't see an issue with operating at 250khz. Since the inductance is 100uH on the transformer, 250khz might be better.
Luck: PA2649NL only support 200kHZ.
2. The gate drive in the TPS23754 is being powered by the VC voltage. Typically 10-12V from the bias winding of the transformer. What voltage are you getting at VC? And what voltage are you getting at GATE?
Luck: VC's waveform picture as follows, and Voltage is about 11V:
3. Can you send a waveform? Is the PSE not turning ON? Or is it passing detection and the converter is not powering up?
Luck: GATE waveform as follows:
MOS's D point waveform:
Pls. kindly help to give some advice!
