Tool/software:
hi expert
This is our flyback power supply schematic scheme, input 350V, output 16.5V, transformer parameters, Lp=1.5mH, turn ratio 9:1:1, now we have two problems in debugging:
1.Problem 1: During the startup process, the PWM output of the chip will be off for a period of time (within 5ms);
Problem 2: When the load is light (less than 200mA), the hiccup will be more serious.
Hi,
1.
Based on your waveform, COMP pin voltage drops < 1.18V, which is in the range of PWM disappear, then after COMP > 1.18V, the PWM resumed. This should be due to FB pin voltage high to cause from Vout overshoot. You need to adjust the feedback loop compensation to make Vout overshoot lower to avoid FB voltage too high then cause COMP voltage too low (< 1.18V in this case) to make PWM disappear.
2.
At very light load, Vout goes high so to make FB high, COMP low, then cause PWM periodically disappear to avoid Vout over voltage then the operation is in hiccup.
