In reply to VVV:
Actually I have a upper and lower limit for the duty cycle: 75% and 25%, respectively. After reading your post, I increase the upper limit to 80%, but it doesn't seem to improve anything.
By the way, I had recheck my circuit, seems unable to find anything wrongly.
Regarding your suggestion to reduce the frequency, actually I tried it before, half the original 93.75kHz. But it doesn't seem to improve anything as well.
Added after 18 minutes:
In reply to lastdance:
lastdance said:
Some questions:
1. Is the output 13V before you turn on the load?
2. How much current is the load drawing?
3. What's the duty cycle after you turned on the load?
4. Is everything voltage compliant? Any soft breakdown?
5. what's the ripple voltage when you turn on the load?
6. Did you try characterize your circuit with different load current?
If you found anything, do post it here to share with us your experience.
1) Yes, the output was 13V, before the additional load was added.
2) Sorry, I'm not able to check this now.
3) Below is my benchmark output before turn on the load:
volt = 12.96V (measure from AN1), with multimeter I got 12.7V.
Duty Cycle: 135 -> equivalent to 26.5%
after turn,
volt = 10.50V (measure from AN1), with multimeter I got 10.2V.
the duty cycle is the max, 80%
4) Can you please explain your question again?
5) I don't have access to oscilloscope now. Perhaps I will check this next week.
6) Yes. At least 2 kind of load. With Q3 on or off. But I will try other load when I back to my post.
Thanks. Surely I will keep this thread updated.
Added after 5 minutes:
In reply to IanP:
IanP said:
My guess is that the value of the inductor L1 is to big ..
The original design was 680uH. I change it to 560uH because I could not find 680uH in hand. But you said 100uH...? I think the higher the inductance, the better the result, isn't it?
Thanks.