eem2am said:is that off-load?
it looks like it.......it looks like it is bursting on and off....as if it were on no load or light load.
ripple i s at switch freq.....so it is probably mostly due to your ESR of your output caps.
dick_freebird said:That's not "ripple", that's ringing.
Potential causes include excess switch node capacitance
and inductor self-capacitance, poor input supply
decoupling (quantity or Q), and possibly even things
like ground bounce induced supply reswitching (a
direct coupled ramp=comparator to output path can
easily be perturbed by 100mV of ground noise).
The sources may be distinguishable by looking at the
frequency of those bursts; parasitic LC effects are
liable to be 100MHz+ while through-chip paths will
likely be 10MHz or below (maybe faster in low voltage
technologies, but classic 40V PWMs are pretty slow).
You should look at the switch node for signs of
reswitching / chatter, more likely on the H-L edge.
Look at the supply pin for gross droop or ringing.
Look at ground plane vs some exposed internal
signal if you can find one, see if there's an evident
bounce inside the bond wires or core:board.
I've had to redesign eval boards for ground bounce,
tight tight tight ground routing is the key.
eem2am said:also,
is it flyback?
maybe you get bad ringing from output diode.
maybe you need to snub it.
did you use RCD snubber across primary?
It is weird, cuzz your output cap should not allow its voltage to ring like that.....unless you have very very bad layout
jagspaul said:One question, the ringing tendency is less in case of flyback continuous mode rather than discontinuous mode. Please tell me whether it is correct or not.
If it is correct then if I could change the design to continuous mode the ringing problem will be solved.
Please let me know. I am waiting for your answer.
Regards
Jagadish
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