Jim Yanik wrote in message
4...
"N_Cook" wrote in -
september.org:


UC3842 PWM controller , instead of simple RtCt pin , it uses the o/p of
a
555 so that there can be diode steering for different timings




Ah,nothing like taking a great simple PWM IC circuit and making it more
complex....

Now I wonder about the circuit makes the ramp for the internals of the
3842,while not using the RtCt function.Seems like that could affect the
current limit function.

--
Jim Yanik
jyanik
at
localnet
dot com


There is a lot more SM around the UC and 555 than any of the datasheets I've
seen. There are at least 1 diode for changing the duty cycle of the 555
waveform. But increasing the single timing cap from 2 to 29nF upped the
error mode frequency. Perhaps the duty cycle changed so much that it
inverted and played havoc with timings or limits in the UC. I will use x5
rather than x10 next time . Incidently slowing things down so less likely to
be destructive to drivers if the problem is shorted turns in the
transformer.