M
Michael
- Jan 1, 1970
- 0
Hi
I am in the process of bringing up 300W offline forward converter
based on UC3844. The specs are similar to the ATX power supply. The
problem I am stuck with is that the UC3844 is outputting constant duty
cycle signal (45% or so); so, the "regulation" is done by controlling
burst mode duty cycle. UC3844 pin 1 (comp) is swinging from max to min
=> PWM latch is never reset by the current sense signal=> constant
duty cycle.
I tried to estimate the transfer function after fiddling with the
compensation
(http://www.switchingpowermagazine.com/downloads/Apr 02 feature.pdf);
quick scan gave me same signal on both sides of the transformer
secondary from 100Hz to 1kHz. Very confusing, does it mean that open
loop gain is 0? It cannot be...
Any clues?
Thank you
I am in the process of bringing up 300W offline forward converter
based on UC3844. The specs are similar to the ATX power supply. The
problem I am stuck with is that the UC3844 is outputting constant duty
cycle signal (45% or so); so, the "regulation" is done by controlling
burst mode duty cycle. UC3844 pin 1 (comp) is swinging from max to min
=> PWM latch is never reset by the current sense signal=> constant
duty cycle.
I tried to estimate the transfer function after fiddling with the
compensation
(http://www.switchingpowermagazine.com/downloads/Apr 02 feature.pdf);
quick scan gave me same signal on both sides of the transformer
secondary from 100Hz to 1kHz. Very confusing, does it mean that open
loop gain is 0? It cannot be...
Any clues?
Thank you