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Need Current mode controller with direct access to PWM comparator

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cupoftea

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Hi,
We are doing four paralleled opto isolated Flybacks 75W each, 10-36vin, 32vout, 300wout total.
Using UCC28C43s.
We want a single error amp feedback signal to the PWM comparator of each UCC28C43.
However, the UCC28C43 has diodes in the way.
All the current mode controllers seem to have these diodes.
Do any give direct access to the PWM comparator input?
 

Hi,
You need to have a reason not to have the diodes before you look for controllers that don't have them. What are you challenges with those diodes?
 
Thanks, the diodes may have different vf from chip to chip

Looks like MCP1630 fits the bill..but needs a micro to give it its oscillator to set fsw.
 
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Thanks, the diodes may have different vf from chip to chip
Yes, but I don't think you need to bother much about such errors. The system has feedback and actually compensates for it. If the Vf is slightly higher, then the controllers increases the voltage upstream of the diodes.
 
Sorry but we are pulling the 4 COMP pins down with the output of a single buffer, which is buffering the feedback signal.....different diodes will mean different current throughput for each flyback.
--- Updated ---

Thanks, do you agree the attached is THE modus operandi for paralleling multiple flybacks with cheap circuitry and still ensuring pretty equal load sharing (LTspice and PDF)
--- Updated ---

They are each 75W flybacks
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Also jpg
 

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  • 3 PLLEL Flybacks.pdf
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  • Flyback 300W X3.zip
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  • 3 pllel flybacks.jpg
    3 pllel flybacks.jpg
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Its funny how one can draw out a schem for a "great idea"........and you realise its just trash.....the schem of #5 is trash, wouldnt you agree?
This is a job for a UCC29002 Load share controller...more expensive than the schem of #5, but oh so needed.

UCC29002

Just a metter of comparing the old UC3907 , to see if thats any better than UCC29002

UC3907

The only difference between UC3907 and UCC29002 seems to be that the voltage error amp is inside UC3907 , but not in UCC29002.
The UCC29002 seems to have no 50mV offset, and this offset is needed in the '3907 in order to stop the master from adjusting its own reference...so ucc29002 must have some other trick up its sleeve for this function.
 
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If you only want one error amp then why not just take one regular
PWM's output and drive remote MOSFET drivers via the opto links?

Or pick a 5V PWM controller and do same.

Or pick one where the error Amp output is exposed and wire them
all together, and tolerate any Vf mismatch in those diodes. Ought
to clean up some at the big end, and who cares about the little end
for load sharing?
 
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