ok, finally went out and opened my charger. it is hardwired to the battery so i have to look outside with the sun reflecting off the lens of magnifying glass. danm. almost blind now.
everything i thought about those parts is totally wrong. i thought it was the switch for fan but i am totally totally wrong.
the U1 is UC3842BN which is the IC pwm controller used to switch that mosfet 2SQ1808.
look for a resistor on the source leg and that is how the power delivered by the mosfet is controlled. i don't have the document in this computer but there is a white paper on how they work somewhere i read at one time. pin 2 is where the feedback goes onto the 3842 and if you look at the traces you will see where the output of the optotransistor IC202 is attached to pin 2 on the 3842.
https://www.google.com/search?q=uc3842b ... d=0CD8QsAQ
i see that the R210 is attached to the gate leg of the mosfet, and R209 and the diode D205 which i assume is a zener to protect the gate. so gate drive is from R210 and the R209 may be there to do the initial startup for the oscillator by taking a signal off the trace that seems to come off the choke there in the upper left. that would make sense if the choke has an initial voltage impulse on power up. not sure how it works though.
C210 is 103J100
R210 is 100R
R209 is 10kR i think, could not read it but measured about 9.9kR on one scale and 8.63kR on another scale while in the circuit. i think the last ring is red so that means 2% i think.
do you need C207, the electrolytic?
so sorry i mislead you and i looked for the voltage regulator under the lip of the heat sink and it is not there either. all of that may be on the daughter board. so there is no 4 diodes on a secondary winding that deliver power to the back end.
this design is fundamentally different from the kingpan design used in the low power chargers. it uses the 3842 for the oscillator instead of using a TL494 like the other chargers. i guess that is because it does not require much current to switch the IGBTs in the front end as it takes to switch the big big npn transistors used in the kingpan type charger.