This is a fairly simple buck converter. The HV comes in from the upper plenum on pink(HV+ or P) and blue(HV- or N) wires. there is a fuse on the (-) side before going thru an EMI filter, Cap-Coil-Cap. The (+) side goes to the Drain of Q103 and Q104, 2SK3697 N-Mosfets, the (-) side goes to the Source of Q101 and Q102. So these 4 FETs make an H-bridge where the Source-Drain connections at the midpoint of the upper-lower legs go to the ends of the primary of Transformer, labelled as TR103-1 and -2. The UC2825A PWM controller chip, IC201, generates the drive signals for the FET Gates. A couple of isolation transformers are used to create the gate drive voltage from the LV 12V supply.
The secondary has a center tap connected to chassis ground. The ends are rectified by a dual Schottky Barrier Diode Module made by Nihon, P2H80QH20, rated 80Amps and 200Vrms. There is a temperature sensor near the diode and voltage sense lines on the input and output of the diode module. The two outputs are connected together and routed thru a thick inductor which uses flat "wire" with 8 x 2mm cross-section. This is the "12V" output and runs thru a current sensor and then a 125A fuse and then on to the fat white wire that runs up to the fusible link on the Aux battery positive terminal.
There is no microcontroller on the DCDC board (at least on the top side, i didn't remove it to inspect the bottom), so as i mentioned earlier i think it could be commanded by the two discretes, DCSW and SDW. Don't know what they are...?
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