wickedweed
New Member
Hi. The above partially completed schematics is part of my car's (VOLVO) fan speed controller. This controller basically switches the fan in 3 States: OFF, LOW SPEED, HIGH SPEED. At this moment, the HIGH speed is not working (fan doesn't turn at all).
The Drain and Source of the BUK7908 are paralleled together and the gates are controlled by the same output on the logic board. The gate of the BUK7508 is controlled by another i/o pin on the logic board.
I have no clue what is connected to the point marked 'X' and also what is connected to the other pin of the inductor (definitely not the supply/ground pins). Are there anyone out there who can possibly guess what the mosfet/caps and inductor connected on the +12V rail of this circuit do?
I do suppose that PWM pulses on the BUK7908 gates are used to determine the fan speed?
Thanks!