Comair Rotron PWM Control Circuit


I have a customer usign Comair DC fan PN 17001130A. I am interfacing to the fan’s PWM control wire (yellow) through J27 pin 4 in the schematic below. PWM signal PWM_SYS_FAN_OUT1 (3.3V logic from an MCU) will run at 1Khz with and be controlled so the fan yellow wire has a 15% to 40% duty cycle to control fan speed. Q13 inverts PWM_SYS_FAN_OUT1 and drives yellow wire high at 5V with 10.2K source impedance and low at close to 0V with 2ohm of source impedance.

Signal GPI_TIMER_SYS_FAN_TAC_IN_1 goes to an MCU with 3.3V I/O. R154 pulls the open collector (to be confirmed) signal from the fan to create a 3.3V logic level high for the MCU.

Please confirm that this PWM and tach circuit is compatable with this fan.
A schematic of the PWM input and Tach output signals on the fan side woudl also be nice to have.

Kind regards,
Todd Daynes


The datasheet would appear to call for open-collector interfaces on both signals, as is common due to flexibility in regard to logic levels that technique affords. Such devices generally provide their own input pull-ups, so an external one (R155) should not be necessary, and it would be prudent to chose Q13 so as to tolerate being pulled up to the fan supply voltage.