Service manual

Edition 101222
-- 24 --
s1Cad160
AP2:4L. Wire feeder motor speed controller
The motor drive is supplied from the auxiliary winding on the main trafo as shown
on the figure below.
The wire speed motor controller is built on the peak current mode PWM controller
IC. This IC does not provide the reference input, the internal reference is +2,5V.
In this case the negative voltage feedback is provided in the form of the sourcing
current, and the reference value is provided in the form of the sinking current. PWM
controller commands the MOSFET Q17, which delivers PW modulated voltage to
the motor.
When the motor must be switched off the Q26 MOSFET short circuits the motor,
providing effective way of fast stopping of the motor.