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APPENDIX A
The transition to the plug braking mode is detected (plug detect) by monitoring the voltage across the plug
diode. When this diode becomes forward biased, it indicates that the motor field has been reversed and the
controller has gone into plug mode. The current limit is reduced as described, and the frequency of the
oscillator is reduced from 15 kHz to 1 kHz, to allow finer control of the controller output while plugging.
During plug braking operation, the acceleration circuit is reset to a low level so that when drive operation
resumes, the controller will go through a normal acceleration ramp. When the motor has come to a stop, the
plug diode will again become reverse biased and the controller will revert to normal drive operation.
AUXILIARY SECTION
The auxiliary section accepts all user control from the keyswitch, forward, reverse, and emergencv reverse
inputs, provides contactor drivers for the direction and optional bypass contactors, and monitors and controls
the logic and power sections. Input signal conditioning filters and clamps all inputs to provide logic level
signals for the control logic. Three PTC resistors protect the keyswitch, forward, and reverse inputs against
erroneous activation from external leakage paths, which can be created by moisture or conductive material that
settles between the controller's connections during vehicle use or cleaning. A 12V regulator powered by B+
provides power for all auxiliary section circuits. The auxiliary section power supply is independent of the logic
section power supply; logic section failures therefore do not affect the ability of the auxiliary section to detect
faults. Power-on reset initializes the control logic when B+ is connected to the controller.
Controllers with SRO (static return to off) must have the proper sequencing of KSI and forward/reverse input,
as determined by the control logic, to enable the controller and allow it to operate. KSI must turn on before
forward or reverse for the control logic to release pulse disable (thereby turning on the controller). If KSI is
turned on simultaneously with or later than forward or reverse, pulse disable will remain on (controller
disabled).
Controllers without the SRO option may require a keyswitch input (dependent on vehicle wiring) if the
controller has HPD.
A valid turn-on sequence enables the logic section so it will respond to throttle inputs, and turns on the
forward/reverse contactor driver to actuate the selected direction contactor. If a fault is detected (fault detect)
or the logic board's power supply is out of range (logic board check), the controller and contactor driver will
not be allowed to operate even if a valid turn-on sequence occurs.
The bvpass contactor driver will turn on the bypass contactor if the requested throttle input level is at least
90% for at least one second (bypass timer). When it reduces below 90%, the bypass contactor is turned off
instantly.
Both contactor drivers are short circuit protected. Current sense detects contactor driver current, which then
signals over-current control in the event of a shorted contactor. Over-current control responds very rapidly
(≈10µs) to turn off the contactor driver(s) and then waits approximately 10 ms before trying to turn them back
on again. If the coil short is still present, over-current control will keep trying to turn back off and on until
Curtis PMC 1204X/1205X/1209/1221 Manual
A-4
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