Flyback Circuit

Power Transistors T314, T315 And T316 All ON

When T314 and T315 are ON, current flows through T314,T315 emitter/collector into the base of the power transistors, causing them to turn ON. With the power transistors ON, high amperage motor current can flow through them, the motor field, forward contact tips, motor armature, forward contact tips, current sensor and regen contact tips back to battery negative. When T314 and T315 are OFF, the power transistors are OFF.

The percent “on-time” of the voltage at logics P125 is also the percent “on-time” of the power transistors. As the “on-time” increases, the average voltage applied to the drive motor increases, which increases the speed of the lift truck. The percent “on-time” out of the logics is determined by how far the accelerator is depressed.

At the same time the logics is pulsing the drive motor circuit, a constant voltage (about 1.5 volts) is being supplied on P12-8 to the base of T371, turning it 100% ON. With T371 ON, current can flow through the drive shunt fuse, drive shunt field and T371 back to battery negative. When the drive shunt field is ON 100%, at maximum strength, it adds to the motor torque.