Current regulator for stepper motor controller - has feedback transformer for rapid reduction of motor current at end of step

摘要

The current regulator is used in a stepper motor driving the character disc of a teleprinter. In order to achieve accurate disc positioning it is desirable to reduce the current in the motor windings (M) as fast as possible. The desired result can be achieved with low power loss by adding a feedback transformer (RT). The transformer primary winding is connected through a freewheel diode (D3) to one side of the transistor switch (ST) controlling the output of a power source (S) to the motor windings. The secondary winding is connected, via a further freewheel diode (D2), directly to the power source. A typical transformer ratio is 1:2. When the switch (ST) turn off the stored energy in the motor windings and the external choke (L) is rapidly fed back to the power source (S). If at the same time all the winding routing transistors (T) are off, the stored energy in the choke (L) can be fed back through a further freewheel diode (D1).