Chopper circuit using a BC337 and Diode

The circuit below is a chopper using a BC337 NPN transistor, 1K resistor, and IN4001 Diode. The current sense resistor is 2 Ohms. The design starts limiting the current flowing in the motor coil by switching X5 on and off rapidly when Q1 conducts. A diode has been used to bias the transistor and increase the current sense switching point. Without the diode present the current would be limited to around 310mA. This has the effect of raising the desired switching current level.

Diode-Transistor Chopper Circuit (Download A/D 2000 | A/D v4)

Note: No attempt has been made to model the motor's magnetic characteristics in this simuation.