Chopper Motor Circuit
By Mike Rooke
Chopper Circuit Using a Current Controlled Switch
The circuit below is a chopper circuit using a current controlled switch (X1) to limit the amount of current flowing in the coil. The switch X1 is configured to sense current from resistor R3. Once the current is over 460ma the virtual switch in X1 is turned on and pulls to low the drive to the main coil switching transistor X5. When the current falls below 400ma, X5 will energize the coil and the process repeats. Note that the large difference between the on and off current sensing has been used for illustrative purposes only.
Note: No attempt has been made to model the motors magnetic characteristics in this simuation.
The same circuit using a transistor and diode can be found in the next section.
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.
Note: No attempt has been made to model the motor's magnetic characteristics in this simuation.