The China small 12v dc motor manufacturers tells you about DC motor switching and control.
Small DC motors can be switched on or off via switches, relays, transistors, or circuits. The simplest form of motor control is "linear" control. This type of circuit uses a bipolar transistor as a switch to control a single power supply motor. How does the DC motor work? By changing the base current flowing into the transistor, the speed of the motor can be controlled. For example, if the transistor is "halfway" connected, only half of the power supply voltage flows to the motor. If the transistor is "fully conductive"(saturated), all power voltage will enter the motor and rotate faster. Then, for this linear control, the power supply is continuously transferred to the motor.
DC Motor Speed Control
The above simple switch circuit shows the circuit used for unidirectional(only one direction) motor speed control. Since the speed of the DC motor is proportional to the voltage at both ends, we can use the transistor to adjust the voltage at the end.
Two transistors are connected to control the main armature current of the motor. Optional continuation diodes are connected at both ends of the switch transistor and motor terminal to prevent any reverse electromotive force generated when the motor rotates. The adjustable potentiometer is applied directly to the circuit input and the motor is "fully connected"(saturated) or "completely disconnected"(cut off) to switch from the microcontroller or port, respectively.
In addition to this basic speed control, the same circuit can also be used to control the speed of the motor. By repeatedly switching the motor current "ON" and "OFF" at a sufficiently high frequency, the speed of the motor can change between stationary and full speed by changing its marking space ratio. This is achieved by changing the ratio of "ON" time(T ON) to "OFF" time(T OFF), which can be achieved using a process called pulse width modulation.
