CD40106 DC Motor Speed ​​Controller

For a 5V pulse train, the average DC voltage of a pulse with a duty cycle of 0% is 0; the average DC voltage of a pulse train with a duty cycle of 25% is 1.25V; the average DC voltage of a pulse train with a duty cycle of 50% is 2.5V. If the duty cycle is 75%, the average DC voltage is 3.75V… and so on. The maximum duty cycle of any pulse train can be 100%, which is equivalent to a DC waveform. Therefore, by changing the pulse width of the pulse train, the average DC voltage and speed of the DC motor can be changed.

The attached diagram is a circuit diagram for speed control of a small DC motor used in tape recorders and toys. In the figure, inverter N1 is connected to form a multivibrator with a fixed frequency or period but a variable duty cycle. The pulse width is changed by a variable resistor VR1. Inverter N2 simply acts as a buffer, and the driver drives transistor T1 in the positive half cycle. Therefore, the average amplitude of the DC drive pulse or the speed of the motor M is proportional to the set position of the center contact of VR1. Capacitor C2 can make the circuit work stably.

By changing VR1, the duty cycle can be changed from 0% to 100%, and the motor speed can be smoothly and continuously changed from "stop" to "full speed". Diodes D1 and D2 allow timing capacitor C1 to have different timing resistance values ​​during charging and discharging.

The pulse period or rest period of the pulse train can be approximately calculated from the following formula: Pulse period or rest period (seconds) = 0.4 × C1 (farad) × VR1 (Ω). The fixed frequency is given by the following formula: Frequency = 2.466 / (VR1 × C1) = 250Hz. In the formula, VR1 = 100kΩ, C1 = 0.1uF.

If different VR1 and C1 are used, it is recommended that VR1 should be greater than 50kΩ but less than 2MΩ; C1 should be greater than 100pF but less than 1uF.