# DC motor speed control with 4049 (PWM)

This DC motor speed control with 4049, is a circuit that allows varying the speed of small DC motors of 3 or 6 Volts that are often found in toys or small electronic devices.

Controlling the speed of a direct current motor is normally accomplished by varying the supply voltage. Another method to achieve the same using a constant voltage is by controlling the time that this voltage is applied to the DC motor (PWM – Pulse Width Modulation).

In this way, the speed at which the motor turns depend only on an oscillator that applies voltage pulses of an adjustable width. The wider the pulse, the faster the motor turns. DC motor speed control with 4049

## DC motor speed control operation

There are many ways to make an oscillator to control the speed of a DC motor. In our circuit the integrated circuit 4049 is used. This “IC” has six inverters or NOT gates. Two inverters are used to make the oscillator.

The frequency of this oscillator is controlled with a 1M potentiometer and the oscillation frequency is given approximately by the formula: 1 / (1.4RC), where R is the resistance of the potentiometer R1 and C is the capacitor C1. See the diagram. 4049 IC Pinout

The output signal of this oscillator is connected to the inputs of 4 inverters that are placed in parallel in order to be able to supply enough current to the base of the transistor Q1. 2N3055 NPN transistor pinout

The transistor works in the cutoff and saturation states.

• When the transistor is in its saturation state, the supply voltage is applied to the motor.
• When the transistor is in its cut-off state, the voltage between the motor terminals is 0 volts.

Thus, if the time that the transistor is saturated is increased, the speed of the motor is increased.

## Circuit component list

• 1  CMOS CD4049 IC (six NOT gates) (IC1)
• 1  2N3055 NPN transistor (Q1)
• 2  1N914 semiconductor diodes (D1, D2)
• 1  1k resistor (R2)
• 1  1M potentiometer (R1)
• 1  0.02 microfarads (uF) capacitor (C1)
• 1  6V DC motor maximum. (M)
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