DC motor speed control using the 4049 IC

Oct 102022

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DC motor speed control using the 4049 IC (PWM)

This DC motor speed control uses a 4049 hex buffer inverter circuit to change the speed of small 3 or 6 volt DC motors, which are often found in toys and small electronic devices.

The speed of a DC motor is usually controlled by varying the supply voltage. Another method of achieving this with a constant voltage is to control the time that this voltage is applied to the DC motor using Pulse Width Modulation (PWM) techniques.

In this way, the motor’s speed depends 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 using 4049 IC

Operation of DC motor speed control

There are many ways to build an oscillator for controlling the speed of a DC motor. In our circuit, we use the 4049 integrated circuit. This IC has six inverters. Two of these inverters are used to create the oscillator.

The frequency of this oscillator is controlled using a 1 MΩ potentiometer, and the oscillation frequency can be approximated using the formula: 1/(1.4RC), where R is the potentiometer’s resistance (R1) and C is the capacitor’s capacitance (C1). See the image above.

Pinout for the 4049 hex inverter buffer IC

This oscillator’s output signal is connected to the inputs of four inverters placed in parallel, which supply sufficient current to the base of transistor Q1.

Pinout of the 2N3055 NPN transistor

The transistor operates in the cutoff and saturation regions.

When it is in the saturation region, the supply voltage is applied to the motor.
When the transistor is in its cutoff region, the voltage between the motor terminals is zero volts.

Therefore, increasing the time that the transistor is saturated increases the motor’s speed.