Speed Control of DC Motor Using IC 555

Components Requirement

IC-555 • MOSFET(TIP-310)

100(2) Ohms & 1k Resistors


5/9 Volt Battery

Few Jumper Wires

1uF Capacitor

10k Variable Resistor

• Led • Breadboard


In this circuit, the DC motor is operated by a 555 integrated circuit. The IC 555 in this circuit is being operated in astable mode, which produces a continuous HIGH and LOW pulses. 

In this mode, the 555 IC can be used as a pulse width modulator with a few small adjustments to the circuit. The frequency of operation of the circuit is provided by the passive parameters of resistances and capacitors attached to it.

The duty cycle of the circuit can be changed by changing the value of the potentiometer. If we increase the duty cycle, the speed of the motor increases and if we decrease the duty cycle, the speed of the motor decreases.

Ways to control speed of Motor :-

To control the speed of the motor, we have to control certain electrical parameters that directly affect its speed. Obviously, we have to adjust the voltage and current supplied to it.

One way is that at constant supply voltage, you might want to put a variable resistor(potentiometer) in series with the motor to adjust/limit the current that it draws during operation. The bad thing about this method is that by limiting the current flow changes the value of the series resistor which also changes the voltage across the motor. When the motor is loaded, it draws a significantly large amount of current thus increasing the power across the series resistor. The power across the resistor will just be converted into wasted heat.

Another way is to use a Common emitter but transistor configuration with the motor as the load to adjust the current through the motor by changing the supply voltage at the base-emitter junction of the transitory. However, this is harder to predict since the relationship between the Vbe and Ic of the transistor is exponential. Aside from additional transistor concepts that you have to keep in mind, the transistor itself dissipates additional power as heat.

Another alternative and probably the most popular among speed control methods is the pulse width modulation. This method generates a pulse signal of voltage or current switching from on(HIGH) and off(LOW) with definite intervals on each state and a defined constant frequency overall. Note that this kind of voltage signal would still look like a constant DC voltage as seen by the motor. If you supply a DC motor with a 9V source and a switch but you constantly press the switch between On and Off reduces the average voltage supply as seen by the motor thus reducing its speed.

ZL_9173] Dc Motor Speed Controller Circuit Schematic Free Diagram
Circuit Diagram
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