Simple H-Bridge PWM Driver Circuit using IC 555

A Simple H-bridge PWM driver circuit that makes use of a IC 555 integrated circuit is used to regulate the direction and speed of a DC motor.

In this circuit the important part is driver transistors are not used, instead the load which is a motor is driven directly through the two IC 555s.

Circuit Working:

Parts List:

As was already said, this circuit relies heavily on the two IC 555, designated as IC1 and IC2.

The PWM signal is produced by IC1, as an astable multivibrator.

The frequency and duty cycle of the PWM signal produced at pin 3 of IC1 are controlled by the timing components R1, C1 and the variable resistor pot.

IC2 is configured like a set-reset, or a flip flop circuit.

When pin 3 of IC1 is high it causes the pin 2 and pin 6 of IC2 to become higher than 2/3 of VCC, which causes the pin 3 of IC2 to become low.

This allows the motor to rotate clockwise.

When pin 3 of IC1 is low it causes the pin 2 and pin 6 of IC2 to become lower than 1/3 of VCC, which causes the pin 3 of IC2 to become high.

This allows the motor to rotate anti clockwise.

The resistance value changes when the potentiometer is adjusted affecting C1s charge and discharge timings and eventually the output signals duty cycle.

The DC motor is the load in the circuit, the H-Bridge configuration regulates the motors direction and speed.

The H-Bridge enables the motor to rotate in clockwise and anti clockwise depending on the ON/OFF PWM signal from IC1.

A PWM signal is produced by the IC1 555, the motor speed is determined by the duty cycle of this signal.

Modifying the duty cycle involves adjusting the potentiometer.

A 9V power supply powers the whole circuit.

Formulas:

In order to manage the switching of an H Bridge configuration or regulate the speed of a DC motor, we want to create an astable multivibrator circuit utilizing the IC 555 for an H Bridge PWM driver.

The formulas are provided below:

Formula for Frequency (f):

The settings of the resistor R and capacitor C define the oscillation frequency (f) in the astable mode of the IC 555.

f = 1.44​ / (R1 + 2R2) *C

where,

• Resistors R1 and R2 are attached to the IC 555.
• C stands for timing capacitor.

Duty Cycle:

The output waveforms duty cycle D which expresses the proportion of the outputs high ON to low OFF times, is as follows:

D = R2​ / R1 + 2R2

To give your H Bridge PWM driver circuit the required PWM characteristics, adjust these values as needed.

How to Build:

To build a Simple H-Bridge PWM Driver Circuit using IC 555 follow the below mentioned connections steps:

• Gather all the components as shown in above diagram.
• Connect pin 1 of IC1 555 to ground
• Connect pin 2 to pin 6 of IC1 555.
• Connect pin 3 of IC1 555 to positive leg of DC motor.
• Connect pin 4 of IC1 555 to positive supply of 9V.
• Connect pin 6 of IC1 555 to pin 2 of IC1 555.
• Connect pin 7 of IC1 555 to two diodes D1 and D2.
• Connect pin 8 of IC1 555 to positive supply of 9V.
• Connect capacitor C1 from pin 2 and pin 6 of IC1 555 to ground.
• Connect P1 pot center leg to pin 2 and pin 6 of IC1 555.
• Connect P1 Pot 1st leg and 3rd leg to two diodes respectively.
• Connect R1 resistor between diodes D1 and D2 to positive supply of 9V.
• Connect pin 1 of IC2 555 to ground.
• Connect pin 2 to pin 6 of IC2 555.
• Connect pin 3 of IC2 555 to negative leg of DC motor.
• Connect pin 4 of IC2 555 to positive supply of 9V.
• Connect pin 6 to pin 2 of IC2 555.
• Connect pin 8 of IC2 555 to positive supply of IC2 555.

Conclusion:

To conclude, the speed and direction of a DC motor may be basic controlled with an H-bridge and a 555 timer PWM driver.

Although there are issues with the projects seamless direction shift and present management, overall it is a fantastic learning exercise.

Dedicated H-bridge driver ICs are advised for applications requiring more power and better performance.

References:

H-Bridge: forward and backward dc motor with ic 555 by esp8266 gpio