## H-Bridge Circuit

In modern electronic circuits such as motor control circuits, Inverter circuits, charger circuits H-Bridge circuits are used. Here you will see how an H-Bridge Circuit works. We will see the H-Bridge Circuit design, Applications, and Advantages.

### What is the H-Bridge Circuit?

The connection of switches(generally four switches) in such a manner we can change the polarity of the voltage applied to a load and the circuit looks like the capital letter 'H' is called an H-Bridge circuit.
A simple circuit diagram of H-Bridge is given below.

As you see in the above figure the circuit looks like the capital letter 'H'. The circuit has four switches. On the left side of the load, two switches are connected in series, and on the right side of the load, two switches are connected in series.

### How H-Bridge Circuit works?

As we know that the H-Bridge circuit is mainly used to change the polarity of the voltage applied to a load. So let's see the working principle of the H-Bridge circuit with an example.

As you see in the above figure we have taken a PMDC motor as a load and the PMDC motor is connected with the H-Bridge circuit.

Now let's see how we can change the direction of the PMDC motor by the H-Bridge Circuit.
We know that if we change the polarity of the applied voltage applied to the PMDC motor then the rotation of the motor will be changed and it can be done by the H-Bridge circuit.

In the H-Bridge circuit, four switches are connected named as S1, S2, S3, and S4.

(1) When switches S1 and S4 are closed and S2 and S3 are open then the positive voltage will be applied across the motor and the motor will be run in the forward direction. In this case, the direction of the flow of current is indicated in the below circuit diagram.

(2) When switches S2 and S3 are closed and S1 and S4 are open then the negative voltage will be applied across the motor and the motor will be run in the backward direction. In this case, the direction of the flow of current is indicated in the below circuit diagram.

(3) Using the H-Bridge, we not only change the direction of rotation of the motor, but we can also brake the motor. We know that in the case of a DC motor during rotating condition if we remove the motor from the main supply and connect the terminals of the motor together then the motor will brake and it stops rotating.

As you see in the above circuit diagram, S1 and S3 are closed and S2 and S4 are open. So the motor is removed from the main supply and the terminals are connected together. So the motor will brake or stop.
The same will happen if we close S2, S4, and open S1, S3.

One most important thing to remember that S1 and S2 never be connected together otherwise it will create a short circuit with the input supply. S3 and S4 also never be connected together.

### Practical H-Bridge Circuit Design

H-Bridge circuits are available with Integrated Circuit(IC) in the market. L293X series ICs are examples of H-Bridge circuits. L9110, and L293D are H-Bridge ICs.

We can also make or design an H-bridge circuit with discrete components.

#### H-Bridge Circuit design using Transistors

Here the H-Bridge circuit using transistor are given above. As you see we have used two types of transistors. Two PNP transistors and two NPN transistors.
The top two transistors are PNP transistors and the Bottom two transistors are NPN transistors. If you connect the NPN transistor to the top then the circuit will not run.

We know that when we apply current to the base terminal of the transistor it will conduct. So we can give supply to the base using a Microcontroller to run the circuit.

Generally, the PWM signal is given to control the motor using an H-Bridge circuit.

We know that the Motor will also generate electrical energy when it running and the supply is off. As you can see in the above diagram we have used PN junction diodes as Freewheeling Diode to release the energy. Of course, if you use an H-Bridge circuit for other purposes you may not need to use freewheeling diodes.

In the next article, we will design the practical Motor Driver Circuit using H-Bridge with all proper component ratings.

### Applications of H-Bridge Circuit

1. The most important application of the H-Bridge circuit is the motor driver circuit.
2. In Robotics Technology, H-bridge circuits are used.
3. The H-Bridge circuit is also used as an Invertecircuitut.
4. In modern battery chargers for electrical vehicles, H-bridge circuits are used.

1. Very high efficiency.
2. Very low loss.
3. This circuit can be placed in small places.

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[Explained] H-Bridge Circuit design, Applications, Advantages Reviewed by Author on March 31, 2019 Rating: 5