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What exactly is this H-Bridge ? The short answer to this is it is a circuit that enables you to change the polarity of the current going through a inductive load. It is however normally used with motors. A bipolar stepper motor can also be driver with an H-Bridge, but you will need two of them 🙂

In this article, I will focus on the circuit, and how it actually works. I shall try to be as detailed as possible, while still keeping it easy to get started and also to understand. Please note that this article does not discuss all the H-Bridge theory. I will also not deal with regenerative and de-generative braking. That is for a later time 🙂 So let us start.
To understand the H-Bridge, it is easiest to first start with a circuit comprised of switches and a motor.

Implementing an H- Bridge with Switches, Learning the theory of operation

This circuit will simulate all the valid states of an H-Bridge, but without using actual transistors. This is ideal for somebody that wants to learn how it works, and want to truly understand what happens.
Study the circuits above well, or even better than that, build it on a breadboard, and play with it. That will give you a great understanding of what it does and how it works.The next stage of our journey, is to start using transistors to build the circuit above, but before we do that, we first need to see exactly what a transistor does when used as a switch, and what this NPN and PNP stuff means, and also how it affects our circuit …

I will not go into transistor theory in this article, but the diagrams below will give you a clear idea of what transistors can do and how they do it as well.

Using transistors to switch on motors. Note the position of the load (motor) differs depending on what type of transistor ( NPN or PNP ) you use…

Now that we had a look at these circuits, and hopefully built them on a breadboard, lets construct half of our bridge, so that we can start to see how to change the circuit with switches only, into a circuit that you can control with a micro controller like Arduino.

One half of an H-Bridge Motor controller. This circuit can be controlled by switches or a microcontroller

Well done, hopefully you have built this one on the breadboard as well, and may be anxious to see the full circuit.
Well, lets not keep you waiting then.

Full H-Bridge Motor Controller

Now that we had a look at where the circuit originates, and have a clear understanding of how it works, I would like to invite you to read my tutorial on actually building and using it. It does repeat some of the things mentioned here, but also contains things that I have not mentioned on purpose as to not complicate this any more that it has to be.

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