Bipolar Junction (BJT) H-Bridges
November, 2003
The simplest type of H-bridge you can build uses Bipolar Junction Transistors (BJTs), just called transistors from here on out. If you've never built any sort of power controller then the circuits in this section are a good introduction. The circuits can be built cheaply, control a number of easily obtained motors, and even if you burn them up you will learn something!
The tutorial is quite long and I have broken it up into several parts. If you are familiar with transistors then you can skip the Transistor Theory part.
1.0 Transistor Theory
The first part of this sub-section talks a bit about the theory of operation for Bipolar Junction Transistors. Read more ...
2.0 Selecting the Right Transistors
Now that you understand what the transistors do for us, lets use them. This section jumps into the details of selecting some transistors to build into an H-bridge. Read more ...
3.0 Implementing H-Bridge Elements with BJT Transistors
The transistors in hand, now it is just a matter of implementing the four corners of the "H" and adding some way to control it from a computer port. Read more ...
4.0 The Complete BJT based H-Bridge
Putting the pieces together to form a single unit. A little cleverness in our shopping and we've got a $5 H-bridge. Read more ...
5.0 Circuit Analysis and Bring-up
Designing a circuit is only half the fun, understanding how it works and why is the real prize. This section builds up a test harness that analyses the H-bridge we're building. Read more ...
6.0 Using this H-Bridge design in a Robot
This section discusses laying out a printed circuit board for use in mobile robots. Ergonomics, economics, and physics all play a role. Read more ...
Kits of this design are available for a modest fee, contact Chuck McManis on this server for details. The kinds of motors that a power transistor H-bridge will control are generally DC gearhead motors and model motors in the 3 - 12V range. Motors that are compatible with this H-bridge can be purchased from the following vendors:
Pretty much any Mabuchi 3V, 4.5V, 6V or 12V DC motor.
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