Build This Low Cost 1/2 H-Bridge

How It All Works

The "motor interface chip" can decode the signals from the "VEX" receiver to control up to 8 motor's 1/2 H-bridges. It can also receive commands from another microcontroller chip to control the motors. This interface chip uses 2 PWM output pins to control a motor's 1/2 H-Bridge.

The chip uses the input from the two buttons on channel 5 to control the input from the "VEX" transmitter left joystick so that it can control 6 motors. The chip uses the input from the other 2 buttons on channel 6 to lock in the high or low output on pin 14 of the motor interface chip.

The motor interface chip has the following features. These features may not work since a receiver may pick up a signal from anywhere. We assume no responsible directly or indirectly from using these parts. If your robot goes out of transmitter range; the motor interface chip may shut down the motors and give control to a microcontroller if your robot is using one. This may also be true if you turn your transmitter off.

The motor interface chip does not use a serial port to communicate with other microcontrollers. This means you can use a very inexpensive microcontroller chip to be the brains of your robot.

Putting a low on pin 2 will cause all the motors to operate at half the power level when using the transmitter. This is how we get a high or low power range.

There are many advances to using a 1/2 H-bridge.

1) Cost. You need only half the amount of MOSFETs, heatsinks and rectifiers.

2) Less parts, mean it will take less room.

3) Since there is only one MOSFET on at a time, there is only the lost of one voltage drop and not two as in a H-bridge. So you loose less power and generate less heat.

On the con side you just have.

1) You need a split power supply also known as a center tap power supply.

Here Are The Specifications
The 1/2 H-bridge was designed to run best at 14.4 volts. It can run as high as 24 volts. As the power supply voltage goes down, the MOSFET will turn on less and less. At 7.2 volts 2.8 amps the drop was .5 volts across the MOSFET.

Depending where you mount the board, you should be able to draw 3 to 5 amps from the 1/2 H-bridge without using a heat sink.

For the people who want to know about peak current. I ran the board at 24 volts 15 amps for 30 seconds. Yes, it gets very hot.

The motor controller chip that is used in this design can only be used in this 1/2 H-bridge design. The reason is that in a normal H-bridge design there is guiding logic so that the right MOSFETs are turned on. Here the motor controller chip does that.

This design shows two 1/2 H-bridges but the motor controller chip can control up to eight 1/2 H-bridges.

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