Build an H-Bridge Motor Control with Power MOSFETS (Tutorial)

using MOSFETs for H-bridge
Figure 1 very basic H-bridge.

Build an H-Bridge Motor Control with Power MOSFETS (Tutorial)

by Lewis Loflin

Permanent magnet DC motors have been around for many years and come in a variety of sizes and voltages. Their direction of rotation is dependant upon the polarity of the applied voltage. Reverse the voltage, the direction of rotation reverses. One of the most common solid-state controls is known as the H-bridge.

In figure 1 we has a very basic H-bridge using two single-pole, double-throw switches. The normally closed (NC) contacts are grounded and normally open (NO) contacts are connected to +12 volts. A DC motor is connected between the two commons. In its normal state, both motor connections are grounded through the switches. Both switches are spring loaded.

If we press SW1 the NC contact opens and the NO closes supplying +12 volts to one side of the motor while the other side is still grounded through SW2. The motor will spin at full speed say counter-clockwise. Release SW1 and press SW2 and +12 volts is supplied to the '+' side of the motor while the negative side is grounded through SW1. The direction now is clockwise. Press both switches and both sides of the motor will be at +12 volts and won't run.

Switching on a MOSFET

In the above examples we are switching a DC motor on/off using power MOSFETs. In the case of the P-channel (IRF9630) on the left, when the gate (G) is grounded as the switch is pressed the motor cuts on. With the N-channel (IRF630) on the right when voltage is supplied to the gate (G) when the switch is pressed the motor will turn on. There is no way to reverse the motor rotation other than disconnect and reverse the motor wires. The resistor on the gate of the N-channel is to bleed-off the electric charge and turn off the MOSFET when the switch is released.

Basic Transistor Driver Circuits for Micro-Controllers
Opto-Isolated Transistor Drivers for Micro-Controllers

IRF630 N-Channel Power FET 9 Amps 200 volts
IRF9630 P-Channel Power FET 6.5 amps 200 volts

using MOSFETs for H-bridge
Figure 4.

In this example we use four power MOSFETs and this circuit operates in an identical manner as the two switches in figure 1. Q3 and Q4 operate as NC contacts while Q1 and Q2 act as NO contacts. The two switches SW1 and SW2 could be replaced by transistors and switched on/off with a microcontroller.

using MOSFETs for H-bridge
Figure 5.

In this case I've used opto-isolators to switch the MOSFETs on/off. This circuit is fully functional and will operate from 5 volts to 30 volts.

The above can be used in the same manner as ATMEGA168/Arduino with the TA8050 Motor Controller project.

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ATMEGA168 Arduino Micro Controller

For more technical details on this see ATMEGA168 Arduino Micro Controller Projects

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