Motor｜Basic

Driving Brushed DC Motors with an H-Bridge:High-Side Voltage Linear Control

2022.07.06

Points of this article

・A circuit is configured to enable linear control of the H-bridge circuit high-side voltage.

・By controlling the H voltages of OUT pins, linear control of the rotation rate/torque of the motor is possible.

Starting with this article, a number of methods for driving brushed DC motors using an H-bridge circuit are explained.

Driving Brushed DC Motors with an H-Bridge:
High-Side Voltage Linear Control

In this driver circuit example, the voltage applied to a motor is controlled with the H voltage of the OUT terminals made variable, by linear control of high-side P-channel MOSFETs. The H voltage of the OUT terminals is controlled by the DC voltage applied to the Vref terminal; theoretically the voltage is the same as the voltage applied to the Vref terminal. As a result, the motor rotation rate/torque can be controlled.

In this example, when the H-bridge switching control logic turns on the high-side MOSFETs (Q1, Q3), op-amps apply a bias to the high-side MOSFET gates to turn on the MOSFETs, and the MOSFET drain voltages are fed back to the non-inverting inputs of the op-amps. In accordance with the principles of op-amp feedback circuits, in this circuit, feedback control is performed such that the voltages at the inverting input and the non-inverting input are equal. In this example, the voltage applied to the Vref pin, which is the voltage at the op-amp’s inverting input terminal, is equal to the H voltage of the OUT terminal, which is the MOSFET drain voltage and the voltage at the op-amp’s non-inverting input terminal. The gain of this feedback circuit is +1, and therefore the voltage ratio of Vref to OUT is 1:1.

The reader may find it strange that feedback is applied to the non-inverting input terminal; but because a P-channel MOSFET is active-low, the inverted voltage of the op-amp output is fed back. The general idea is the same as for a feedback circuit that uses PNP transistors as boosters.

The operation of the H-bridge control circuit is the same as that explained in “Switching Output States”.

【Download Documents】 Basics of Brushed DC Motors and Drive Methods

Brushed DC motors are the most versatile motors and are used in a great many applications. This handbook provides the basics of brushed DC motors, explaining their construction, principle of operation, characteristics, and driving methods.

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