Motores Dc

DC Motor Control Tips ‘n Tricks

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Tips ‘N Tricks Introduction
TIP #1: TIP #2: TIP #3: TIP #4: TIP #5: TIP #6: TIP #7:

Tips ‘n Tricks
Table of Contents

Brushed DC Motor Drive Circuits ................ 2 Brushless DC Motor Drive Circuits .............. 5 Stepper Motor Drive Circuits ....................... 9 Drive Software........................................... 13 Writing a PWMValue to the CCP Registers with a Mid-Range PICmicro® MCU ........... 17 Current Sensing ........................................ 19 Position/Speed Sensing ............................ 23

© 2006 Microchip Technology Inc.

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© 2006 Microchip Technology Inc.

Tips ‘n Tricks TIPS ‘N TRICKS INTRODUCTION
Every motor control circuit can bedivided into the drive electronics and the controlling software. These two pieces can be fairly simple or extremely complicated depending upon the motor type, the system requirements and the hardware/software complexity trade-off. Generally, higher performance systems require more complicated hardware. This booklet describes many basic circuits and software building blocks commonly used to controlmotors. The booklet also provides references to Microchip application notes that describe many motor control concepts in more detail. The application notes can be found on the Microchip Technology web site at www.microchip.com. Additional motor control design information can be found in the Motor Control Design Center (www.microchip.com/motor).

© 2006 Microchip Technology Inc.

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Tips ‘n Tricks TIP #1 Brushed DC Motor Drive Circuits

All motors require drive circuitry which controls the current flow through the motor windings. This includes the direction and magnitude of the current flow. The simplest type of motor, to drive, is the Brushed DC motor. Drive circuits for this type of motor are shown below.
FIGURE 1-1: HIGH SIDE DRIVE

PICmicro® MicrocontrollerDigital output MOSFET Driver

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This drive can control a Brushed DC motor in one direction. This drive is often used in safety critical applications because a short circuit at the motor terminals cannot turn the motor on.

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© 2006 Microchip Technology Inc.

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FIGURE 1-2: LOW SIDE DRIVE

PICmicro® Microcontroller

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Digital Output MOSFETDriver

This is the lowest cost drive technique because of the MOSFET drive simplicity. Most applications can simply use an output pin from the PICmicro® microcontroller to turn the MOSFET on.

© 2006 Microchip Technology Inc.

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FIGURE 1-3: H-BRIDGE DRIVE

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A-D are digital outputs from a PICmicro® MCU.

The H-Bridge derivedits name from the common way the circuit is drawn. This is the only solid state way to operate a motor in both directions. Application notes that drive Brushed DC motors are listed below and can be found on the Microchip Technology web site at www.microchip.com. • AN847 – “RC Model Aircraft Motor Control” (DS00847) • AN893 – “Low-cost Bidirectional Brushed DC Motor Control Using the PIC16F684”(DS00893) • AN905 – “Brushed DC Motor Fundamentals” (DS00905)

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© 2006 Microchip Technology Inc.

Tips ‘n Tricks TIP #2 Brushless DC Motor Drive Circuits

A Brushless DC motor is a good example of simplified hardware increasing the control complexity. The motor cannot commutate the windings (switch the current flow), so the control circuit and software must control the currentflow correctly to keep the motor turning smoothly. The circuit is a simple half-bridge on each of the three motor windings. There are two basic commutation methods for Brushless DC motors; sensored and sensorless. Because it is critical to know the position of the motor so the correct winding can be energized, some method of detecting the rotor position is required. A motor with sensors will...