Electronica

PICmicro® DC Motor Control Tips ‘n Tricks

M
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........................................... 13Writing a PWM Value to the CCP Registers with a Mid-range PICmicro® MCU............. 17 Current Sensing ........................................ 19 Position/Speed Sensing ............................ 23

© 2004 Microchip Technology Inc.

DS41233A-page i

Tips ‘n Tricks

DS41233A-page ii

© 2004 Microchip Technology Inc.

Tips ‘n Tricks TIPS ‘N TRICKS INTRODUCTION
Every motor controlcircuit can be divided 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 usedto control motors. The booklet also provides references to Microchip application notes that describe many motor control concepts in more detail.

© 2004 Microchip Technology Inc.

DS41233A-page 1

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 ofthe 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® Microcontroller Digital output MOSFET Driver

V+

M

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

DS41233A-page 2

© 2004 Microchip Technology Inc.

Tips ‘n Tricks
FIGURE 1-2: LOW SIDE DRIVE

PICmicro® Microcontroller

V+

M

Digital Output MOSFET Driver

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.

© 2004 Microchip TechnologyInc.

DS41233A-page 3

Tips ‘n Tricks
FIGURE 1-3: H-BRIDGE DRIVE

V+

V+

A

D

M

B

C

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

The H-bridge derived its 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: • AN847 – “RC Model Aircraft MotorControl” (DS00847) • AN893 – “Low-cost Bidirectional Brushed DC Motor Control Using the PIC16F684” (DS00893) • AN905 – “Brushed DC Motor Fundamentals” (DS00905)

DS41233A-page 4

© 2004 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 cannotcommutate the windings (switch the current flow), so the control circuit and software must control the current flow 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 types of Brushless DC motors; sensor 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 motor position is required. A sensor motor will directly report to the controller, the current position of the motor. Driving a sensor motor requires a look-up table. The current sensor position directly correlates to a commutation pattern for the bridge circuits. A sensorless motor requires that the induced voltage in the un-driven winding be sensed and used to...