arduino application: speed control of small dc motors v cb o collector -bas e v oltag e 60 v v ebo...

ME 120: Speed control of small DC motors

Arduino Application:

Speed control of small DC Motors

ME 120Mechanical and Materials Engineering

Portland State University

http://web.cecs.pdx.edu/~me120


Learning Objectives

• Be able to describe the use of a transistor as a high

speed switch

• Be able to build a breadboard circuit that uses a

transistor as a high speed switch

• Be able to explain the role of a snubber diode

• Be able to implement PWM speed control of a DC motor

• Additional references:

❖ Circuit 12 (p. 64) in the SIK manual

❖ ME 120 course notes on PWM

❖ http://learn.adafruit.com/adafruit-arduino-lesson-13-dc-

motors/overview

2


Using a transistor as a high

speed switch

3


Transistor as a switching device

• Each Arduino output channel has a 40 mA limit

❖ Only current to power a very small DC motor

❖ Arduino is not designed as a power supply

• Maximum current draw for an Arduino is 200 mA

• Use the Arduino as the brain

• Let another switching element be the brawn

4


Use an NPN Transistor as a switch

5

NPN General Pupose Amplifier

This device is designed for use as a medium power amplifier and

switch requiring collector currents up to 500 mA.

MMBT44012N4401

Absolute Maximum Ratings* TA = 25°C unless otherwise noted

*These ratings are limiting values above which the serviceability of any semiconductor device may be impaired.

NOTES:

1) These ratings are based on a maximum junction temperature of 150 degrees C.

2) These are steady state limits. The factory should be consulted on applications involving pulsed or low duty cycle operations.

Symbol Parameter Value Units

VCEO Collector-Emitter Voltage 40 V

VCBO Collector-Base Voltage 60 V

VEBO Emitter-Base Voltage 6.0 V

IC Collector Current - Continuous 600 mA

TJ, Tstg Operating and Storage Junction Temperature Range -55 to +150 °C

Thermal Characteristics TA = 25°C unless otherwise noted

Symbol Characteristic Max Units

2N4401 *MMBT4401

PD Total Device Dissipation

Derate above 25°C

6255.0

3502.8

mW

mW/°C

RqJC Thermal Resistance, Junction to Case 83.3 °C/W

RqJA Thermal Resistance, Junction to Ambient 200 357 °C/W

CB

E

TO-92

C

B

E

SOT-23Mark: 2X

*Device mounted on FR-4 PCB 1.6" X 1.6" X 0.06."

ã 2001 Fairchild Semiconductor Corporation

2N

44

01

/ MM

BT

44

01

2N4401/MMBT4401, Rev A

This device is designed for use

as a medium power amplifier

and switch requiring collector

currents up to 500 mA


Use Digital I/O pin to switch LED on/off

Digital I/O pin → LED


Code to control brightness of an LED

int LED_pin = 11; // PWM pin LED or motor control

void setup() {

pinMode( LED_pin, OUTPUT );

}

void loop() {

int duty, pot_pin=0, reading;

reading = analogRead(pot_pin); // read potentiometer

duty = map(reading,0,1023,0,255); // rescale to 8-bit

duty = constrain(duty,0,255); // be safe

analogWrite(LED_pin,duty); // set duty cycle

}

In the following examples, the Arduino code does not

need to change when the electrical circuit is changed.

The Arduino code only needs to use a single digital

output pin, which in this code is LED_pin.


Use Digital I/O pin to switch LED on/off

Use of a potentiometer

Digital I/O pin → LED

(Analog pin A0)

Pot. Pin

Potentiometer


(Analog pin A0)

Pot. Pin

Potentiometer

Use a Transistor to switch LED on/off

Digital I/O pin → Transistor → LED


NPN Transistors as Switches

C is the collector.

B is the base

E is the emitter

Transistors can be used as switches: By applying

relatively small voltage to the Base, electrical

current will flow from the collector to the emitter.




MMBT44012N4401



NOTES:











2N4401 *MMBT4401


Derate above 25°C

6255.0

3502.8

mW

mW/°C



CB

E

TO-92

C

B

E

SOT-23Mark: 2X



2N

44

01

/ MM

BT

44

01



NPN Transistors as Switches

C is the collector.

B is the base

E is the emitter

When used as a switch, ICE, the current from

the collector to the emitter is large compare to

IBE, the current from the base to the emitter.




MMBT44012N4401



NOTES:











2N4401 *MMBT4401


Derate above 25°C

6255.0

3502.8

mW

mW/°C



CB

E

TO-92

C

B

E

SOT-23Mark: 2X



2N

44

01

/ MM

BT

44

01



What is a snubber diode, and

why should I care?

15


Simplest DC Motor Circuit

Connect the motor to a DC power supply

16


Current continues after the switch is opened

Opening the switch does not immediately stop current

from flowing in the motor windings

17


Reverse current

Charge build-up can cause damage

18


Motor Model

• Simple model of a DC motor:

❖ Windings have inductance and resistance

❖ Electrical energy is stored in the windings – the inductance

effect

❖ We need a way to safely dissipate electrical energy when

the switch is opened after the motor has been running

19


Flyback diode or snubber diode

Adding a diode in parallel with the motor provides a path

for the dissipation of stored energy when the switch is

opened

20


DC motor speed control circuit

The circuit for DC motor speed control uses the idea from

the LED brightness control circuit. Replace the LED circuit

with the DC motor and snubber diode

21

(Analog pin A0)Pot. Pin

Potentiometer

(Digital pin ~11)

flyback diodeDC motor

Motor Pin

330Ω

+5V

transistor


DC motor speed control circuit

The circuit for DC motor speed control uses the idea from

the LED brightness control circuit. Replace the LED circuit

with the DC motor and snubber diode

22

(Analog pin A0)Pot. Pin

Potentiometer

(Digital pin ~11)

flyback diodeDC motor

Motor Pin

330Ω

+5V

transistor

arduino application: speed control of small dc motors v cb o collector -bas e v oltag e 60 v v ebo...

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