MAE156A

January 11, 2007UCSD

H. Ali Razavi

PMMotor

10A: Start/Stall2A: ContinuousV: 10-12V

Design Example 1:

Objective: To Turn On and Off a Permanent Magnet DC motor using a Micro Processor with the requirement of passing 10A during On Time with 10-12V on motor terminals.

Pin x

Microprocessor

TP

[n.m] T

[rad/sec]

A typical permanent magnet DC motor curve (copied from an actual spec sheet):

Measured at specific constant voltage:V

VI

T

Stall/Start Current

No Load Current

:Output Power

:Efficiency

:Measured Current

:Measured data points ,TNo Load Speed

Stall/Start Torque

Design Example: 9A +Margin: 10A

Design Example: 1.5A +Margin: 2A

M

Permanent DC Motor

After http://www.aosmithmotors.com/pdf/brochures/bulletin3100/ACDC.PDF

Coil (modeled: ) L

Resistance (modeled: ) R

dt

diLLV

iRRV Electro Motive ForceGenerator (modeled: )

VKEMFV VK

Electrical to Mechanical Conversion (modeled: ) TK

Model:

V

0

iRV

iTKT

dt

diLiRV

Kdt

diLiRV

Kirchhoff's Voltage law: 0 Kdt

diLiRV

iTKT

Kdt

diLiRV

R

KVTKT

dt

di 0- Steady State:

R

VTKT 0- Stall/Start:

Maximum TorqueUnder voltageV

For fixed linear relationshipbetween & T

V

- Power output:

R

KVTKTP

- Efficiency:ActualVi

T

PMMotor

10A: Start/Stall2A: ContinuousV: 10-12V

Design Example 1:

Objective: To Turn On and Off a Permanent Magnet DC motor using a Micro Processor with the requirement of passing 10A during On Time with 10-12V on motor terminals.

Problem 1: 10A is too high current to be provided by Microprocessor

Problem 2: Switching it off and on using microprocessor

Problem 3: Interfacing components and programming

Pin x

MicroprocessorConcept Generation

Risk Reduction

Trouble Shooting

Optimization

Problems Definition

Bipolar Junction Transistors

CiBiEi

000 EiCiBithVEVBVBEV

Bi

Ci

CiBiEiCiBithVEVBVBEV 00

BiFEhEiBiFEhCiBiCi 1

Switch

Current Amplifier

npnBV

CV

EV

Darlington Transistor

BIFEhCI

BI

CIBIEI

Darlington Transistors (achieving high gain by stack of transistors):

Field Effect Transistors

thVgV

thVgV

nMOS FET

PMMotor

10A: Start/Stall2A: ContinuousV: 10-12V

Design Example 1:

Objective: To Turn On and Off a Permanent Magnet DC motor using a Micro Processor with the requirement of passing 10A during On Time with 10-12V on motor terminals.

Problem 1: 10A is too high current to be provided by Microprocessor

Problem 2: Switching it off and on using microprocessor

Problem 3: Interfacing components and programming

Pin x

Microprocessor

Idea 1: Use of MOSFET to switch the Motor On/Off

Idea 2: Use of Bipolar Transistor to switch the Motor On/Off

Concept Generation

Risk Reduction

Trouble Shooting

Optimization

Problems Definition

Concept Generation

Idea 3: Use of Darlington Transistor to switch the Motor On/Off

# of components

Design Merits

CostPower (Start/Stall)

Power (Continuous)Efficiency (Start/Stall)

Efficiency (Continuous)

Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design

* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.414-417)

… Design Example 1:

Risk Reduction: Analysis of Idea 1

PMMotor

Pin x

Microprocessor

MD

S

G

External Supply

Solving Problem 1

Problem 2(needs further detail)

Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.)

* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.414-417)

… Design Example 1:

… Risk Reduction: Analysis of Idea 1

PMMotor

MD

S

G

External Supply

- This is an nMOSFET

- One can look catalog under “Power nMOSFET”

- http://www.fairchildsemi.com/

- Search “Power MOSFET”

- Picked “HUF764323D”

Step 3. Downloaded and Reviewed Spec sheet

Step 4. Analysis to determine - : required voltage to turn On - : the external voltage - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Power

… Design Example 1:

… Risk Reduction: Analysis of Idea 1

Case 1: Continuous Mode Operation (2A current through motor)

V12ddV

PMMotor

MD

S

GggV

ssV

ggV

ddV

ssV

TorqueSpeed

Eff

Thermal waste at MOSFET

External Supply

Case 2: Start/Stall Mode Operation (10A current through motor)

HUF764323D

VΩA

VΩA

6.1104.01012

92.1104.021212 DSRDSIDSVddVssV √Good! 10-12V on motor terminals.

The objective is to have 10-12V on motor terminals, so assume and verify if it would workV12ddV

P

Step 4. Analysis to determine - : required voltage to turn On - - - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Power

… Design Example 1:

… Risk Reduction: Analysis of Idea 1

Case 1: Continuous Mode Operation (2A current through motor)

V12ddV

PMMotor

MD

S

GggV

ssV

ggV

ddV

ssVEff

Thermal waste at MOSFET

External Supply

Case 2: Start/Stall Mode Operation (10A current through motor)

HUF764323D

Continuous Efficiency

√√

%7.96

12

6.11

%3.9912

92.11

ddVssV

DIddVDIDSVDIddVEff

Stall/Start Efficiency

P

W

W

1201012

24212DIddVP

Continuous Power

Stall/Start Power

Step 4. Analysis to determine - : required voltage to turn On - - - -

… Design Example 1:

… Risk Reduction: Analysis of Idea 1

Case 1: Continuous Mode Operation (2A current through motor)

V12ddV

PMMotor

MD

S

GggV

ssV

ggV

ddV

ssVEff

External Supply

Case 2: Start/Stall Mode Operation (10A current through motor)

HUF764323D

√√

P√√

Assuming 25◦C Junction Temperature

V5.4ggVOverdrive for uncertainty

V

V

15.3

75.2ggV

Continuous Power

Stall/Start Power

Good! Microprocessor Can directly turn it On.

… Step 4. Analysis

… Design Example 1:

… Risk Reduction: Analysis of Idea 1

PMMotor

Pin x

Microprocessor MD

S

G

External Supply

Problem 1: Solved

Problem 2: Solved

V12

%7.96lStart/StalEff

%3.99ContinuousEff

Pull down resistoris added to preventpin floating and accidental turn onof motor.Desire: Small leakagecurrent.

MA0.1

V5

5

M5 HUF764323D

… Step 4. Analysis

… Design Example 1:

… Risk Reduction: Analysis of Idea 1

PMMotor

Pin x

Microprocessor MD

S

G

External SupplyV12

%7.96lStart/StalEff

%3.99ContinuousEff

M5

Design merits of Idea 1:

Cost= $A

# of Components = 2

HUF764323D

WlStart/Stal 120P

WContinuous 24P

Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design

* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408)

… Design Example 1:

Risk Reduction: Analysis of Idea 2

PMMotor

Pin x

Microprocessor

External Supply

Solving Problem 1

Problem 2(needs further detail) BI

BIFEh

To protect against reversecurrent[Note this was build in for nMOSFET]

To limit current and protect transistor

- This is an NPN Bipolar Transistor

- Download “Bipolar Power Transistor Selection Guide” from

- http://www.fairchildsemi.com/

- Looked in column under General Purpose Transistors

- Picked “KSH3055” with

Step 3. Downloaded and Reviewed Spec sheet

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.)

- (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408) - Looked at in the spec sheet of Chips it returned (to select a high gain transistor)FEh

FEh

10020 FEh

PMMotor

External Supply

Solving Problem 1

BI

BIFEh

IN4002

KSH3055

Standard Diode

PMMotor

External Supply

Solving Problem 1

BI

BIFEh

IN4002

KSH3055

Step 4. Analysis to determine - : required current to turn On - : the external voltage - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

BI

CV

EV

TorqueSpeed

Eff

Thermal waste at Bipolar TransistorCase 1: Continuous Mode Operation (2A current through motor)

Case 2: Start/Stall Mode Operation (10A current through motor)

AA

AA

Overdrive

AA

AA

2.110

10

05.050

2

110

10

04.050

2

1FEhEI

BIBIFEhBIFEhEI

EI

Continuous

Stall/Start

The objective is to have 10-12V on motor terminals, so assume and verify if it would workV12CV

CV

EV

Typical Characteristic

BR

BR

PMMotor

External Supply

Solving Problem 1

BIFEh

IN4002

KSH3055

Case 1: Continuous Mode Operation (2A current through motor)

Case 2: Start/Stall Mode Operation (10A current through motor)

EI

√√

V12CV

VsatCEA 2.02 VCI

V-

V-satCE 0.110.112

8.112.012VCVEV

Typical Characteristic

VsatCEA 110 VCI

Continuous

Stall/Start√ Good! 10-12V on motor terminals.

Step 4. Analysis to determine - - - : the voltage seen by Motor (there must be enough voltage and current to power the motor) - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

BI

CV

EV

TorqueSpeed

Eff

Thermal waste at Bipolar Transistor

BI

BR

BR

Step 4. Analysis to determine - - - - : Efficiency (what percentage of power delivered by external supply is delivered to motor) - : Protective resistor

PMMotor

External Supply

Solving Problem 1

BIFEh

IN4002

KSH3055

Case 1: Continuous Mode Operation (2A current through motor)

Case 2: Start/Stall Mode Operation (10A current through motor)

EI

√√

V12CV

Case 1: Continuous Mode Operation (2A current through motor)

√

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

BI

CV

EV

TorqueSpeed

Eff

Thermal waste at Bipolar Transistor

Continuous

Stall/Start

BI

BR

BR

1021

1

A

2V

.BICV

BRBR

A2.1BIHighest Voltage

Lowest Voltage

V12CV

V0

(Maximum required current)

%3.861012

2.11220.11012

%8.95212

050.01222.0212

CICVBICVCIVCICV

EffSATCE

Estimate of power wasted at BR

Worst Casing:

PMMotor

External Supply

Solving Problem 1

IN4002

KSH3055

10

Turn On byA2.1

V12

… Design Example 1:

Risk Reduction: Analysis of Idea 2

Pin x

Microprocessor

Problem 2(1.2A Exceeds what Micro-Processor

can provide)

… Step 4.

PMMotor

Pin x

Microprocessor

External Supply

IN4002

V12

… Step 4. Analysis

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

Problem 3More data needed

KSH3055

10

Turn On byA2.1

To protect against excessive current

Sub-Step A. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design

* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408)

- This is an PNP Bipolar Transistor

- Look at downloaded “Bipolar Power Transistor Selection Guide” from

- http://www.fairchildsemi.com/

- Looked in and column under General Purpose Transistors

- Picked “KSH210” with and

Step 3. Downloaded and Reviewed Spec sheet

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

Step 2. Selecting the chip (Handbook, Catalog, Consulting, Book, etc.)

- (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408) - Looked at and in the spec sheet of Chips it returned (to select a reasonable gain and current output)FEh

FEh

18045 FEh

A2.1 BIFEhCI

CI

CI

A5CI

V12

BI

Step 4. Analysis to determine - : required current to turn On - : Protective resistor

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

2BI

2BR

A2.1 BIFEhCI

V12

2BI

2BR

To simplify modeling and calculations, losses in this transistor is ignored compared to the other one

Minimizing leakage current when ON: KΩΩA

V11000

012.0

122 BR

KSH210

mAAA

25017.070

2.1

FEhCI

BIBIFEhCI

Overdrive

PMMotor

Pin x

Microprocessor

External Supply

IN4002

V12

… Step 4. Analysis

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

Problem 3The current is small.

However, the circuit on right has high current.Need to protect the microprocessor.

KSH3055

10

Start Motor bymA25

kΩ 1

KSH210

PMMotor

Pin x

Microprocessor

External Supply

IN4002

V12

… Step 4. Analysis

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

KSH3055

10

Start Motor bymA25

kΩ 1

KSH210

Opto Isolator http://www.fairchildsemi.com/ HSR312

kΩ 1 Ω400

Ω)(overdrive

Ω0.025

12V

400

480

Ω0.005

5V1000

Bipolar T Bridge

… Step 4. Analysis

… Design Example 1:

… Risk Reduction: Analysis of Idea 2

PMMotor

Pin x

Microprocessor

External Supply

IN4002

V12

KSH3055

10

kΩ 1

KSH210

kΩ 1 Ω400

Design merits of Idea 2:

Cost= $B

# of Components = 8

WlStart/Stal 120P

WContinuous 24P

%8.95lStart/StalEff

%3.86ContinuousEff

HSR312

Step 1. Thinking, looking at Handbook, Catalog, Internet, Book, Consulting, … to pick a design

* (Stiffler, A. K., Design with Microprocessors for Mechanical Engineers, McGraw-Hill, Inc., 1992, pp.406-408)

… Design Example 1:

Risk Reduction: Analysis of Idea 3

PMMotor

Pin x

Microprocessor External Supply

IN4002

V12

Darlington Transistor

kΩ 1

HSR312

BIFEhCI

3BI

3R

CIBIEI

4R

Assignment: - Determine a Darlington Transistor Part number- Download its spec sheet and determine and for two cases: Continuous and Start/Stall - Follow similar analysis to idea 2 and determine * Determine (Worst Casing) * Determine to have the transistor ON for 2 cases: Continuous and Start/Stall * Determine efficiency for 2 cases: Continuous and Start/Stall * Determine to minimize leakage current when ON

FEh satCEV

3BI3R

Restriction: ONLY one (2-sided) sheet of paper

4R

Make a decision

...%lStart/StalEff

...%ContinuousEff

Design merits of Idea 3:

Cost= $C

# of Components = 5

MOSFET Bipolar T Bridge

Darlington

Build

Trouble Shoot

Optimize

Design merits of Idea 2:

Cost= $B

# of Components = 8

WlStart/Stal 120P

WContinuous 24P

%8.95lStart/StalEff

%3.86ContinuousEff

%7.96lStart/StalEff

%3.99ContinuousEff

Design merits of Idea 1:

Cost= $A

# of Components = 2

WlStart/Stal 120P

WContinuous 24P

WlStart/Stal 120P

WContinuous 24P

… What could happen if no analysis was done?