1 final control introduction thermal circuits –thermal resistance –heat sinks –2n3904 example...

1

Final Control

• Introduction• Thermal Circuits

–Thermal resistance–Heat Sinks–2N3904 example–OPA512 example

•JFET/MOSFET Review•Summary

2

Types of Heat Sinks

http://www.wakefield.com/

Ball Grid Array

For:IntelAMDPowerPC

SurfaceMount,WaveSolderable,Snap-down

3

System Parameters

Type of System

Parameter

Quantity Potential Time

Electrical Charge EMF or Voltage

Second

Liquid Volume Pressure Second

Gas Mass Pressure Second

Thermal Heat Temperature Second

Mechanical Distance Force Second

4

Defining Resistance

Type of System Change in Quantity Parameter

Description Name (SI Units)

Electrical Charge xfrd.

per sec.

Current (amperes)

Liquid Volume

Xfrd. per sec.

Flow Rate (Cubic meters per second)

Gas Gas xfrd.

per sec.

Flow Rate (kilograms per second)

Thermal Heat xfrd.

per sec.

Flow rate of energy (joules per second)

Mechanical Distance

per sec.

Velocity (meters per second)

dt

dq

dt

dV

dt

dmass

dt

dW

dt

dx

5

Thermal Definitions

Rθ

TJ

TA

TC

RθJC

RθCA

T= TJ -TA

J = junctionC=caseA=ambient

PD = power dissipated

PD

6

A simple thermal circuit

PD = 120 mW =.12 W

TJ

TA

RθJA = 2000C/W

T = 240 C = TJ – TA = PD*RθJA

TJ(max) = 1500CMax power:

BJT ~ PCE

FET ~ PDS

SCR ~ PAK

7

A complete thermal circuit with heat sink

PD

TJ

TC

TA

TS

RθJC

RθCS

RθSA

RθJC = Thermal Resistance from Junction to Case

T

RθSA = Thermal Resistance from Case to ambientRθCS = Thermal Resistance from Case to sink

T

http://www.electronics-cooling.com/Resources/EC_Articles/JUN95/jun95_01.htm

8Common Cases

http://sound.westhost.com/heatsinks.htm#introduction

9Mounting a heat sink

http://www.gensemi.com/launch/ITO-220Rectifiers-external.ppt

10

Mounting a TO-3 Heat Sink

11

2N3904 BJT

Specs

http://www.onsemi.com/pub/Collateral/2N3903-D.PDF

12

BJT Amplifier Circuit: Spec

says max. ambient

temperature will be 1200C

Example 1: RθJA for the 2N3904 is 200 0C/W,

VC = 10 volts

VE = 1.05 volts

VCE = 9 volts

PD = 9*20 = 180 mWPD = 180 mW =.18 W

TJ

TA

RθJA

T = 360C = TJ – TA = PD*RθJA

TJ(max) = 1500C

TO-92 Style Case

13Adding a heat sink

TO-92 Heat Sink

From Digikey: RθSA= 640C per Watt

PD

TJ

TC

TA

TS

RθJC

RθCS

RθSA

T

From 2N3904 spec: RθJC= 83.30C per Watt

From general: RθCS= 50C per Watt

RθTotal = 148.30C/WattT = TJ-TA = 26.70C

PD = 180 mW =.18 W

TJ(max) = 1500C

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OPA 512

http://focus.ti.com/docs/prod/productfolder.jhtml?genericPartNumber=OPA512

Absolute MaxInternal powerDissipation =125 Watts

15

OPA512 Problem

• OPA512, 125W, 15A

• RθJA = 30 0C/ Watt

• RθJC = .9 0C/ Watt

PD = 9*20 = 180 mWTJ

TA

RθJA

PD = (TJ – TA)/RθJA=

110/30 = 3.67Watts

TJ(max) = 1500C TA= 400C

Need 30 watt AC amplifierfor an audio application. Themax temp will be 1040F

First look at no heat sink:

http://www-s.ti.com/sc/ds/opa512.pdf

TJ

TC

TA

TS

RθJC=.9

RθCS

RθSA

T

30 = (TJ – TA)/RT=110/RT

RT = 3.67 0C/Watt total

So RθCS+RθSA=3.67-.9=2.77

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TO3 Mounting Kit

Mounting a TO-3 Heat Sink

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Pentium 4 Heat Sinkhttp://www.aavidthermalloy.com/products/microp/desktop.shtml#Pentium%20IV

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Athlon Heat Sinkhttp://www.aavidthermalloy.com/products/microp/desktop.shtml#AMD%20Processors

http://www.aavidthermalloy.com/technical/index.shtml

http://www.electronics-cooling.com/Resources/EC_Articles/JUN95/jun95_01.htm

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Power Derating Curve150 0C

5 W

25 0C

5W125

= 25 0C/WattRθJC=

20

JFET & MOSFET Review

http://www.nzart.org.nz/nzart/exam/

21IRL630 HEXFET Switching Power MOSFET

http://www.irf.com/product-info/datasheets/data/irl640s.pdf

RθJC= 1.7 0C/Watt (max) RθCS= .50C/Watt (flat, greased surface)

RθJA= 62 0C/Watt (max)

22Another Heat Sink Problem

RθJC= 1.7 0C/Watt (max)

RθCS= .50C/Watt (flat, greased surface)RθJA= 62 0C/Watt (max)

Max continuous drain current = 9 ampsRds = .4ΩMax power dissipated = 74 W @ 250CLinear derating factor = .59 W/0C

62125

= 2.02 WPD=150 0C

25 0C

PD

TTJ

TC

TA

TS

RθJC=1.7

RθCS=.5

RθSA

T

So the max power that can be dissipated is: RθJC+RθCS+RθSA=1.7+.5+4=6.20C/W and

PD=125/6.2=20.2W

Best TO-220 at Digikey is:RθSA=4 0C/W

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CMOS: Complementary Metal-Oxide Semiconductor

CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor.

http://tech-www.informatik.uni-hamburg.de/applets/cmos/cmosdemo.html

http://www.webopedia.com/TERM/C/CMOS.html

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Summary• Thermal Circuits

– Thermal resistance– Heat Sinks– 2N3904 example– OPA512 example

• JFET/MOSFET Review– IRL630 Heat Sink example

• Next– Industrial Electronics

•SCR•TRIAC•DIAC

–Stepping Motors