Prof R T KennedyProf R T Kennedy 11

Determine all operational powers and temperatures

(a) When the mosfet operational temperature is 100 oC

(b) When the rectifier operational temperature is 100 oC

Tamb= 50 oC

R =10

L= large

E=100 V

NTD12N10

BY229

6.0

40

mosfet

sw

D

kHzf

Thermal management of theNTD 12N10 mosfet and the BY229 rectifier in the dc-dc converter is provided by a ‘common’ heat sink of thermal resistance 3 oC / W.

Prof R T KennedyProf R T Kennedy 22

DEVICE RTH, j-c RTH, c-s RTH, j-a

RECTIFIER BY229 2.0 0 60 0C/W

MOSFET NTD12N10 2.65 0 85 0C/W

Tamb= 50 oC

R =10

L= large

E=100 V

NTD12N10

BY229

6.0

40

mosfet

sw

D

kHzf Rth,j-c(mosfet)

Rth,s-a(heatsink)

Tjn,mosfet

Rth,j-c(rectifier)

Tsink

Tambient

Tjn,rectifier

Prof R T KennedyProf R T Kennedy 33

4.06.0 rectmosfet DD

AR

VI

VEDV

avloadaveload

mosfetavload

610

60

601006.0

,,

,

RECTIFIER

58.14.0

11

4.264.0,,

rectav

rmsi

avloadrectavrect

DI

Iff

AIDI

Prof R T KennedyProf R T Kennedy 44

BY229

POWER LOSS

3.75 W

2.4 A

Prof R T KennedyProf R T Kennedy 55

NTD12N10 MOSFET

ON-STATE RESISTANCE

NTD12N10 MOSFET

Tstorage 175 oC

Tjunction,max 175 oC

Rth,junction-case 2.65 oC / W

Rth,junction-ambient 85 oC / W

RDS, 25 o

C 0.14

Prof R T KennedyProf R T Kennedy 66

NTD12N10 MOSFET

ON-STATE POWER LOSS /DISSIPATION

AI

IDI

rmsmosfet

avloadmosfetrmsmosfet

65.466.0,

,,

14.025, CoDS

R

Co

CoDSDSNonDS RRR

25,,

onDSrmsmosfetD RIP ,2

,

Tjunction 25 50 75 100 125

RDSN 1 1.2 1.375 1.625 1.875

0.14 0.168 0.1925 0.2275 0.2625

3.03 3.63 4.16 4.92 5.68 W

Prof R T KennedyProf R T Kennedy 77

MOSFET & RECTIFIER POWER LOSS CURVES

25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 1250

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

11

11.5

12DC-DC CONVERTER THERMAL

PO

WE

R D

ISS

IPA

TIO

N

TEMPERATURE

Pmosfet

Prectifier

Prof R T KennedyProf R T Kennedy 88

THERMAL ELECTRICAL ANALOGY

Rth,j-c(mosfet)

Rth,s-a(heatsink)

Tjn,mosfet

Rth,j-c(rectifier)

Tsink

Tambient

Tjn,rectifier

Prof R T KennedyProf R T Kennedy 99

25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 1250

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10

10.5

11

11.5

12DC-DC CONVERTER THERMAL

PO

WE

R D

ISS

IPA

TIO

N

Prect= 3.75 W

SELECT Tjn,mosfet as ref

Pmos= 5 W

CT

RPTT

P

TR

omosk

moscjthmosmosjnmosk

th

75.86)65.25(100

(

,sin

)(,,,sin

Tjn,rectt,= 94.25oC

65.2

11

,

sjthRslope

Tsink,mosfet= Tsink,rectifier

CT

RPTT

P

TR

orectjn

rectcjthrectkrectjn

th

25.94)0.275.3(75.86

(

,

)(,sin,

Prectifier

Pmosfet

0.2

11

,

sjthRslope

Ptot= 8.75 W

Tamb,= 50oC

2.4

11

,

asthRslope

Tsink,= 86.75oC

Tjn,mos= 100oCWCR

P

TTR

P

TR

oasth

total

ambnksiasth

th

/2.475.8

5075.86,

,

Prof R T KennedyProf R T Kennedy 1010

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REPEAT THE EXERCISE STARTING WITH Tjn rect