Iec Tr 63091-2017.Pdf

IEC TR 63091 Edition 1 0 201 7 05 TECHNICAL REPORT Study for the derating curve of surface mount fixed resistors – Derating curves based on terminal part temperature IE C T R 6 3 0 9 1 2 0 1 7 0 5 (e[.]

IEC TR 63091

Editio 1.0 2 17-0

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IEC TR 63091

Edit io 1.0 2 17-0

FOREWORD 7

INTRODUCTION 9

1 Sco e 10 2 Normative ref eren es 10 3 Terms an def i ition 10 4 Stu y f or the deratin c rve of s r ace mou t fixed resistors 1

4.1 General 1

4.2 Usin the deratin c rve b sed on the terminal p rt temp rature 12 4.3 Me s rin method of the terminal p rt temp rature of the SMD resistor 13 4.4 Me s rin method of the thermal resistan e R th s s-t fom the terminal p rt to the s r ace hotsp t 19 4.5 Con lu ion 21

An ex A (informative) Bac grou d of the esta l s ment of the deratin c rve b sed on ambient temp rature 2

A.1 Tracin the history of the mou tin an he t dis ip tion f i uration of resistors 2

A.2 How to esta l s the hig temp rature slo e p rt of the deratin c rve 2

A.2.1 General 2

A.2.2 Deratin c rve for the semicon u tors 2

A.2.3 Deratin c rve for resistors 2

An ex B (informative) The temp rature rise of SMD resistors an the influen e of the printed circ it b ard 4

B.1 Temp rature rise of SMD resistors 4

B.2 The influen e of the printed circ it b ard 4

An ex C (inf ormative) The influen e of the n mb r of esistors mou ted on the test b ard 4

C.1 General 4

C.2 The influen e of the n mb r of resistors mounted on the test b ard 4

C.3 The delay of cor esp n en e for c r ent prod cts with non tan ard dimen ion 51

An ex D (inf ormative) Influen e of the air flow in the test c amb r 5

D.1 General 5

D.2 Influen e of the win sp ed 5

An ex E (informative) Val dity of the new deratin c rve 6

E.1 Su gestion f or esta l s in the deratin c rve b sed on the terminal p rt temp rature 6

E.2 Con lu ion 6

An ex F (informative) The thermal resistan e of SMD resistors 6

An ex G (inf ormative) How to me s re the s race hotsp t temp rature 7

G.1 Target of the me s rement 7

G.2 Recommen ed me s rin eq ipment 7

G.3 Points to b careful when me s rin the s r ace hotsp t of the resistor with an inf rared thermogra h 7

G.3.1 General 7

G.3.2 Sp tial resolution an ac urac of p ak temp rature me s rement 7

G.3.3 Influen e of the an le of the me s rement target normal l ne an the

An ex H (informative) How the resistor man facturers me s re the thermal resistan e

of esistors 7

H.1 The me s rin s stem 7

H.2 Definition of the two kin s of temp ratures 8

H.3 Er ors in the me s rement 8

An ex I (informative) Me s rement method of the terminal p rt temp rature of the SMD resistors 8

I 1 Me s rin method u in an inf ared thermogra h 8

I 2 Me s rin method u in the thermocouple 8

I 3 Estimatin the er or ran e of the temp rature me s rement u in the thermal resistan e of the thermocouple 9

I 3.1 General 9

I 3.2 When u in the typ T thermocouples 9

I 4 Thermal resistan e of the b ard 9

I 5 Con lu ion of this an ex 10

An ex J (inf ormative) The variation of the he t dis ip tion f action cau ed by the

diff eren e b twe n the resistor an its mou tin config ration 101

J.1 He t dis ip tion ratio of c l n rical resistors wired in the air 101

J.2 He t dis ip tion ratio of SMD resistors mou ted on the b ard 10

J.3 He t dis ip tion ratio of the c ln rical resistors mou ted on the throu h

-hole printed b ard 10

An ex K (informative) Influen e of airlow on SMD resistors 10

K.1 General 10

K.2 Me s rement s stem .10

K.3 Test res lts (orthogonal) 10

K.4 Test res lts (p ral el) .1 0

An ex L (informative) The in uen e of the sp tial resolution of the thermogra h 1 5

L.1 The a pl cation for u in the thermogra h when me s rin the temp rature

of the SMD resistor 1 5

L.2 The relation b twe n the minimum are that the ac urate temp rature could

b me s red an the pixel mag if i ation p rcentage 1 5

L.3 Example of the RR16 8M SMD resistor hotsp t's actual me s rement 12

L.4 Con lu ion 121

An ex M (informative) Future s bjects 12

Biblogra h 12

Fig re 1 – Existin deratin c rve b sed on ambient temp rature 12

Fig re 2 – Su gested deratin c rve b sed on terminal temp rature 12

Fig re 3 – At ac ment p sition of the thermocouple when me s rin the temp rature

of the terminal p rt 13

Fig re 4 – At ac in typ K thermocouples 14

Fig re 5 – Wirin routin of the thermocouple 15

Fig re 6 – The true value an the actual me s red value of the terminal p rt

temp rature 16

Fig re 7 – Thermal resistan e R

th eq

of the FR4 sin le side b ard ( hic nes 1,6 mm) 17

Fig re 8 – L n th that cau e the he t dis ip tion an the thermal resistan e of the

typ -K thermocouple (calc lated) 18

Fig re 9 – Example of calc lation of the me s rement er or ∆T cau ed by the he t

Fig re 10 – Recommen ed me s rement s stem of T

s s

t for calc latin R

th

s s-t

2

Fig re A.1 – Wired in the air u in the lu terminal 2

Fig re A.2 – He t p th when wired in the air u in the lu terminal 2

Fig re A.3 – Test con ition for resistors with category p wer 0 W 2

Fig re A.4 – Test con ition for resistors with category p wer other than 0 W 2

Fig re A.5 – Example of reviewin the deratin c rve 2

Fig re A.6 – T j , T c an R th j-c of tran istors 2

Fig re A.7 – Deratin c rves f or tran istors 2

Fig re A.8 – Trajectory of T j when P is red ced ac ordin to the deratin c rve 2

Fig re A.9 – L aded resistors with smal temp rature rise 3

Fig re A.10 – L aded resistors with large temp rature rise 31

Fig re A.1 – Trajectory of T h for the le d wire resistors with smal temp rature rise 31

Fig re A.12 – Trajectory of T h for the le d wire resistors with large temp rature rise 3

Fig re A.13 – Trajectory of T h for resistors with category p wer other than 0 W 3

Fig re A.14 – T sp an MAT for le d wire resistors with large temp rature rise 3

Fig re A.15 – T sp an MAT f or le d wire resistors with smal temp rature rise 3

Fig re A.16 – Resistors f or whic the hotspot is the thermal y sen itive p int 3

Fig re A.17 – Resistor that have deratin c rve simiar to the semicon u tor 3

Fig re B.1 – Temp rature distribution of the SMD resistors mou ted on the b ard 41

Fig re B.2 – Temp rature rise of the SMD resistors fom the ambient temp rature 4

Fig re B.3 – Me s rement s stem layout an b ard dimen ion 4

Fig re B.4 – Temp rature rise of RR2 12M ( hic nes 3 μm, 0,2 W a pl ed) 4

Fig re B.5 – Temp rature rise of RR2 12M ( hic nes 7 μm, 0,2 W a pl ed) 4

Fig re B.6 – Trajectory of the terminal p rt an hotsp t temp rature of the SMD resistors 4

Fig re B.7 – Op ratin temp rature of the resistor on the b ard with nar ow p t ern 4

Fig re C.1 – Test b ard compl ant with the IEC stan ard for RR16 8M 5

Fig re C.2 – Relation b twe n the n mb r of samples an the s race hotsp t temp rature rise 5

Fig re C.3 – Inf rared thermogra h image in the same s ale when p wer is a pl ed to 5 samples an 2 samples 51

Fig re D.1 – Win sp ed an the terminal p rt temp rature rise of the RR6 3 M 5

Fig re D.2 – Test s stem f or the natural con ection flow 5

Fig re D.3 – Observin the influen e of the agitation win in the test c amb r 5

Fig re D.4 – Win sp ed an the terminal p rt temp rature rise of the RR5 2 M 5

Fig re D.5 – Win sp ed an the terminal p rt temp rature rise of the RR3 2 M 5

Fig re D.6 – Win sp ed an the terminal p rt temp rature rise of the RR3 16M 5

Fig re D.7 – Win sp ed an the terminal p rt temp rature rise of the RR2 12M 5

Fig re D.8 – Win sp ed an the terminal p rt temp rature rise of the RR16 8M 5

Fig re D.9 – Win sp ed an the terminal p rt temp rature rise of the RR10 5M 5

Fig re E.1 – Deratin con ition of SMD resistors on the resistor man facturer test b ard 6

Fig re E.2 – New deratin c rve provided by the resistor man f acturer to the

Fig re E.3 – Deratin c rve b sed on the terminal p rt temp rature 6

Fig re E.4 – Deratin c rve b sed on the terminal p rt temp rature 6

Fig re F.1 – Definition of the thermal resistan e in a strict sen e 6

Fig re F.2 – Thermal resistan e of the resistor 6

Fig re G.1 – Dif feren e of the me s red hotsp t temp rature cau ed by the sp tial resolution 7

Fig re G.2 – Me s rin s stem for the er or cau ed by the an le 7

Fig re G.3 – Er or cau ed by the an le of the o tical axis an the target s rf ace (natural convection) 7

Fig re G.4 – Er or cau ed by the an le of the o tical axis an the target s rf ace (0,3 m/s air venti ation fom the side) 7

Fig re H.1 – Me s rin s stem f or calc latin the thermal resistan e b twe n the s race hotsp t an the terminal p rt 8

Fig re H.2 – Simulation model 81

Fig re H.3 – Temp rature distribution of the co p r bloc s r ace (calc lated) 8

Fig re H.4 – Isothermal l ne of the fi et p rt (calc lated) 8

Fig re I 1 – Temp rature dro cau ed by the at ac ed thermocouple 8

Fig re I 2 – Example of the printed b ard 9

Fig re I 3 – Printed b ard s own with the thermal network 91

Fig re I 4 – Eq ivalent circ it of the printed b ard s own with the thermal network 9

Fig re I 5 – Eq ivalent circ it when the thermocouple is con ected 9

Fig re I 6 – Ambient temp rature an the sp ce ne d f or the he t dis ip tion of the thermocouple 9

Fig re I 7 – Eq ivalent circ it when the thermocouple is con ected 9

Fig re I 8 – L n th that cau es the he t dis ip tion an the thermal resistan e of the typ K thermocouple (calc lated) 9

Fig re I 9 – L n th that cau e the he t dis ip tion an the thermal resistan e of the typ T thermocouple (calc lated) 9

Fig re I 10 – Thermal resistan e R th eq of the FR4 sin le side b ard ( hic nes 1,6 mm) 9

Fig re I 11 – Calc latin the thermal resistan e of the b ard f om the f il et side 9

Fig re J.1 – Simulation model of the le d wire resistors wired in the air 101

Fig re J.2 – He t dis ip tion ratio of the le ded c ln rical resistors (calc lated) 10

Fig re J.3 – Me s rement s stem of the he t dis ip tion ratio of SMD resistors

mou ted on the b ard .10

Fig re K.1 – Me s rement s stem 10

Fig re K.2 – Relation hip b twe n the terminal p rt temp rature rise an the win

sp ed f or the RR6 3 M (orthogonal) 10

Fig re K.3 – Relation hip b twe n the terminal p rt temp rature rise an the win

sp ed f or the RR5 2 M (orthogonal) 10

Fig re K.4 – Relation hip b twe n the terminal p rt temp rature rise an the win

sp ed f or the RR3 2 M (orthogonal) 10

Fig re K.5 – Relation hip b twe n the terminal p rt temp rature rise an the win

sp ed f or the RR3 16M (orthogonal) 10

Fig re K.6 – Relation hip b twe n the terminal p rt temp rature rise an the win

sp ed f or the RR2 12M (orthogonal) 10

Fig re K.7 – Relation hip b twe n the terminal p rt temp rature rise an the win

Fig re K.8 – Relation hip b twe n the terminal p rt temp rature rise an the win

Fig re K.16 – Terminal p rt temp rature rise of RR63 2M, dif feren e b twe n the

win ward an le ward sides when placed p ralel 1 4

Fig re L.1 – Ste resp n e of the Gau sian fi ter of the variou c t-of f sp tial

f req en ies (calc lated) 1 6

Fig re L.2 – Temp rature distribution (cros -section) when me s rin the o ject that

b comes hig temp rature only in the ran e of 0,2 mm in diameter 1 7

Fig re L.3 – Me s rin s stem of sp tial feq en y fi ter of the inf rared thermogra h 1 8

Fig re L.4 – Actual me s red value of the ste resp n e of variou mag ifier len es 1 9

Fig re L.5 – Comp rison of the actual me s red value an the calc lated value (ste

resp n e) 12

Fig re L.6 – Comp rison of the actual me s red value an the calc lated value

(s rf ace hotsp t of the resistor) .121

Ta le D.1 – Numb r of samples mou ted an the a pl ed p wer 5

Ta le H.1 – Res lts of the fi et p rt temp rature simulation (calc lated value) 8

Ta le H.2 – Simulation res lt of the fi et p rt's temp rature where it is me s ra le

(calc lated value) 8

Ta le H.3 – Simulation res lt of the fi et p rt's temp rature where it is me s ra le

(calc lated value) 8

Ta le H.4 – Thermal resistan e simulation res lts b twe n the s rf ace hotsp t an the

terminal p rt b sed on the co p r bloc temp rature (calc lated value) 8

Ta le J.1 – Analy is res lt of the he t dis ip tion ratio of SMD resistors (calc lated

value an value actual y me s red) 10

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The main tas of IEC tec nical commit e s is to pre are International Stan ard However, a

tec nical commit e may pro ose the publcation of a tec nical re ort when it has col ected

data of a diff erent kin f om that whic is normal y publs ed as an International Stan ard, f or

example "state of the art"

IEC TR 6 0 1, whic is a tec nical re ort, has b en pre ared by IEC tec nical commit e 4 :

Cap citors an resistors f or electronic eq ipment

The text of this tec nical re ort is b sed on the fol owin doc ments:

En uiry draft Re ort o v tin

Ful information on the votin f or the a proval of this tec nical re ort can b f ou d in the

This doc ment has b en drafted in ac ordan e with the ISO/IEC Directives, Part 2.

The commite has decided that the contents of this doc ment wi remain u c an ed u ti the

sta i ty date in icated on the IEC we site u der "htp:/ we store.iec.c " in the data related to

Work b gan in 2 12 to ado t the new deratin c rve s ita le for the s r ace mou t f i ed

resistors that u e the terminal p rt temp rature as the horizontal axis

The deratin c rves for s race mou t fixed resistors are def i ed in JIS C 5 01-8:2 14

However, the prin iple of the deratin c rve was esta l s ed when the resistors were

c l n rical y s a ed, wired in the air an the he t was dis ip ted directly fom the resistor

b d into the ambient en ironment Therefore, it is not s ita le for the s rf ace mou t fixed

resistors that u e the printed circ it b ard as the main he t p th

It is neces ary to fulf il the deman s fom the electric an electronic device man f acturers f or

raising the p wer ratin s safely Ad itional y, it is req ired to esta l s a new deratin c rve

that is s ita le f or the s r ace mou t fixed resistors so that they can b u ed safely in a hig

temp rature en ironment, typical y in automotive electronic devices

Makin a c an e of the temp rature rule f or evaluation of the fixed resistors f rom the ambient

temp rature to the temp rature of the con ection p int ( erminal p rt temp rature of the

resistor) wi aff ect man defined contents of multiple stan ard in the IEC 6 1 5 series

Ad itional y, it wi me n c an in the u ers' evaluation rules, so the imp ct wi b enormou

Therefore, it has b en decided to is ue the Tec nical Re ort first to at ract atention of the

relevant market players an then, we wi start workin on c an in the defined contents of

the IEC 6 1 5 series

STUDY FOR THE DERATING CURVE

OF SURFA CE MOUNT FIXED RESISTORS –

Derating curves based on terminal part temperature

This Tec nical Re ort is a plca le to SMD resistors with sizes eq al or smaler than the

RR6 3 M, in lu in the typical rectan ular an c l n rical SMD resistors mentioned in

IEC 6 1 5-8

The fol owin doc ments are ref er ed to in the text in s c a way that some or al of their

content con titutes req irements of this doc ment For dated referen es, only the edition

cited a ples For u dated referen es, the latest edition of the referen ed doc ment (in lu in

an amen ments) a pl es

IEC 6 1 5-1:2 0 , Fixed resist ors for use in el ectro ic e uipme t – Part 1: Ge eric

sp cific tio

IEC 6 1 5-8:2 09, Fixed resistors for use in ele tro ic e uipme t – Part 8: Se t ion l

sp cific t io : Fix ed c ip resistors

3 Terms and def initions

For the purp ses of this doc ment, the f ol owin terms an def i ition a ply

ISO an IEC maintain terminological data ases f or u e in stan ardization at the f ol owin

ad res es:

• IEC Electro edia: avai a le at ht p:/ www.electro edia.org/

• ISO Onl ne browsin platf orm: avai a le at htp:/ www.iso.org/o p

rate terminal part temperature

terminal p rt temp rature of the resistor at the time of the rated lo d lfe test

3.3

hotspot of the re istor

hotest p rt of the resistor that is cau ed by the Joule he t generated fom the resistive

element when the c r ent is a pl ed an is general y located in ide resistor's b d

3.4

hotspot temperature

T

hs

temp rature of the s rf ace hotsp t of the resistor

Note 1 to e try: Ge eraly, th intern l h ts ot temp rature is hig er th n th s rf ac h ts ot temp rature

3.7

th rmal re ista ce of the re istor

R

th

restraint of the thermal flow f rom the resistor's hotsp t to the en ironment

Note 1 to e try: Th rmal re ista c is c lc late b dividin th difere c b twe n th s ra e h ts ot

maximum temp rature of the terminal p rt of the resistor

4 Study f or the derating c rve of surf ace mount f ix d resistors

The electric/electronic device desig ers are red cin the p wer a pled to the resistor b low

the level s own in the deratin c rves provided by the resistor man facturer b sed on the

ambient temp rature of the u lo ded resistor, but the ambient temp rature of the b ard rises

when they u e SMD resistors

But, the b d temp rature of the SMD resistor may b come hig er than the temp rature

verified in the test implemented by the resistor man f acturer even when this rule is o served

On the other han , in some cases ex es ive deratin is req ested an an extremely large

margin is set

In this Tec nical Re ort, the re son why the deratin c rves, whic are def i ed in

2.2.4 of IEC 6 1 5-1:2 0 an in 2.2.3 of IEC 6 1 5-8:2 0 , provided by the resistor

man facturers sometimes can ot b u ed by electric/electronic device desig ers in their

desig activity wi b given, an the method of c an in them into a practical desig in to l

wi b s g ested

There are thre key p ints The first an most imp rtant p int is to u e the deratin c rve

b sed on the terminal temp rature in te d of the ambient temp rature The secon p int is

the me s rin method of the terminal p rt temp rature of the SMD mou ted on the printed

resistor terminal p rt to the s race hotsp t The secon an third p ints are the is ues that

ne d to b defined in as ociation with the first p int

4.2 Using the derating c rv ba e on the terminal part temperature

Usin Fig re 2 in te d of Fig re 1 is s g ested f or the desig of hig -p wer a pl cation of

the SMD resistors in ex es of the con entional rated dis ip tion (e.g 10 mW for RR16 8M)

The val dity of u in the deratin c rve b sed on the terminal p rt temp rature is explained in

Rate ambie t temp rature

Figure 1 – Existin derating c rv ba e on ambie t temperature

Termin l p rt temp rature

MT Ma imum termin l temp rature

4.3 Me s rin method of the terminal part temperature of the SMD re istor

The me s rement wi b done on the commonly-u ed printed circ it b ard, but the resistor

man facturer can re lace it with the b ard defined in the stan ard The temp rature

me s rement p sition wi b the centre p rt of the fi et regardles of the size The

me s rement sen or wi b the thermocouple The me s rement p int is s own in Fig re 3

A typ K thermocouple with a wire diameter (sin le wire) of 0,1 mm is recommen ed As in

Fig re 4, the tips of the typ K thermocouple s ould b sp t-welded an pre-tre ted by

a plyin s ita le flu an dip ed in melted solder so that it can b s rely an directly

soldered to the fi et of the target resistor

This re ort is b sed on the u e of typ K thermocouples d e to their low thermal con u tivity

If other thermocouples are to b u ed, their thermal pro erties ne d to b con idered, as

s own for typ T thermocouples in An ex I

The me s red value s ould b cor ected as neces ary by estimatin the in uen e of the he t

dis ip tion throu h the thermocouple The method wi b mentioned in Formula (1)

(b) Ata hme t p sitio of th th rmo o ple wh n f ilet is larg (c ntre of s ld r me is u )

(c) Ata hme t p sitio of th th rmo o ple wh n f ilet is smal (c ntre of s ld r me is u )

Figure 3 – At a hme t position of the thermocouple

wh n mea uring the temperature of the terminal part

Fig re 4 – At a hin type K thermocouple

The thermocouple con ected to the me s rin p int wi b wired alon the isothermal l ne

When the isothermal lne is u k own, make s re that the thermocouple is not af fected directly

by other he t-generatin prod cts on the b ard The thermocouple s ould not b closel

y-at ac ed with other prod cts or the b ard, an they s ould b wired p ral el to the b ard as

Key

1 Wirin clo e to th p rts with larg h at g n ratio s c a th d te ln s al b a oid d

2 No me h nic l stre gth wh n o ly th tip of th th rmo o ple is s ld re , s f i th wirin a d tru kin o to

th p rts with n h at g n ratio

3 Av id th h at g n ratin p rts wh n wirin

(A) In d q ate wirin

(B) Suita le wirin

Figure 5 – Wiring routing of the thermocouple

Next, the temp rature dro cau ed by the heat dis ip tion fom the thermocouple wi b

estimated by comp rin the me s red temp rature T

L rg SMD re istor with larg h at g n ratio

Smal SMD re istor with smal h at g n ratio

Semic n u tor s c a T F, IGB (larg h at g n ratio )

(A)

(a) True terminal temperature (b) A ctual me sured temperature

Key

2 Co p r p tern

3 Printe b ard

4 Th rmo o ple for me s rin th termin l p rt temp rature

5 Th rmo o ple for me s rin th h at dis ip tio s a e temp rature

6 Th rmo o ple for me s rin th sta d rd temp rature

Th rmal re ista c wh n th th rmo o ple is pre ume a ah atsin a d th th rmal re ista c b twe n

th tip of th th rmo o ple a d th h at dis ip tio s a e of th th rmo o ple (T

Th rmal re ista c of th printe b ard viewe f rom th termin l p rt a d th e uiv le t th rmal

re ista c b twe n th termin l p rt wh re th th rmo o ple is c n e te a d th sta d rd temp rature

me s re s a e (T

b se

me s reme t p sitio )

Fig re 6 – The true value a d the a tual me s re

v lue of the terminal part temperature

The temp rature that is actual y me s red by the thermocouple is T

t

’ an the T

tcan ot b

me s red But the dif feren e ∆T = T

t– T

t h

t c a

/'

is the thermal resistan e f om the terminal p rt of the printed circ it b ard to the

s r ou din sp ce, set as a stan ard, s c as the sp tial temp rature in whic the b ard is

set An example value is s own in Fig re 7

2

3

IEC

Dime sion in mil l imet re

Key

Patern thic n s 3 µm

Patern thic n s 7 µm

on the actual b ard for me s rin the temp rature, p wer P s al b

a pl ed only to the target resistor f or me s rin T

This is only an a proximate estimate However, there wi not b a controversial er or u les

the thermal resistan e b twe n the terminals of the resistor itself is extremely large Refer to

Key

R

thtc

Th rmal re ista c wh n th th rmo o pleis re ard d a a h atsin

L L n th f rom th me s reme t p int th t c u e th h at dis ip tio of th th rmo o ple

D Wire diameter of th th rmo o ple

Figure 8 – Le gth that c us the h at dis ipation a d the thermal

re ista c of the type-K thermocouple (c lc late )

The air sp ed 0 m/s in Fig re 8 me n that the thermocouple is set horizontal y in a sp ce

with no f orced air an the he t dis ip tion is only by natural con ection

For the same typ of thermocouples, the thin er the stran of wire diameter is, the hig er the

thermal resistan e is an the len th that cau es the he t dis ip tion L gets s orter

have the lowest temp rature ne d to b me s red

The typical calc lation res lt of ∆T is s own in Fig re 9 The place where the b ard is set is

as umed to b a natural con ection en ironment For the purp se of c ec in the o eratin

temp rature of the resistor, it is u derstan a le when it is actual y calc lated that ∆T is

negl gible in most cases when a typ K thermocouple of 0,1 mm in diameter is u ed

(m/s)

Ambie t temp rature of th b ard

L L n th f rom th me s reme t p int th t c u e th h at dis ip tio of th th rmo o ple

H Heig t wh re th th rmo o ple wi b wire

Figure 9 – Ex mple of c lc lation of the me s reme t er or ∆T

c u e by the he t dis ipation of the th rmocouple

However, when typ K thermocouples with wires 0,2 mm in diameter or thic er are u ed, or

when there is air low, ∆Twould b come larger It is neces ary for the resistor man facturer

an electric/electronic device desig ers to take on the resp n ibi ty an p rf orm the

(a pled p wer) is u ed for calc latin the pro ortional con tant R

The recommen ed me s rin s stem is s own in Fig re 10

The co p r bloc on whic the resistor is mou ted wi b an alternative to the ide l zed

s ould b on the to s rf ace of the co p r bloc an close to the f il et of the resistor (within

3 mm f rom the fi et ex lu in the f il et The p ints that s ould b con idered d rin

me s rin are as fol ows

1) The sp ce resolution an the p ak detection ca a i ty of the inf rared thermogra h is not

the same Select the len with a mag if i ation p rcentage that can me s re the hotsp t

p ak temp rature cor ectly

2) If the sp ce resolution an hotsp t p ak detection ca a i ty of the inf rared thermogra h

is not clarified, the data s al cle rly state whic len was u ed for mag ifyin whatever

μm p r pixel

3) The to s rf ace of the co p r bloc on whic the target resistor is mou ted an the

temp rature me s red by the inf rared thermogra h s ould b co ted evenly with blac

4) L n es with large mag ification have a s ort foc s in general Therefore, even a smal

misal g ment of the foc s could le d to a large er or in the temp rature me s rement

Esp cial y precise adju tment of the foc s would b ne ded when me s rin the hotsp t

of a smal are

4.5 Conclusions

There are 3 p ints to s g est in this Tec nical Re ort, as mentioned in the o enin of this

clau e:

1) u e of the deratin c rve b sed on the terminal temp rature in te d of the ambient

temp rature f or the desig of hig p wer a pl cation of the SMD resistors in ex es of

the con entional rated dis ip tion (e.g 10 mW for RR16 8M);

2) me s rement method of the terminal p rt temp rature of the SMD resistor mou ted on the

printed b ard;

3) me s rement method of the thermal resistan e R

th s s-t

f rom the terminal p rt of the

resistor to the s rf ace hotsp t

The deratin c rve that u es the ambient temp rature as the horizontal axis was esta l s ed

as a stan ard more than 5 ye rs ago, at an era when vac um tub s were b in u ed As

s own in Fig re A.1, the resistors in those day were mainly made with le d wires, an lu

terminals were u ed for mou tin

As s own in Fig re A.2, al the he t generated in any kin of resistors wi b rele sed

throu h the fol owin thre phenomena

The first phenomenon is he t con u tion The he t is con u ted throu h the con ection p rt

s c as the le d wire to the lu terminals an other p rts with lower temp ratures

The secon phenomenon is he t tran f er by con ection to the ambient atmosphere of the

resistor The ambient air is exp n ed with the he t provided f rom the resistor an b comes

les den e res ltin in updraft The risin air wi siphon of the new co l air fom the low

s r ou din to the ambient air of the resistor By re e tin this, an as en in c r ent wi

con istently oc ur arou d the resistor an the he t wi b tran f er ed into the atmosphere

This is cal ed he t dis ip tion by con ection flow

The third phenomenon is radiation by infared

He t dis ip tion by either of the phenomena (he t con u tion, con ection an radiation)

would b larger when the temp rature diff eren e b twe n the resistor an the le d wire an

the other p rts con ected is larger For the resistors wired in the air by the lu terminal, the

he t con u tion via the le d wires are smal comp red with the he t dis ip tion by con ection

an radiation The le d wires are mainly made with co p r an the co ff i ient of thermal

con u tivity is hig but the s a e is nar ow an lon , so the thermal resistan e wi not b so

low In a breviated calc lation, the thermal resistan e of the le d wire 0,8 mm in diameter

an 3 mm in len th wi b 19 K/W, whic is q ite a large value On the other han , the he t

dis ip tion is pro ortionate to the s rf ace are of the resistor, so the he t dis ip tion

p rorman e f rom the s rf ace of the c l n rical resistor to the atmosphere wi b f avoura le

an the calc lated thermal resistan e is s rprisin ly low

Figure A.2 – He t path wh n wire in the air using the lug terminal

The n merical simulation was implemented f or the he t dis ip tion ratio of e c he t typ

(con u tion, con ection an radiation) in the resistor model The simulation model is a

c l n rical resistor of 2 ,5 mm in b dy len th, 9 mm in b dy diameter, 0,8 mm in le d wire

diameter an 3 mm in le d wire len th This sample was wired in the air u der 2 °C with a

no-air low con ition an 1 W wi b a pl ed As a res lt, the he t dis ip tion ratio was 51 %

f om con ection, 3 % fom radiation an the remainin 17 % was f rom the con u tion via the

3 mm le d wire Sin e a large p rtion of the he t dis ip tion is implemented f rom the

con ection an radiation throu h the atmosphere, it is natural to set the ambient temp rature

However, the resistor man facturer is exp cted to implement lo d l fe tests to verify the

c aracteristic of the resistor, esp cial y the sta i ty u der o erational con ition The method

is to set the le d wire resistor horizontal y as if it were f lo tin in the air an a ply the rated

p wer in a test c amb r with the temp rature set at the predetermined value The he t

dis ip tion ratio is the same as the con ition of the actual u e by electric/electronic device

desig ers

Therefore, introd cin the ambient temp rature arou d the resistor as the temp rature in ex

to cor esp n to the test con ition by the resistor man f acturer an the actual u e con ition

of electric/electronic device desig ers was re sona le for the mou tin con ition of the

resistors in those day Sin e then, the mou tin method c an ed to le d wire resistors on

printed circ it b ard an then SMD resistors At the same time, miniaturization of the resistor

itself has ad an ed as wel As ociated with a c an e in the mou tin method an

miniaturization, the he t dis ip tion ratio of the he t generated in the resistor has c an ed

The ratio of the con ection an radiation has decre sed grad al y an the con u tion to the

printed circ it b ard has in re sed This c an e s mmarised in An ex J

A 2 How to establ sh the high temperature slope part of the derating curve

It is neces ary to have a go d k owled e of the the retical b se of how the deratin c rves of

resistors are esta l s ed to u derstan the content of this tec nical re ort Furthermore, this

the retical b se is of ten mis on eived with the analog of the deratin c rve for

semicon u tors

The deratin c rve for resistors is esta l s ed to not ex e d the temp rature an he t stres

that is tested by the resistor man f acturer It is verif ied that the resistor can kee its f un tion

when the lo d is red ced as the ambient temp rature rises ac ordin to the deratin c rve

provided by the resistor man f acturer, even when the thermal y sen itive p rt of the resistor is

Rate ambie t temp rature (n rmaly 7 °C)

U T Up er c te ory temp rature

Point A L a lfe te t c n itio

Point B Hig temp rature e p s re te t c n itio

Point C Betwe n Point A a d Point B

IE C

Point A

Point BPoint C

r

In prin iple, the deratin c rve is esta l s ed by con ectin the two test con ition with a lne,

the lo d l f e test (rated lo d a pl ed at ambient temp rature) an the hig -temp rature

exp s re test (UCT without lo d as s own in Fig re A.3) or the test con ition of the UCT with

the category p wer lo ded as s own in Fig re A.4

Ex e t for sp cial cases, the resistor man facturers do not test the mid le con ition l ke

Rate ambie t temp rature (n rmaly 7 °C)

U T Up er c te ory temp rature

Point A L a lfe te t c n itio

Point B Hig temp rature e p s re te t c n itio

Point C Betwe n Point A a d Point B

Figure A.4 – Te t condition f or re istors with c te ory power other tha 0 W

However, it could b predicted that the l ne formed by 10 % rated p wer is the electrical lmit

but, it is p s ible to double the rated p wer by c an in the test con ition even when u in

the same resistor as se n in Fig re A.5 Theref ore, it can ot b said that the present l ne

s own is purely the electrical l mit When the a pl ed p wer is at its maximum, the

temp rature diff eren e in ide the resistor wi also b come maximum The he t stres cau ed

by the temp rature ga within the resistor b comes maximum Theref ore, it could b said that

this l ne verif ied by the resistor man facturer could b u ed u der a certain con ition Verified

u der a certain con ition me n that, when the resistor is u ed u der the con ition des rib d

in the sp cification, the c aracteristic , s c as the resistan e value c an e, are ke t within

the toleran e values

Ad itional y, the UCT is also not the gen ine temp rature lmit of the material that makes up

the resistor The UCT is a test con ition for ran clas ification of resistors Theref ore, there

are resistors that have no eff ect on their c aracteristic even when it gets hot er than the

category up er temp rature If the test con ition is reviewed an the resistor with a maximum

o eratin temp rature of 12 °C is tested in a hig temp rature exp s re test of 15 °C, an

the c aracteristic is verified, it would b p s ible to c an e the maximum o eratin

temp rature to 15 °C However, the c aracteristic of the con tru tion material of e c

IE C T

r

It is imp rtant to k ow that the deratin c rve of the resistor is b sical y determined ac ordin

Rate ambie t temp rature

1 Deratin c rv b f ore re iewin th rate p wer

2 Deratin c rv wh n rate p wer is rais d

3 Deratin c rv wh n ma imum o eratin temp rature is re iewe

4 Existin UCT

Figure A.5 – Ex mple of re iewing the derating c rv

A.2.2 Derating c rv f or the s micond ctors

Given their simiar a p aran e, they are often mis n ersto d, but it is imp rtant to k ow that

the deratin c rve f or resistors an semicon u tors are completely dif ferent The

semicon u tor in the example is a tran istor that is u ed by fit in on a he t sin The rated

p wer P

r

of the tran istor is a p wer that the temp rature of the tran istor sen itive p int wi

re c the certain l mited value when fixed to the he t sin set at 2 °C The temp rature of

the sen itive p int of the tran istor s al not ex e d the certain l mited value u der an

circ mstan es

The ju ction temp rature of the bip lar tran istor an the c an el f or the field-ef fect tran istor

would b the sen itive p int that determines the o eratin temp rature l mit The tran istor

can ot b u ed when the sen itive p int temp rature ex e d the def i ed temp rature s c

as 15 °C (general y 15 °C but some are 17 °C) The sen itive p int of temp rature rise

an the l mited temp rature are cle rly determined f or the semicon u tors

The relation hip b twe n the case temp rature T

c, whic the ju ction temp rature T

j

do s not

ex e d, the l mit temp rature T

j-ma, an the al owa le p wer P that can b a pl ed to the

tran istor u der that case temp rature wi b con idered, u in the bip lar tran istor as an

The temp rature rise ΔT

j-c

of the case to the ju ction is as umed to b pro ortionate to the

p wer P con umed by the tran istor This pro ortional con tant s al b R

th j-c This R

j

would b calc lated as s own in F rmula (A.1)

PR

TT

cj

t hc

that man er An the a pl ed p wer P would b s own as P (T

c) as the f un tion of T

c, as

s own in Formula (A.2)

ccj

t hcmaj

TPRTT

t hcmajc

r, it can b calc lated in Formula

(A.4) Then Formula (A.5) is tran f ormed f rom Formula (A.4)

cj

t hma

jr

/25

jcj

c

( ) ( )/( 25)

majcmajrc

PTP

rcould b p s ible in F rmula (A.6), but in the

doc ment the a pl ed p wer can ot ex e d P

r

The l mited p wer that the tran istor can have a pl ed would b as s own in Formula (A.7)

when the a ove con ition are con idered

majcmajrc

PT

The o eratin ran e of the tran istor in icated f rom this formula would b s own as

Fig re A.7 This f i ure is often se n in the he t desig textb ok for tran istors The

tran istor s al alway b u ed u der the con ition that do s not ex e d the deratin c rve

This c rve lo k very al ke to the deratin c rves for resistors

Ju ctio u p r temp rature

Figure A.7 – Derating curv s f or tra sistors

The trajectory of T

j

when P(T

c) is derated ac ordin to the deratin c rve, alon with the rise

to the in re sed T

c

an the s m with the T

cwould alway s ow T

j-ma

When the lo d p wer to the semicon u tor is red ced ac ordin to the deratin c rve as the

temp rature rises, the thermal y sen itive p int (ju ction temp rature T

jfor bip lar tran istors)

would alway b the certain l mited temp rature T

j-ma, but this is b cau e the deratin c rve

is made to b so

A.2.3 Derating c rv f or re istors

As des rib d in this s bclau e, the deratin c rves for resistors are b sed on a diff erent p int

of view But, the deratin c rves for resistors an semicon u tors are simi ar in s a e, so

they are often misinterpreted The largest dif feren e is that the temp rature of the thermal y

sen itive p int of the resistor wi c an e when the p wer is red ced ac ordin to the deratin

c rve In contrast, the temp rature of the thermal y sen itive p int of the semicon u tor would

b a con tant temp rature as s own in Fig re A.8 However, the ran e of the c an e of the

thermal y sen itive p int temp rature in lu in the he t stres cau ed by the temp rature

dif feren e b twe n the resistor p rts would b ke t b low the l mited temp rature whic is

tested an verif ied by the resistor man f acturer

As f or the le d wire resistors, the he t dis ip tion throu h the le d wire by the he t

con u tion is smal comp red to the con ection an radiation Theref ore, u der the natural

con ection en ironment, the temp rature rise again t the ambient temp rature T

a

of e c p rt

of the resistor is a proximately the a pl ed p wer an the sp cific pro ortional con tant of the

resistor wherever the le d wire tip is con ected

In this example, the hotsp t temp rature T

h

wi b u ed as the re resentative temp rature of

e c p rt The hotsp t is the hotest p rt of the resistor as mentioned in the terms an

definition in Clau e 3 an is general y located in the centre of the resistive element The

R

th j-c

P (T

3)

R

th j-c

P (T

4)

T

1

T

2T

with the rise of the ambient temp rature ac ordin to the deratin c rve b sed on Fig re A.3,

wi b con idered u in the temp rature rise ΔT

h -a

f rom the hotsp t ambient temp rature T

a

The hotsp t is only a re resentative example, so b aware that the hotsp t temp rature T

The rate of the temp rature rise by self he tin fom the a pl ed p wer dif fers by e c

resistor, so two cases are to b con idered One is a smal temp rature rise, an the other is

a large temp rature rise f rom the a pl ed p wer In the gra h in Fig re A.9, the horizontal

axis s ows the temp rature rise ΔT

h -a

f om the ambient temp rature T

a, the vertical axis

s ows the p rcentage of the a pl ed p wer P

rp

to the rated p wer Fig re A.9 s ows the

example of a smal temp rature rise, an Fig re A.10 s ows the example of a large

temp rature rise comp red to the a pl ed p wer ratio General y, if the a pl ed p wer is the

same, the temp rature rise wi b smal when the con titution is large, an the temp rature

rise wi b large when the con titution is smal

When the rated p wer is in icated with P

r(W), the thermal resistan e R

to the hotsp t f or the resistors

with a large temp rature rise would b s own in Formula (A.9)

rL

dis ip ted into the atmosphere, so the thermal resistan e calc lated f om Formula (A.8) an

Formula (A.9) would serve to s ow the c aracteristic of the resistor

0

Figure A.10 – Le de re istors with large temperature ris

First the trajectory of the hotsp t temp rature T

h

o tained f om the Fig re A.3 an Fig re A.9

wi b stu ied The trajectory of T

hcan b calc lated by simply addin the self generated

he t ( emp rature rise f rom the ambient temp rature T

Hots ot temp rature (traje tory wh n lo d is d rate )

U T Up er c te ory temp rature

D Ve tor re re e tatio of temp rature ris f rom th ambie t temp rature to th h ts ot

UCT

T

hD

In Fig re A.1 , the hotsp t would re c the maximum temp rature in the hig -temp rature

exp s re test, but the he t stres cau ed by the temp rature diff eren e in ide the resistor wi

b the largest at the lo d lfe test This is when the temp rature diff eren e b twe n the

ambient an the hotsp t temp ratures b comes maximal an when the rated p wer a pl ed at

T

a

is eq al to the rated ambient temp rature

This me n , for example, that the temp rature gradient b comes large at the p int where the

generated he t den ity is hig , s c as at the tip of the trimmin l ne when the c r ent is

a pl ed, an the he t stres wi b come local y large The local he t stres can b the cau e

of degradation for some of the resistive elements

The he t stres cau ed by the temp rature rise of the entire resistor would b largest at the

hig -temp rature exp s re test when the entire resistor b comes u if ormly the maximum

temp rature On the deratin c rve, or within the entire are of the b t om lef t-han side of

the deratin c rve, u les u der sp cial condition , the hotsp t temp rature an the he t

stres wi not ex e d the a ove-mentioned maximum value If the electric/electronic device

desig ers u ed the resistors by red cin the p wer as the rise of the ambient temp rature T

a

ac ordin to the deratin c rve, the resistor wi not b u ed u der the con ition that ex e d

the maximum stres es (hig temp rature an he t stres ) verif ied in the lo d l f e test an

hig -temp rature exp s re test implemented by the resistor man facturer

Next, f or the resistor with a large temp rature rise s own in Fig re A.10, the p wer lo d ratio

red ced as the temp rature rises ac ordin to the deratin c rve made f rom the test in

Fig re A.3 wi b con idered The hotsp t temp rature T

h

makes a trajectory as s own in

Fig re A.12

Hots ot temp rature (traje tory wh n lo d is d rate )

U T Up er c te ory temp rature

Point A L a lfe te t p int

Point B Hig temp rature e p s re te t p int

C Deratin c rv ma e b th meth d in Fig re A.3 (h riz ntal a is is th ambie t temp rature T

a)

D Ve tor re re e tatio of temp rature ris f rom th ambie t temp rature to th h ts ot

In this case, the hotsp t temp rature an the he t stres cau ed by the temp rature

dif feren e in ide the resistor b comes the largest d rin the lo d lf e test, whic is when the

rated p wer P

r

is a pled at the rated ambient temp rature T

ra It is not cle r whic con ition,

the lo d l f e test or the hig -temp rature exp s re test, wi make the he t stres cau ed by

the temp rature rise of the entire resistive element the largest However, on the deratin

c rve or within the entire are of the b t om left-han side of the deratin c rve, the hotsp t

temp rature an the he t stres wi not ex e d the a ove-mentioned maximum value

Therefore, if the electric/electronic device desig ers u ed the resistors by red cin the p wer

ac ordin to the deratin c rve, the resistor wi not ex e d the maximum stres (hig

temp rature an he t stres ) verif ied in the lo d lfe test an the hig -temp rature exp s re

test implemented by the resistor man facturer

There may b stran e f eel n s that there is a case that s ows T

ambient temp rature to the hotsp t temp rature T

s) a pl ca le to e c p wer a pled to the

resistor on the deratin c rve as s own in Fig re A.13 ΔT

h -a

is pro ortionate to the p wer

a pl ed to the resistor, so it is trivial without an sp cif i data

IE C

T (°c) 5

Hots ot temp rature (traje tory wh n lo d is d rate )

U T Up er c te ory temp rature

Point A L a lfe te t p int

C Deratin c rv ma e b th meth d in Fig re A.4 (h riz ntal a is is th ambie t temp rature T

a)

D Ve tor re re e tatio of temp rature ris f rom th ambie t temp rature to th h ts ot

The UCT is ju t a segment to categorize the test con ition so they are not defined ac ordin

to the up er temp rature l mit of the materials that con titute the resistor This is why

T

h

> UCT is ac e ta le

A resistor alway has a thermal y sen itive p int that wi lose f un tion when the temp rature

b comes hig Therefore, if the thermal y sen itive p int temp rature T

s

is set, the

temp rature ju t b fore the fu ction of the resistor is lost would b the maximum alowa le

temp rature (MAT) The con ition for the resistor to f un tion normal y would b alway MAT ≥

T

s

To p s the hig -temp rature exp s re test, MAT ≥ UCT s al b true Ad itional y, the

hig est temp rature in the resistor is T

h, so T

al owa le temp rature (MAT) an s owin it vis al y, it would b e s to explain the re son of

the deratin c rve for resistors an the re son wh T

s

> MAT,

then it wi not b a le to p s the lo d lfe test On the other han , MAT > UCT would b

o viou

The imp rtant thin is that if the resistor p s es the lo d lfe test, it inevita ly ac ompl s es

this relation hip even when the thermal y sen itive p int again t he t can ot b f ou d an the

However, in Fig re A.14, this example s ows a resistor that has a hotsp t that is not the

thermal y sen itive p int, but f or most of the resistors, the hotsp t is also the thermal y

C Deratin c rv ma e b th meth d in Fig re A.3 (b s d o ambie t temp rature)

D (Sold arow) temp rature ris fom th ambie t temp rature to th h ts ot

a d MAT for le d wire re istors with large temperature ris

As s own in Fig re A.15, the resistors with a smal temp rature rise as s own in Fig re A.9

wi also come into ef fect

In this case, if the resistor p s es the hig -temp rature exp s re test, it inevita ly

ac ompl s es this relation hip even when the thermal y sen itive p int can ot b fou d an

the MAT is u k own

From the a ove explanation, f or resistors with large or smal temp rature rises, the deratin

c rves can b esta l s ed by implementin the tests s own in Fig re A.3 or Fig re A.4 if the

lo d l f e test an the hig -temp rature exp s re test are implemented an the determined

in ex, s c as the resistan e value c an e rates, is b th within the stan ard values

If the p wer is red ced alon with the rise of the ambient temp rature ac ordin to the

deratin c rves provided by the resistor man facturer, the resistor wi not b u ed in the

than the tests implemented by the resistor man facturer This is the the retical rationale that

the method of esta l s in an u in the present deratin c rve is cor ect

C Deratin c rv ma e b th meth d in Fig re A.3 (Ba e o ambie t temp rature)

D (Sold arow) Temp rature ris fom th ambie t temp rature to th h ts ot

a d MAT for le d wire re istors with smal temperature ris

However, man of the hotsp ts of the resistors are the thermal y sen itive p ints For these

kin s of resistors, Fig re A.14 an Fig re A.15 can b simplfied as in Fig re A.16

From this p int, the word "hotsp t" wi b u ed in place of "thermal y sen itive p ints"

Therefore, f or the resistors that have thermal y sen itive p ints other than hotsp ts, take

"hotsp t" to me n "thermaly sen itive p int"

a) Ca e A : Re istor with large temperature ris

b) Ca e B: Re istor with smal temperature ris

Th rmaly s n itiv p int temp rature

U T Up er c te ory temp rature

MAT Ma imum alowa le temp rature

Point A L a lf e te t p int

C Deratin c rv ma e b th meth d in Fig re A.3 (b s d o ambie t temp rature)

D Temp rature ris fom th ambie t temp rature to th h ts ot

Figure A.16 – Re istors f or whic the hotsp t is th thermal y s nsitiv point

A resistor that is l ke the one s own in Fig re A.17 can exist on rare oc asion This resistor

s)

wp)

case, when the p wer is red ced as the ambient temp rature T

arises in ac ordan e with the

deratin c rve, the trajectory of T

hwould alway b a con tant value of UCT When the

hotsp t of this resistor is the thermal y sen itive p int an ad itional y UCT = MAT, this

deratin c rve wi have a very simi ar me nin as that of the deratin c rves f or the

semicon u tors

Th rmaly s n itiv p int temp rature

U T Up er c te ory temp rature

MAT Ma imum alowa le temp rature

Point A L a lf e te t p int

C Deratin c rv ma e b th meth d in Fig re A.3 (b s d o ambie t temp rature)

D Temp rature ris f rom th ambie t temp rature to th h ts ot

Figure A.17 – Re istor that ha e deratin c rv simi ar to the s micon uctor

The common mistake that electric/electronic device desig ers make is to thin that al the

resistors have the c aracteristic as s own in Fig re A.17 by analog with the deratin c rves

f or semicon u tors If al resistors have these kin s of c aracteristic , the me nin of the

deratin c rve wi b very simple an , in a way, ide l But, the core elements of materials an

stru tures that make up the resistors are not as u if orm as those of the semicon u tors The

material an stru ture varies As for the resistors, it is dif fic lt to identify the thermal y

sen itive p int an the MAT in most cases Therefore, it is very diff i ult to intentional y cre te

a resistor that has a deratin c rve as s own in Fig re A.17 an , more ver, even if it is

develo ed, there is no ad antage over the c r ent deratin c rves

If there was a resistor that has a deratin c rve as s own in Fig re A.17 an a hotsp t

( hermal y sen itive p int that can b o served e si y, the deratin c rve for this resistor

would b u neces ary The con ition for u e that would be provided to electric/electronic