Precaution for use～Bipolar transistor～
To use transistor safely
Transistor is used for switching or amplifying, but may have failure when use in inappropriate
condition.
Therefore, to use the transistor safely, it is necessary to verify whether condition is appropriate.
Here, we introduce three points about verification to be required to a minimum.
Verification1．Are there all conditions within the maximum ratings?
Verification2．Is there it within ASO (area of safety operation)?
Verification3．Is there junction temperature within the maximum ratings?
3-1.When use in DC
3-2.When use in single pulse
3-3.When use in continuous pulse© ISAHAYA ELECTRONICS CORPORATION

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Precaution for use～Bipolar transistor～
Verification1．Are there all conditions within the maximum ratings?
Please confirm the maximum ratings listing in the data sheet of the target part.
On this occasion please confirm to refer the following caution points.
・Collector to emitter voltage must be within the maximum ratings (following example 50V).
・Collector current must be within the maximum ratings (following example 200mA).
・Collector dissipation VCE×IC must be within the maximum ratings (following example
200mW).
・Base current IB ratings is not usually listed because it is smaller than collector current.
When base current is large depending on use condition, it must satisfy the followingcondition.
VBE×IB + VCE×IC < PC (collector dissipation maximum ratings)
It is 1/3～1/10 of collector current.
MAXIMUN RATINGS（Ta=25℃）

IC
IB

VBE

Symbol
VCBO
VEBO
VCEO
ICPC
Tj
Tstg

Parameter
Collector to Base voltage
Emitter to Base voltage
Collector to Emitter voltage
Collector current
Collector dissipation
Junction temperature
Storage temperature

Ratings
50
650200200+150-55～+150Unit
VVVmAmW℃℃

VCE

Verification2．Is there it within ASO (area of safety operation)?
Collector dissipation PC listing maximum ratings is for direct current. In case exceedingcollector dissipation when use in pulse driving or inductive load, it is necessary to use within
the area of safety operation to show as follows.
ASO(area of safety operation)

B
point

1
Single pulse
Ta=25℃

Collector current IC (A)Icmax=0.2A

1sec

A
point

0.1

1msec
10msec100msec

Bpoint

DC200mW

0.01

VCEOmax=50VA
point

0.0010.1

110100

Collector to Emitter voltage VCE (V)In addition, when a data sheet does not have the ASO (area of safety operation) by kind, sorryfor inconvenience but, please ask to sales office.

© ISAHAYA ELECTRONICS CORPORATION

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Precaution for use～Bipolar transistor～
Verification3．Is there junction temperature within the maximum ratings? (direct current case)
Since maximum ratings of power dissipation and ASO (area of safety operation) are defined as
the power when junction temperature reach maximum ratings(usual 150℃) in case ambient
temperature is 25℃, it is necessary to consider to derate maximum ratings by the following
derating curve in case ambient temperature is more than 25℃.
Since derating curve is the power when junction temperature reaches maximum ratings, we
can consider as follows.
Tj=Ta+Rth(j-a)×Pc

250※Tj: junction temperature、Ta: ambient temperature
Pc: applying power、Rth(j-a): thermal resistanceIn case right graph,when Ta=25℃, Pcmax=200mW, Tjmax=150℃,
then Rth(j-a)=(150-25)/200=625(℃/W)
In case Ta=75℃, power dissipation Pcmax isas follows.

Allowable power
dissipation is120mW when
ambient
temperature 75℃

200

Collector dissipation Pc (mW)between junction and ambient

Collector dissipation－Ambient temperature

150
1005000

Pcmax=(Tjmax-Ta)/Rth(j-a)=(150-75)/625=0.12(W)2550
75100125
Ambient temperature Ta (℃)

150

In case Ta=75℃, applying power Pc=0.1(W),Junction temperature Tj=Ta+Rth(j-a)×Pc=75+625×0.1=137.5(℃)
Since it is within maximum rating of junction temperature Tjmax=150℃,
we can consider use condition has no problem .
Verification3．Is there junction temperature within the maximum ratings? (single pulse case)
It is also necessary to consider to derate maximum ratings of ASO (area of safety operation)in case ambient temperature is 25℃.
When Ta=25℃,1msec, allowable power dissipation

Area of safety operation

becomes 26V×0.2=5.2W from right figure .

1Single pulse

When Ta=25℃, Pcmax=5.2W, Tjmax=150℃

Icmax=0.2A

then rth(j-a)=(150-25)/5.2=24(℃/W)

Pcmax=(Tjmax-Ta)/Rth(j-a)=(150-75)/24=3.1(W)Blue line in right figure shows the area limited byPcmax=3.1(W). In case Ta=75℃, applying power
Pc=2(W), junction temperature

1msec
Ta=75℃

0.1

VCEOmax=50VPcmax becomes as follows.

Ta=25℃

Collector current IC (A)In case Ta=75℃,allowable power dissipation(26, 0.2) 1msec

0.01

0.001

Tj=Ta+Rth(j-a)×Pc=75+24×2=123(℃). Since it is0.1

110100
Collector to Emitter voltage VCE (V)within maximum rating of junction temperature
Tjmax=150℃, we can consider use condition has no problem.

© ISAHAYA ELECTRONICS CORPORATION

3Precaution for use～Bipolar transistor～
Verification3．Is there junction temperature within the maximum ratings? (continuous pulsecase)
For confirmation of junction temperature in continuous pulse, it is necessary to calculate
power wave form from current wave form and voltage wave form in continuous pulse, andcalculate junction temperature increasing according to the following equation. Let calculated
junction temperature increasing as ΔTj, ambient temperature as Ta, we can consider use
condition has no problem if Ta+ΔTj is within Tjmax .

ΔTj = [ D×Rth-a + (1-D)×rth(T1+T) + rth(T1) - rth(T) ] × P
whereD:duty
Rth-a: static thermal resistance between junction and ambientrth(T1)：transient thermal resistance at pulse width T1
rth(T): transient thermal resistance at pulse width Trth(T1+T)：transient thermal resistance at pulse width T1+T
P：peak power dissipation
Assuming continuous pulse as Icpeak=175mA,VCE(sat)=0.6V, period T=3msec, D=50%,

Transient thermal resistance-Pulse width graph1000

then P=175mA×0.6V=105mW, T1=1.5msec
From the transient thermal resistance graph of right figure,rth(1.5msec)=17.4(℃/W)
rth(3msec)=26.5(℃/W)
rth(4.5msec)=31.5(℃/W)

Transient thermal resistance （℃/W）

Rth-a=(Tjmax-Ta)/PT=(150-25)/0.2=625(℃/W)

Ta=25℃
Single pulse

100rth(4.5msec), 31.5rth(1.5msec), 17.4rth(3msec),
26.5

10

ΔTj = [ D×Rth-a + (1-D)×rth(T1+T) + rth(T1) - rth(T) ] × P= [0.5×625 + (1-0.5)×31.5 + 17.4 - 26.5]×0.105= 33.5(℃)

1110100

1000

Pulse width Pw（ms）

Since Ta+ΔTj = 25 + 33.5 = 58.5(℃) < Tjmax(150℃), we can consider use condition has noproblem.

Since maximum ratings are limit value of usable condition, the device has degradation orfailure when use exceeding them. Please use within maximum ratings to prevent thedegradation or failure of the devices, and to realize the high reliability of equipment.

© ISAHAYA ELECTRONICS CORPORATION4