3. Thermal Design

( 1 )

Heat Producting

(1-1)

(1-2)

Internal power transistor produces the hest mentioned following equation.

= (Vin-Vout) x Iout

(W)

Therefore, the total heat producing PLOSS is :

(W)

( 2 )

Thermal Resistance

(2-1)

Definition of Thermal Resistance : θ

Thermal resistance (θ ) is a degree of heat radiation mentioned following equation.

= (T1 - T2)/P (℃ /W)

Heat Producing Quantity

: P (W)

Ambient Temperature or case temperature

:T2 (℃ )

Heat Source Temperature

:T1 (℃ )

(2-2)

Thermal resistance of TO-220

θjc :

θja :

REV B

thermal resistance between IC chip (junction point) and ambience.

There are two kinds of thermal resistance of TO-220. One is "θjc" for the application with the heat

sink, the other is "θja" for the application without the heat sink.

thermal resistance between IC chip (junction point) and the package back side

contacting with the heat sink.

Input

GND

IN

OUT

Output

Vin

Vout

Iout

T1

T2

P(W)

Rp

T1 > T2

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