ML7818FA(2005) 查看數據表（PDF） - Micro Electronics

零件编号

产品描述 (功能)

生产厂家

ML7818FA
(Rev.:2005)

3-TERMINAL POSITIVE VOLTAGE REGULATOR

Micro Electronics 

3. Thermal Design

(1)

Heat Producting

There are two kinds of heat producting (PLOSS-1, PLOSS-2) in three terminal regulator and the sum of

them is total heat producting of IC (PLOSS).

(1-1)

PLOSS-1 : heat producting by own operation

Input voltage (Vin) and quiescent current (IQ) produce the heat mentioned below equation.

PLOSS-1 = Vin X IQ

Input

Vin

IN

OUT Iout

GND

IQ

Output

Vout

(1-2)

(2)

(2-1)

PLOSS-2 : heat producing by output current and the input-output differential voltage.

Internal power transistor produces the hest mentioned following equation.

PLOSS-2

= (Vin-Vout) x Iout

(W)

Therefore, the total heat producing PLOSS is :

PLOSS

= PLOSS-1 + PLOSS-2

= Vin X IQ + (Vin-Vout) X Iout (W)

Thermal Resistance

Definition of Thermal Resistance : θ

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

= (T1 - T2)/P (℃ /W)

Heat Producing Quantity

Ambient Temperature or case temperature

Heat Source Temperature

P(W)

: P (W)

:T2 (℃ )

:T1 (℃ )

(2-2)

Rp

T1

T2

T1 > T2

Thermal resistance of TO-220

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.

θjc :

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

contacting with the heat sink.

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

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