The best analogy for PC board copper is to compare it with

parallel resistors Beyond some point additional resistors

are not significantly effective beyond some point additional

copper area is not effective

TLH10051 – 5

FIGURE 2 TO-92 Thermal Equivalent Circuit

(Lead at other than Ambient Temperature)

High Dissipation Applications

TLH10051 – 6

TLH10051 – 7

Where it is necessary to operate a LM78L00 regulator with a

large inputoutput differential voltage the addition of series

resistor R1 will extend the output current range of the de-

vice by sharing the total power dissipation between R1 and

the regulator

(2)

where

Regulator power dissipation at maximum input voltage and

maximum load current is now

(3)

where

The presence of R1 will affect load regulation according to

the equation

(4)

e

a

line regulation (mV per V)

c

As an example consider a 15V regulator with a supply volt-

be 10 mA

e

8

343

j

240X

(5)

e

e

470 mW which permit operation up to

70 C in most applications

Line regulation of this circuit is typically 110 mV for an input

range of 25V – 35V at a constant load current ie 11 mVV

(6)

a

(typically 53 mV)

e

63 mV for a load current change of

Typical Applications

TLH10051 – 8

Note 1

To specify an output voltage substitute voltage value for ‘‘00’’

Note 2

Bypass capacitors are recommended for optimum stability and tran-

sient response and should be located as close as possible to the regulator

8