MC78L00, A Series

7

MOTOROLA ANALOG IC DEVICE DATA

APPLICATIONS INFORMATION

Design Considerations

The MC78L00 Series of fixed voltage regulators are

designed with Thermal Overload Protection that shuts down

the circuit when subjected to an excessive power overload

condition. Internal Short Circuit Protection

limits the

maximum current the circuit will pass.

In many low current applications, compensation

capacitors are not required. However, it is recommended that

the regulator input be bypassed with a capacitor if the

regulator is connected to the power supply filter with long wire

lengths, or if the output load capacitance is large. The input

bypass capacitor should be selected to provide good

high–frequency characteristics to insure stable operation

under all load conditions. A 0.33

µF or larger tantalum, mylar,

or other capacitor having low internal impedance at high

frequencies should be chosen.The bypass capacitor should

be mounted with the shortest possible leads directly across

the regulators input terminals. Good construction techniques

should be used to minimize ground loops and lead resistance

drops since the regulator has no external sense lead.

Bypassing the output is also recommended.

Figure 7. Current Regulator

Figure 8.

± 15 V Tracking Voltage Regulator

Figure 9. Positive and Negative Regulator

The MC78L00 regulators can also be used as a current source

when connected as above. In order to minimize dissipation the

MC78L05C is chosen in this application. Resistor R determines

the current as follows:

For example, a 100 mA current source would require R to be a

50

Ω, 1/2 W resistor and the output voltage compliance would be

the input voltage less 7 V.

IO =

5.0 V

+ IB

IIB = 3.8 mA over line and load changes

Input

0.33

µF

R

IO

MC78L05

Constant

Current to

Grounded Load

–

+

MC1741

+20V

0.33

µF

MC78L15

+VO

10k

10k

–VO

7

6

2

3

4

6.5

20V

MPS A70

MPS U55

0.33

µF

0.33

µF

+VI

–VI

MC78LXX

MC79LXX

+VO

–VO

0.33

µF

0.1

µF

0.1

µF

R