MC78L00A Series, NCV78L00A
www.onsemi.com
8
APPLICATIONS INFORMATION
Design Considerations
The MC78L00A 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 mF 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 9. Current Regulator
Figure 10. +15 V Tracking Voltage 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
50W, 1/2 W resistor and the output voltage compliance would be
the input voltage less 7 V.
I
O
=
5.0 V
+ I
B
I
IB
= 3.8 mA over line and load changes
Input
0.33mF
R
I
O
MC78L05A
Constant
Current to
Grounded Load
-
+
MC1741
+20V
0.33mF
MC78L15A +V
O
10k
10k
-V
O
7
6
2
3
4
6.5
20V
MPS A70
MPS U55
0.33mF
0.33mF
+V
I
-V
I
MC78LXXA
MC79LXXA
+V
O
-V
O
0.33mF
0.1mF
0.1mF
R
Figure 11. Positive and Negative Regulator
