Input
CI
1
0.33μF
LM78XX
2
3
Output
CO
0.1μF
Figure 9. Fixed-Output Regulator
Input
CI
1
0.33μF
LM78XX
2
IQ
3
Output
CO
0.1μF
V XX
R1
IO
RL
IO
=
VXX
R1
+ IQ
Notes:
29. To specify an output voltage, substitute voltage value for “XX”. A common ground is required between the input and
the output voltage. The input voltage must remain typically 2.0 V above the output voltage even during the low point on
the input ripple voltage.
30. CI is required if regulator is located an appreciable distance from power supply filter.
31. CO improves stability and transient response.
Figure 10.
Input
1
3
LM78XX
CI
0.33μF
2
CO
IQ
0.1μF
Output
VXX R1
R2
IRI ≥ 5 IQ
VO = VXX(1 + R2 / R1) + IQR2
Figure 11. Circuit for Increasing Output Voltage
© 2006 Fairchild Semiconductor Corporation
LM78XX / LM78XXA Rev. 1.3.0
19
www.fairchildsemi.com