APL78L05/12
www.anpec.com.tw8Copyright ANPEC Electronics Corp.
Rev. A.11 - Jun., 2011
Application Information
Input
Constant
Current to
Grounded
Load
R
APL78L05
lO
0.33µF
The APL78L05/12, series of fixed voltage regulators, are
designed with thermal overload protection that shuts down
the circuit when subjected to an excessive power overload
condition. In addition, the APL78L05/12 have the func-
tion of internal short circuit protection to limit the maxi-
mum current the circuit will pass.
In many low current applications, compensation capaci-
tors are not required. However, it is recommended that
the regulator input will be bypassed with a capacitor if the
regulator connects 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. If the value of the
capacitor is greater than 0.33µF, the capacitor with tan-
talum or mylar, or other capacitor having low internal im-
pedance at high frequencies should be chosen. The by-
pass capacitor should be mounted with the shortest pos-
sible leads directly across the regulators input terminals.
Good construction techniques should be used to mini-
mize ground loops and lead resistance drops since the
regulator has no external sense lead. Bypassing the out-
put is also recommended.
Figure 1. Current Regulator
MC1741
0.33µF
+20V
0.33µF
20V MPSU55
6.5 MPSA70
10K
10K
+VO
-VO
3
2
4
67
APL78L05
The APL78L05 regulators can also be used as a cur-
rent source when connected as above. In order to mini-
mize dissipation, the APL78L05 is chosen in this
application. Resistor R determines the current as be-
low :
IO = + IB
5.0V
R
IB =3.8mA over line and load changes
For example, a 100mA current source would require R to
be a 50Ω, 1/2W resistor and the output voltage compli-
ance would be the input voltage less 7V.
Figure 2. ±15V Tracking Voltage Regulator
Figure 3. Positive and Negative Regulator
+VI
0.1µF
APL78LXX
0.33µF
APL79LXX
0.33µF0.1µF
+VO
-VO
-VI