LM2931, NCV2931 Series
Input
V
in
51 k
C
in
0.1
2
1
I
B
Input
V
in
C
in
0.1
LM2931−5.0
Fixed
Output
I
B
GND
Output
V
out
Switch Position 1 = Output On", 2 = Output Off"
V out
+
V
ref
1
)
R2
R1
)
I
R
Adj 2
22.5 k
w
R1 R 2
GND
Output
Inhibit
LM2931C
Adjustable
Output
Output
V
out
R
1
Adjust
C
O
I
Adj
R
2
C
O
R 1
)
R2
Figure 17. Fixed Output Regulator
Figure 18. Adjustable Output Regulator
Input
≥
6.0 V
68
R
D45VH7
Input
R
LM2931−5.0
5.0 V @ 5.0 A
+
Output
R
SC
Output
LM2931−5.0
+
100
100
+
+
100
100
The LM2931 series can be current boosted with a PNP transistor. The
D45VH7, on a heatsink, will provide an output current of 5.0 A with an input
to output voltage differential of approximately 1.0 V. Resistor R in
conjunction with the V
BE
of the PNP determines when the pass transistor
begins conducting. This circuit is not short circuit proof.
The circuit of Figure 19 can be modified to provide supply protection against
short circuits by adding the current sense resistor R
SC
and an additional PNP
transistor. The current sensing PNP must be capable of handling the short
circuit current of the LM2931. Safe operating area of both transistors must be
considered under worst case conditions.
Figure 19. (5.0 A) Low Differential
Voltage Regulator
Figure 20. Current Boost Regulator with
Short Circuit Projection
Input
6.4 V to 30 V
LM2931C
2.0 k
100
8.2 k
+
CM
#345
+
100
33 k
6.2 V
0
f
osc
= 2.2 Hz
Figure 21. Constant Intensity Lamp Flasher
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