LM2931 Series

8

MOTOROLA ANALOG IC DEVICE DATA

0.1

1.0

0.01

Figure 17. Fixed Output Regulator

Figure 18. Adjustable Output Regulator

Figure 19. (5.0 A) Low Differential

Voltage Regulator

Figure 20. Current Boost Regulator with

Short Circuit Projection

Figure 21. Constant Intensity Lamp Flasher

Figure 22. Output Noise Voltage versus

Output Capacitor Impedance

|ZO|, MAGNITUDE OF CAPACITOR IMPEDANCE (mΩ)

10

100

1.0 k

10 k

Vin

Input

Output

Vout

CO

IB

Gnd

Cin

0.1

LM2931–5.0

Fixed

Output

Switch Position 1 = Output “On”, 2 = Output “Off”

LM2931C

Adjustable

Output

Vin

Cin

0.1

Vout

CO

Output

Input

51 k

1

2

Output

Inhibit

Adjust

Gnd

IAdj

R1

R2

IB

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 VBE of the PNP determines when the pass transistor

begins conducting. This circuit is not short circuit proof.

Input

≥ 6.0 V

D45VH7

5.0 V @ 5.0 A

Output

100

+

100

+

68

LM2931–5.0

The circuit of Figure 19 can be modified to provide supply protection against

short circuits by adding the current sense resistor RSCandanadditionalPNP

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.

Input

R

RSC

Output

LM2931–5.0

100

100

++

LM2931C

Input

6.4 V to 30 V

2.0 k

8.2 k

100

+

CM

#345

100

+

33 k

6.2 V

fosc = 2.2 Hz

0

10

100

Vin = 5.6 V

Vout = 5.0 V

IO = 100 mA

Vnrms 10 Hz to 10 MHz

|ZO| @ 40 kHz

TA = 25°C

22.5 k

w

R

1

R

2

R

1 )

R

2

Vout + Vref 1 )

R

2

R

1

) I

Adj

R

2

R

Unstable

Marginally

Stable

Stable