TLV431

Issue 1 - June 2008

10

www.zetex.com

© Zetex Semiconductors plc 2008

Figure 4. Basic series regulator

A very effective and simple series regulator can be implemented as shown in Figure 4 above. This

may be preferable if the load requires more current than can be provided by the TLV431 alone and

there is a need to conserve power when the load is not being powered. This circuit also uses one

component less than the shunt circuit shown in Figure 2 above.

Figure 5. Series regulator with current limit

Figure 5 adds current limit to the series regulator in Figure 4 using a second TLV431. For currents

below the limit, the circuit works normally supplying the required load current at the design

voltage. However should attempts be made to exceed the design current set by the second

TLV431, the device begins to shunt current away from the base of Q1. This begins to reduce the

output voltage and thus ensuring that the output current is clamped at the design value. Subject

only to Q1's ability to withstand the resulting power dissipation, the circuit can withstand either

a brief or indefinite short circuit.

R3

0.1µF

C1

GND

V

IN

V

OUT

R1

R2

TLV431

Q1

ZXTN25020CFH

I

K

I

OUT

V

REF

I

B

⎟

⎠

⎞

⎜

⎝

⎛ +

=

2

1

1

R

R

V

V

REF

OUT

K

B

BE

OUT

IN

I

I

)

V

V

(

V

3

R

+

+

−

=

mA

15

I

h

I

B

(min)

FE

(max)

OUT

≤

<

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

R3

0.1µF

C1

GND

V

IN

V

OUT

R1

R2

TLV431

Q1

ZXTN25020CFH

TLV431

Rs

VREF

I B

⎟

⎠

⎞

⎜

⎝

⎛ +

=

2

1

1

R

R

V

V

REF

OUT

K

B

BE

OUT

IN

I

I

)

V

V

(

V

3

R

+

+

−

=

mA

I

h

I

B

FE

OUT

15

(min)

(max)

≤

<

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

(max)

OUT

REF

S

I

V

R

=