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HA17432UA

Shunt Regulator

Hitachi -> Renesas Electronics 

HA17431 Series

Application Examples

As shown in the figure on the right, this IC operates as an inverting amplifier, with the REF pin as input

pin. The open-loop voltage gain is given by the reciprocal of “reference voltage deviation by cathode

voltage change” in the electrical specifications, and is approximately 50 to 60 dB. The REF pin has a high

input impedance, with an input current Iref of 3.8 µA Typ (V version: Iref = 2 µA Typ). The output

impedance of the output pin K (cathode) is defined as dynamic impedance ZKA, and ZKA is low (0.2 Ω) over

a wide cathode current range. A (anode) is used at the minimum potential, such as ground.

K

REF – VCC OUT

VZ ≅ 2.5V

+ VEE

A

Figure 1 Operation Diagram

Application Hints

No. Application Example

1

Reference voltage generation circuit

Vin

GND

R

K

REF A

Vout

CL

GND

2

Variable output shunt regulator circuit

Vin

GND

R

R1

R2

Iref

K

REF

A

Vout

CL

GND

Description

This is the simplest reference voltage circuit. The value

of the resistance R is set so that cathode current IK ≥ 1

mA.

Output is fixed at Vout ≅ 2.5 V.

The external capacitor CL (CL ≥ 3.3 µF) is used to

prevent oscillation in normal applications.

This is circuit 1 above with variable output provided.

Here, Vout ≅ 2.5 V × (R1 + R2)

R2

Since the reference input current Iref = 3.8 µA Typ (V

version: Iref = 2 µA Typ) flows through R1, resistance

values are chosen to allow the resultant voltage drop to

be ignored.

Rev.1, Sep. 2002, page 14 of 24

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