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HA17432UPA

Shunt Regulator

Hitachi -> Renesas Electronics 

HA17431 Series

Application Hints (cont.)

No. Application Example

Description

3

Single power supply inverting

comparator circuit

VCC

Vin

GND

RL

Rin

K

REF A

Vout

GND

This is an inverting type comparator with an input

threshold voltage of approximately 2.5 V. Rin is the

REF pin protection resistance, with a value of several

kΩ to several tens of kΩ.

RL is the load resistance, selected so that the cathode

current IK • 1 mA when Vout is low.

Condition Vin

Vout

IC

C1

Less then 2.5 V VCC (VOH)

OFF

C2

2.5 V or more Approx. 2 V (VOL) ON

4

AC amplifier circuit

Cf

Vin

Cin R3

VCC

RL

R1

Vout

K

REF A

R2

GND

This is an AC amplifier with voltage gain G = –R1 /

(R //R ). The input is cut by capacitance Cin, so that

23

the REF pin is driven by the AC input signal, centered

on 2.5 VDC.

R2 also functions as a resistance that determines the

DC cathode potential when there is no input, but if the

input level is low and there is no risk of Vout clipping to

V , this can be omitted.

CC

To change the frequency characteristic, Cf should be

connected as indicated by the dotted line.

Gain G = R1 (DC gain)

R2 // R3

1

Cutoff frequency fc =

2π Cf (R1 // R2 // R3)

5

Switching power supply error

This circuit performs control on the secondary side of a

amplification circuit

transformer, and is often used with a switching power

supply that employs a photocoupler for offlining.

R4

V+

+ LED

R3

The output voltage (between V+ and V–) is given by the

following formula:

–

Vout ≅ 2.5 V × (R1 + R2)

R1

R2

(Note)

Cf

Secondary

side GND

R2

V–

Note: LED : Light emitting diode in photocoupler

R3 : Bypass resistor to feed IK(>Imin)

when LED current vanishes

R4 : LED protection resistance

In this circuit, the gain with respect to the Vout error is

as follows:

G = R2 ×

(R1 + R2)

HA17431 open

loop gain

×

photocoupler

total gain

As stated earlier, the HA17431 open-loop gain is 50 to

60 dB.

Rev.1, Sep. 2002, page 15 of 24

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