HA17431H Datasheet, PDF (7/15 Pages) Hitachi Semiconductor – Shunt Regulator

HA17431H Series
Application Hints (cont.)
No. Application Example
Description
3
Single power supply inverting
comparator circuit
V_CC
Vin
GND
R_L
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.
R_L is the load resistance, selected so that the cathode
current
I
K
≥
0.2
mA
when
Vout
is
low.
Condition Vin
Vout
IC
C1
Less then 2.5 V V_CC (V_OH)
OFF
C2
2.5 V or more Approx. 2 V (V_OL) ON
4
AC amplifier circuit
Cf
Vin
Cin R₃
V_CC
R_L
R₁
Vout
K
REF _A
R₂
GND
Gain G = ^R1 (DC gain)
R₂ // R₃
1
Cutoff frequency fc =
2π Cf (R₁ // R₂ // R₃)
This is an AC amplifier with voltage gain G = –R₁ /
(R₂//R₃). The input is cut by capacitance Cin, so that
the REF pin is driven by the AC input signal, centered
on 2.5 V .
DC
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_CC, this can be omitted.
To change the frequency characteristic, Cf should be
connected as indicated by the dotted line.
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
Secondary
side GND
(Note)
Cf
R₂
V^–
In this circuit, the gain with respect to the Vout error is
as follows:
G = ^R2 ×
(R₁ + R₂)
HA17431H open
loop gain
×
photocoupler
total gain
Note: LED : Light emitting diode in photocoupler
R3 : Bypass resistor to feed IK(>Imin)
when LED current vanishes
R4 : LED protection resistance
As stated earlier, the HA17431H open-loop gain is 50
to 60 dB.
Rev.0, Sep. 2001, page 7 of 15