ha17431pnaj Renesas Electronics Corporation., ha17431pnaj Datasheet - Page 12

• Manufacturer Part Number: ha17431pnaj
• Description: Shunt Regulator
• Manufacturer: Renesas Electronics Corporation.

HA17431VPJ/PJ/PAJ/FPJ/FPAJ/PNAJ/UPA, HA17432UPA
Application Hints (cont.)
REJ03D0892-0100 Rev.1.00 Apr 03, 2007
Page 12 of 17
No.
3
4
5
Single power supply inverting
comparator circuit
GND
AC amplifier circuit
Gain G =
Cutoff frequency fc =
Switching power supply error
amplification circuit
Note: LED
Vin
Vin
Secondary
side GND
R3
R4
Cf
Rin
Cin
R
: Light emitting diode in photocoupler
: Bypass resistor to feed IK(>Imin)
: LED protection resistance
Application Example
when LED current vanishes
2
REF
R
// R
R
1
3
R
3
V
K
A
2
CC
R
(DC gain)
R
+
–
L
1
2π Cf (R
REF
(Note)
LED
V
K
A
Vout
GND
1
1
R
CC
// R
L
R
Vout
4
GND
2
// R
Cf
R
3
3
)
V
V
R
R
+
–
1
2
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
mA when Vout is low.
Condition
C1
C2
This is an AC amplifier with voltage gain G = –R
input is cut by capacitance Cin, so that the REF pin is driven by the
AC input signal, centered on 2.5 V
R
potential when there is no input, but if the input level is low and
there is no risk of Vout clipping to V
To change the frequency characteristic, Cf should be connected as
indicated by the dotted line.
This circuit performs control on the secondary side of a transformer,
and is often used with a switching power supply that employs a
photocoupler for offlining.
The output voltage (between V+ and V–) is given by the following
formula:
Vout ≅ 2.5 V ×
In this circuit, the gain with respect to the Vout error is as follows:
G =
As stated earlier, the HA17431 open-loop gain is 50 to 60 dB.
L
2
is the load resistance, selected so that the cathode current I
also functions as a resistance that determines the DC cathode
(R
1
R
+ R
2
Vin
Less then 2.5 V
2.5 V or more
2
)
×
(R
HA17431 open
loop gain
1
R
+ R
2
2
)
Vout
V
Approx. 2 V (V
CC
Description
(V
OH
)
× photocoupler
DC
total gain
CC
.
OL
, this can be omitted.
)
IC
OFF
ON
1
/ (R
2
//R
3
). The
K
≥ 1