HA17431P HITACHI [Hitachi Semiconductor], HA17431P Datasheet - Page 17

• Manufacturer Part Number: HA17431P
• Description: Regarding the change of names mentioned in the document, such as Hitachi Electric and Hitachi XX, to Renesas Technology Corp.
• Manufacturer: HITACHI [Hitachi Semiconductor]

Application Hints (cont.)
No.
3
4
5
Application Example
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
when LED current vanishes
2
REF
R
// R
R
1
3
R
3
A
V
K
2
CC
R
(DC gain)
R
+
–
L
1
2π Cf (R
REF
(Note)
LED
A
V
K
Vout
GND
1
1
R
CC
// R
L
R
Vout
4
GND
2
// R
Cf
R
3
3
)
V
V
R
R
+
–
1
2
Description
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
current I
Condition
C1
C2
This is an AC amplifier with voltage gain G = –R
(R
the REF pin is driven by the AC input signal, centered
on 2.5 V
R
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
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.
CC
L
2
2
is the load resistance, selected so that the cathode
//R
also functions as a resistance that determines the
, this can be omitted.
(R
3
). The input is cut by capacitance Cin, so that
1
R
K
+ R
DC
2
• 1 mA when Vout is low.
Vin
Less then 2.5 V
2.5 V or more
.
2
)
×
(R
HA17431 open
loop gain
1
R
+ R
2
2
Rev.1, Sep. 2002, page 15 of 24
)
Vout
V
Approx. 2 V (V
CC
(V
OH
HA17431 Series
)
× photocoupler
total gain
OL
)
IC
OFF
ON
1
/