HA17431_15 Datasheet, PDF (13/21 Pages) Renesas Technology Corp – Shunt Regulator

HA17431 Series
Application Hints (cont.)
No.
Application Example
3 Single power supply inverting
comparator circuit
Vin
GND
V_CC
R_L
Rin
K
REF A
Vout
GND
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_L is the load resistance, selected so that the cathode current I_K ≥ 1
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 transformer,
amplification circuit
and is often used with a switching power supply that employs a
photocoupler for offlining.
Secondary
side GND
+ _LED
–
(Note)
R₄
V+
R₃
R₁
Cf
R₂
V–
The output voltage (between V+ and V–) is given by the following
formula:
Vout ≅ 2.5 V × ^{(R1 + R2)}
R₂
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.
Note: LED : Light emitting diode in photocoupler
R3 : Bypass resistor to feed IK(>Imin)
when LED current vanishes
R4 : LED protection resistance
R03DS0086EJ0400 Rev.4.00
Jan 10, 2014
Page 13 of 20