HA17431FPAJ RENESAS [Renesas Technology Corp], HA17431FPAJ Datasheet - Page 14

• Manufacturer Part Number: HA17431FPAJ
• Description: Shunt Regulator
• Manufacturer: RENESAS [Renesas Technology Corp]

HA17431VPJ/PJ/PAJ/FPJ/FPAJ/PNAJ/UPA, HA17432UPA
Design Guide for AC-DC SMPS (Switching Mode Power Supply)
1. Use of Shunt Regulator in Transformer Secondary Side Control
2. Determination of External Constants for the Shunt Regulator
REJ03D0892-0100 Rev.1.00 Apr 03, 2007
Page 14 of 17
This example is applicable to both forward transformers and flyback transformers. A shunt regulator is used on the
secondary side as an error amplifier, and feedback to the primary side is provided via a photocoupler.
A. DC characteristic determination
B. AC characteristic determination
In figure 2, R
resistor to feed I
be obtained separately from the manufacturer. Using the parameters in figure 2, the following formulas are
obtained:
V
is the current shunt resistance for the light emitting diode, in which a bias current I
Next, the output voltage can be determined by R3 and R4, and the following formula is obtained:
The absolute values of R
characteristics described in the next section. The Iref value is around 3.8 µA Typ. (V version: 2 µA Typ)
This refers to the determination of the gain frequency characteristic of the shunt regulator as an error amplifier.
Taking the configuration in figure 2, the error amplifier characteristic is as shown in figure 3.
R
V
K
0
1
is the HA17431 operating voltage, and is set at around 3 V, taking into account a margin for fluctuation. R
=
=
Phototransistor
V
R
HA17384
HA17385
PWM IC
0
3
R
– V
+ R
I
F
4
+ I
F
4
1
Transformer
– V
B
and R
× Vref, Vref = 2.5 V Typ
K
K
minimum, and these are determined as shown below. The photocoupler specification should
, R
Photocoupler
2
Figure 3 HA17431 Error Amplification Characteristic
are protection resistor for the light emitting diode in the photocoupler, and R
2
Figure 2 Typical Shunt Regulator/Error Amplifier
3
=
and R
V
I
B
F
4
SBD
are determined by the HA17431 reference input current Iref and the AC
emitting diode
G
f
1
1
V
Light
F
f
AC
* f
OSC
HA17431
f
2
: PWM switching frequency
G
2
I
F
When R
f
OSC
I
When R
V
B
K
K
Frequency f (Hz)
5
R
R
A
= 0
1
2
C
5
1
≠ 0
REF
R
5
Vref
GND
B
of around 1/5 I
R
R
3
4
Output
V
0
2
(+)
(–)
F
is a bypass
flows.
2