HA16138PS Datasheet, PDF (16/20 Pages) Hitachi Semiconductor – AC/DC Switching Converter Controller IC With High-Voltage Power MOS FET

HA16138PS
Application Circuit Examples 2
The application circuit example shown here detects the primary-side back-up output voltage of a flyback
power supply. As the back-up output voltage, VDD is resistance-divided and feedback is performed to the
FB pin. The back-up output voltage and secondary-side output voltage are proportional to the ratio of
transformer windings. Using this characteristic enables the system to be configured with simple circuitry
as shown in the figure below.
The VDD-to-FB feedback resistance can also be used as the back-up output voltage OVP detection
resistance.
AC
INPUT
0.1µ
Line Filter
: Primary GND
2200p
100µ
400V ₊
VR
260V
Transformer
P: 90T / 1.43mH
S: 6T / 8.1µH
B: 14T / 30.8µH
PS
51k
B
SBD
15µ
HRW26F
+
+
560µ
25V
180µ
25V
+
DC
OUTPUT
5V/1A
−
: Secondary GND
HA16138PS
R1
240k
+ ^C1
47µ
R2
120k
VR
15V
20V
1 DRAIN SOURCE 8
2 DRAIN SGND 7
3 VDD
CT 6
4 FB
COMP 5
C2 0.1µ
R3 1M
R4
15k
C3 C4
2200p 220p
* If feedback resistance R1 = 240 kΩ and R2 = 120 kΩ,
feedback is performed so that the FB pin voltage is
non-inverting input voltage V_(+)EA, and the VDD voltage
is stabilized.
VDD(reg) = V_(+)EA ×
R1 + R2
R2
= 3.8V × ^{240kΩ + 120kΩ}
120kΩ
= 11.4V
Units R: Ω
C: F
When the FB pin voltage reaches OVP latch set
voltage Vovp, the OVP latch circuit operates, shutting
down the IC. The VDD voltage in this case is given
by the following formula.
VDD(ovp) = Vovp × ^{R1 + R2}
R2
= 5.0V × ^{240kΩ + 120kΩ}
120kΩ
= 15V
16