Voltage Regulators
AN8028
■ Terminal Equivalent Circuits (continued)
Pin No.
Equivalent circuit
Description
I/O
8
TIM/OVP:
I
Terminal for use both OVP (overvoltage protec-
tion circuit) and timer latch.
[OVP]
When overvoltage signal of the power supply is
detected and high is inputted to the terminal, it
turns off the internal circuit. At the same time, it
holds that condition (latch). To reset the OVP
latch, the VCC should be decreased to a voltage
lower than the release voltage.
VCC
7.3 V
Comp.
[Timer latch]
It detects the output voltage fall due to the
overcurrent condition of the power supply out-
put through the current level inputted to IFB.
When the IIFB decreases under the current of
certain value, the charge current flows in the
capacitor which is connected to this terminal.
Then, when the capacitor is charged up to the
threshold voltage of the OVP, the OVP works so
that the IC could keep the operation stop condi-
tion.
5 µA
8
9
FB:
I
VCC
Terminal for connecting the photocoupler for
error voltage feedback of the power supply out-
put.
It is possible to cancel about 180 µA of the dark
current of photocoupler.
9
TON
■ Application Notes
After AC rectification
Start resistance
R1
[1] Operation descriptions
1. Start/stop circuit block
• Start mechanism
VCC
When AC voltage is applied and the supply
voltage reaches the start voltage through the
current from start resistor, the IC starts opera-
tion. Then the power MOSFET driving starts.
Thereby, bias is generated in the transformer
and the supply voltage is given from the bias
coil to the IC. (This is point a in figure 1 )
During the period from the time when the
start voltage is reached and the voltage is gen-
erated in the bias coil to the time when the IC
is provided with a sufficient supply voltage,
the supply voltage of the IC is supplied by the
C8
VOUT
GND
Before start
Start
Voltage supplied
from bias coil
a
Start
voltage
Start condition
c
Start failure
Stop
voltage
b
capacitor (C8) connected to VCC
.
Figure 1
5
PANASONIC [ PANASONIC ]
