an8021l Panasonic Corporation of North America, an8021l Datasheet - Page 10

• Manufacturer Part Number: an8021l
• Description: Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8021L, AN8021SB
10
[2] Operation descriptions (continued)
3. Overvoltage protection circuit (OVP) (continued)
Application Notes (continued)
in the worst case, the guaranteed breakdown voltage of the IC (35 V) can be exceeded. In order to prevent the rise
of supply voltage, the IC is provided with such characteristics as the supply current rises in the constant resistance
mode. This characteristics ensure that the OVP can not be released unless the AC input is cut, if the supply voltage
V
selection). (Refer to figure 4.)
I
After AC rectification
CC
Operating supply current characteristics
After AC rectification
CC
While the OVP is operating, the decrease of the supply current causes the rise of the supply voltage V
under OVP operation is stabilized over the OVP release supply voltage (which depends on start resistor
GND
V
GND
CC OVP
V
OVP
V
V
OUT
V
OUT
CC
CC
Start resistor
Start resistor
R1
R1
V
CC
Figure
It detects abnormal voltage applied from the outside to the
power supply output (the voltage which is higher than voltage
of the power supply output and may damage the load) by the
primary side of the bias coil and operates the OVP.
FRD
Figure
3
* Select the resistance value so that the following
After OVP starts operation, since the output is
stopped, this bias coil does not supply current.
At V
the operating current is temporarily increased.
This prevents V
voltage through the current from above mentioned.
The current supply from the start resistor continues
as long as the voltage of the power supply input (AC)
is given.
4
relationship can be kept by current supply from
the start resistor: V
CC-OVP
Power supply output
Load
(voltage under which OVP is released),
CC
from exceeding its breakdown
CC
Abnormal voltage
applied from outside
V
Voltage Regulators
CC OVP
CC
, and