an8027 Panasonic Corporation of North America, an8027 Datasheet - Page 23

• Manufacturer Part Number: an8027
• Description: Ac-dc Switching Power Supply Control Ic With Standby Mode
• Manufacturer: Panasonic Corporation of North America

Voltage Regulators
[1] Operation descriptions (continued)
13. Overvoltage protection (OVP) circuit (continued)
Application Notes (continued)
Rectified AC
Rectified AC
I
CC
Operating supply current characteristics
voltage V
resistance mode when the OVP circuit operates, and thus prevent increases in the supply voltage.
(note that this value depends on the value of the startup resistor) that is larger than the OVP release voltage,
the OVP circuit will not be reset as long as the AC input is not cut. (Refer to figure 23.) Note that this does not
apply to an external reset.
V
GND
GND
Startup resistor
When the OVP circuit operates and the power supply current drops, this can induce a rise of the supply
Therefore, the circuit is provided with characteristics that cause the supply current to rise in constant
Due to these characteristics, if the supply voltage V
CC OVP
V
V
Out
Out
SD
CC
CC
Startup resistor
CC
. In the worst case, it may exceed the IC's guaranteed breakdown voltage (24 V).
R1
R1
V
CC
Figure 22
Figure 23
Should there be abnormal voltage (i.e., voltage that is higher than
the power output voltage and may damage the load) applied to
the power output from outside, the IC detects the abnormal voltage
through the bias winding on the primary side and triggers OVP.
There is a surge of operating current at V
voltage that resets overvoltage protection). This prevents
V
caused by a decrease in current supply from the startup resistor.
No current is supplied to the V
if OVP is triggered and the output of the IC is stopped.
Current is continuously supplied to the V
the startup resistor as long as voltage is applied to the
startup resistor from commercial AC power.
* Select the startup resistor so that the V
CC
the following condition according to the current
supplied through the startup resistor.
from exceeding the absolute maximum rating of the IC
CC
when the OVP circuit operates is stabilized at a value
V
Power output
CC
Load
V
CC OVP
CC
Abnormal voltage applied
from outside.
pin from this bias winding
AN8027, AN8037
CC OVP
CC
CC
pin through
satisfies
(i.e., a
23