AN8021L データシートの表示（PDF） - Panasonic Corporation
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AN8021L Datasheet PDF : 16 Pages
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AN8021L, AN8021SB
Voltage Regulators
s Application Notes (continued)
[2] Operation descriptions (continued)
3. Overvoltage protection circuit (OVP) (continued)
After AC rectification
Start resistor
R1
VCC
Power supply output
Abnormal voltage
FRD
applied from outside
OVP
VOUT
GND
Load
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.
Figure 3
• Operating supply current characteristics
While the OVP is operating, the decrease of the supply current causes the rise of the supply voltage VCC , and
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
VCC under OVP operation is stabilized over the OVP release supply voltage (which depends on start resistor
selection). (Refer to figure 4.)
After AC rectification
Start resistor
R1
VCC
The current supply from the start resistor continues
as long as the voltage of the power supply input (AC)
is given.
After OVP starts operation, since the output is
stopped, this bias coil does not supply current.
VOUT
GND
* Select the resistance value so that the following
relationship can be kept by current supply from
the start resistor: VCC > VCC−OVP
ICC
VCC− OVP
At VCC-OVP (voltage under which OVP is released),
the operating current is temporarily increased.
This prevents VCC from exceeding its breakdown
voltage through the current from above mentioned.
VCC
Figure 4
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