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參數(shù)資料
| 型號： | AN8028 |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Self-excited RCC pseudo-resonance type AC-DC switching power supply control IC |
| 中文描述： | 1 A SWITCHING CONTROLLER, PSIP9 |
| 封裝： | PLASTIC, SIP-9 |
| 文件頁數(shù)： | 9/13頁 |
| 文件大小： | 133K |
| 代理商： | AN8028 |
9
Voltage Regulators
AN8028
I
Application Notes (continued)
[1] Operation descriptions (continued)
6. Overcurrent protection circuit (continued)
The R6 and C6 in figure 7 construct the filter circuit for removing the
noise generated by the parasitic capacitance equivalently accompanied
when turning on the power MOSFET.
For overcurrent detection resistance R7, the carbon resistor should
be used but not the wire winding resistor, because the high-frequency
current flows in it.
Notes on the detection level precision
This overcurrent detection level reflects on the operating current level of the power supply overcurrent
protection. Therefore, if this detection level fluctuates with temperature or dispersion, the operating current level
of the overcurrent protection of power supply itself also fluctuates. Since such level fluctuation means the neces-
sity for an increase in the withstanding capability of used parts and in the worst case it means the cause of
destruction, the accuracy of detection level is increased as much as possible for the AN8028 (approximately
±
4%).
7. Overvoltage protection circuit (OVP)
OVP is an abbreviation of over voltage protection. It refers to a self-diagnosis function, which stops the power
supply to protect the load when the power supply output generates abnormal voltage higher than the normal output
voltage due to failure of the control system or an abnormal voltage applied from the outside. (Refer to figure 8.)
Figure 8
Abnormal voltage applied
from outside
Power supply
output
Load
GND
Start resistor
R1
V
CC
TIM/OVP
V
OUT
After AC rectification
FRD
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 7
R7
C6
R8
R6
to AC (
)
CLM
GND
Basically, it is set to monitor the voltage of supply voltage V
CC
terminal of the IC. Normally, the V
CC
voltage
is supplied from the transformer drive coil. Since this voltage is proportional to the secondary side output voltage,
it still operates even when the secondary side output has overvoltage.
1) When the voltage input to the OVP terminal exceeds the threshold voltage (7.3 V typical) as the result of
power supply output abnormality, the protective circuit shuts down the internal reference voltage of the IC to
stop all of the controls and keeps this stop condition.
2) The OVP reset is done by decreasing the supply voltage (V
CC
<
8.2 V typical: OVP release supply voltage).
(1) When the supply voltage becomes lower than the stop voltage,
(2) When the supply voltage becomes lower than the OVP release voltage,
The discharge circuit is incorporated so that the electric charge which is charged in the capacitor connected to
the OVP terminal can be discharged momentarily for the next re-start.
secondary side output voltage under normal operation V
OUT
V
CC
terminal voltage under normal operation
V
7
=
V
th(OVP)
+
V
Z
V
th(OUT)
: Secondary side output overvoltage threshold value
V
th(OVP)
: OVP operation threshold value
V
Z
: Zener voltage (externally attached to OVP terminal)
V
th(OUT)
=
×
V
7
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