an8029 Panasonic Corporation of North America, an8029 Datasheet - Page 9

• Manufacturer Part Number: an8029
• Description: Self-excited Rcc Pseudo-resonance Type Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

Voltage Regulators
[1] Operation descriptions (continued)
6. Overcurrent protection circuit (continued)
7. Overvoltage protection circuit (OVP)
Application Notes (continued)
1) When the voltage input to the OVP terminal exceeds the threshold voltage (7.3 V typical) as the result of
2) The OVP reset is done by decreasing the supply voltage (V
noise generated by the parasitic capacitance equivalently accompanied
when turning on the power MOSFET. For overcurrent detection resis-
tance R7, the carbon resistor should be used but not the wire winding
resistor, because the high-frequency current flows in it.
protection. Therefore, if this detection level fluctuates with temperature or variability, 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 AN8029 (approximately 4%).
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.)
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 is in overvoltage.
Notes on the detection level precision
After AC rectification
TIM/OVP
The R6 and C6 in figure 7 construct the filter circuit for removing the
This overcurrent detection level reflects on the operating current level of the power supply overcurrent
OVP is an abbreviation of over voltage protection. It refers to a self-diagnosis function, which stops the power
Basically, it is set to monitor the voltage of supply voltage V
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.
(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.
GND
V
V
V
V
th(OUT)
7
OUT
CC
V
th(OVP)
Start resistor
secondary side output voltage under normal operation V
V
R1
Z
V
CC
terminal voltage under normal operation
V
V
V
th(OUT)
th(OVP)
Z
: Secondary side output overvoltage threshold value
: OVP operation threshold value
: Zener voltage (externally attached to OVP terminal)
Figure 8
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
Power supply output
CC
CC
terminal of the IC. Normally, the V
8.2 V typical: OVP release supply voltage).
Load
OUT
Abnormal voltage applied
from outside
CLM
GND
V
7
R8
Figure 7
C6
AN8029
R6
CC
voltage
R7
9