an8022l Panasonic Corporation of North America, an8022l Datasheet - Page 10

• Manufacturer Part Number: an8022l
• Description: Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8022L, AN8022SB
10
[2] Operation descriptions (continued)
3. Over voltage protection circuit (OVP) (continued)
4. Overcurrent protection circuit (OVP)
Application Notes (continued)
I
in the primary side (power MOSFET). Taking advantage of the above fact, by regulating the upper limit of the pulse
current flowing in the main switch, the circuit protects the parts which are easily damaged by the overcurrent.
ends of the low resistance, which is connected between the source of power MOSFET and the power supply GND.
When the power MOSFET is turned on and the threshold voltage of CLM (Current Limit) is detected, the
overcurrent protection circuit controls so that current can not flow further by turning off the output to turn off the
power MOSFET. The threshold voltage of CLM is approximately 200 mV (typical) under T
to GND of the IC. This control is repeated for each cycle. Once the overcurrent is detected, the off condition is
kept during that cycle, and it can not be turned on until the next cycle. The overcurrent detection method described
in the above is called pulse-by-pulse overcurrent detection. (Refer to figure 6.)
functions to remove the noise generated by the parasitic capaci-
tance which is equivalently formed at turning-on of the power
MOSFET.
protection. Therefore, if this detection level fluctuates with temperature or dispersion, the operating current level
of the power supply overcurrent protection also fluctuates. Since such level fluctuation increases the necessity of
withstand capability for the parts to be used and in the worst case it means the cause of destruction, the accuracy
of detection level is raised as much as possible for these ICs, the AN8022L and AN8022SB.
After AC rectification
CC
Notes on the detection level precision
The overcurrent of the power supply output is proportional to the value of current flowing in the main switch
For the current flowing in the main switch, the current detection is achieved by monitoring the voltage in both
The R4, R5 and C3 in figure 5 construct the filter circuit, which
This overcurrent detection level is reflected on the operating current level of the power supply overcurrent
V
GND
CC OVP
V
V
OUT
CC
Start resistor
R1
V
CC
Figure
* 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
(voltage under which OVP is released),
CC
from exceeding its breakdown
CC
GND
CLM
V
Voltage Regulators
CC OVP
R4
Figure 5
a
25 C with respect
C3
R5
R3