an8038 Panasonic Corporation of North America, an8038 Datasheet - Page 18

• Manufacturer Part Number: an8038
• Description: Ac-dc Switching Power Supply Control Ic With Rcc Local Resonance Circuit For Improved Conformance With Energy Conservation Laws
• Manufacturer: Panasonic Corporation of North America

AN8038, AN8038S
18
[2] Operation descriptions (continued)
5. Output block (continued)
Application Notes (continued)
That is to say, a high average current is not required in steady state operation. This is because the power MOSFET
is a capacitive load, and while a large peak current is required to drive such a load rapidly, once the load has been
charged or discharged a much smaller current suffices to retain that state.
considering the capacitance of the power MOSFETs that will be used.
the power MOSFET can cause ringing, and pull
down the output pin below the ground level. If
the output pin goes to a negative voltage that is
larger than the voltage drop of the diode, this
state can turn on the parasitic diode formed by
the collector of the output NPN transistor and
the substrate. Insert a Schottky barrier diode be-
tween the output and ground if this is a prob-
lem. (See figure 9.)
1) If, as a result of an abnormality in the power supply output, the voltage input to the V
2) The OVP circuit is released (reset) by lowering the supply voltage (V
The main requirement on the control IC in this type of power supply is the ability to provide a large peak current.
This IC has a guaranteed peak current capability of 1 A and 2 A, values which were determined by
The parasitic inductance and capacitance of
Overvoltage protection circuit (OVP)
shuts down the power supply to protect the load if a voltage that is significantly and abnormally higher than
the normal output voltage occurs in the power supply output, due to, for example, a malfunction in the control
system or an abnormal voltage applied externally. (See figure 10.)
supplied from the transformer bias winding, this voltage is proportional to the secondary side output voltage.
Thus the overvoltage protection circuit operates when an overvoltage occurs in the secondary side output.
Current supply from the startup resistor
continues as long as the power supply
input voltage (AC) is applied.
OVP stands for overvoltage protection. The overvoltage protection circuit is a self-diagnostic function that
The overvoltage detection function monitors the V
threshold value (20.5 V typical), the IC internal reference voltage is shut down, and all control operation
is stopped. The IC then holds this state.
release supply voltage.)
20.5 V typ.
operating
voltage
OVP
Rectified AC
OVP release voltage
7.5 V typ.
RS latch
S
R
Q
Figure 10. OVP operating circuit
CC
pin voltage. Since the V
Startup resistor
R1
CC
Figure 9
7.5 V typical). (This is the OVP
Voltage Regulators
Power supply output
CC
Since output is stopped
after the OVP circuit
operates, no current is
supplied from
the bias winding.
pin voltage is normally
Schottky diode
When an abnormal
voltage is applied
by some external
source.
CC
pin exceeds the