an8022l Panasonic Corporation of North America, an8022l Datasheet - Page 8

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

AN8022L, AN8022SB
8
[2] Operation descriptions (continued)
2. Oscillation circuit
3. Overvoltage protection circuit (OVP)
Application Notes (continued)
1) When the voltage input to the OVP terminal exceeds the threshold voltage (6.0 V typical) as the result of power
2) The OVP is released (reset) under the following conditions:
which is converted from the current input to IFB terminal and dead-time control level which is fixed internally is
compared with the internal triangular oscillation level through PWM comparator, and optimal duty is determined,
and then it is output via output driving stage.
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 (figure 2 and
figure 3).
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 over voltage.
The PWM is an abbreviation of Pulse Width Modulation. In this IC, a smaller voltage between the voltage level
Triangular wave oscillation
discharge to/from the external capacitor connected to the CT. The ratio of the charge current to the discharge
current is set inside, and the current value is determined by the external resistor connected to the RT terminal.
reference voltage (which is determined by Zener diode and V
compensated). For this reason, the effect of fluctuation with temperature and dispersion is small. By the use
of a temperature-compensated external resistor, the effect of the fluctuation with temperature and dispersion
on the charge and discharge current value will be reduced further.
divider internal reference voltage, the effect of fluctuation with temperature and dispersion has been
suppressed.
division of internal reference voltage, the effect of fluctuation with temperature and dispersion has been
suppressed.
(Reference calculation of oscillation frequency)
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
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.
• Decreasing the supply voltage (V
temperature and dispersion in the design of the triangular wave oscillation frequency.
connected to the OVP terminal can be discharged with the constant current of 5 A (typical) for the next re-start.
The triangular waveform oscillation is performed through constant current charge/constant current
The RT terminal voltage is determined by the level which is a resistor-divided voltage of the internal
Moreover, since the upper/lower voltage level of the triangular wave oscillation is given by the resistor-
Moreover, since the upper/lower voltage level of the triangular wave oscillation is given by the resistor-
f
As described above, the sufficient consideration has been given to the effect of fluctuation with
OSC
The discharge circuit is incorporated so that the electric charge which is charged in the capacitor
V
V
th(OUT)
7
V
V
V
V
6
th(OUT)
th(OVP)
Z
th(OVP)
C
5
T
Secondary side output voltage under normal operation V
: Secondary side output overvoltage threshold
: OVP operation threshold
: Zener voltage (external parts of OVP terminal)
R
V
T
Z
V
CC
[Hz]
terminal voltage under normal operation
CC
8.4 V typical: OVP release supply voltage)
CC
terminal of the IC. Normally, the V
BE
of NPN transistor, and temperature-
OUT
Voltage Regulators
V
7
CC
voltage