an8021l Panasonic Corporation of North America, an8021l Datasheet - Page 8

• Manufacturer Part Number: an8021l
• Description: Ac-dc Switching Power Supply Control Ic
• Manufacturer: Panasonic Corporation of North America

AN8021L, AN8021SB
8
[2] Operation descriptions
1. Start/stop circuit block
2. Oscillation circuit
Application Notes (continued)
Note) To start up the IC operation, the startup current which is a pre-start current plus a circuit drive current is necessary.
Start mechanism
ply voltage reaches the start voltage through
the current from the start resistor, the IC starts
operation. Then the power MOSFET driving
starts. Thereby, bias is generated in the trans-
former and the supply voltage is given from the
bias coil to the IC. (This is point a in figure 1.)
start voltage is reached and the voltage is gen-
erated in the bias coil to the time when the IC
is provided with a sufficient supply voltage,
the supply voltage of the IC is supplied by the
capacitor (C1) connected to V
is not able to start (state c in figure 1), if the stop voltage of the IC is reached before the sufficient supply voltage
is supplied from the bias coil.
Function
of IC when V
voltage (9.2 V typical). A large voltage difference is set between start and stop (5.0 V typical), so that it is easier
to select the start resistor and the capacitor to be connected to V
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.
When AC voltage is applied and the sup-
During the period from the time when the
Since the supply voltage continuously decreases during the above period (area b in figure 1), the power supply
The start/stop circuit block is provided with the function to monitor the V
Set the resistance value so as to supply a startup current of 450 A.
The PWM is an abbreviation of pulse width modulation. In this IC, the 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.
division of internal reference voltage, the effect of fluctuation with temperature and dispersion has been
suppressed.
ture and dispersion in the design of the triangular wave oscillation frequency.
(Reference calculation of oscillation frequency)
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-
As described above, the sufficient consideration has been given to the effect of fluctuation with tempera-
f
OSC
CC
6
voltage reaches the start voltage (14.2 V typical), and to stop when it decreases under the stop
C
5
T
R
T
CC
[Hz]
.
Start voltage
Stop voltage
After AC rectification
CC
Before start
GND
.
Start resistance
V
BE
V
OUT
CC
of NPN transistor, and temperature-
CC
voltage, and to start the operation
R1
Figure 1
C1
a
Voltage Regulators
b
Start
c
Voltage supplied
from bias coil
Start failure
Start condition