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參數(shù)資料
| 型號： | AN8021L |
| 廠商： | PANASONIC CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | AC-DC switching power supply control IC |
| 中文描述： | 1 A SWITCHING CONTROLLER, 225 kHz SWITCHING FREQ-MAX, PSIP9 |
| 封裝： | PLASTIC, SIP-9 |
| 文件頁數(shù)： | 8/16頁 |
| 文件大小： | 141K |
| 代理商： | AN8021L |
8
AN8021L, AN8021SB
Voltage Regulators
I
Application Notes (continued)
[2] Operation descriptions
1. Start/stop circuit block
Start mechanism
When AC voltage is applied and the sup-
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.)
During the period from the time when the
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
CC
.
Since the supply voltage continuously decreases during the above period (area b in figure 1), the power supply
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
The start/stop circuit block is provided with the function to monitor the V
CC
voltage, and to start the operation
of IC when V
CC
voltage reaches the start voltage (14.2 V typical), and to stop when it decreases under the stop
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
CC
.
Note) To start up the IC operation, the startup current which is a pre-start current plus a circuit drive current is necessary.
Set the resistance value so as to supply a startup current of 450
μ
A.
2. Oscillation circuit
The PWM is an abbreviation of pulse width modulation. In this IC, the smaller voltage between the voltage level
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.
Triangular wave oscillation
The triangular waveform oscillation is performed through constant current charge/constant current
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.
The RT terminal voltage is determined by the level which is a resistor-divided voltage of the internal
reference voltage (which is determined by Zener diode and V
BE
of NPN transistor, and temperature-
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.
Moreover, since the upper/lower voltage level of the triangular wave oscillation is given by the resistor-
division of internal reference voltage, the effect of fluctuation with temperature and dispersion has been
suppressed.
As described above, the sufficient consideration has been given to the effect of fluctuation with tempera-
ture and dispersion in the design of the triangular wave oscillation frequency.
(Reference calculation of oscillation frequency)
5
[Hz]
6
×
C
T
×
R
T
f
OSC
=
Start voltage
After AC rectification
Start resistance
Stop voltage
a
b
Start condition
Start failure
c
Voltage supplied
from bias coil
Before start
Start
Figure 1
V
OUT
R1
V
CC
GND
C1
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| AN8021NS | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:External excitation flyback AC-DC switching power supply control IC |
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| AN8022L | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:AC-DC switching power supply control IC |
| AN8022SB | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:AC-DC switching power supply control IC |
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