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參數(shù)資料
| 型號： | AS3844D1413 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Current Mode Controller |
| 中文描述： | 電流模式控制器 |
| 文件頁數(shù)： | 12/20頁 |
| 文件大小： | 155K |
| 代理商： | AS3844D1413 |
12
ASTEC Semiconductor
the following paragraphs. The basic operation of
the oscillator is as follows:
A simple RC network is used to program the fre-
quency and the maximum duty ratio of the
AS3842 output. See Figure 15. Timing capacitor
(C
T
) is charged through timing resistor (R
T
) from
the fixed 5.0 V at V
REG
. During the charging time,
the OUT (pin 6) is high. Assuming that the output
is not terminated by the PWM latch, when the
voltage across C
T
reaches the upper oscillator
trip point (3.0 V), an internal current sink from
pin 4 to ground is turned on and discharges C
T
towards the lower trip point. During this dis-
charge time, an internal clock pulse blanks the
output to its low state. When the voltage across
C
T
reaches the lower trip point (1.3 V), the cur-
rent sink is turned off, the output goes high, and
the cycle repeats. Since the output is blanked
during the discharge of C
T
, it is the discharge
time which controls the output deadtime and
hence, the maximum duty ratio.
The nature of the AS3842 oscillator circuit is such
that, for a given frequency, many combinations of
R
T
and C
T
are possible. However, only one value
of R
T
will yield the desired maximum duty ratio at
a given frequency. Since a precise maximum
duty ratio clamp is critical for many power supply
designs, the oscillator discharge current is
trimmed in a unique manner which provides sig-
nificantly improved tolerances as explained later
in this section. In addition, the AS3844/5 options
have an internal flip-flop which effectively blanks
every other output pulse (the oscillator runs at
twice the output frequency), providing an
absolute maximum 50% duty ratio regardless of
discharge time.
1.3.1 Selecting timing components R
T
and C
T
The values of R
T
and C
T
can be determined
mathematically by the following expressions:
(1)
AS384x
Current Mode Controller
5 V REG
OSCILLATOR
AS3842
6 OUTPUT
7 V
CC
8
R
T
C
T
I
D
5 GND
CLOCK
PWM
C
T
OUTPUT
Large R
T
/Small C
T
C
T
OUTPUT
Small R
T
/ Large C
T
4
Figure 15. Oscillator Set-up and Waveforms
C
D
R
R
T
T
T
=
=
OSC
L
H
OSC
K
K
ln
1.63D
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AS3844D14T | Current Mode Controller |
| AS3844D813 | Current Mode Controller |
| AS3844D8T | Current Mode Controller |
| AS3844N13 | Current Mode Controller |
| AS3844NT | Current Mode Controller |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AS3844D14T | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS3844D813 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS3844D8T | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS3844N13 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
| AS3844NT | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Current Mode Controller |
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