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參數(shù)資料
| 型號： | LD7550BL |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Green-Mode PWM Controller |
| 中文描述： | 綠色模式PWM控制器 |
| 文件頁數(shù)： | 7/10頁 |
| 文件大?。?/td> | 216K |
| 代理商： | LD7550BL |
LD7550
7
Leadtrend Technology Corporation
LD7550-DS-00 August 2004
R1
OUT
CS
VCC
GND
LD7550
C1
Cbulk
D1
Rs
Comp
Vin
Fig. 8
A 250nS leading-edge blanking time is included in the input
of CS pin to prevent the false-trigger caused by the current
spike and further to eliminate the need of R-C filter which is
usually needed in the typical UC384X application (Fig. 9).
CS
VCC
GND
LD7550
remove
OUT
250ns
blanking
time
Fig. 9
Output Stage and Maximum Duty-Cycle
An output stage of a CMOS buffer, with typical 300mA
driving capability, is incorporated to drive a power MOSFET
directly. And the maximum duty-cycle of LD7550 is limited
to 75% to avoid the transformer saturation.
Oscillator and Switching Frequency
Connecting a resistor from RT pin to GND according to the
equation can program the normal switching frequency:
)
KHz
(
100
RT
5
66
f
)
K
(
SW
×
=
The suggested operating frequency range of LD7550 is
within 50KHz to 130KHz.
Voltage Feedback Loop
The voltage feedback signal is provided from the TL431 in
the secondary side through the photo-coupler to the COMP
pin of LD7550. The input stage of LD7550, like the
UC384X, is with 2 diodes voltage offset then feeding into the
voltage divider with 1/3 ratio, that is,
)
V
2
V
(
3
1
)
V
F
COMP
PWM
(
COMPARATOR
×
=
+
A pull-high resistor is embedded internally thus can be
eliminated on the external circuit.
Internal Slope Compensation
A fundamental issue of current mode control is the stability
problem when its duty-cycle is operated more than 50%. To
stabilize the control loop, the slope compensation is needed
in the traditional UC384X design by injecting the ramp signal
from the RT/CT pin through a coupling capacitor. In LD7550,
the internal slope compensation circuit has been
implemented to simplify the external circuit design.
On/Off Control
The LD7550 can be controlled to turn off by pulling COMP
pin to lower than 1.2V. The gate output pin of LD7550 will
be disabled immediately under such condition. The off mode
can be released when the pull-low signal is removed.
Dual-Oscillator Green-Mode Operation
There
are
many
difference
implemented in different chips for the green-mode or power
saving requirements such as “burst-mode control”,
“skipping-cycle Mode”, “variable off-time control “…etc. The
basic operation theory of all these approaches intended to
topologies
has
been
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PDF描述 |
|---|---|
| LD7550BN | Green-Mode PWM Controller |
| LD7550IL | Green-Mode PWM Controller |
| LD7550IN | Green-Mode PWM Controller |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LD7550BN | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Green-Mode PWM Controller |
| LD7550BOBN | 制造商:Leadtrend 功能描述:PWM IC ,PDIP-8 (PB FREE) |
| LD7550IL | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Green-Mode PWM Controller |
| LD7550IN | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Green-Mode PWM Controller |
| LD7551BN | 制造商:Leadtrend 功能描述:GREEN MODEL PWMIC DIP-8 (PB-FREE) |
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