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參數(shù)資料
| 型號(hào)： | SG6848 |
| 廠(chǎng)商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Low Cost Green-Mode PWM Controller for Flyback Converters |
| 中文描述： | 低成本綠色模式PWM控制器，用于回掃轉(zhuǎn)換 |
| 文件頁(yè)數(shù)： | 8/13頁(yè) |
| 文件大小： | 263K |
| 代理商： | SG6848 |
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Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters
SG6848
System General Corp.
Version 1.2(IRO33.0010.B0)
- 8 -
www.sg.com.tw
May.06, 2003
OPERATION DESCRIPTION
SG6848 devices integrate many useful designs into
one controller for low-power switch-mode power supplies.
The following descriptions highlight some of the features
of the SG6848 series.
Start-up Current
The start-up current is only 5uA. Low start-up
current allows a start-up resistor with a high resistance
and a low-wattage to supply the start-up power for the
controller. A 1.5 M
, 0.25W, start-up resistor and a
10uF/25V V
DD
hold-up capacitor would be sufficient for
an AC-to-DC power adapter with a wide input range
(100V
AC
to 240V
AC
).
Operating Current
The operating current has been reduced to 2mA. The
low operating current results in higher efficiency and
reduces the V
cc
hold-up capacitance requirement.
Green-Mode Operation
The proprietary green-mode function provides
off-time modulation to linearly decrease the switching
frequency under light-load conditions. On-time is limited
to provide stronger protection against brownouts and
other abnormal conditions. The feedback current, which is
sampled from the voltage feedback loop, is taken as the
reference. Once the feedback current exceeds the
threshold current, the switching frequency starts to
decrease. This green-mode function dramatically reduces
power consumption under light-load and zero-load
conditions. Power supplies using the SG6848 can easily
meet even the strictest regulations regarding standby
power consumption.
Oscillator Operation
A resistor connected from the RI pin to ground will
generate a constant current source for the SG6848. This
current is used to charge an internal capacitor. The
charge-time determines the internal clock speed and the
switching frequency. Increasing the resistance will reduce
the amplitude of the input current and reduce the
switching frequency. A 95k
resistor R
i
results in a 50uA
constant current I
i
and a 70kHz switching frequency. The
relationship between R
i
and the switching frequency is:
)
(
kHz
)
(k
R
6650
PWM
f
=
The range of the oscillation frequency is designed to
be within 50kHz ~ 100kHz.
Leading-Edge Blanking
Each time the power MOSFET is switched on, a
turn-on spike will inevitably occur at the sense-resistor.
To avoid premature termination of the switching pulse, a
250 nsec leading-edge blanking time is built in.
Conventional RC filtering can therefore be omitted.
During this blanking period, the current-limit comparator
is disabled and it cannot switch off the gate driver.
Constant Output Power Limit
When the SENSE voltage across the sense resistor R
s
reaches the threshold voltage (around 1.0V), the output
GATE drive will be turned off following a short
propagation delay t
D
. This propagation delay will
introduce an additional current proportional to t
D
*V
in
/L
p
.
The propagation delay is nearly constant regardless of the
input line voltage V
IN
. Higher input line voltages will
result in larger additional currents. At high input line
voltages, the output power limit will be higher than at low
input line voltages.
To compensate for this output power limit variation
across a wide AC input range, the threshold voltage is
adjusted by adding a positive ramp. This ramp signal rises
from 0.85V to 1.0V, and then flattens out at 1.0V. A
smaller threshold voltage forces the output GATE drive to
terminate earlier. This reduces the total PWM turn-on
time and makes the output power equal to that of low line
input. This proprietary internal compensation ensures a
constant output power limit for a wide AC input voltage
range (90VAC to 264VAC).
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| SG6848D | Low Cost Green-Mode PWM Controller for Flyback Converters |
| SG6848T | Low Cost Green-Mode PWM Controller for Flyback Converters |
| SG7883B | THREE-TERMINAL POSITIVE FIXED VOLTAGE REGULATORS |
| SG78883B | THREE-TERMINAL POSITIVE FIXED VOLTAGE REGULATORS |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SG6848D | 制造商:未知廠(chǎng)家 制造商全稱(chēng):未知廠(chǎng)家 功能描述:Low Cost Green-Mode PWM Controller for Flyback Converters |
| SG6848DY1 | 功能描述:電流型 PWM 控制器 Highly Integrated Gr Mode PWM Contrl RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| SG6848DZ | 制造商:Rochester Electronics LLC 功能描述: 制造商:Fairchild Semiconductor Corporation 功能描述: |
| SG6848DZ1 | 功能描述:電流型 PWM 控制器 Lo Cost Gr-Mode PWM Ctrl Flyback Cnvrt RoHS:否 制造商:Texas Instruments 開(kāi)關(guān)頻率:27 KHz 上升時(shí)間: 下降時(shí)間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數(shù)量:1 最大工作溫度:+ 105 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TSSOP-14 |
| SG6848T | 制造商:未知廠(chǎng)家 制造商全稱(chēng):未知廠(chǎng)家 功能描述:Low Cost Green-Mode PWM Controller for Flyback Converters |
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