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参数资料
| 型号： | SG5701DZ_SB82166 |
| 厂商： | Fairchild Semiconductor |
| 文件页数： | 8/13页 |
| 文件大小： | 0K |
| 描述： | IC REG CTRLR FLYBK ISO PWM 8-DIP |
| 产品变化通告： | Product Discontinuation 27/Feb/2012 |
| 标准包装： | 59 |
| PWM 型： | 电流模式 |
| 输出数： | 1 |
| 频率 - 最大： | 75kHz |
| 占空比： | 80% |
| 电源电压： | 11.7 V ~ 24 V |
| 降压： | 无 |
| 升压： | 无 |
| 回扫： | 是 |
| 反相： | 无 |
| 倍增器： | 无 |
| 除法器： | 无 |
| Cuk： | 无 |
| 隔离： | 是 |
| 工作温度： | -30°C ~ 105°C |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 包装： | 管件 |
Product Specification
Low Cost Green-Mode PWM Controller for Flyback Converters
SG5701
OPERATION DESCRIPTION
SG5701 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 SG5701 series.
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:
Start-up Current
f PWM =
6650
R I (k ? )
( kHz )
The start-up current is only 10uA. 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
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
200 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.
reduces the V cc hold-up capacitance requirement.
Constant Output Power Limit
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 SG5701 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 SG5701. This
current is used to charge an internal capacitor. The
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).
? System General Corp.
Version 1.0(IAO33.0025.B1)
-8-
www.sg.com.tw
Mar. 28, 2006
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