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參數(shù)資料
| 型號(hào)： | SG6741 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Highly-Integrated Green-Mode PWM Controller |
| 中文描述： | 高度集成的綠色模式PWM控制器 |
| 文件頁(yè)數(shù)： | 9/13頁(yè) |
| 文件大?。?/td> | 623K |
| 代理商： | SG6741 |
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Product specification
Highly-Integrated Green-Mode PWM Controller
Operation Description
Start-up Current
SG6741
System General Corp.
Version 1.2.1 (IAO33.0047.B2)
- 9 -
www.sg.com.tw www.fairchildsemi.com
September 19, 2007
For start-up, the HV pin is connected to the line input or
bulk capacitor through an external resistor, R
HV
, which is
recommended as 100K
. Typical start-up current drawn
from pin HV is 2mA and it charges the hold-up capacitor
through the resistor R
HV
. When the V
DD
capacitor level
reaches V
DD-ON
, the start-up current switches off. At that
moment, the V
DD
capacitor only supplies the SG6741 to
maintain the V
DD
before the auxiliary winding of the main
transformer to carry on provide the operating current.
Operating Current
Operating current is around 4mA. The low operating
current enables better efficiency and reduces the
requirement of V
DD
hold-up capacitance.
Green-Mode Operation
The patented green-mode function provides an off-time
modulation to reduce switching frequency in light-load
and no-load conditions. The on time is limited for better
abnormal or brownout protection. VFB, which is derived
from the voltage feedback loop, is used as the reference.
Once VFB is lower than the threshold voltage, switching
frequency is continuously decreased to the minimum
green-mode frequency, around 22KHz (R
I
=26K
).
Oscillator Operation
A resistor connected from the RI pin to GND generates a
constant current source for the SG6741 controller. This
current is used to determine the center PWM frequency.
Increasing the resistance reduces PWM frequency. Using
a 26K
resistor, R
I
, results in a corresponding 65KHz
PWM frequency. The relationship between R
I
and the
switching frequency is:
(KHz)
1690
)
(K
R
Ω
=
PWM
f
---------------------
(1)
The range of the PWM oscillation frequency is designed
as 47kHz ~ 109kHz.
Current Sensing / PWM Current Limiting
Peak-current-mode control is utilized in SG6741 to
regulate output voltage and provide pulse-by-pulse
current limiting. The switch current is detected by a sense
resistor into the SENSE pin. The PWM duty cycle is
determined by this current-sense signal and V
FB
, the
feedback voltage. When the voltage on the SENSE pin
reaches around V
COMP
= (V
FB
–1.2)/3.2, the switch cycle is
terminated immediately. V
COMP
is internally clamped to a
variable voltage around 0.85V for output power limit.
Leading-Edge Blanking
Each time the power MOSFET is switched on, a turn-on
spike occurs on the sense-resistor. To avoid premature
termination of the switching pulse, a leading-edge
blanking time is built in. During this blanking period, the
current-limit comparator is disabled and cannot switch off
the gate driver.
Under-Voltage Lockout (UVLO)
The turn-on and turn-off thresholds are fixed internally at
16.5V/10.5V. During start-up, the hold-up capacitor must
be charged to 16.5V through the start-up resistor so that
IC is enabled. The hold-up capacitor continues to supply
V
DD
before the energy can be delivered from auxiliary
winding of the main transformer. V
DD
must not drop
below 10.5V during this start-up process. This UVLO
hysteresis window ensures that hold-up capacitor is
adequate to supply V
DD
during start-up.
Gate Output / Soft Driving
The SG6741 BiCMOS output stage is a fast totem pole
gate driver. Cross conduction has been avoided to
minimize heat dissipation, increase efficiency, and
enhance reliability. The output driver is clamped by an
internal 18V Zener diode to protect power MOSFET
transistors against undesirable gate over-voltage. A soft
driving waveform is implemented to minimize EMI.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SG6741 WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| SG6741_08 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG6741A | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Highly Integrated Green-Mode PWM Controller |
| SG6741ASY | 功能描述:電流型 PWM 控制器 Highly Integrated Gr Mode PWM Controller RoHS:否 制造商:Texas Instruments 開關(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 |
| SG6741ASZ | 功能描述:電流型 PWM 控制器 Highly-Integrated Green-Mode PWM Cont. RoHS:否 制造商:Texas Instruments 開關(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 |
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