參數(shù)資料
型號(hào)： FSCQ0765RT
廠商： Fairchild Semiconductor Corporation
英文描述： Green Mode Fairchild Power Switch (FPS) for Quasi-Resonant Switching Converter
中文描述： 綠色模式飛兆半導(dǎo)體功率開關(guān)（FPS）的準(zhǔn)諧振開關(guān)變換器
文件頁(yè)數(shù)： 14/24頁(yè)
文件大?。?/td> 726K
代理商： FSCQ0765RT
FSCQ0765RT
14
second minimum level as shown in Figure 10, which reduces
the switching frequency. Once FSCQ0765RT enters into
extended quasi-resonant operation, the first sync signal is
ignored. After the first sync signal is applied, the sync
threshold levels are changed from 4.6V and 2.6V to 3V and
1.8V, respectively, and the MOSFET turn-on time is
synchronized to the second sync signal. The FSCQ0765RT
goes back to its normal quasi-resonant operation when the
switching frequency reaches 45kHz as the load increases.
Figure 10. Extended quasi-resonant operation waveforms
3. Feedback Control
: FSCQ0765RT employs current mode
control, as shown in Figure 11. An opto-coupler (such as the
H11A817A) and shunt regulator (such as the KA431) are
typically used to implement the feedback network.
Comparing the feedback voltage with the voltage across the
Rsense resistor plus an offset voltage makes it possible to
control the switching duty cycle. When the reference pin
voltage of the KA431 exceeds the internal reference voltage
of 2.5V, the H11A817A LED current increases, thus pulling
down the feedback voltage and reducing the duty cycle. This
event typically happens when the input voltage is increased
or the output load is decreased.
3.1 Pulse-by-pulse current limit
: Because current mode
control is employed, the peak current through the Sense FET
is limited by the inverting input of PWM comparator (Vfb*)
as shown in Figure 11. The feedback current (I
FB
) and
internal resistors are designed so that the maximum cathode
voltage of diode D
2
is about 2.8V, which occurs when all I
FB
flows through the internal resistors. Since D
1
is blocked
when the feedback voltage (Vfb) exceeds 2.8V, the
maximum voltage of the cathode of D2 is clamped at this
voltage, thus clamping Vfb*. Therefore, the peak value of
the current through the Sense FET is limited.
3.2 Leading edge blanking (LEB)
: At the instant the
internal Sense FET is turned on, there usually exists a high
current spike through the Sense FET, caused by external
resonant capacitor across the MOSFET and secondary-side
rectifier reverse recovery. Excessive voltage across the
R
sense
resistor would lead to incorrect feedback operation in
the current mode PWM control. To counter this effect, the
FSCQ0765RT employs a leading edge blanking (LEB)
circuit. This circuit inhibits the PWM comparator for a short
time (T
LEB
) after the Sense FET is turned on.
Figure 11. Pulse width modulation (PWM) circuit
4. Protection Circuit
: The FSCQ0765RT has several self
protective functions such as over load protection (OLP),
abnormal over current protection (AOCP), over voltage
protection (OVP) and thermal shutdown (TSD). OLP and
OVP are auto-restart mode protection, while TSD and AOCP
are latch mode protection. Because these protection circuits
are fully integrated into the IC without external components,
the reliability can be improved without increasing cost.
-Auto-restart mode protection
: Once the fault condition is
detected, switching is terminated and the Sense FET remains
off. This causes Vcc to fall. When Vcc falls down to the
under voltage lockout (UVLO) stop voltage of 9V, the
protection is reset and FSCQ0765RT consumes only startup
current (25uA). Then, Vcc capacitor is charged up, since the
current supplied through the startup resistor is larger than the
current that FPS consumes. When Vcc reaches the start
voltage of 15V, FSCQ0765RT resumes its normal operation.
If the fault condition is not removed, the SenseFET remains
off and Vcc drops to stop voltage again. In this manner, the
auto-restart can alternately enable and disable the switching
of the power Sense FET until the fault condition is
eliminated (see Figure 12).
-Latch mode protection
: Once protection triggers,
switching is terminated and the Sense FET remains off until
the AC power line is un-plugged. Then, Vcc continues
charging and discharging between 9V and 15V. The latch is
reset only when Vcc is discharged to 6V by un-plugging the
Ac power line.
Vsync
Vds
MOSFET Gate
2V
RO
4.6V
2.6V
3V
1.8V
ON
ON
4
OSC
Vcc
Vref
I
delay
I
FB
V
SD
R
2.5R
Gate
driver
OLP
D1
D2
+
V
fb
*
-
Vfb
KA431
C
B
Vo
H11A817A
R
sense
SenseFET
相關(guān)PDF資料
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
FSCQ0765RTYDTU 功能描述:軟開關(guān) PWM 控制器 7A/650V QRC Power Switch RoHS:否 制造商:Fairchild Semiconductor 輸出端數(shù)量: 輸出電流: 開關(guān)頻率: 工作電源電壓:30 V 電源電流: 最大工作溫度:+ 105 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
FSCQ0965RT 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Green Mode Fairchild Power Switch (FPS TM)
FSCQ0965RTYDTU 功能描述:軟開關(guān) PWM 控制器 POWER_CONVERSION RoHS:否 制造商:Fairchild Semiconductor 輸出端數(shù)量: 輸出電流: 開關(guān)頻率: 工作電源電壓:30 V 電源電流: 最大工作溫度:+ 105 C 最小工作溫度:- 40 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel
FSCQ1265RT 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Green Mode Fairchild Power Switch (FPS TM)
FSCQ1265RTYDTU 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 12A/650V QRC Power Switch RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel
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