参数资料
型号: FSQ0465RUWDTU
厂商: Fairchild Semiconductor
文件页数: 12/22页
文件大小: 0K
描述: IC SWIT PWM GREEN UVLO HV TO220F
产品变化通告: Product Discontinuation 27/Feb/2012
标准包装: 400
系列: FPS™
输出隔离: 隔离
频率范围: 59.6kHz ~ 75.8kHz
输入电压: 8.5 V ~ 21 V
输出电压: 650V
功率(瓦特): 60W
工作温度: -25°C ~ 85°C
封装/外壳: TO-220FL
供应商设备封装: TO-220F-6L(成形)
包装: 管件
产品目录页面: 1222 (CN2011-ZH PDF)
Functional Description
1. Startup : At startup, an internal high-voltage current
source supplies the internal bias and charges the
external capacitor (C a ) connected to the VCC pin, as
illustrated in Figure 22. When V CC reaches 12V, the
FPS? begins switching and the internal high-voltage
current source is disabled. The FPS continues its normal
switching operation and the power is supplied from the
auxiliary transformer winding unless V CC goes below the
stop voltage of 8V.
V DC
C VCC
2.1 Pulse-by-Pulse Current Limit : Because current-
mode control is employed, the peak current through the
SenseFET is limited by the inverting input of PWM
comparator (V FB *), as shown in Figure 23. Assuming
that the 0.9mA current source flows only through the
internal resistor (3R + R = 2.8k), the cathode voltage of
diode D2 is about 2.5V. Since D1 is blocked when the
feedback voltage (V FB ) exceeds 2.5V, the maximum
voltage of the cathode of D2 is clamped at this voltage,
clamping V FB *. Therefore, the peak value of the current
through the SenseFET is limited.
2.2 Leading-Edge Blanking (LEB) : At the instant the
internal SenseFET is turned on, a high-current spike
usually occurs through the SenseFET, caused by
primary-side capacitance and secondary-side rectifier
3
V CC
6
V STR
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
I start
FPS employs a leading-edge blanking (LEB) circuit. This
circuit inhibits the PWM comparator for a short time
8V/12V
V cc good
V REF
(t LEB ) after the SenseFET is turned on Pulse-Width-
Modulation (PWM) Circuit
Internal
FSQ0465 Rev.00
Figure 22. Startup Circuit
Bias
3. Synchronization : The FSQ-series employs a quasi-
resonant switching technique to minimize the switching
noise and loss. The basic waveforms of the quasi-
resonant converter are shown in Figure 25. To minimize
2. Feedback Control : FPS employs current-mode
control, as shown in Figure 23. An opto-coupler (such as
the FOD817A) and shunt regulator (such as the KA431)
are typically used to implement the feedback network.
Comparing the feedback voltage with the voltage across
the R sense resistor makes it possible to control the
switching duty cycle. When the reference pin voltage of
the shunt regulator exceeds the internal reference
the MOSFET's switching loss, the MOSFET should be
turned on when the drain voltage reaches its minimum
value, which is indirectly detected by monitoring the V CC
winding voltage, as shown in Figure 24.
V ds
V RO
voltage of 2.5V, the opto-coupler LED current increases,
pulling down the feedback voltage and reducing the duty
cycle. This typically happens when the input voltage is
increased or the output load is decreased.
V CC
V REF
I delay
I FB
V sync
V DC
T F
V RO
V ovp (8V)
V O
H11A817A
V FB
C B
4
D1
D2
3R
OSC
SenseFET
1.2V
1.0V
+
V FB *
R
Gate
driver
MOSFET Gate
230ns Delay
KA431
-
V SD
OLP
R sense
ON
ON
FSQ0465 Rev.00
FSQ0465 Rev.00
Figure 23. Pulse-Width-Modulation (PWM) Circuit
? 2009 Fairchild Semiconductor Corporation
FSQ0465RU Rev. 1.0.0
12
Figure 24. Quasi-Resonant Switching Waveforms
www.fairchildsemi.com
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