Green Mode Fairchild Power Switch (FPSTM) for
Quasi-Resonant Switching Converter
• Optimized for Quasi-Resonant Converter (QRC)
• Advanced Burst-Mode operation for under 1 W standby
• Pulse by Pulse Current Limit (5A)
• Over load protection (OLP) - Auto restart
• Over voltage protection (OVP) - Auto restart
• Abnormal Over Current Protection (AOCP) - Latch
• Internal Thermal Shutdown (TSD) - Latch
• Under Voltage Lock Out (UVLO) with hysteresis
• Low Startup Current (typical : 25uA)
• Low Operating Current (typical : 4mA)
• Internal High Voltage SenseFET
• Built-in Soft Start (20ms)
• Extended Quasi-resonant Switching for Wide Load Range
• DVD Receiver
• Audio Power Supply
OUTPUT POWER TABLE
Table 1. Notes: 1. Maximum practical continuous power
in an open frame design at 50°C ambient. 2. 230 VAC or
100/115 VAC with doubler.
In general, Quasi-Resonant Converter (QRC) shows lower
EMI and higher power conversion efficiency compared to the
conventional hard switched converter with a fixed switching
frequency. Therefore, it is well suited for applications that are
sensitive to the noise, such as color TV and audio. The
FSCQ0765RT is an integrated Pulse Width Modulation
(PWM) controller and Sense FET specifically designed for
Quasi-resonant off-line Switch Mode Power Supplies
(SMPS) with minimal external components. The PWM
controller includes integrated fixed frequency oscillator, under
voltage lockout, leading edge blanking (LEB), optimized gate
driver, internal soft start, temperature compensated precise
current sources for a loop compensation and self protection
circuitry. Compared with discrete MOSFET and PWM
controller solution, it can reduce total cost, component count,
size and weight simultaneously increasing efficiency, produc-
tivity, and system reliability. This device is a basic platform
well suited for cost effective designs of Quasi resonant
switching flyback converters.
Figure 1. Typical Flyback Application
©2004 Fairchild Semiconductor Corporation
Internal Block Diagram
4.6V/2.6V : Normal QR
3.0V/1.8V : Extended QR
Power off Reset
Figure 2. Functional Block Diagram of FSCQ0765RT
Pin Function Description
High voltage power SenseFET drain connection.
This pin is the control ground and the SenseFET source.
This pin is the positive supply input. This pin provides internal operating
current for both start-up and steady-state operation.
This pin is internally connected to the inverting input of the PWM comparator.
The collector of an opto-coupler is typically tied to this pin. For stable
operation, a capacitor should be placed between this pin and GND. If the
voltage of this pin reaches 7.5V, the over load protection triggers resulting in
shutdown of the FPS.
This pin is internally connected to the sync detect comparator for quasi
resonant switching. In normal quasi-resonant operation, the threshold of the
sync comparator is 4.6V/2.6V. Meanwhile, the sync threshold is changed to
3.0V/1.8V in extended quasi-resonant operation.
Figure 3. Pin Configuration (Top View)
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