Friday, December 25, 2015

SHARP LL-171A-W/B POWER SUPPLY CIRCUIT - SG6841

SHARP LL-171A-W/B

Resetting all adjustment values.
While pressing MENU + MODE DOEN , turn on the power.
ADJUSTMENT menu reset
Press MENUE + LEFT ARROW  simultaneously.
Adjustment lock and lock release
While pressing MENU  , turn on the power.
Version display (for service)
1. Press and hold down both the MENU button and the RIGHT ARROW button (VOL/ BRIGHT) on the system unit while pressing the POWER button on the system unit, to turn on the power supply of the system. Hold the three buttons down until the version is displayed on screen.
2. The software version and checksum appears on screen.
3. Turn off the power supply of the system or terminate the display of the version by pressing the MENU button on the system unit.
Execute All reset.
Hold down the [MENU] + [MODE] buttons and press the [POWER] button. All reset is executed and the [ENGLISH] OSD is displayed.
SG6841 PWM CONTROLLER DESCRIPTION
This highly integrated PWM controllers, SG6841 series, provides several features to enhance the performance of low power flyback converters. To minimize standby power consumption, the proprietary green-mode function provides off-time modulation to linearly decrease the switching frequency under light-load conditions. This green-mode function assists the power supply to easily meet the power conservation requirement. Due to BiCMOS process, the start-up current and operation current is reduced to 30uA and 3mA, respectively, to improve power conversion efficiency. Large start-up resistance can be used for further power saving. Built-in synchronized slope compensation ensures the stability of peak current mode control. A proprietary internal compensation ensures
constant output power limit for universal AC input voltage from 90VAC to 264VAC. SG6841 provides many protection functions. Pulse by pulse current limit ensures a constant output current under short circuit. If a short circuit failure or over load happens, the SG6841 will shut off after a continuous high voltage detection on FB pin. The gate output is clamped at 18V to protect the power MOS from over voltage damage. An external NTC thermistor can be applied to sense the ambient temperature for over-temperature protection. The SG6841 series are available in 8-pin DIP and SO packages.
PIN CONFIGRATION
1 GND
Ground Ground.
2 FB Feedback
The signal from external compensation circuit is feed into this pin. The PWM duty cycle is determined by this FB pin and current sense signal from Pin 6.
 3 VIN Start-Up Input
This pin is pulled high to the rectified line input through a resistor for start-up. Since the start-up current requirement for SG6841 is very small, a large start-up resistance can be used to minimize power loss. Under normal operation, this pin is also used to detect line voltage to compensate for constant output power limit for universal AC input.
4 Ri Reference Setting
A resistor from RI pin to ground will generate a constant current source forSG6841. This current is used to charge an internal capacitor and hence the switching frequency are determined. Increasing the resistance will decrease the current source and reduce the switching frequency. A 26kΩ resistor Ri creates a 50uA constant current Ii and generates 65kHz switching frequency.
5 RT Temperature Protection
For over-temperature protection. An external NTC thermistor is connected from this pin to ground. The impedance of the NTC will decrease under high temperature. Once the voltage on RT pin drops below a fixed limit, the PWM output will be disabled.
6 SENSE Current Sense
Current sense. The sensed voltage is used for current mode control and pulse-by-pulse current limiting.
7 VDD Power supply
Power Supply.
8 GATE Driver Output
The totem-pole output driver for the power MOSFET. A soft driving waveform is implemented to improve EMI.
POWER SUPPLY CIRCUIT 
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