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U1 is a low cost Switched Mode Power Supply (SMPS) controller IC intended for flyback
topologies.U1 operates in fixed frequency mode. To reduce EMI, frequency jitter has been
implemented. For Continuous Conduction Mode (CCM) operation, slope compensation is
integrated. The controller can be set to accept an over-power situation for a limited amount of time.
In a typical application the mains input voltage can be detected by the VSENSE pin. As long
as the voltage on VSENSE has not reached the Vstart(VSENSE) voltage (typ.0.93V), switching is
inhibited. When during operation the VINSENSE voltage drops below Vlow(VSENSE) (typ. 0.69V)
or exceeds Vhigh(VSENSE) (typ.3.5V), the converter stops switching and performs a restart.If the
pin is left open or disconnected, the pin is pulled up by the internal 20nA (typ.) current source and
subsequently the Vhigh(VSENSE) level is reached. This will than trigger a restart protection. An
internal clamp of 4.6 volts (typ.) protects this pin from excessive voltages.
In the example given, the PROTECT pin (pin 6) is used for over-voltage protection (OVP) .
The OVP level is VCC = 25.8 V, The VSENSE pin (pin 5) is used for mains under voltage lock-out
and is set by R5,R6,R7 and R8 to about 80 Vac. The over-power protection time,defined by C10, is
set to 60msec.The restart time, defined by C10 and R25, is set to 0.5 sec.R18 and C13 define the
soft-start time. R18 is added to prevent the soft-start capacitor from being charged during normal
operation due to negative voltage spikes across the current sense resistor R22,C14 is added to
reduce the noise on the CTRL pin. R19 reduces the peak current to C5. U1 control 12V output ,
U2,U402,U201,Q201,Q202,Q204,Q205,Q401,Q402,L201, construct buck circuit to output 12V.
The function of LED Driver circuit is control backlight(on/off) as received AC
signal(on/off). When AC on, LED Driver circuit will output a low voltage to main board, and
main board will drive backlight on. Vice versa for AC off, LED Driver circuit will output a high
voltage to main board, and main board will turn off backlight.
U301 is the SSC9522S is the present specifications shall apply to a Monolithic IC
type SSC9522S for switching regulators
Pin1 is Vsen: Detection of input AC line voltage terminal, Detection of input AC line
voltage.Pin2 is VCC: Power supply terminal,Supply voltage for control. Pin3 is FB: Feed
back terminal,Control for output/detection of over load.Pin5 is Css: Soft start capacitor
terminal, Terminal for connection of capacitor for soft start.
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