4. Electronic Circuit Theory
4.1 Switching Mode Power Supply
4.1.1 AC Current Input Circuit
P801 is a connector for connecting AC Power. F801 is a fuse to protect all the circuit. AC
input voltage is from90V to 264V. R801and R802 joined between two inputting main circuit
to prevent man from shock. L801 is used to clear up low frequency wave. C801 and C802
are used to discharge the waves that L801 produced. High frequency waves are damped
by C801 and C802. D801 is a rectifier which composed of 4 build-in diodes, it invertsAC to
DC.
4.1.2 High Voltage to Low Voltage Control Circuit
C804 is used to smooth the wave from rectifier. IC802 is a highly integrated PWM
controller, which build-in a power MOSFET. When rectified DC high voltage is applied to
the DRAIN pin during start-up, the MOSFET is off initially, and the CONTROL pin
capacitor is charged through a switched high voltage current source connected internally
between the DRAIN and CONTROL pins. When the CONTROL pin voltage Vc reaches
approximately 5.8V, the control circuitry is activated and the soft-start begins. The
soft-start circuit gradually increases the duty
cycle of the MOSFET from zero to the maximum value over approximately 10ms. If no
external feedback/supply current is fed into the CONTROL pin by the end of the soft-start,
the high voltage current source is turned off and the CONTROL pin will start discharging in
response to the supply current drawn by the control circuitry.Resistors R814 are for
external current limit adjustment, and used to reduce the current limit externally to a value
close to the operating peak current of primary about 1.35A. The mean
is power will protected when the primary current over about 1.35A.When PWM is turned
off, the main current flow will be consumed through D802 and ZD802, This will prevent
MOSFET which built-in IC802 from being damaged under large current impulse and
voltage spike. IC801 provide internal Auxiliary current to CONTROL pin during normal
operation. In addition, error amplifier and feedback current to the CONTROL pin are for
duty cycle control.
4.1.3 DC_5V and DC_19V Output Circuit
For DC 5V, D807,D808 and D809 is used to rectify the inducted current. C817 C818
C830and L802 C820 are used to store energy when current is reversed. The parts
including C817 C818 C830and L802 C820 are used to smooth the current waves. For DC
19V, D804 and D805 is used to rectify the inducted current. C816 and C825 are used to
store energy when current is reversed. The parts including C816, C825 are used to
smooth the current waves.
Confidential - Do Not Copy
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X2450W/WM
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LED-1
ViewSonic Corporation
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Содержание VS13518-1W
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