Pic1 and internal oscillator through the outer connected capacitor charging and discharging generate triangle wave oscillation pulse and oscillation frequency by 1 foot and the foot of timing resistance and timing capacitor decided. Oscillation pulse added to PICl inside the PWM comparator and and and and in the other three voltage comparator: compare the CS pin voltage, the FB pin voltage and reference voltage, further enlarged by the push-pull circuit PWM drive pulse output by the feet, by the gate of PD4, PRl3, PRl4 added to PFETl, PFETl into a state of oscillation. Due to PRll, PRl2 power supply circuit in the start current is small, when the PFETl oscillation switch transformer pT1 each winding products electromotive force (EMF), PTL feedback at both ends of the winding electric potential students to form a stable DC voltage through diode PD3 rectifier, PCE3 filter, through a resistance PRl7 toward the foot of the PICl provides working voltage, make the circuit work stable and reliable.

The voltage regulator circuit is composed of an error detection amplifier PIC3, a photoelectric coupler PIC2 and a PICl, and so on. + 5V voltage of secondary winding path through a PR79, PR 25, 26 and to PIC3 (R) end as the sampling voltage. Another way to PIC2 provides working voltage. When some reason to + 5V voltage increase, PIC3 r end of the pin voltage increased, decreased PIC3 K terminal voltage, the PIC2 light emitting diode current increases, luminous tube to emit light intensity increases, PIC2 3, 4 feet resistance decreases. PICl II the pin voltage drops, the PICl internal error after amplification by the foot PICl output PWM drive pulse width becomes narrower and PFETl guide through time is shortened, the secondary voltage drop; for some reason the + 5V voltage drop when the change in the process, the output voltage rise. Through the adjustment of the PWM drive pulse, the output voltage of the various output voltage is kept stable. When the output voltage due to overload or short circuit and greatly decreased, + 5V voltage will also decline, PICl II pin voltage is increased. When the voltage is increased to 2 feet PICl connected to the internal comparator and a voltage reference 2.8V, the pin voltage increases, when the pin voltage exceeds the 7.0v, PICl internal bias circuit is switched off, PICl into lock mode and shut off the output, in order to achieve overload protection.

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