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The 1207AP is voltage mode control, which has the advantages of high efficiency, energy saving and high reliability. After 300v voltage is sent to pin (8) of 1207AP through R648 and enters the integrated block, it is divided into two channels, one of which is added to the drive circuit inside the integrated block as the operating voltage of the drive circuit, and the other one is charged to the external capacitor C622 of pin (6) through the constant current source circuit. When the voltage of pin (6) reaches 12.5V, 1207AP starts working. Output the excitation pulse from pin (5) to the gate of switch tube q601, switch tube starts to work, T601 (12) pin through (D601) rectifier filter, R615 R627 VR601 R633 IC605 sampling voltage regulator through the photoelectric coupler to IC601 (2) pin feedback, The T601(12) pin rectifier filter outputs stable B 140v line voltage, (14) pin rectifier filter outputs line field working voltage, and (15) pin rectifier filter outputs 5V-1, 5V-2, 8.2V working voltage.