Absolutely usable switching power supply: Sanyo 80P power supply

Movements using Sanyo 80P switching power supply include: Sanyo CTP-3515, CTP-3525, CYP3915, CTP6916, CTP6921, CTO3227, Kunlun S371, Shanghai Z651-1 and Kangyi color TV, etc.

The 300V voltage of the oscillation circuit
is added to the B pole of the switching tube Q504 through R518 and R519, and Q504 starts to conduct. Pins (9) and (10) of T501 are positive feedback windings. The polarity of the positive feedback voltage is (9) positive (10) negative. The positive feedback is formed through the B and E poles of Q504, R516, R515 and D509, making Q504 quickly saturation.
After Q504 is saturated, the primary winding current of T501 increases linearly. This linearly increased current generates an upper negative and lower positive sawtooth wave voltage drop on R514. This voltage drop is sent to the B pole of Q502 through R505 and C507, and the sawtooth wave voltage Superimposed on the 6.8V DC voltage of Q502B pole. When the B pole voltage of Q502 is lower than a certain value, Q502 is turned on, making the left end of C510 almost grounded, and the negative voltage on the right end of C510 makes Q504 cut off.
After Q504 is cut off, the polarity of the induced voltage in each winding of T501 is completely reversed, and the secondary winding turns on D510 and D511. After being filtered by C515 and C518, the current voltages of 12V and 111V are obtained.
The cutoff of Q504 is maintained by the (10) positive (9) negative feedback voltage generated by the (10) and (9) windings of T501 through D508 and C510. At the same time, C510 is charged, generating left positive and right negative voltages (about 4V) , at the same time, T501 level (7), (1) windings and C511, R517 and C506 produce free oscillation. After half a cycle, the polarity of the induced voltage of each winding in T501 flips again, and Q504 enters the saturation state again, so The cycle forms an oscillation.

During the voltage stabilization process
, Q501 and peripheral components constitute a sampling voltage stabilizing circuit. Pins (11) and (12) of T501 are error voltage sampling windings. Normally, the voltage on C508 is 30V. Obviously, changes in the output voltage will be reflected on C508. Come out, the E pole of Q501 is connected to the reference voltage, and the sampled voltage is divided by R506, VR501, and R507 and then sent to the B pole of Q501, thus controlling the conduction degree of Q501, which also controls the potential of the B pole of Q502, thus controlling the The length of the Q504 conduction period also controls the output voltage. Adjusting VR501 can change the output voltage.
D506 is a protection tube. When the B-pole voltage of Q502 is greater than 9V, D506 breaks down and conducts, Q502 also conducts, and the switching tube Q504 stops oscillating.