DNC-X50E special switching power supply

This is the working principle diagram of the switching power supply . Its circuit composition and main working principle are basically the same as Figure 7-31
, and are only briefly introduced below. In the figure, VT4 and VTs are switching tubes controlled by the excitation transformer Tz.
Its output is stepped down by the pulse transformer T3, and its secondary output voltage is output after bridge rectification, voltage stabilization, and filtering to
two groups positive and negative symmetrical DC power supply, one of which is ±18V and the other is ±50V.
    The integrated control module in the circuit uses the CF8865 special module, which is equivalent to the 62880 module in Figure 7-31.
    CF8865 can generate 120kHz oscillation pulse, which is output from pins 3 and 4 of the module and drives the switching
tubes VT4 and VTs to work through the excitation transformer T. Pin 9 of CF8865 is the output voltage adjustment terminal, and RPi is the adjustment potentiometer. The adjustment is,
that is, The output voltage value can be changed 0. Pin 8 is the input terminal ol of the output voltage error sampling voltage, and pin 2 is the mains voltage input
fluctuation sampling control input terminal. Since pin 3.4 of CF8865 in addition to outputting push pulses to the excitation transformer Tz,
VT4 and VTs In addition to on and off, another winding is also used to promote the on and off of vrl. When the mains voltage fluctuates,
the 300V DC voltage output by the rectifier will also fluctuate, so that VTi conducts and cuts off at both ends of the primary winding of Ti.
The amplitude of the formed pulse will also fluctuate, and the amplitude of the negative voltage generated after it is coupled to the secondary and rectified by VD4 will also fluctuate,
causing the potential difference between pins 2 and 1 to change. After being detected by the internal circuit To control the width of the push pulse output by pins 3 and 4 , and finally achieve voltage stabilization control of the output voltage
fluctuations caused by mains fluctuations .