An overvoltage problem

shaorc

An overvoltage problem [Copy link]

[Ask if you don't understand] The following figure is a partial schematic diagram of a flyback switching power supply. The P and NE in the upper part are the two ends of the DC bus capacitor, and the circuit detects whether it is overvoltage. The lower part is the primary side of the flyback switching power supply. When the input AC is more than 300 volts, it is rectified and input to the PN bus at about 450VDC, but an error will be reported, reporting undervoltage (DC-OV signal in the figure). The solution now is to reduce a 100k resistor from the vcc pin of 3844, and that's it. What is the principle of this solution? Now we know that the 3844 power supply is first supplied through the winding, and then through the DC bus through several resistors in series to supply power to the vcc.

sngef

These 100K resistors are used for starting. The normal power supply is provided by the winding of the transformer. From your description, the starting voltage is too low. It may be caused by the change of the resistor value.