Why does switching power supply need feedback winding power supply?

Switching power supply is divided into self-excited type and other-excited type. Self-excited type only needs feedback winding to provide excitation pulse signal. It is exciting because it needs an independent control chip to work. The chip needs a DC power supply to work. At the beginning of startup, most power supplies step down the DC high voltage of 300V through a power resistor and provide it to the chip. When the chip outputs multiple pulses, the feedback winding can provide normal power. Because in normal operation, the power consumption of the chip is also large. If the resistance is directly used to reduce the voltage, it will easily lead to unstable operation. Therefore, all other excitation power supplies are powered by feedback windings.

Of course, an external power supply can also be used to supply power to the switch chip alone. But in that case, the cost will be high.