專利摘要：
A kind of programmed isolating starting system and method of a switching power supply. A pulse width modulator (PWM) is placed in the secondary circuit of the invention. The programmed isolating starting circuit provides the necessary power for controlling the IC of the PWM when the system starts. Once the system starts, the programmed isolating starting circuit does not work anymore, and the successive power is provided by the secondary output. If it is necessary to restart, the hardware and the program can automatically restart the system in the invention. At the same time, the system can be started and the working voltage can be provided via the hardware and the software even when the input voltage has a very large difference.