Homemade low-power UPS

This is a low-power online backup power supply. IC1 constitutes a 50Hz clock generator, and outputs symmetrical but square-phase square waves from pins 10 and 11. T1 and T2 form a power amplifier circuit, which is turned on in turn, forming a pulsating current with a frequency of 50Hz on the primary side of X2, and inducing a 220-volt voltage with the same frequency on the secondary side of X2. When making it, X2 can use a (9-12 volt) power transformer with a center tap, whose low-voltage end is connected to T1 and T2, and the center tap is connected to the positive pole of the power supply. The power of the transformer is determined by actual needs, and the power of T1 and T2 must be considered. It is necessary to add a heat sink to T1 and T2. In addition, pay attention to safety during production. C3, C4, and MOV at the output end can be cancelled as needed. If the load is resistive, the oscillation frequency of IC1 can be increased, and the transformer can be replaced with a ferrite transformer to achieve higher power.