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A switched-mode power supply (switching-mode power supply, SMPS, or just switcher) is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power. Like other kinds of power supplies, an SMPS transfers power from a source like the electrical power grid to a load (e.g., a individual computer) whilst converting voltage and current characteristics. An SMPS is usually employed to efficiently supply a regulated output voltage, generally at a level diverse from the input voltage. Unlike a linear power supply, the pass transistor of a switching mode supply switches very quickly (typically between 50 kHz and 1 MHz) between full-on and full-off states, which minimizes wasted energy. Voltage regulation is supplied by varying the ratio of on to off time. In contrast, a linear power supply should dissipate the excess voltage to regulate the output. This higher efficiency will be the chief benefit of a switched-mode power supply.

An H bridge is an electronic circuit that enables a voltage to be applied across a load in either direction. These circuits are usually applied in robotics and various applications to enable DC motors to move forwards and reverse. H bridges are ready as integrated circuits (IC chip – for example: L298N), or can be built from discrete components (transistors).

General
The term H bridge is derived from the typical graphical representation of such a circuit. An H bridge is built with four switches (solid-state or mechanical). When the switches S1 and S4 (based on the first figure) are closed (and S2 and S3 are open) a positive voltage will probably be applied across the motor. By opening S1 and S4 switches and closing S2 and S3 switches, this voltage is reversed, allowing reverse operation of the motor.

This is the another 300W inverter circuit diagram… This circuit uses many power transistors to get high power output before the transformer stepping up the high current-low voltage input to become low current-high voltage output.

Good luck… build this inverter with your own risk.