Principle of DC voltage step-up and step-down conversion

DC-DC circuit principle:

DC-DC is the abbreviation of direct current to direct current in English, so a DC-DC circuit is a circuit that converts a DC power supply into different voltage values. DC-DC is a branch of switching power supply technology, which includes two branches: AC-DC and DC-DC. DC-DC circuits are divided into the following according to their functions:

Boost Converter: A circuit that converts a low voltage into a higher voltage.

Buck Converter: A circuit that converts a high voltage into a low voltage.

Inverter: A circuit that changes the polarity of voltage. There are two types: changing positive power supply to negative power supply and changing negative power supply to positive power supply.

There are three main branches. Of course, when applied, functions such as boost and reverse, buck and boost will exist simultaneously in the same circuit.

The basic circuits of DC-DC converters include boost converter, buck converter, and boost-boost converter.

The schematic diagram of the buck converter is shown in Figure 1. When the switch is closed, the voltage across the inductor is (Vi-Vo). At this time, the inductor is excited by the voltage (Vi-Vo), and the increased magnetic flux of the inductor is: (Vi-Vo)*Ton.

When the switch is turned off, due to the continuity of the output current, the diode VD becomes conductive, the inductor is magnetized, and the magnetic flux reduced by the inductor is: (Vo)*Toff.

When the switch closed and the switch opened states reach a balance, (Vi-Vo)*Ton=(Vo)*Toff. Since the duty cycle D<1, Vi>Vo, achieving the voltage reduction function.

Figure 1 Schematic diagram of a buck converter

The schematic diagram of the boost converter is shown in Figure 2. When the switch is closed, the input voltage is applied to the inductor. At this time, the inductor is excited by the voltage (Vi), and the increased magnetic flux of the inductor is: (Vi)*Ton.

When the switch is turned off, due to the continuity of the output current, the diode VD becomes conductive, the inductor is magnetized, and the magnetic flux reduced by the inductor is: (Vo- Vi)*Toff.

When the switch closing and switch opening states reach equilibrium, (Vi)*Ton=(Vo- Vi)*Toff. Since the duty cycle D<1, Vi.

Figure 2 Schematic diagram of boost converter

The buck-boost converter, with opposite input and output polarities, is shown in Figure 3. When the switch is closed, the inductor is excited by the voltage (Vi), and the magnetic flux increased by the inductor is: (Vi)*Ton; when the switch is open, the inductor is magnetized, and the magnetic flux reduced by the inductor is: (Vo)*Toff. When the state of the switch closing and the state of the switch opening reach a balance, the increased magnetic flux is equal to the reduced magnetic flux, (Vi)*Ton=(Vo)*Toff, depending on the value of Ton to Toff, ViVo may be possible.

Figure 3 Schematic diagram of buck-boost converter