Schematic diagram of polarity conversion chopper type switching regulated power supply

As the name implies, the polarity-reversing power supply output voltage is the opposite of the input voltage, but this is only one aspect of the problem. The absolute value of the output voltage must also be higher than the absolute value of the input voltage, otherwise it will be confused with a step-down switching power supply. It is not difficult to see from this that the polarity-conversion chopper switching power supply is a combination of buck and boost power supplies.

The picture shows the principle diagram of the polarity conversion chopper type switching regulated power supply. When the switching adjustment component transistor VT is turned on, the input voltage Ui is added to the inductor L to generate current, store energy, and the diode VD is reversely cut off. When the transistor VT is turned off, the current on the inductor L gradually decreases, and the polarity of the induced electromotive force is shown in the figure. The induced electromotive force makes the diode VD conduct and charges the capacitor C, and the output voltage Uo on the capacitor C is opposite in polarity to the input voltage Ui. When the voltage on the load is about to drop, capacitor C discharges the load again. At this time, the output voltage Uo can be made higher than the input voltage Ui.

Schematic diagram of boost chopper switching regulated power supply

The switching power supply whose absolute value of the output voltage is lower than or equal to the absolute value of the input voltage is a step-down type. The absolute value of the output voltage of the boost chopper switching regulated power supply must be higher than the absolute value of the input voltage and their polarities must be the same.
The figure is a schematic diagram of a boost chopper switching regulated power supply. When the switching adjustment element is controlled to be saturated and turned on, the current flows through the inductor, which makes it store energy. When the switching element VT is controlled to be turned off, the energy stored in the inductor is supplied to the load through the diode VD, and the capacitor C is charged at the same time. When the load voltage is about to drop, the capacitor discharges again. At this time, a stable voltage higher than the input can be obtained. Because the switching element VT is connected in parallel with the load RL, it is also called a parallel switching power supply.