The switching regulator keeps the output voltage stable by controlling the transistor to switch between ON state and OFF state (switching action). When the transistor is completely ON, Vce (sat) <=1V, and the collector-emitter voltage Vce of the transistor is very small. At this time, even if the collector current Io flows through the transistor, it will not cause excessive power loss.

In addition, when the switching regulator is in the OFF state, there is no collector current, and of course, there is no power loss. This is the main reason for the small power loss of the switching regulator.

Switching regulators are supplied on demand and non-series regulators are always supplied.

The current output of the switching circuit is not DC, and it needs to be connected to the rectified smooth current behind it to convert the pulsating current into DC current.

The rectifier and smoothing circuit of the switching regulator have two types: capacitor input type and choke coil input type, which need to be flexibly used according to the circuit mode of the switching regulator.

The step-down chopper switching regulator uses a choke coil input, while the step-up chopper and reverse polarity chopper switching regulators use a capacitor input.

Supply ON demand (adjust the ON and OFF ratio of the transistor), you can get any value of DC, stable output voltage.

A switching regulator that does not pass through a power transformer but inputs AC directly to the power supply is usually called a linear adjustable power supply or off-line converter.

Linear adjustable type switching regulator structure, a. Self-excited b. Separately excited.

Self-excited type, continuous oscillation generated by switching transistor and output transformer. The composition of the circuit is simple and only suitable for devices with low power output.

Separately excited, there is an oscillator in the control circuit, the circuit structure is complex but the characteristics are good, suitable for high-power equipment.

The linear adjustable switching regulator contains an output transformer, and the input and output must be isolated to avoid induced voltage.

Usually the switching frequency of the switching transistor is set outside the human hearing frequency, more than 20KHz.