What is a Switching Regulator?

Switching regulators use an output stage to repeatedly switch between "on" and "off" states to produce an output voltage with energy storage components (capacitors and inductors). Its adjustment is realized by adjusting the switching timing according to the feedback samples of the output voltage.

Chinese name: Switching regulator

Foreign name: switching regulator

In a fixed-frequency regulator, the output voltage is controlled by adjusting the high and low level time duty cycle in a cycle. It is assumed that it is turned on when the high level is set, and the energy storage element is charged at this time to make the capacitor When the voltage of the capacitor increases, the output voltage is the voltage of the capacitor, and vice versa. This is called PWM control. In a gated oscillator or pulse-mode regulator, the width and frequency of the switching pulses remain constant, but the "on" or "off" of the output switch is controlled by feedback.

According to the arrangement of switches and energy storage components, the output voltage can be greater than or less than the input voltage, and multiple output voltages can be generated with one regulator. In most cases, under the same input voltage and output voltage requirements, pulse (buck) switching regulators are more efficient than linear regulators in converting power, but with lower load capacity than linear ones.

According to the comparison between the output voltage and the input voltage, it can be divided into boost (the output voltage is higher than the input voltage) and buck (the output voltage is lower than the input voltage). They have different topologies.

Boost is generally used for LED series backlight driver and LED driver. Generally, the output voltage is more than ten volts.

Buck Core voltage for the multimedia coprocessor.

Introduction to Switching Regulators

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

In addition, there is no collector current when the switching regulator is in the OFF state, 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, non-series regulators are always supplied.

The current output by the switch circuit is not DC, and a rectified smooth current needs to be connected behind it to convert the pulsating current to DC current. ^[1]

Rectifier, smoothing circuit for switching regulator

There are two types of rectifier and smoothing circuits for switching regulators: capacitor input type and choke coil input type. They need to be flexibly used according to the circuit mode of the switching regulator.

A choke coil input type is used in the step-down chopper switching regulator, while a capacitive input type is used in the step-up chopper and reverse polarity chopper switching regulator.

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

Generally, the switching regulator that does not pass through the power transformer but directly inputs AC power is called a linear adjustable power supply or an offline converter.

Linear adjustable switching regulator structure, a. Self-excitation type, b. Other excitation type.

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

Separate-excitation type. There is an oscillator in the control circuit. The circuit structure is complex but the characteristics are good, which is suitable for high-power equipment. ^[1]

Linearly adjustable switching regulators include an output transformer, and the input and output must be isolated to avoid induced voltages.

Generally, the switching frequency of the switching transistor is set outside the human hearing frequency, and exceeds 20KHz. ^[1]