How to draw a BUCK switching power supply circuit

First understand the concept of alternating straight, understand the role of diodes, understand the uses and parameters of different diodes, the principle of bridge rectifiers, and the role of filter capacitors and voltage regulators.

Then master the principles of linear power supply design, use the above basic knowledge to try to make a power supply, and record the conversion efficiency of different voltages and loads. At this time, the efficiency is still very low, don't worry, to understand the role of each component in the circuit, these are the basis for learning switching power supply, step by step.

Then design the step-up and step-down circuits, in the same way, to understand the chopper, how the voltage rises and falls, the role of capacitance and inductance, pay attention to the direction of current flow in different loops, which acceleration, which storage device stores and discharges in which process. Understand the principle first, and then calculate the charge value and the impedance of the capacitor. If you have mastered or can learn the relevant knowledge of analog electricity, it is best to look at the part of the amplifier, learn BJT first, then learn JFET and MOSFET after understanding, and estimate the switching state and calculate the magnification in combination with the phase of the AC signal.

In fact, although it does not affect the learning of the course, it can give you a deeper understanding of the basic principles of switching power supply.

The buck circuit is a kind of DC-DC converter, which simply means that the continuous current voltage is converted into a high-frequency power supply through the ** circuit, and then the DC voltage required is output through the pulse transformer and the rectifier filter loop, which is similar to the switching power supply.

In the buck step-down circuit, the inductor plays the role of step-down, store-up, and pin-to-reed. Capacitors play the role of energy storage and voltage smoothing.

Without inductance, the circuit cannot act as a step-down. Without capacitors, the circuit cannot smooth the voltage.

The inductance of the buck circuit is generally selected according to the allowable on-current ripple value, and whether the current works continuously and intermittently should be considered. The capacitance is selected according to the allowable voltage ripple value at both terminals. The higher the switching frequency, the smaller the inductance, the smaller the voltage ripple, and the smaller the capacitance.

Equivalent circuit models and basic laws.

1) It can be seen from the circuit that the inductor L and the capacitor C form a low-pass filter, and the principle of this filter design is to make the DC component of US(t) pass through, and suppress the harmonic component of US(T) to pass through; The output voltage uo(t) on the capacitor is the dc component of us(t) with a tiny ripple(t) added.

2) The working frequency of the circuit is very high, and the ripple uripple(t) caused by the charge and discharge of the capacitor in a switching cycle is very small, and the voltage on the capacitor can be regarded as constant macroscopically relative to the DC voltage Uo output on the capacitor. When the circuit works in steady state, the voltage on the output capacitor is composed of a small ripple and a large DC component, which can be regarded as a constant DC on a macro scale, which is the principle of small ripple approximation in the steady-state analysis of switching circuits.

3) When the charging charge of the capacitor is higher than the discharge charge in a cycle, the capacitor voltage increases, resulting in the decrease of the charging charge and the increase of the discharge charge in the subsequent cycles, so that the rise rate of the capacitor voltage slows down, and the continuation of this process is until the charge-discharge balance is reached, and the voltage remains unchanged at this time.