"Switching Power Supply Simulation and Design-Based on SPICE" Reading Notes 1 From Resistor Divider to Linear Voltage Regulator

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"Switching Power Supply Simulation and Design-Based on SPICE" Reading Notes 1 From Resistor Divider to Linear Voltage Regulator [Copy link]

 

To be honest, this book is much harder to read than I thought! The knowledge points are too difficult. There are also some translation problems that are a bit translated, which reminds me of the pain of using foreign-language textbooks in college. The translated versions always have some strange and difficult-to-understand problems.

Let's start with the first chapter

It is true that any commercially successful simulation software must have a user-friendly interface.

The most commonly used simulation software should be multisim. Thanks to the popularity of university courses (and the popularity of pirated software), the interface of multisim is very easy to use. You can pull out the components and then start connecting the wires directly. You can connect the circuit diagram as you draw it with a pen, and then press the start button to start the simulation.

The book says that simulation can avoid wasting time and money. Before preparing for an experiment or waiting for the experimental samples to be delivered, you can download the component model for simulation to familiarize yourself with the main unit circuits. This is true. When I was in college, when I first started learning about op amps, my teacher asked us to use multisim to simulate several basic op amp circuits, and then use simulated oscilloscopes and spectrometers to observe signal changes. For example, adders, differential circuits, and the most basic in-phase and inverting amplifiers. However, the amplifier models of multisim seem to have basically the same parameters, and they all use universal models. I remember that when I was checking the signal-to-noise ratio or noise, I changed several amplifiers of different "models" and they were all the same. However, the model parameters can also be modified by yourself.

Third, when designers do not have the appropriate test equipment and are unable to conduct actual tests, SPICE can always provide simulation tests for designers. For example, spectrometers are very expensive, and the teacher emphasized this when I used them for the first time.

Fourth, the power bank is absolutely safe and will not explode! In short, this is a power joke.

Chapter 1 introduces switching power supply technology and types of converters, and introduces several important results that help readers better understand averaging technology.

The first section of the text uses resistors to convert power. The principle is very easy to understand, which is the so-called resistor voltage division. Because on the same circuit board, MCU and DSP need 3.3V, front-end acquisition card needs 15V, logic devices need 5V, and most boards only provide a single power supply. In order to provide different voltages to different devices, resistor voltage division is the simplest and fastest method.

But the resistor will produce a continuous voltage drop, which will generate power dissipation in the form of heat. After calculation, the system efficiency of the resistor divider that drops 12V to 3.3V and 5V is 33%. Not very high.

The second section is a closed loop system. This means that, with the first resistor divider, feedback is added to be able to regulate the changing input voltage. If the load changes or the input voltage drifts, the output voltage will also change. For a well designed system, the converter needs to be able to regulate properly independent of the input voltage changes. Several special components are used in this, the first is a reference voltage (TL431 adjustable Zener diode), and the second is an operational amplifier to observe a portion of the output voltage and compare it to the reference voltage. As a series element with the variable resistor, a MOSFET or bipolar transistor operating in linear mode.

This is a linear regulator. When the difference between the output voltage and the input voltage is small, the linear regulator can achieve higher efficiency. However, if the output voltage is much larger than the difference, it can also achieve high efficiency.

The third section uses a linear voltage regulator to derive a practical formula. The derivation process is not described here. The result is that increasing the DC gain G(0) can help reduce the static error, which ultimately affects the output voltage accuracy. Another important parameter affected by the loop gain is the closed-loop output impedance.

The following conclusions are drawn

1 If the DC loop gain is large, the output impedance is infinitely close to 0

2 For stability purposes, the circuit has a compensation feedback loop G(s). When the frequency increases, the loop gain T(s) decreases and the output impedance begins to increase. Impedance increases with frequency just like an inductor.

3 When the closed-loop gain T(s) drops to 0, the output impedance of the system is the same as when there is no feedback, and the system operates in an open-loop state.

The actual output voltage consists of two parts, the theoretical output voltage and the contribution of the output voltage

The circuit has a large DC gain, which can ensure good suppression of input voltage ripple. When T(s) decreases in the high frequency region, the system operates in an open loop.

The fourth section is an example of SPICE simulation of a complete theoretical voltage regulator.

Download spice software

Download (spice-space.org)

Section 5: Building a simple and universal linear voltage regulator

The voltage regulator mentioned above, coupled with simple integral compensation, enables the voltage regulator to present stable performance.

The negative regulator has a wider bandwidth than the positive regulator, and the circuit is stable.

Summary of Linear Regulator:

Not suitable for high frequency conversion unless the difference between input and output is reduced to a few hundred millivolts. However, they can suppress ripple very well. They can be used as filter rectifiers on noisy output lines. They are safe for powering noise-sensitive circuits such as AD converters.

Jacktang

Linear regulators are not suitable for high-frequency conversion unless the difference between input and output is reduced to a few hundred millivolts. However, they can suppress ripple very well.

This is a perfect summary.