Detailed explanation of the working principle of the linear regulated power supply unit
Let's first use the following diagram to illustrate the principle of voltage regulation in a linear regulator power supply.
Uo=Ui × RL/(RW+RL), so by adjusting the size of RW, the output voltage can be changed. Please note that in this equation, if we only look at the change in the value of the adjustable resistor RW, the output of Uo is not linear, but if we look at RW and RL together, it is linear. Also note that our diagram does not depict the RW's lead end as connected to the left, but rather on the right. Although there is no significant difference from the formula, the drawing on the right perfectly reflects the concepts of "sampling" and "feedback" - in reality, the vast majority of power supplies work in sampling and feedback mode, and feedforward methods are rarely used or only used as auxiliary methods.
Let's continue: if we replace the variable resistor in the diagram with a transistor or field-effect transistor, and control the resistance of this "variable resistor" by detecting the output voltage to maintain a constant output voltage, we will achieve the goal of voltage stabilization. This transistor or field-effect transistor is used to adjust the voltage output size, so it is called an adjusting transistor.
Due to the adjustment tube being connected in series between the power supply and the load, it is called a series stabilized power supply. Correspondingly, there is also a parallel type regulated power supply, which adjusts the output voltage by connecting the regulating tube in parallel with the load. The typical reference regulator TL431 is a parallel type regulator. The meaning of parallel connection is like the voltage regulator in Figure 2, which ensures the "stability" of the emitter voltage of the attenuation amplifier tube through shunt. Perhaps this diagram may not immediately show that it is "parallel", but upon closer inspection, it is indeed true. However, it should also be noted that the voltage regulator here operates using its nonlinear region. Therefore, if it is considered a power source, it is also a nonlinear power source. For the convenience of everyone's understanding, let's look for a suitable image to see until it can be easily understood.
Due to the fact that the regulating tube is equivalent to a resistor, it generates heat when current flows through the resistor. Therefore, regulating tubes operating in a linear state generally generate a large amount of heat, resulting in low efficiency. This is one of the main drawbacks of linear regulated power supplies. For a more detailed understanding of linear regulated power supplies, please refer to the textbook on analog electronic circuits. Our main purpose here is to help everyone clarify these concepts and their relationships.
