The linear regulated power supply mentioned here refers to the DC regulated power supply in which the adjustment tube works in a linear state. The adjustment tube works in a linear state, which can be understood as follows: RW (see the analysis below) is continuously variable, that is, linear. In the switching power supply, it is different. The switching tube (in the switching power supply, we generally call the adjusting tube a switching tube) works in two states: on and off: on - the resistance is very small; off - the resistance is very high big. The tube operating in the switching state is obviously not in a linear state.
Linear regulated power supply is a type of DC regulated power supply used earlier. The characteristics of the linear regulated DC power supply are: the output voltage is lower than the input voltage; the response speed is fast, the output ripple is small; the noise generated by the work is low; the efficiency is low (the LDO that is often seen now appears to solve the efficiency problem) ; Large heat generation (especially high-power power supplies) indirectly increases thermal noise to the system.
Working principle: We first use the following figure to illustrate the principle of the voltage regulation of the linear regulated power supply. As shown in the figure below, the variable resistor RW and the load resistor RL form a voltage divider circuit, and the output voltage is:
Uo="Ui"×RL/(RW+RL), so by adjusting the size of RW, the size of the output voltage can be changed. Note that in this formula, if we only look at the value change 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 picture does not draw the RW terminal to the left, but to the right. Although there is no difference from the formula, it is drawn on the right, but it just reflects the concept of "sampling" and "feedback" - the actual power supply, most of them work in the mode of sampling and feedback Below, the use of feedforward methods is rare, or even used, it is only an auxiliary method.
Let's continue: If we use a triode or field effect transistor to replace the varistor in the figure, and control the resistance of this "varistor" by detecting the magnitude of the output voltage, so that the output voltage remains constant, then we have The purpose of voltage stabilization is achieved. This triode or field effect transistor is used to adjust the voltage output, so it is called an adjustment tube.
Since the regulating tube is connected in series between the power supply and the load, it is called a series regulated power supply. Correspondingly, there is also a parallel regulated power supply, which is to adjust the output voltage by connecting the regulating tube in parallel with the load. The typical reference regulator TL431 is a shunt regulator. The so-called parallel connection means that, like the Zener tube in Figure 2, the "stable" voltage of the attenuating amplifier tube's emitter is ensured by shunt. Maybe this picture can't let you see that it is "parallel" at once, but If you look closely, it does. However, everyone should also pay attention here: the Zener tube here uses its nonlinear region to work, so if it is considered to be a power supply, it is also a nonlinear power supply. In order to facilitate everyone's understanding, let's look back at a suitable diagram until we can understand it concisely.
Since the adjustment tube is equivalent to a resistor, and the current flows through the resistor, it will generate heat, so the adjustment tube that works in a linear state will generally generate a lot of heat, resulting in low efficiency. This is a major disadvantage of linear regulated power supplies. For a more detailed understanding of linear regulated power supplies, see the textbook on analog electronic circuits. Here we mainly help you to clarify these concepts and the relationship between them.
Generally speaking, the linear regulated power supply is composed of several basic parts such as adjustment tube, reference voltage, sampling circuit, and error amplifier circuit. In addition, it may also include some parts such as protection circuits, start-up circuits and so on. The following figure is a relatively simple schematic diagram of a linear regulated power supply (schematic diagram, omitting components such as filter capacitors). The sampling resistor samples the output voltage and compares it with the reference voltage. After the comparison result is amplified by the error amplifier circuit, the adjustment tube is controlled. The degree of conduction keeps the output voltage stable.
