What is the working principle of linear regulated power supply
According to the working state of the regulating tube, we often divide the regulated power supply into two categories: linear regulated power supply and switching regulated power supply. In addition, there is a small power supply that uses a Zener tube.
The linear regulated power supply mentioned here refers to the DC regulated power supply in which the regulator tube works in a linear state. The adjustment tube works in a linear state, which can be understood in this way: RW (see the analysis below) is continuously variable, that is, linear. It is different in the switching power supply. 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 small big. A tube working in an on-off state is obviously not in a linear state.
The linear regulated power supply is a type of DC regulated power supply that was 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 supply), which indirectly increases thermal noise to the system.
Working principle: Let's first use the following figure to illustrate the principle of linear regulated power supply to regulate voltage.
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 output voltage can be changed. Please 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 figure does not draw the lead-out of RW to the left, but to the right. Although there is no difference from the formula, the drawing on the right just reflects the concepts of "sampling" and "feedback"--most of the actual power supplies work in the mode of sampling and feedback Below, the feedforward method is rarely used, or if it is used, it is only an auxiliary method.
Let's continue: If we use a triode or field effect transistor to replace the variable resistor in the figure, and control the resistance value of this "varistor" by detecting the output voltage, so that the output voltage remains constant, so that we can The purpose of voltage stabilization is achieved. This triode or field effect tube is used to adjust the voltage output, so it is called an adjustment tube.
Since the regulator 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 shunt-type regulated power supply, which is to adjust the output voltage by connecting a regulator tube in parallel with the load. The typical reference voltage regulator TL431 is a shunt-type voltage regulator. The so-called parallel connection means that like the voltage regulator tube in Figure 2, the "stability" of the emitter voltage of the attenuating amplifier tube is ensured by shunting. Maybe this figure does not let you see that it is "parallel connection", but On closer inspection, it is indeed so. However, everyone should pay attention here: the voltage regulator tube here works in its nonlinear region, so if you think it is a power supply, it is also a nonlinear power supply. In order to make it easier for everyone to understand, let's look back at a reasonably suitable picture until we can understand it concisely.
