Structure and principle of linear regulated power supply Features of linear regulated power supply
Linear regulated power supply is a kind of DC regulated power supply used earlier. It changes and controls its output voltage and current by changing the conduction degree of the transistor. In the linear regulated power supply, the transistor is equivalent to a variable resistor. connected to the power supply circuit. A common characteristic of linear regulated power supplies is that its power device adjustment tube works in the linear region, and the output is stabilized by adjusting the voltage drop between the tube electrodes. Due to the large static loss of the adjustment tube, it is necessary to install a large radiator to dissipate heat.
Structure and principle of linear regulated power supply
Generally speaking, a linear regulated power supply is composed of several basic parts such as a regulator tube, a reference voltage, a sampling circuit, and an error amplifier circuit. In addition, some parts such as protection circuit and start-up circuit may also be included.
Use the figure below to illustrate the principle of linear regulated power supply regulation voltage. As shown in the figure, 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 the output can be changed by adjusting the size of RW The size of the voltage. 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.
If we use a triode or field effect tube to replace the variable resistor in the figure, and control the resistance value of the "varistor" by detecting the output voltage, so that the output voltage remains constant, we have achieved voltage regulation. the goal of. This triode or field effect tube is used to adjust the voltage output, so it is called an adjustment tube.
As shown in the figure, 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.
Features of linear regulated power supply
1. Low efficiency;
2. The noise generated by the work is low;
3. The response speed is fast and the output ripple is small;
4. The output voltage is lower than the input voltage;
5. Large heat generation (especially high-power power supply), which indirectly increases thermal noise to the system.
