Linear voltage stabilized power supply working principle details
The variable resistor RW forms a voltage divider circuit with the load resistor RL and the output voltage is:
Uo = Ui x RL/(RW + RL), so by adjusting the size of RW, we can change the size of the output voltage. Note that in this equation, the output of Uo is not linear if we only look at the change in value of the adjustable resistor RW, but it is linear if we look at RW and RL together. Note also that we don't draw the leads of RW connected to the left in this diagram, but on the right. Although this does not make any difference from the formula, but drawn on the right, but reflects the concept of "sampling" and "feedback" ---- actual power supply, the vast majority of the work in the sampling and feedback mode, the use of feed-forward method is rare, or If they do, it is only an auxiliary method.
Let us continue: If we use a triode or field effect tube, to replace the variable resistor in the figure, and by detecting the size of the output voltage, to control the size of this "variable resistor" resistance, so that the output voltage remains constant, so that we have achieved the purpose of regulating the voltage. The triode or field effect tube is used to adjust the size of the voltage output, so it is called regulator.
Because the regulator is connected in series between the power supply and the load, so it is called series-type voltage regulator. Accordingly, there are parallel-type regulated power supply, that is, the adjustment tube and the load in parallel to regulate the output voltage, a typical reference regulator TL431 is a parallel-type regulator. The so-called parallel means, is like Figure 2 in the regulator, through the shunt to ensure that the attenuation amplifier tube emitter voltage "stability", perhaps this figure does not let you immediately see that it is "parallel", but a closer look, indeed. However, we should also note here: the regulator here, is the use of its nonlinear region of operation, therefore, if you think it is a power supply, it is also a nonlinear power supply. In order to facilitate your understanding, back to us to find a reasonably suitable diagram to see, until you can briefly understand it.
Since the regulator tube is equivalent to a resistor, the current flowing through the resistor will heat up, so the regulator tube operating in the linear state, generally generate a lot of heat, resulting in low efficiency. This is one of the main drawbacks of the linear voltage regulator. For a more detailed understanding of linear regulated power supplies, please refer to the Analog Electronic Circuits textbook. Here we will mainly help you to clarify these concepts and their relationship to each other.
Generally speaking, a linear regulated power supply consists of a few basic parts such as a regulator, a reference voltage, a sampling circuit, and an error amplifier circuit. In addition may also include some other parts such as protection circuit, start-up circuit and so on. The following figure is a relatively simple linear regulated power supply schematic (schematic, omitted filter capacitors and other components), the sampling resistor by sampling the output voltage, and compared with the reference voltage, the comparison result is amplified by the error amplifier circuit to control the degree of conduction of the adjustment tube, so that the output voltage to maintain stability.
