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What is a three terminal regulator?

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2022-11-14 10:29

The principle of three terminal voltage stabilizing tube The three terminal voltage stabilizing tube is a semiconductor device with high resistance until the critical reverse breakdown voltage. During reverse breakdown, the terminal voltage of the voltage stabilizing tube is almost unchanged within a certain current range (or a certain power loss range), showing a voltage stabilizing characteristic, so it is widely used in the voltage stabilizing power supply and amplitude limiting circuit. Three terminal voltage stabilizing tubes are classified into three terminal voltage stabilizing tubes. There are two main types. One is a fixed output voltage, called a fixed output three terminal voltage stabilizing tube, and the other is an adjustable output voltage, called an adjustable output three terminal voltage stabilizing tube. The function of the three terminal voltage stabilizing tube as the three terminal voltage stabilizing block is to reduce the voltage and stabilize it to a fixed value before output. For example, the three terminal voltage stabilizing block 7805 can reduce the voltage less than 35V to a stable 5V output voltage. It is much better than the circuit that only uses one zener diode for voltage stabilization, and the cost is not very high, so it is still widely used. Common three terminal voltage stabilizing blocks can be divided into positive voltage voltage stabilizing blocks and negative voltage voltage stabilizing blocks. There are 78 series of positive voltage stabilizing blocks and 79 series of negative voltage stabilizing blocks. The two series cannot be interchanged, so don't mix them when selecting.
The principle of three terminal voltage stabilizing tube When the input voltage decreases or the load resistance decreases and the output voltage decreases, the sampling voltage decreases accordingly and the base potential decreases. However, because the emitter potential keeps the voltage stabilizing tube stable, the emitter voltage decreases, resulting in a decrease in collector current and an increase in collector potential. Since the collector of the amplifier tube is connected with the base of the adjusting tube, the base potential increases, resulting in an increase in the collector current and a decrease in the tube voltage drop. Because the amplifier tubes are connected in series, the output voltage is basically unchanged. In the working process of the series voltage stabilizing power supply circuit, the adjusting tube is required to be always in the amplification state. The current through the adjusting tube is equal to the load current, so the appropriate high-power tube must be selected as the adjusting tube, and the heat dissipation device must be installed as required. In order to prevent short circuit or long-term overload from burning out the regulating tube, the DC voltage regulator is generally equipped with short circuit protection and overload protection circuits.

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