When zener diodes are connected in series, the regulator value, rated power, external circuit voltage, load and other factors should be considered. Under the condition that all values do not exceed the rated range, the total adjustment value is equal to the sum of the adjustment values of the two (multiple) Zener diodes used.

Details are as follows:

The main loop of this voltage stabilizing circuit consists of a regulating tube T connected in series with the load, and T works in a linear state, so it is called a linear series voltage stabilizing circuit.

The output voltage Vo = v 1-VCE, and its change is sampled by the feedback network and amplified by the amplifier circuit (a) to control the base voltage of the regulator tube T, thus changing the VCE of the regulator tube T. ..

When the input voltage VI increases (or the load current Io decreases), the output voltage Vo increases, and the feedback voltage VF = R2VO/(r 1+R2) = FVO also increases (Fv is the feedback coefficient). VF is compared with the reference voltage VREF, and the difference voltage is amplified by the comparison amplifier circuit, so that VB and IC of the voltage stabilizer are reduced, and the voltage VCE between C and E of the voltage stabilizer T is increased, so that Vo is reduced, thus keeping Vo basically unchanged.

The characteristic of Zener diode is that the voltage at its two ends remains basically unchanged before the reverse current is broken down. In this way, when the voltage regulator is connected to the circuit, if the voltage at each point in the circuit changes due to the fluctuation of power supply voltage or other reasons, the voltage at both ends of the load basically remains unchanged.

Series voltage stabilizing circuit is a kind of DC voltage stabilizing power supply, which is widely used in practical application circuits. For example, the 78 or 79 series three-terminal voltage regulators we usually use are also one of them.