Can voltage regulator diodes be used in series

Zener diodes are also a type of diode. When working normally, Zener diodes operate in the reverse breakdown region, where the current changes greatly while the voltage changes very little, thus achieving a voltage stabilization effect. The current in the series circuit is equal, so the voltage regulator diode can be used in series completely.

The voltage regulator belongs to a PN junction, which is made through a special process using the volt ampere characteristics of the PN junction to operate in the reverse breakdown region. The volt ampere characteristic curve of a voltage regulator diode is shown in the following figure. The current in the reverse breakdown region has a minimum value IZMIN and a maximum value IMAX. When designing the circuit, it is necessary to operate the voltage regulator diode in this current range. If the current is less than this range, the voltage regulator effect cannot be achieved, and if it is greater than this range, the voltage regulator diode will overheat and permanently breakdown, burning out.

After two voltage regulating diodes are connected in series, their voltage regulation value is VZ=VZ1+VZ2. When the voltage regulation effect is achieved, the normal operating current range is between MAX (IZMIN1, IZMIN2) and MIN (IMAX1, IMAX2).

For example, assuming the voltage regulation value of Zener diode 1 is 5.1V, the normal operating current range is 5mA~50mA, the voltage regulation value of Zener diode 1 is 3.3V, and the normal operating current range is 8mA~60mA, then the voltage regulation effect achieved by series connection of Zener diodes 1 and 2 is 5.1V+3.3V=8.4V, and the normal operating current range is 8mA~50mA. So when different types of voltage regulators are connected in series, it is particularly important to pay attention to the calculation of their normal operating current. If not careful, one of the diodes may not achieve the voltage regulation effect or burn out!

Summary: Zener diodes can be used in series because the current in the series circuit is equal. As long as all Zener diodes work in the reverse breakdown region, it is sufficient. When used in series, it is best to use the same type of voltage regulator diode, so that its voltage regulator current range remains unchanged and does not require calculation. If there are different models, it is best to choose a voltage regulator diode with the same or similar working current range, so that its working current range is wider and the voltage regulation effect is better.