What is the working principle of a voltage regulator diode

Zener diode (also known as Zener diode) is a single PN junction diode used for stabilizing voltage. This diode is a semiconductor device that has high resistance until the critical reverse breakdown voltage. At this critical breakdown point, the reverse resistance decreases to a very small value, and in this low resistance region, the current increases while the voltage remains constant. Zener diodes are graded based on the breakdown voltage, and due to this characteristic, they are mainly used as regulators or voltage reference components. As a result, engineers have manufactured more types of voltage regulators to meet market demand.

How does a voltage regulator diode stabilize voltage? The working principle of a voltage regulator diode

A crystal diode is a p-n junction formed by a p-type semiconductor and an n-type semiconductor, with space charge layers formed on both sides of its interface and a self built electric field established. When there is no external voltage, the diffusion current caused by the difference in carrier concentration on both sides of the p-n junction and the drift current caused by the self built electric field are equal and in an electric equilibrium state. When there is a forward voltage bias from the outside, the mutual suppression effect of the external electric field and the self built electric field increases the diffusion current of carriers, causing a forward current. When there is a reverse voltage bias from the outside, the external electric field and the self built electric field are further strengthened, forming a reverse saturation current I0 that is independent of the reverse bias voltage value within a certain range of reverse voltage. When the applied reverse voltage reaches a certain level, the electric field strength in the p-n junction space charge layer reaches a critical value, causing a doubling process of charge carriers and generating a large number of electron hole pairs, resulting in a significant reverse breakdown current, known as the diode breakdown phenomenon.

If the voltage of the power grid increases, the output voltage Usr of the rectifier circuit also increases, causing the load voltage Usc to rise. Due to the parallel connection of the voltage regulator DW and the load Rfz, any slight increase in Usc will cause a sharp increase in the current flowing through the voltage regulator, resulting in an increase in I1 and an increase in the voltage drop across the current limiting resistor R1, thereby offsetting the increase in Usr and keeping the load voltage Usc basically unchanged. On the contrary, if the voltage of the power grid decreases, causing a decrease in Usr and a decrease in Usc, the current in the voltage regulator decreases sharply, resulting in a decrease in I1 and a decrease in the voltage drop on R1, thereby offsetting the decrease in Usr and keeping the load voltage Usc basically unchanged.

If Usr remains constant and the load current increases, the voltage drop across R1 increases, causing a decrease in the load voltage Usc. As long as Usc decreases slightly, the current in the voltage regulator rapidly decreases, causing the voltage drop on R1 to further decrease, thereby keeping the voltage drop on R1 basically unchanged and stabilizing the load voltage Usc.

How does a voltage regulator diode stabilize voltage - main parameters

1) Stable voltage Uz

Stable voltage refers to the working voltage of a voltage regulator diode in the reverse breakdown region, which is the voltage value at both ends of the diode. This value varies slightly with the working current and temperature, and even for the same type of voltage regulator diode, there is a certain degree of dispersion in the stable voltage value. For example, the stable voltage of 2CW14 silicon voltage regulator diode is 6-7.5V.

2) Dissipative power Pz

When reverse current passes through the PN junction of a voltage regulator diode, a certain power loss will be generated, and the temperature of the PN junction will also increase. Determine the dissipated power of the diode based on the allowed PN junction operating temperature. Usually, low-power transistors are around a few hundred milliwatts to a few watts. The maximum dissipated power Pzm: The maximum power loss of the voltage regulator depends on the area of the PN junction and heat dissipation conditions. When working in reverse, the power loss of the PN junction is: Pz=Vz*Iz， Izmax can be determined by Pzm and Vz.

3) Stable current Iz

Minimum stable current Izmin, large stable current Izmax, stable current: the reverse current when the operating voltage is equal to the stable voltage; Minimum Stable Current: The minimum reverse current required for a voltage regulator diode to operate at a stable voltage; Maximum Stable Current: The maximum reverse current allowed to pass through a voltage regulator diode.

The concept of dynamic resistance rz is the same as that of a general diode, except that the dynamic resistance of a voltage regulator diode is obtained from its reverse characteristics. The smaller the rz, the steeper the breakdown characteristics of the voltage regulator. rz=△Vz/△Iz

4) Temperature coefficient

The change in temperature will cause a change in VZ. In a voltage regulator, when | VZ |>7V, Vz has a positive temperature coefficient, and reverse breakdown is avalanche breakdown. When | Vz |<4V, VZ has a negative temperature coefficient, and the reverse breakdown is a Zener breakdown.

When 4V<| Vz |<7V, the voltage regulator can achieve a temperature coefficient close to zero. This type of voltage regulator diode can be used as a standard voltage regulator.