Voltage Regulators

Zener Regulator :

Figure 9-2 shows different versions of linear voltage regulators. The simplest of these is shown in Figure 9-2a. It consists of a zener diode and a resistor connected to a voltage VIN. A zener diode is a semiconductor diode designed to operate in the reverse-biased avalanche region (similar to breakdown) that has the characteristic of maintaining a constant voltage across it as the current through it varies. It must have a minimum current, IZ(min), through it to operate properly, and because of a power dissipation temperature limit, it can handle only up to a maximum current, IZ(max). Here is how it works as a regulator. IZ can be any value from IZ(min) to IZ(max), and VO will remain within a specified percentage of VO. Initially with no-load, IL = 0, the series resistor is set so that the current is IZ(max). When IL is increased, IZ decreases, but VO will remain within specified limits until IZ = IZ(min). Thus, IL varies over its range but VO remains within specified limits. The zener diode is not a regulator for wide variations in current; it is more a regulator for a constant load with little variations. Currents that it can handle are usually less than 100 milliamperes (100 mA). Example 1. Zener Voltage Regulator A Zener diode has the characteristics shown for points 1 and 2. What is the percent load regulation when the load changes between point 1 and point 2 ? 

Vz = Point 1 6.0V

Point 2 6.42V

Iz=1 mA (maximum current drawn by load)

100 mA (minimum current drawn by load)

Solution:
% Load Regulation = VNO LOAD – VLOAD/VLOAD × 100
% Load Regulation = 6.42 – 6.0/6.0 × 100 = 0.42/6 × 100 = 0.07 × 100
% Load Regulation = 7%