Regulator Zener Diode
The most simple regulator circuit shown in Figure 6. In this circuit, zener works on the breakdown region, thus producing the same output voltage with a zener voltage or Fout = VZ. However, this circuit is only useful if the load current less than 50mA.
The principle of such a power supply circuit is called a shunt regulator, one of his trademark is a regulatory component in parallel with the load. Another feature of the shunt regulator is susceptible to short-circuit. Notice when Fout connected short (short-circuit) then the current is fixed I = Vin/R1. In addition to a shunt regulator, there is also a series called by the regulator. The main principle of such series regulator circuit in Figure 7 below. In this circuit output voltage is:
Fout = VZ + VBE
VBE is the base-emitter voltage of transistor Q1 of the magnitude between 0.2 - 0.7 volts depending on the type of transistor used. By ignoring the IB currents flowing at the base of the transistor, to determine the magnitude of R2 resistance that is needed is:
R2 = (Vin - VZ) / Iz
Iz is the minimum flow required by the zener diode to achieve the zener breakdown voltage. These large currents can be detected from a datasheet which amount to approximately 20 mA.