Voltage Regulation: is the measure of a circuit’s ability to maintain a constant output voltagefor changes in load condition or input voltage
Zener diodeA zener is a specially doped p-njunction diode that is designed to Characteristic Curveoperate in reverse bias without IFdamage. Zener Diode Symbol A K V VR Z 0.1 IZ max VF Practical Working Range 0.1 to 0.8 I Z IZ MAX is known as the Zener region. Vz 0.8 IZ max remains almost IR constant.
As the resistor is in series with the zener diode, the voltage drop across the resistor and the voltage drop across the zener equal the supply voltage. Voltage across the resistor is 6V the zener is 12V. Vs = VRload. + Vz The series resistor and the zener diode essentially form a series circuit, therefore the voltage across the series resistor plus the zener voltage will equal the supply voltage. Component functions Rs Limits the zener current to a safe value. Vz maintains a constant voltage across the load unit by controlling thecurrent through the series resistor.
Three Terminal Regulators.• Three terminal regulators are integrated circuits (IC’ s) that have been designed to input a varying low voltage D.C. and provide a low voltage fixed output D.C. voltage. They also have many built in features that make them easy to use and very versatile.• They require very few additional components.•• They have protection against short circuit currents.•• They have automatic thermal shutdown (they reduce the output when they reach a predetermined temperature)• They have very constant output voltage.• They have very small ripple output.
Regulator• Voltage Regulator is a compact device that can provide precise voltage control The 3 Terminal integrated Circuit with the addition of only a few external components.• The 3-T regulator also has built-in over- current, short-circuit and over-temperature protection• The 3-T regulator has high ripple rejection and good transient response. Revision 01 7
The terminal regulators come in a range of fixed voltages or can be adjustable to almost any desired voltage by the addition of a simple zener diode or resistor network• A complete power supply using a fixed voltage three-terminal regulator is shown below.
In the above circuit the voltage between the output terminal and the adjustableterminal is set internally in the regulator at 1.25V. This voltage is connectedacross the 220Ω resistor which will cause a current of 5.7mA to flow through it.This current will also flow through the 1kΩ resistor causing a 5.7 V drop across it.(Ohm’s law, V=I x R, 0.057 x 1000 = 5.7 V).Therefore, the output voltage can now be determined by adding VR1 plus VR2V output = VR1 + VR2 = 1.25 V + 5.7 V = 6.92 volts.