The Bipolar Transistor

What is the bipolar transistor ? Explain about it.

Zener Diodes

               Since a conducting zener diode maintains the voltage across it at a value around its zener voltage, its main purpose is to serve as a voltage regulator.  A very simple circuit that demonstrates this is shown in Figure 2. This is a shunt voltage regulator circuit, since the zener diode is connected in shunt (parallel) with the load.  In this circuit, Vout will be maintained by the zener diode at the zener voltage level even if Vin changes, as long as Vin exceeds the zener voltage.

   

                If Vin increases, the current flowing through the zener diode ZD1 increases as well, causing the voltage across the resistor R to increase while allowing the voltage across the zener diode to remain at the zener voltage level.  Of course, if Vin falls below the zener voltage of ZD1, ZD1 stops conducting, and Vout starts falling with Vin. Note that this circuit is also a very inefficient way to regulate a voltage, since regulation is achieved by shunting current to ground, which is like simply throwing the excess energy away.