Zener diodes are having a wide applications commercially and industrially. Some of the important applications of a Zener Diodes are – as a Voltage Regulator or Stabilizer, as a Meter Protector. They are discussed below in detail. Before discussing Applications of Zener Diodes, we need to know about the basic working of Zener diode. Read Zener diode working here
Zener Diode as a Voltage Stabilizer
We can use Zener diodes in the electronic circuit as a Voltage Regulator. It provides a constant voltage to the load from a source whose voltage may vary over a sufficient range. The figure below shows the circuit arrangement of Zener diode as a voltage regulator.
In the above circuit the Zener diode of Zener Voltage VZ is connected across the load RL in reverse condition. The constant voltage (V0 = VZ) is the desired voltage across the load. The output voltage fluctuation is absorbed by a series resistor R which is connected in series with the circuit. This maintains a constant voltage (V0) across the load.
Let a variable voltage Vin be applied across the load RL. When the value of Vin is less than Zener voltage VZ to the Zener diode no current flows through it and the same voltage appearing across the load. The Zener diodes conduct a large current is, when the input voltage Vin is more than the Zener Voltage Vz. As a result large amount of current flows through series resistor R which increases the voltage drop across it.
Thus, the input voltage, excess of Vz (i.e. Vin – VZ) is absorbed by the series resistor. Hence, a constant voltage V0 = Vz is maintained across the load RL. When a Zener diode of Zener voltage Vz is connected in reverse direction parallel to the load, it maintains a constant voltage across the load equal to Vz and hence stabilizes the output voltage.
Zener Diode as Meter Protector
Zener diodes are generally used in multi meters to protect the meter movement against the damage from the accidental overloads. The Zener diode is connected in parallel with the meter from the safety point of view. The circuit diagram for Zener Diode as Meter Protector is shown below.
When we measure any electrical signal in multi meter, there may be a chance of excess current through the meter. This may be due to following reasons.
- The multi meter may be connected wrongly to the circuit.
- The rating of the meter is selected wrongly for the measurement.
- Occurrences of over current in the circuit itself during measurement.
Over current causes overheating in the meter which may ultimately lead to a permanent damage to the meter. Although The reasons of the over current cannot be avoided completely. Therefore it is required to protect the meter from the effect of over current. This is done by using Zener diode of suitable rating.
Whenever a multi meter is connected in the circuit to measure an electrical signal, there must be a voltage drop across it. If the current through the meter is increased beyond safety limit, the voltage drop also crosses the rated limit. Suppose the rated voltage drop limit of the meter is 0.6 volt. Now, let us connect a Zener diode across the meter, whose forward barrier voltage is 0.6 volt. Now, if due to excess current through the meter, if the voltage drop across the meter becomes more than 0.6 volt, the diode becomes short-circuited, since this excess voltage also appears across the Zener diode.