Diodes form the most fundamental element in the modern electronics and without a diode, the electronic circuit will be incomplete.
The diodes are manufactured using germanium or silicon as the semiconductor material.
Diodes are the simplest form of semiconductor with a single p-n junction.
Polarity Identification of Diodes
In diode the lead having a white or black band is cathode terminal and the other terminal is anode.
Diodes are polarized hence they must be inserted in required direction for proper operation of circuit.
Diode Biasing
Forward bias:
If a positive voltage is applied to the semiconductor junction, the diode will conduct allowing the current to flow in the anode-cathode direction.
Reverse bias:
The reverse flow of current will not occur in a diode unless it enters the breakdown level.
VI Characteristic of Diodes
Consider the circuit diagram for diode VI characteristics
DC voltage source is connected in forward bias direction.Voltage applied to diode is increased by varying the resistor port.
It is observed that there is no current in the circuit unless the voltage across diode is above 0.6V.This is called threshold or Knee voltage
When the voltage across diode increase above 0.6V the current in the circuit also increase linearly.
In most of the electrical circuits the diodes operate in this region.
In reverse biased region the voltage source is connected with the reverse polarity.
There is no current flowing in the circuit .When the voltage across the diode is increased sufficiently such that heavy current flows through the circuit.
This voltage is known as break down voltage. If the voltage is further increased the diode may get permanently damaged.
Be sure in designing a circuit that you never apply breakdown voltage to diode.
Important diode parameters
Before you go for selection of diodes do get the their datasheets.Important diode parameter are
Peak inverse voltage (PIV):
It denotes the maximum voltage that a diode can withstand in the reverse direction.
Forward maximum current(If):
It is the current that a diode can conduct without being damaged
Forward voltage drop (Vf):
When the diode conducts, a voltage drop occurs, this is known as the forward voltage drop
Reverse recovery time (trr):
Maximum time for the device to switch from on to off stage
Testing of Diodes
In modern digital multimeter (DMM) there is facility to test the diodes.Connect positive terminal of DMM to anode and COM terminal to cathode terminal, the display shows low resistance for healthy diode or sounds a beep.
Now connect the positive terminal of DMM to cathode and COM terminal to anode lead ,the DMM will show some value.
If both this conditions are satisfied than your diodes are okay.
Acceptance of ignorance is true path of knowledge -Pujya Dadashri
