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Everything about Diode - What is Diode - How Diode works - Diode Rectifier - Diode Application
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May Allah's peace, mercy, and blessings be upon you
I was read alot of information about Diodes to understand it completely and i Collected the best i read ,, to understand it very easy .
What is Diode ?
How it works ?
Forward Voltage Drop - Forward Bias
Reverse Voltage - Reverse Bias
Types of semiconductor diode :
?How Diodes works
Diode operation: (a) Current flow is permitted; the diode is forward biased. (b) Current flow is prohibited; the diode is reversed biased.
Depletion region expands with reverse bias.
Inceasing forward bias from (a) to (b) decreases depletion region thickness.
Connecting and soldering
Diodes must be connected the correct way round, the diagram may be labeled a or +k or - for cathode (yes, it really is k, not c, for cathode!). The cathode is marked by a line painted on the body. Diodes are labeled with their code in small print, you may need a magnifying glass to read this on small signal diodes! for anode and Small signal diodes can be damaged by heat when soldering, but the risk is small unless you are using a germanium diode in which case you should use a heat sink clipped to the lead between the joint and the diode body. A standard crocodile clip can be used as a heat sink.
Rectifier diodes are quite robust and no special precautions are needed for soldering them.
Testing a diode with a multimeter
The techniques used for each type of meter are very different so they are treated separately:
a = anode
k = cathode
Testing a diode with a DIGITAL multimeter
Testing a diode with an ANALOGUE multimeter
Connect the black (+) lead to anode and the red (-) to the cathode. The diode should conduct and the meter will display a low resistance (the exact value is not relevant).
Reverse the connections. The diode should NOT conduct this way so the meter will show infinite resistance (on the left of the scale).
Signal diodes (small current)
Rectifier diodes (large current)
Diodes do not obey Ohm's law!
How a PN-Junction Diode Works ?
To understand how a pn-junction diode works, begin by imagining two separate bits of semiconductor, one n-type, the other p-type.
Bring them together and join them to make one piece of semiconductor which is doped differently either side of the junction.
Free electrons on the n-side and free holes on the p-side can initially wander across the junction. When a free electron meets a free hole it can 'drop into it'. So far as charge movements are concerned this means the hole and electron cancel each other and vanish.
As a result, the free electrons and holes near the junction tend to eat each other, producing a region depleted of any moving charges. This creates what is called the depletion zone.
Now, any free charge which wanders into the depletion zone finds itself in a region with no other free charges. Locally it sees a lot of positive charges (the donor atoms) on the n-type side and a lot of negative charges (the acceptor atoms) on the p-type side. These exert a force on the free charge, driving it back to its 'own side' of the junction away from the depletion zone.
The acceptor and donor atoms are 'nailed down' in the solid and cannot move around. However, the negative charge of the acceptor's extra electron and the positive charge of the donor's extra proton (exposed by it's missing electron) tend to keep the depletion zone swept clean of free charges once the zone has formed. A free charge now requires some extra energy to overcome the forces from the donor/acceptor atoms to be able to cross the zone. The junction therefore acts like a barrier, blocking any charge flow (current) across the barrier.
Usually, we represent this barrier by 'bending' the conduction and valence bands as they cross the depletion zone. Now we can imagine the electrons having to 'get uphill' to move from the n-type side to the p-type side. For simplicity we tend to not bother with drawing the actual donor and acceptor atoms which are causing this effect!
The holes behave a bit like balloons bobbing up against a ceiling. On this kind of diagram you require energy to 'pull them down' before they can move from the p-type side to the n-type side. The energy required by the free holes and electrons can be supplied by a suitable voltage applied between the two ends of the pn-junction diode. Notice that this voltage must be supplied the correct way around, this pushes the charges over the barrier. However, applying the voltage the 'wrong' way around makes things worse by pulling what free charges there are away from the junction!
This is why diodes conduct in one direction but not the other.
This is a avideo to explain what is diode ?how it works?
A diode is an electrical component acting as a one-way valve for current.
When voltage is applied across a diode in such a way that the diode allows current, the diode is said to be forward-biased.
When voltage is applied across a diode in such a way that the diode prohibits current, the diode is said to be reverse-biased.
The voltage dropped across a conducting, forward-biased diode is called the forward voltage. Forward voltage for a diode varies only slightly for changes in forward current and temperature, and is fixed by the chemical composition of the P-N junction.
Silicon diodes have a forward voltage of approximately 0.7 volts.
Germanium diodes have a forward voltage of approximately 0.3 volts.
The maximum reverse-bias voltage that a diode can withstand without “breaking down” is called the Peak Inverse Voltage, or PIV rating.
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