The Diode




Introduction: The Diode

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Diode is one of the basic and an important component in electronics.

Mostly, every electronic circuit consists of atleast a single diode.
You can also find it out in the circuits lying around you.

Diode is a two-terminal unidirectional device. It allows conduction or acts as a closed-switch when it is forward biased.
When reverse biased , it acts as a open- switch and prevents conduction.

This instructable teaches you the basics of a Diode and its certain uses.

You can also watch the above video for a short info. about the Diode or you can check here -

Step 1: Understanding the Diode

Diode is a two- terminal electronic component.
The two terminals are -

The Cathode is marked with a Grey coloured band in normal diodes or with a Black coloured band in zener diodes.

A Diode allows conduction only in one direction, hence known as Unidirectional component.
The Current in a normal Diode is mainly due to the two components,
They are -----
- flow of electrons (negatively charged)
- flow of holes (positively charged)

Note - - - - -
(Holes at a location, are created due to the movement of electrons from that location to a new location.

When an electron moves from its place, an empty space is created, which is referred to as 'hole', having charge opposite to that of the electron.)

There are three modes of operation of a Diode --
- Forward Biased Mode
- Reverse Biased Mode
- Breakdown Mode


-In forward biased mode, the diode conducts.
- In this mode, the Positive terminal of the battery/circuit is connected to Anode (p-side) of the diode & the Negative terminal of the battery/circuit is connected to the Cathode (n-side) of the Diode.
- In short, the Anode must be at a higher potential than the Cathode, for Forward-Biasing the Diode.
- Due to this connections arrangement, the electrons in the N-side (Cathode) of the Diode, are attracted towards the P-side (Anode) of the Diode & the holes from the P-side (Anode) are attracted towards the N-side (Cathode) of the Diode.
- This leads to the flow of electrons from the N-side to P-side (i.e. from Cathode to Anode) & also to the folw of holes from the P-Side to N-side (i.e. from the Anode to Cathode), giving rise to a current, whose direction is from Anode to Cathode Of the Diode.
- The diode thus acts as a 'Closed-Switch' in Forward-Biased Mode.


-In reverse biased mode, the diode doesn't conducts.
- In this mode, the Positive terminal of the battery/circuit is connected to Cathode (n-side) of the diode & the Negative terminal of the battery/circuit is connected to the Anode (p-side) of the Diode.
-In short, the Cathode must be at a higher potential than the Anode, for Reverse-Biasing the Diode.
- Due to this arrangement of connections, the electrons in the N-side (Cathode) of the Diode, are attracted towards the N-side (Cathode) of the Diode & the holes from the P-side (Anode) of the Diode, are attracted towards the P-side (Anode) of the Diode.
- This prevents the transfer of electrons and holes between the two terminals of the Diode.
- As no flow of electrons and holes takes place in either directions, there is no current flowing through the Diode.
- The diode thus acts as a 'Open-Switch' in Reverse-Biased Mode.


-This mode is a complement part of the Reverse biased mode.
- When a Diode is used in Reverse Biased Mode, and if the applied voltage is increased over the Reverse breakdown voltage, the Diode goes into Breakdown mode.
- At this point, the Diode starts conducting heavily in the Reverse direction.
- This mode is generally used in Zener Diode Circuits.

All these working operations of Diode are used in various different circuits as required.

There are some important considerations to be made while selecting a Diode for a certain application. They are discussed in the next step.

Step 2: Something Important...!!!

There are certain important points that are needed to considered before choosing a Diode for a certain application.

Some of them are mentioned as follows :-

1) Voltage range ------
- The operating voltage range of a Diode must be taken into consideration for it suitable use.
- A Diode with much higher voltage rating is preferred more.

2) Reverse-Breakdown Voltage ------
- The maximum reverse blocking voltage of a Diode must be high in order to protect the circuit from reverse voltage protection.
- A Diode with a high reverse voltage blocking is preferred.

3) Forward voltage drop ------
- When a Diode is used in a circuit in Forward-Biased Mode, there's some potential drop across the Diode ( from 0.3V to 0.7V or more).
- The forward voltage drop of a Diode must be as low as possible, in order to prevent lowering the voltage level of the circuit due to Diode.

4) Forward Current ------
- The forward current of a Diode also plays an important role in High Current circuits.
- The requirement of current in a circuit must be known, inorder to choose a proper high current Diode.

5) Frequency response ------
- The frequency response of a Diode matters when it is used in high frequency applications.
- A Diode must have a high frequency response, inorder to use it in high frequency applications.
- Special Diodes such as Schottky Diodes are preferred for a high frequency application.

There are also many more things to be referred. But the above points are the most common points about a Diode.
You can search more about it. Just Google it out...

Step 3: Types of Diodes

There are Various types of Diodes available today.
Every type of Diode has a different property and abilities of operation.
Some of the common diodes are discussed below in short ----

1) Rectifier Diodes - Theses are normal p-n junctions diodes used for Rectification purposes. They are cheap and easily availble.

2) Zener Diodes - These are p-n juctions diodes used for voltage regulation purposes other than rectification. They are available in various voltage ranges.

3) Schottky Diodes - These are metal-semiconductor 'High Speed' diodes used in high speed circuit or as high speed rectifiers. The forward current of a schottky diode is much higher than a normal Diode.

4) Varactor Diodes - These Diodes are also known as variable capacitance diodes. The capacitance between the Anode and Cathode, varies with the applied voltage-bias to the Diode. They are mostly used in tunning and oscillator circuits.

5) Tunnel diode & Gunn diode - These diodes are special diodes which exhibit negative resistance. They are used in radio frequency oscillation circuits.

6) L.E.D(Light-Emitting Diode) - It is a type of diode which emits light, when used in Forward-Biased Mode. They are available in various different colours.

7) Photodiode - These diodes are Light dependent Diodes. They are used in Reverse-Biased Mode. When light strikes the Reverse-Biased Diode, the diode starts conducting heavily.

For more info. on types of Diodes, you can Google out them....!!!

Step 4: Using Diodes

There are a lot of different uses of Diodes. Some of them are discussed below.

1) Rectifiers Circuits --
- Diodes are generally used as Rectifiers for the conversion of an A.C. signal to D.C. signal.
- There are three types of rectifiers which are mostly used, viz.,
1) Half-wave Rectifiers
2) Full-wave Rectifiers
3) Bridge Rectifiers
- Out of these, Bridge Rectifiers are the most commonly used in all circuits.

2) Reverse Voltage Protection Circuits --
- In order to protect circuits from reverse voltage polarity, Diodes are used in series as the protection part.

3) Voltage - Regulation Circuits --
- Zener diodes are used in Reverse-bias mode, for the regulation of voltage in circuits.
- They are available in various different voltages for regulation.
- Refer the above image for a short idea about thier use.

4) Flyback Diodes --
- Diodes are used as Flyback Diodes, inorder to protect the circuit from lage voltage spikes.
- They are used across an inductive load, inorder to supress the induced negative voltage spikes genereated due to the load, hence protecting the control circuit.

5) S.M.P.S --
- Scottky Diodes and High power diodes are used in S.M.P.S (Switch Mode Power Supply ) , for fast switching of signals and for boosting low D.C voltages to a high D.C voltages.

6) Oscillation and Tunning circuits --
- Tunnel Diodes and Gunn Diodes are used in oscillation and Tunning circuits.
- Clock pulse generators, timers, Radio frequency generation,etc., are the some more applications.

7) Light Generation/ Indication --
- L.E.D (Light - Emitting Diodes) Are used as a source of light in many devices such as Led Bulbs, Rechargeable Lights, Torches, etc.
- Also for various indications such as Danger/Alert, Battery-Level, On/Off, etc., Led's are used.

8) Light Sensor Circuits/ Light Dependent Circuits --
- Photodiodes are used as a source of Light - Detection in various automotive circuits.
- They are used in Automatic Street Lightings, Light Intensity measurment circuits, Burglar Alarms, etc.

These were the Most Common uses of Diodes. Refer the above images for quick reference.

Step 5: Finishing It ...!!!

This was all about the Diodes, their operation, and their uses.

You can refer more instructables for more information about the Diode.

Also, Google helps in every way, if you plan to learn more....!!!

Thanks for watching out this instructable.....

Check out the other instructables too:

The Resistor -

The Capacitor -

The LED -

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    10 Discussions


    4 years ago

    actually forward bias and reverse bias is mentioned wrong
    when anode is at higher potential and cathode is at lover potential it is forward bias and reverse is reverse bias
    not +ve at anode and -ve at cathode ....


    Reply 4 years ago

    yups... got your point.....thanks for the help....!!!


    4 years ago

    can i use two dioude as transistor?


    Reply 4 years ago

    yes you can but you have to use two different diode Not both same


    Reply 4 years ago

    Theory says, Transistors are two diodes connected in opposite direction. But practically, this won't work as a real transistor, because the dopings and widths of the 'P' and 'N' regions differ than of a real transistor...
    Better, prefer a cheap transistor instead.

    Phil B
    Phil B

    4 years ago

    I have used diodes as a voltage dropping device capable of handling 1 amp. of current. Common resistors are not able to do that. While printed material says a diode will drop voltage 0.6 volts, I found my actual results were more like 0.3 volts per diode.


    Reply 4 years ago

    I have enjoyed using series of diodes as a fine tune on power supplies voltage, at times with a zener stuff to make your own...


    Reply 4 years ago

    The forward voltage drop of Diode goes on varying as the current through the diode changes. This voltage drop is maximum when current is maximum through the diode and vice versa.
    Refer to the data sheet of the Diode - 1N5821, as an example.


    4 years ago

    Just correct your forward / reverse biased explanation in first paragraph. Forward biased diode acts like an open gate...


    Reply 4 years ago

    Nevermind...I just read it wrong...