Diode

Diodes is a simple P-N junction electronic component for DIY projects with leads from both P and N regions. P-N junction is the interface between a P type semiconductor and N type semiconductor. When impurities (either P-type or N-type) are added to an intrinsic semiconductor, free electrons or holes are generated in it. This will increase the conductivity of the substrate. A P-N junction is made by doping a semiconductor crystal with P type semiconductor on one side and the other side with N type semiconductor. Doping the substrate with two different materials (group 3 and group 5) on opposite sides provides the device with different property. Device allow current to pass through it only in one direction and blocks in the other.  An ideal P-N junction diodes is a perfect conductor in one direction and a perfect insulator in the other. Structure and symbol of a diode is shown below. 

Structure of PN junction

      Diodes- Electronic Component for DIY Projects 

Depletion region of Diodes

Diode is a two layer device formed by P-type and N-type semiconductor. In the N region, each impurity atom has an extra electron left behind after forming four covalent bonds with the silicon atom. Therefore electrons are majority carriers in this region. Similarly in the P region of diodes one electron is short to form covalent bonds with the four valence silicon atom. Absence of electron is called holes. Therefore at P-region of diodes, holes are the majority carriers. Due to the concentration difference of majority carriers in each region, electrons from N region will diffuse into the P region of diodes and holes from the P region will diffuse into the N region of diodes. The free electrons from the N-region will move into the P region where it fits itself in the holes. The movement of each electron will reduce charge carrier in both P region and N region of diodes. The process is continued and a region develops itself as a perfect insulator. The insulator region thus developed in both N region and P region of diodes together is called depletion region

The growth of the depletion region will not continue for a longer time. When an electron is diffused into P region, a positive ion is created in the N region. The electrostatic force between positive ion and free electron will resist the movement of electron. So diffusion will reach equilibrium when this electrostatic force equals the force of diffusion. Due to the generation of ions, a voltage is developed across the depletion region. This voltage difference is called Barrier potential.

Junction formed between P and N layer

Biasing of P-N Junction Diodes

For different operating conditions predetermined voltage is applied across the P-N junction diodes.  Diodes can be biased in two possible methods depending on the polarity of the applied voltage. 

(a). Forward biasing of Diodes

Under zero biasing condition, no voltage is applied across the diodes. No free carriers are present in the depletion regionand there is small voltage across the junction (barrier potential). When diodes is configured in forward bias mode, positive and negative terminal of the battery is connected to the P and N region respectively. Now negative voltage push electrons from the N region into the depletion region and similarly positive voltage push holes from the P region into the depletion region of diodes. This decreases the width of the depletion region. Presence of free carriers in the depletion region increases its conductivity therefore current flows through the diodes. In other words, electrons from the N region are pushed into the P region through the depletion region. Electrons in P region are attracted by the positive terminal of the battery, and flows in the opposite direction of current flow. 

 

Forward Biasing

                                 Forward Biasing in Diodes

(b). Reverse biasing of Diodes

For the diodes to operate in reverse biased condition, negative and positive terminal of the battery is connected to P and N regions respectively. Negative voltage connected to the P region will give electron to vacant spaces in it. Similarly positive voltage at N region of diodes attracts electrons. So it removes free electrons from the N region of diodes. As the charge carriers are removed, depletion region (region without free charge carriers) width will increase. Since depletion region behaves like a perfect insulator no current can flow through the diodes in reverse biased configuration.

Reverse Biasing

                                                                                                                                                                           

V-I Characteristics of P-N Junction Diodes

Forward characteristics of Diodes

When forward bias voltage is increased it is opposed by the barrier potential across the depletion region. When the applied voltage is greater than the barrier potential, carrier density in the depletion region equals to the carrier density of P or N region. Resulting device is close to a perfect conductor. Therefore from this point, a small increase in voltage results in a very large increase in current. This voltage is called Knee voltage Vf .

 Characteristics of Diode

Reverse characteristics of Diodes

In the reverse characteristics, we can see that current is not increased even if we increase the voltage across the device. Diodes in reverse biased configuration behaves like a perfect insulator till the applied voltage is less than breakdown voltage. 

Breakdown Voltage – Zener and Avalanche Breakdown

The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive. We explained the concepts of forward bias and reverse bias by considering the electrons in the outermost shell, because under normal conditions only free electrons in the outer most shell of an atom can move around. In reverse biased mode, no current flows through the device. All free electrons in the outer shell are removed when the applied voltage is increased. When the voltage is increased further electrons from the lower layer will gain energy and jump to the outer shell. This process is called tunneling and this type of break down is called Zener break down. After Zener breakdown, the conductivity of the diodes increases and large amount of current flows through the diodes. 

There is a second type of breakdown called Avalanche breakdown. When reverse voltage is applied, free electrons from the N region move towards the positive terminal and holes from the P region move to the negative terminal. Moving electrons may collide with other electrons and transfer its energy. Energy will be sufficient to break its bond. So a new free electron is created. The newly created electrons collide with the neighboring electrons and energy is transferred. This process continues as a chain reaction and keeps on generating more free electrons. This process can turn out to be uncontrollable and the heat produced due to repeated collision can damage the device. In a particular device, occurrence of Zener and avalanche breakdown may either be independent or simultaneous.

Specification of Diodes 

  1. Peak Inverse Voltage

It is the maximum voltage that can be given to the PN Junction diodes without any damage.

  1. Average Forward Current

The current that a diodes can pass at normal temperature is the average surge current.

  1. Forward Surge Current

It is the large amount of current that a diodes can safely pass through it.

  1. Maximum forward voltage

It is the maximum forward voltage that a diodes can have without any damage.

  1. Power Dissipation

It is the power that the diodes can dissipate.

  1. Reverse Recovery Time

Time taken by the diodes to switch from ON to OFF.

Tips and Tricks: Diodes

Eventhough the theory part is known to everyone, most of us are unaware on how to identify diodes. Below are some tips and tricks to identify diodes. Now you guys may be thinking why this topic is important???? The answer is diodes are essentially "one-way", hence it's important to know to identify diodes easily.

                                                Diode

Tips and Tricks

  1. Look for the ring band printed on the diodes. Always the band will be printed near to the cathode, i.e, N side of the PN junction diodes.
  2. In a circuit you can identify the P and N side of the diodes by checking whether the diode is conducting current. If the diode is conducting large amount of current, then positive side of the battery is definitely connected to the P side of the diode and negative side of the battery is connected to the N side of the diode. Thus the diode is in Forward Bias.
  3. The diode in reverse bias will conduct current, but upto a limit only. Here positive side of the battery will be connected to the P side of the diodes and the negative side of the battery will be connected to the N side.
  4. Multimeter is another electronic instrument that can help to identify the diodes. First turn the multimeter to the diode setting. Place the probe tips to the diodes ends. If the diode displays a reading (voltage, current), then red probe is connected to the P side of the diode and the black probe is connected to the N side of the diode. If the multimeter does not display any reading, then the connections are reverse.

                  Multimeter test with diodes

Tips and Tricks: How to read a Diode Code????

Similar to transistor coding, the diodes also follow a special coding system. One is known as the Pro-electron coding scheme. The other coding system is the JEDEC system.

Coding System for Diodes

  1. Pro-electron Coding system

The Pro-electron coding system uses the format shown below and the table shows the meaning of each:

                                            Pro electron coding

                    Coding System

Examples

  1. BBY10
  2. From the table, it is clearly understood that the diode is silicon based variable capacitance diodes used for commercial purposes.
  3. JEDEC Numbering or Coding System

JEDEC coding system uses the format shown in the figure below and the table below shows the meaning of each character.

                                            JEDEC Coding

                      Coding using JEDEC

Thus a 1N914 is a diode. Here 1 represents the number of PN junctions present in a diode. Letter ‘N’ represents that the material used is a semiconductor and the sequential number represents the device number.

Tips and Tricks to read a Diode Code?

By going through these simple tips and tricks you can easily read your diode code. Quickly read below:

  1. Learn the JEDEC, Pro-Electron coding system of the diode.
  2. Now read the diodes code.
  3. Check whether the diodes code belongs to Pro-electron or JEDEC coding system.
  4. If the diode starts with ‘1N’ then follow JEDEC system and if the diodes code starts with ‘Two letters’ then follow Pro-electron coding system.
  5. After identifying the coding system (JEDEC/ Pro-Electron), follow the rules and steps described in ‘Coding system for diodes’ above.
  6. Now look the diodes catalog to get more information about the working, specifications, characteristics, applications etc.

                                           TIPS AND TRICKS

Tips and Tricks: How to make a simple bridge rectifier circuit on a breadboard?

After knowing how to identify a diode in terms of its anode and cathode terminals, now it’s time to learn how to connect a simple diode circuit to the breadboard.

Circuit for Study:  Bridge Rectifier Circuit

Here we are choosing a simple bridge rectifier circuit. This simple circuit helps you to connect the diodes efficiently to the breadboard and gives you a better knowledge to identify the diodes in terms of its anode and cathode terminals either by using a multimeter or by understanding the band.

Bridge rectifier circuit is a simple full wave rectifier circuit which uses a combination of four diodes to form the bridge. It helps in the conversion of both the half cycles of AC input into DC output. Being a major part of the power supplies, it is really important to know about it. Also, bridge circuits find applications in many motor controllers, welding purposes, modulation purposes, in home appliances etc.

Tips and Tricks: How to select the Bridge Rectifier Circuit Components?

Step Down Transformer

You can use a 230 volt to 12 volt or 110 volt to 12 volt step down transformer. Also it will be reliable if you can use a center tapped transformer. Now while using the center tapped transformer, connect either the terminal points across the bridge rectifier or connect one of the terminal point and the middle point to the bridge rectifier circuit.

Diodes

Here we are using four IN4007 diodes. It is a pn junction diode with better voltage range of 50 to 1000 volts and current 1 Ampere. Its features like low cost, less leakage, low voltage and high current makes them better for the bridge rectifier circuit.

Capacitor & Resistor

Capacitor used here is a 470microFarad capacitor.  It is used for the conversion of full wave ripple output into smooth DC output. In a bridge rectifier circuit, working voltage and the capacitance value has to be determined while choosing the capacitor.

Note: The working voltage must be higher than the non-load output value of the rectifier. Also, capacitance value must be chosen in such a way that the ripple will be less.

The resistor used here is 1K and across it the output voltage is taken.

bridge rectifier

Working of Bridge Rectifier Circuit

Case1: Positive Cycle

  • D2 and D3 are forward biased.
  • D1 and D4 are reverse biased.
  • Current flows through the diode D2, load and diode D3.

Case2: Negative Cycle

  • D1 and D4 are forward biased.
  • D2 and D3 are reverse biased.
  • Current flows through D4, load, D1.

Output: Pulsating DC Output.

Tips and Tricks: How to make a Simple Bridge Rectifier Circuit on a Breadboard?

At first, measure all the circuit components prior to the construction of the circuit using the multimeter.

  • Take the breadboard.
  • First, connect four diodes to the breadboard.
  • Connect cathode of D1 to cathode of D2.
  • Connect the cathode of D1 to cathode of D2.
  • Connect anode of D2 to cathode of D3.
  • Connect anode of D3 to anode of D4.
  • Connect cathode of D4 to anode of D1.
  • Give AC supply to the primary winding of the transformer .
  • Wire rectifier to transformer secondary.
  • The transformer secondary is connected to cathode of D3 and cathode of D4.
  • Connect the resistor and capacitor.
  • Check the output.

Note:

  • Take positive output of rectifier from the cathodes of D1 and D2 join.
  • Take negative output of rectifier from anodes of D3 and D4 join.

Clipper and Clamper circuits are considered to be one of the applications for diodes. Clipper also known as limiter is used to remove portions of the AC signal. Clamper also known as DC Restorer on the other hand is used to change the dc reference of the AC signal.

Application of Diodes

Clamper Circuits

Clamping circuits place the negative and positive peaks of the waveform at a desired DC level. In other words, these circuits shift the input signal by an amount defined by the independent voltage source. Today, Clamping circuits are also known popularly as Clamped Capacitors.

                                       Clampers

                                                                                              Application of Diodes

The basic idea of the clamper circuits are shown in the figure above.  Here the input signal is a sine wave having a peak to peak value of 10V. In case of a positive clamper, it pushes the signal to upwards so that the negative peak falls on the zero level. While in the case of the negative clamper, it pushes the signal downwards so that the positive peak of the signal falls on the zero level. One thing can be seen that the orginal shape of the signal is not changed in any of the clamper outputs.

Basics

Inorder to change the dc reference of the input signal, a clamper circuit usually uses:

  • A diode,
  • Load resistor and
  • A capacitor for its operation.

General principle of the clamper circuit is that, the charging time of the capacitor in the clamper must be small compared to the discharging time of the capacitor in the clamper.

Positive Clamper

Figure below shows the circuit of a positive clamper. The input signal Ito the circuit is a square waveform. The output signal Owill be obtained across the load resistor. Here C represents the capacitor, D a diode, V voltage supply and Rrepresents the load resistor.

                            positive clamper

                                                                          Application of Diodes: Positive Clamper

Proper operation of the clamper follows two points:

  • Time constant z= RLC must be very large.
  • Time constant must be greater than the time period of the input signal.

Positive Clamper Operation

During Negative Half Cycle

  • D is forward biased.
  • D is short.
  • Charging Time Constant ?= RC is small.
  • Rrepresents forward resistance of the diode.
  • Capacitor charges to V volts.
  • Voltage across Ris zero.

During Positive Half Cycle

  • D is reverse biased.
  • D is open.
  • Discharging time very large.
  • Capacitor remains at V volts.

Positive clamper output

                                                                      Application of Diodes: Positive Clamper Waveform

Negative Clamper

Figure below shows the circuit of a negative clamper. The input signal Ito the circuit is a sine waveform. The output signal Owill be obtained across the load resistor. Here C represents the capacitor, D a diode, V voltage supply and Rrepresents the load resistor.

                       Negative clamper

                                                                       Application of Diodes: Negative Clamper

Negative Clamper Operation

During Positive Half Cycle

  • D is forward biased.
  • D is short.
  • Charging Time Constant z= RC is small.
  • Rrepresents forward resistance of the diode.
  • Capacitor charges to V volts.
  • Voltage across Ris zero.

During Negative Half Cycle

  • D is reverse biased.
  • D is open.
  • Discharging time very large.
  • Capacitor remains at V volts.

                                                                                                   Application of Diodes: Negative Clamper Output

Example for Clamper Circuits

  1. Consider the circuit shown in the figure below and find its output waveform.
  2. Here input voltage is 5V.
  3. During positive cycle:
  4. D is forward biased.
  5. D is short.
  6. Vout= 2V.
  7. Using Kirchoffs Law:

Vin – Vc – Vout= 0

5- Vc- 2 = 0

Vc =3V.

  • During negative cycle:
  • D is reverse biased.
  • D is open.
  • Using Kirchoffs Law:

Vin-Vc-Vout = 0

Vout= - 8V.

The output waveform tells that the circuit given is a negative clamper and the dc reference level here is 2V.

Tips and Tricks for Clamper Circuits

  1. To identify the type of clamper circuit, just look at the diode. If the diode points in the upward direction, it is a positive clamper. While if the diode points in the downward direction, it forms a negative clamper.
  2. Use Kirchoffs Law to find Vc and Vout.

Clipper Circuits

Clippers are classified into three types:

  1. Positive Clipper
  2. Negative Clipper

Positive Clipper

Positive Clipper is used to remove the positive half cycles of the input voltage. The circuit is shown in the figure below. In this, during the positive half cycle, diode is forward biased and it conducts. Diode acts as a short and the voltage across the load is zero. While during the negative half cycle, diode is reverse biased and behaves as an open.

Negative Clipper

Negative Clipper is used to remove the negative half cycles of the input voltage. In this, during the positive half cycle, diode is reverse biased and it becomes open. While during the negative half cycle, diode is forward biased and it acts as a short and the voltage developed across the load resistor is zero.

Rectifiers

P-N junction diode conducts current only in one direction, that is, when anode is positive with respect to its cathode. This property of diode is used in half wave rectifier to convert AC to DC. In the rectifier circuit, diode is connected in series with the load resistance. Sine wave given as the input is rectified by the diode. During the positive half cycle, diode is forward biased, so current passes through it and reaches the load. And during the negative half cycle, diode is reverse biased so it blocks current from reaching the load. Half wave rectifier is shown in the following figure, which is the simplest circuit used as rectifier and it is considered to be the simplest application of diodes.

Half Wave Rectifier

Full-Wave Rectifier

In half-wave rectifier, negative half of the input signal is chopped off, therefore efficiency of the rectifier is only less than fifty percentage. In full wave rectifier, both positive and negative half of the input signal is used. Since both halves are used, efficiency of the full wave rectifier is double than that of half wave rectifier. A multiple winding transformer whose secondary winding is split equally into two halves is used in full wave rectifier. A diode which conducts only in one direction is connected in each half. During positive half cycle, diode D1 is forward biased and Diode D2 is reverse biased. Therefore current reaches load through the diode D1. Similarly, during negative half cycle, diode D2 is forward biased and diode D1 is reverse biased. In both half cycles, current passes through the load in the same direction and returns back to the secondary winding through the center tap. Thus we get a unidirectional output current. Full-Wave Rectifier

Full Wave Bridge Rectifier

In full wave bridge rectifier, four diodes in bridge configuration replaces the combination of center tap transformer and two diodes. Therefore, size and cost of the device is reduced. Following figure shows the circuit of a bridge rectifier connected to its load.

Positive half cycle

Diodes D1 and D2 are forward biased and diodes D3 and D4 are reverse biased during positive half cycle. Current from input end pass through diode D1, reaches load resistance and then flows out through diode D2.

Full Wave Bridge Rectifier

                                                                                   

Negative half cycle

During negative half cycle, didoes D3 and D4 are forward biased and diodes D1 and D2 are reverse biased. Current reaches the load through diode D3 and flows out through diode D4.Notice that in both half cycles, the current flows through the load in the same direction. That means bi-directional input AC signal is converted into unidirectional DC output.

User Review (1)

kanith kar   Coimbatore,Tamil Nadu

can some one list out the basic electronic components most used in our day today life

Reply  Report Abuse   14 November,2017 12:11
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