Rectifier Diode : Circuit Working, Testing & Its Applications

Diodes are widely used semiconductor devices. A rectifier diode is a two-lead semiconductor that allows current to pass in only one direction. Generally, the P-N junction diode is formed by joining together n-type and p-type semiconductor materials. The P-type side is called the anode and the n-type side is called the cathode. Many types of diodes are used for a wide range of applications. Rectifier diodes are a vital component in power supplies where they are used to convert AC voltage to DC voltage. The Zener diodes are used for voltage regulation, preventing unwanted variations in DC supplies within a circuit.

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What is a Rectifier Diode?

A rectifier diode is a semiconductor diode, used to rectify AC (alternating current) to DC (direct current) using the rectifier bridge application. The alternative of rectifier diode through the Schottky barrier is mainly valued within digital electronics. This diode is capable to conduct the values of current which changes from mA to a few kA & voltages up to a few kV.

The designing of rectifier diodes can be done with Silicon material and they are capable of conducting high electric current values. These diodes are not famous but still used Ge or gallium arsenide-based semiconductor diodes. Ge diodes have less allowable reversed voltage as well as a lesser allowable junction temperature. The Ge diode has a benefit as compared to Si diode that is low threshold voltage value while operating in a forward-bias.

The rectifier diode has two groups of technical parameters like permissible limit parameters and characteristic parameters. The symbol of a rectifier diode symbol is shown below, the arrowhead points in the direction of conventional current flow.

Rectifier Diode Circuit Working

Both the n-type & p-type materials are chemically combined with a special fabrication technique which results in the formation of a p-n junction. This P-N junction has two terminals which can be called as electrodes and due to this reason, it is called to be a &#;DIODE &#;(Di-ode).

If an external DC supply voltage is applied to any electronic device through its terminals, it is called as Biasing.

Unbiased Rectifier Diode

• When no voltage supplied to a rectifier diode then it is called an Unbiased Diode, N-side will have a majority number of electrons, and very few numbers holes (due to thermal excitation) whereas the P- side will have a majority of charge carriers holes and very few numbers of electrons.
• In this process, free electrons from N-side will diffuse (spread) into the P side and recombine takes place in holes present there, leaving +ve immobile (not moveable) ions in the N- side and creating -ve immobile ions in the P side of the diode.
• The immobile in the n-type side near the junction edge. Similarly, the immobile ions in the p-type side near the junction edge. Due to this, numbers of positive ions and negative ions will accumulate at the junction. This region so formed is called as depletion region.
• At this region, a static electric field called Barrier Potential is created across the PN junction of the diode.
• It opposes the further migration of holes and electrons across the junction.

Forward Biased Diode

• Forward Biasing: In a PN junction diode, the positive terminal of a voltage source is connected to the p-type side, and the negative terminal is connected to the n-type side, the diode is said to be in forwarding bias condition.
• The electrons get repelled by the negative terminal of the DC voltage supply and drift towards the positive terminal.
• So, under the influence of applied voltage, this electron drift causes current to flow in a semiconductor. This current is termed as &#;Drift current&#;. As majority carriers are electrons, current in n-type is the electron current.
• As holes are majority carriers in p-type, these get repelled by the positive terminal of DC supply and move across the junction towards the negative terminal. So, the current in p-type is the hole current.
• So, the overall current due to majority carriers creates a Forward current.
• The direction of conventional current flows from positive to negative of battery in the direction of conventional current is opposite to the electrons flow.

Reverse Biased Diode

• Reverse Biased condition: if the diode is the positive terminal of the source voltage is connected to the n-type end, and the negative terminal of the source is connected to the p-type end of the diode, there will be no current through the diode except reverse saturation current.
• This is because at the reverse biased condition the depletion layer of the junction becomes broader with increasing reverse-biased voltage.
• Although there is a small current flowing from the n-type to p-type end in the diode due to minority carriers. This current is called Reverse Saturation Current.
• Minority carriers are mainly thermally generated electrons/ holes in p-type semiconductor and n-type semiconductor respectively.
• Now if reverse applied voltage across the diode is continually increased, then after certain voltage the depletion layer will destroy which will cause a huge reverse current to flow through the diode.
• If this current is not externally limited and it reaches beyond the safe value, the diode may be permanently destroyed.
• These fast-moving electrons collide with the other atoms in the device to knock off some more electrons from them. The electrons, so released further release much more electrons from the atoms by breaking the covalent bonds.
• This process is called carrier multiplication and leads to a considerable increase in the flow of current through the p-n junction. The associated phenomenon is called Avalanche Breakdown.

Half-Wave Rectifier

One of the most common uses for the diode is to rectify the AC voltage into a DC power supply. Since, a diode can only conduct current one way, when the input signal goes negative, there will be no current. This is called a half-wave rectifier. The below figure shows the half-wave rectifier diode circuit.

Full-Wave Rectifier

• A full-wave rectifier diode circuit builds with four diodes, by this structure we can make both halves of the waves positive. For both positive and negative cycles of the input, there is a forward path through the diode bridge.
• While two of the diodes are forward biased, the other two are reverse biased and effectively eliminated from the circuit. Both conduction paths cause current to flow in the same direction through the load resistor, accomplishing full-wave rectification.
• The Full-wave rectifiers are used in power supplies to convert AC voltages to DC voltages. A large capacitor in parallel with the output load resistor reduces the ripple from the rectification process. The below figure shows the full-wave rectifier diode circuit.

Parameters

Based on the following limiting parameters, the rectifier diode is characterized

• VF &#; Forward voltage through determined IF forwarding current
• IR &#; The current in reverse at VRWM peak reverse voltage operation.
• IFN &#; The diodes max average current or rated current in the forward bias
• IFRM &#; Peak, Repeatable current diode conduction
• IFSM &#; Peak, non-repeatable current conduction
• VRWM &#; Peak, Reverse Voltage Operation
• VRRM &#; Peak, Repetitive Reverse Voltage
• VRSM &#; Peak, Non-Repetitive Reverse Voltage
• PTOT &#; The whole value of the dissipated power on the electronic component
• Tj &#; Highest Temperature of Junction in Diode
• Rth &#; Thermal Resistance below Operating Conditions

Maximum Temperature

The different parameters which are listed above can be affected through different factors like the ambient temperature where the rectifier diode is working. All the semiconductor devices generate heat, particularly those used within power supplies. One of the most problems is the avoidance of thermal runaway wherever a diode enhances its temperature which leads to an amplify the current with the device until the device is destroyed.

To avoid this trouble, each of the reference temperatures of diode parameters, for instance, the Si diodes reverse leakage current is generally extracted at 25°C of an ambient temperature but it is approximately twice for every 10°C. Once the temperature is increased then the forward junction potential will be decreased to 2 mV to 3 mV for each 1°C of temperature.

High Current

The rectifier diode with the double high current is the best example of a high-performance diode including 2x 30A of a current.

STMicroelectronics implemented a rectifier diode with double high voltage namely STPS60SM200C. This diode is applicable for welders, base stations, AC/DC power supplies as well as industrial applications.

The VRRM breakdown voltage value is 200V, conduction voltage is 640mV & its current memory will be 2x30A. An extra protection can from an ESD which is called electrostatic discharge to 2kV. The range of operating temperature of this diode ranges from -40° C &#; 175° C. These values will allow the diodes to be utilized below all circumstances within the base stations.

How to Test a Rectifier Diode?

The rectifier diode can be tested by using the following methods.
The simple multimeter is mainly used to decide the rectifier diode&#;s polarity like anode or cathode. There is a minimum of three methods for doing this but here the two simple methods to do that are using Ohmmeter and VDC measurement function.

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Using Ohmmeter

In forward-bias, the Ohmmeter will specify the estimated value of the diode&#;s forward voltage that is nearly 0,7. In reverse-bias, the ohmmeter will specify &#;1&#;&#;, which means it is extremely high resistance.
The function of a diode check will provide an equal result like the above-used method.

VDC Measurement Function

• In forward-bias, a multimeter will display the voltage drop for silicon diode is 0.7V
• In reverse-bias, a multimeter specifies the estimated value of the full voltage supply.

Rectifier diodes are mainly used for rectification which means to change AC to DC. They are used in circuits wherever a huge current should flow throughout the diode.

The rectifier diodes have a forward voltage drop of 0.7V and they made with Si. So, the following tabular form list outs the maximum and minimum reverse voltage for some rectifier diodes. The 1N diode is apt for the circuits which have low voltage & less than 1A of current.

The diodes characteristic is that flow of current otherwise current does not supply based on the applied voltage direction. This performs to change AC voltage to DC. The two electrode terminals of this diode are the anode & the cathode & current supplies once the anode electrode is on the +ve terminal.

Diode Highest Current

Highest Reverse Voltage

1N

1A 50V 1N 1A

100V

1N

1A V 1N 3A

100V

1N 3A

V

Applications

The rectifier diodes have many applications. Here are a few of the typical applications of diodes include:

• Rectifying a voltage, such as turning the AC into DC voltages
• Isolating signals from a supply
• Voltage Reference
• Controlling the size of a signal
• Mixing signals
• Detection signals
• Lighting systems
• LASER diodes

Thus, a rectifier diode allows the flow of electrical current in simply one direction, used for the operation of the power supply. These diodes can handle the maximum flow of current as compared to normal diodes. These diodes are normally used to alter alternating current (AC) to direct current (DC). The designing of these can be done like discrete components otherwise integrated circuits. These are designed from Si & distinguished through a quite large PN junction surface so, it results in high capacitance in reverse-bias conditions. The two rectifier diodes are connected to high-voltage supplies in series to enhance the rating of PIV (peak-inverse-voltage) for the combination.

Do you know any other diodes that are regularly used in real-time electrical and electronics projects?  Then, please give your feedback by commenting in the comments section below. Here is a question for you, How the depletion region is formed in a Diode?

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