Difference Between Diode and SCR (Silicon Controlled Rectifier)

Hello guys, welcome back to our blog. In this article, we will discuss the difference between a diode and SCR (silicon-controlled rectifier ), what is a diode, and what SCR or silicon-controlled rectifier is.

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Difference Between Diode and SCR

The main difference between the diode and SCR is that an SCR is a three-terminal device used for the switching function & rectification process and a diode is a two-terminal device that is also used for the switching function and rectification process. Generally, both SCR and diode is a semiconductor device designed by a combination of p and n-type semiconductor materials.

A diode is a two-terminal semiconductor electronic device. The most general purpose of a diode is to allow an electric current to pass in one direction (in forwarding bias) while blocking it in the opposite direction. By this, we say diode is a unidirectional device used for rectification means converts alternating current into direct current. A semiconductor diode’s V-I characteristic can be decided by choosing semiconductor materials and the doping impurities are added to the material during manufacture.

When the positive terminal of the supply is connected to the anode and the negative terminal of the source is connected to the cathode, the diode becomes forward biased and it will allow current to flow through it. When the negative terminal of the supply is connected to the anode and the positive terminal of the source is connected to the cathode, the diode becomes reverse biased and it will not allow current to flow through it.

These techniques are used to introduce the special-purpose diodes that perform many different works. For example, a diode used for the voltage regulator is called a Zenor diode, and the diode used to protect circuits from high voltage surges is called an avalanche diode. Similarly, different types of diodes are used for alternate applications based on the requirement.

A silicon control rectifier is a four-layered, three-terminal, and three-junction semiconductor device. In this device, the four layers are PNPN, and three terminals are the anode, cathode, and gate with three junctions namely j1, j2, and j3. Here the anode and cathode terminals are connected to the main power circuit whereas the gate terminal is connected to the control circuit. The gate terminal carries the low-level gate current in the direction gate to the cathode. Generally, the gate current terminal is placed at the P-layer nearer to the cathode terminal. Hence it is known as the cathode gate.

Whenever the P-layer near the anode is made more positive when compared to the N layer near the cathode, junctions j1 and j3 get forward biased whereas the middle junction j2 gets reverse biased. Junction j2 is known as junction capacitance as it acts as a capacitor in this mode. Due to the formation of the depletion layer, there is no chance to flow of current. But the drift of mobile charge carriers a small amount of leakage current flows through the circuit. As the leakage current is negligibly small, the device does not conduct.

This state is known as the forwarding blocking state or off state of the device as it blocks the forward-biased voltage. Whenever the N layer near the cathode is made more positive compared to the P-layer near to the anode. junction j1, j3 gets reverse biased(as the opposite charges repel each other). Now the middle junction j2 gets forward biased. Small leakage current flows in the circuit. So, the SCR will treat as a switch and will be in the off state. This state is called Reverse Blocking Mode.

Differences between Diode and SCR

Diode	SCR
The diode has only two terminals the anode and cathode.	SCR has three terminals they are anode, cathode, and gate.
It is an uncontrolled rectifying device (there is no requirement of triggering pulse)	It is a controlled turn on the device(there is a requirement of triggering pulse)
The diode has two layers(Player and N layer) and one junction(j1).	SCR has four layers(PN layer, PN layer) and three junctions(j1, j2, j3).
The diode has good power handling ability.	Silicon Controlled Rectifier has a better power handling ability.
The operating voltage of the diode is low.	The operating voltage of SCR is high.
Less expensive.	High expensive.
The diode having lightweight.	SCR has a heavyweight.
Whenever the rated current flows in a silicon diode the voltage drop is about 0.6 to 0.7 volts.	Whenever the rated current flows in the SCR, during this the maintained voltage is 1 to 1.5volts
It consumes less power.	SCR consumes high power.
There are several types of diodes are present in electronic devices like a Zenor diode, Light-emitting diode, low signal diode, high signal diode, Shokkty diode, etc.	SCR is one type of thyristor. In thyristors, there are several types of devices present.
Applications: Used for rectification process, switching purposes, Used in clippers, clampers, etc.	Applications: Used for switching purposes, used to protect the circuit from high voltages, Used in high-power applications, etc.

So from the above, we say that the diode and SCR both are semiconductor devices. But comparatively, these two are quite different. There are a lot of applications are having these two devices used for different purposes.

This was about “Difference Between Diode and SCR“. I hope this article helps you to understand the difference between Diode and SCR. Thank you for reading.

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Indu R

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