Basics of Silicon Controlled Rectifiers & its Operations and Applications

Silicon Controlled Rectifiers

Current power gadgets genuinely started with the appearance of thyristors. Thyristors are otherwise called the silicon controlled rectifiers or SCRs. These are four layered and three-terminal semiconductor gadgets. Also thyristors are unidirectional gadgets.

Silicon Controlled Rectifiers are semiconductor gadgets commonly used to control high power combined with high voltage. In this way these gadgets observe applications in high voltage AC power control frameworks, light dimmer circuits, controller circuits, and so on SCR additionally observes application in the amendment of high power AC in high volt DC power transmission. The SCR has a place with the group of Thyristors and really, the name SCR is the business trademark of the Thyristor from General Electrics.

The SCR is a four-layered gadget with rotating N and P-type materials. The SCR comprise of a four-layer of semiconductor which structures PNPN or NPNP structure. Silicon is utilized as the natural semiconductor, to which the appropriate dopants are added. It has three terminals called anode, cathode, and entryway. The cathode is the most intensely doped and the door and anode are less vigorously doped. The focal N-type layer is just delicately doped and is likewise thicker than different layers engaging it to help a high obstructing voltage.

The SCR has three intersections to be specific J1, J2, and J3. The Anode is associated with the P-type material of the PNPN structure while the cathode is associated with the N-type material. The Gate is associated with the P-type material close to the cathode.

These are unidirectional gadgets and behaviors current just one way. That is from Anode to Cathode. Setting off of SCR happens when its door gets a positive voltage. SCR is by and large utilized in exchanging applications like transfer driver, battery chargers, and so forth



The thyristor has three essential states:

Turn around impeding: In this express, the thyristor blocks the current similarly as that of a converse one-sided diode.

Forward hindering: In this express, the thyristor activity is to such an extent that it blocks forward current conduction that would regularly be conveyed by a forward-one-sided diode.

Forward leading: In this express, the thyristor has been set off into conduction. It will remain leading until the forward current dips under a limit esteem known as the holding current.

Thyristor Operation

The SCR begins conduction when it is forward one-sided. For this reason, the cathode is kept at a negative and anode at positive voltage. At the point when the forward inclination voltage is applied to the SCR, the intersection J1 and J3 become forward one-sided while the intersection J2 becomes converse one-sided. At the point when a positive voltage is applied at the door the intersection J2 becomes forward one-sided and the SCR turns on.

THYRISTOR

In activity the thyristor might be considered as NPN and PNP semiconductor associated one after the other, framing a positive criticism circle inside the gadget. The semiconductor with its producer associated with the cathode of the thyristor is a NPN gadget while the semiconductor with its producer associated with the anode of the thyristor is PNP gadget. The door is associated with the foundation of the NPN semiconductor. The result of one semiconductor is taken care of to the contribution of the second and the result of the subsequent semiconductor is, thusly, taken care of back to the contribution of the first. This implies that when a current begins to stream, it rapidly develops until the two semiconductors are completely turned on or soaked. How about we see a little model:

At the point when the entryway is open three break-over not set in stone on the base forward voltage at which thyristor leads intensely. Presently, the greater part of the stockpile voltage shows up across the heap obstruction. The holding current is the most extreme anode current door being open when break over happens.

At the point when the entryway at the OFF express the thyristor gives vastness obstruction than in ON state, it offers exceptionally low opposition, which is in the scope of 0.010 to 10.

Method of Triggering

In the typical off state, SCR forestalls the progression of current through it yet when the entryway to cathode voltage increments and surpasses a specific level, SCR turns on and conducts like a semiconductor. One significant eccentricity of SCR is that, whenever it is directed, it remains locked and keeps on leading even after the door voltage is eliminated. The SCR stays on until the holding current of the gadgets drops to a low worth. Yet, assuming the door gets a throbbing voltage and the current through it is underneath the locking current, the SCR will stay in the off state. SCR can be set off without a positive voltage at the door. The SCR is generally associated with the anode to the positive rail and cathode to the negative rail. In case the applied voltage to the anode builds, the capacitive coupling in the gadget incites surge into the door and SCR triggers. This sort of setting off without the outer entryway current is known as" DV/dt setting off". This normally happens at power on. This is known as the Rate impact.

However, the DV/dt setting off won't turn on the SCR completely and the to some degree set off SCR will scatter a lot of force and the gadget might harm. To forestall the DV/dt setting off, a snubber organization is utilized. One more method of setting off is by expanding the forward voltage of SCR over it's evaluated breakdown voltage. Forward voltage setting off happens when the voltage across the SCR increments with its entryway opened. This is called 'Torrential slide breakdown' during which the intersection 2 of the gadget breakdown. This additionally turns on the SCR to some extent and will harm the gadget. So the voltage ought not surpass the evaluated voltage of the SCR.

How to turn off the SCR?

When the SCR is turned on, it will be in the leading mode even after the door current is eliminated. This is SCR locking. The SCR can be turned off through switch setting off. It very well may be finished by applying a negative voltage to the entryway. The gadget can likewise be turned off either by eliminating the Anode current or by shorting the entryway and cathode immediately.

Utilizations of Thyristor:

Thyristors are for the most part utilized in gadgets where the control of high power, potentially combined with high voltage is requested. Their activity makes them reasonable for use in medium to high-voltage AC power control applications, for instance, light diminishing, regulators, and engine control.

If the switch S1 is quickly squeezed, Relay will turn on. It tends to be wound down by squeezing S2.

If the switch S1 is supplanted with a LDR and R1 with 4.7K preset, the transfer will turn on when light falls on LDR. Preset change the setting off point.

On the off chance that the switch S1 is supplanted with a 4.7 K NTC (Negative Temperature Coefficient) Thermister and R1 with a 1K preset, the transfer turns on when the temperature increments. Preset change the setting off point.