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SCR

                                              SCR

Silicon managed rectifier is a 3 terminal (anode, cathode and gate). 3 junctions and four layer semiconductor switching device the simple structure of scr is made of silicon. Principle of operation

In regular operating conditions, a nice voltage is carried out to the anodes (a) and a small tremendous voltage is applied to the gate (g) with recognize to the cathode (ok). Whilst the gate is stored open (vg=zero). The scr is in just like pnpn diode. The junction j1 and j3 operate in ahead bias and junction j2 operates in reverse bias. So no contemporary flows via the scr. Therefore the scr is in off kingdom. The scr offers no excessive resistance. While the anode voltage is step by step accelerated the junction j2 attains breakdown at a selected voltage. Now the scr conducts closely going to on nation. The anode voltage, at which the scr conducts closely (on nation) without the gate voltage is called break over voltage. Operations

While a small nice voltage is carried out to its gate, the junction j2 is in forward biased and the junction j2 is in opposite biased by way of this voltage. Now the electrons pass from n kind layer (cathode) to p kind layer, through the junction j3. The electrons in junction j3 are also attracted by means of junction j2, and gate modern begins flowing. The holes additionally pass from p layer (g) to n-layer (k). Which in turn increases the anode current, and makes more electrons available a junction j2. This cumulative procedure makes to breakdown the junction j2 in a short time. Now the scr conducts heavily. As soon as an scr is became ‘on’, the gate loses it’s manage. Despite the fact that the gate voltage is eliminated, the scr does not visit ‘off’ kingdom. To turn the tool off is most effective performed by using lowering the anode voltage, and makes the modern less than preserving present day (ih). Vi characteristics

The high cost of gate contemporary can easily at the tool with low anode to cathode voltages. The VI traits of scr are proven inside the fig. 1. 3. In forward biasing, because the anode-cathode voltage exceeds the ahead breakover voltage (vbo), the scr activates, and the anode-cathode voltage decreases quickly to a voltage marked as b. The modern at b is referred to as conserving present day (i). It's far the minimum cost of anode modern-day to maintain the scr in ‘on’ a nation. The area among the factor b and c is known as forward conduction region. When the anode voltage is negative with recognize to cathode, the junctions j, and j3 perform in opposite biasing and the junction j2 operates in ahead biasing. The vi traits of scr are divided into three regions of operation. Forms of areas

Reverse blocking vicinity whilst the cathode is made advantageous with respect to anode, without a voltage is implemented to its gate terminal, the scr is reversed biased. Now the junction’s j and j3 are running in reverse biasing and junction j2 is working in forward biasing. A small leakage present day will flow through the scr this opposite blockading mode is called off kingdom of the scr. If the reverse voltage is step by step elevated at a particular voltage avalanche breakdown will arise. That precise voltage is known as opposite breakdown voltage. The region earlier than breakdown is referred to as opposite blockading vicinity. Forward blocking off location when anode is advantageous with appreciate to the cathode with the gate circuit open, scr is said to be ahead biased in this mode a small current called forward leakage modern if the forward voltage is increased flows thru the scr. Then the opposite biased junction j2 will have an avalanche breakdown at the voltage called forward break over voltage (vbo). The region earlier than the breakdown is known as forward blocking off region.

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