Electronics Tutorial about the Thyristor also called a Silicon Controlled Rectifier used in a Thyristor Switching Circuit to A Thyristors Two Transistor Analogy. ELECTRICAL ENGINEERING POWER ELECTRONICS SCR-Two Transistor analogy. SCR-Two Transistor analogy. Pradeep Chaudhary POWER. 19 Jan this is all about engineering thyristor is a very important in engineering specially in electrical and electronics engineering.

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Silicon Controlled Rectifier SCR | Two Transistor Model | Operating Principle

It can block both forward and anaolgy voltage but can conduct only in one direction. Similarly, the collector current for transistor Two transistor analogy of scr 2 is I C2 where.

Similarly, the collector current for transistor Q 2 is I C2 where Combining the two collector currents I C1 and I C2 yields The two transistor analogy of scr in twl of both a 1 and a 2 would transsistor increase the value of anode current I A which is a regenerative or positive feedback effect. By substituting this valyue of I k in iii we get, From this relation we can assure that with increasing the value of towards unity, corresponding anode current will increase.

That means we have control upon its turn ON, once it goes to conduction mode, we lose control over it. It is a silicon based semiconductor device, which is used in electrical circuits for switching operation. The current through capacitor C j2 can be expressed as. Under transient conditions, transistpr capacitances of the pn junctions influence the characteristics of the thyristor.

This device has tow states i. This model is used to demonstrate the regenerative or latching action due to positive feedback in the thyristor.

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The value current then can only be controlled by external resistance of the circuit. This continuous positive feedback effect increases towards unity and anode current tends to flow at a very large value.

In other words, two transistor analogy of scr can be said, that the characteristic of thyristor is combination of characteristics of thyratron tube and transistor.

Here is the explanation using two transistor model of SCR. We can turn it ON by sending a gate current signal between second P layer and cathode.

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One being pnp and the other npn. The device has ideal states, i. Related pages Concept of Power Electronics. Now the question is how increasing? The capacitance of the pn junctions are shown in figure 4.

If the gate current I G is increased from zero to some positive value, this will increase the anode current I A as shown by equation 6. A typical sct of current gain a with emitter current I E is shown in figure 4. The content is copyrighted to www. If we see from the constructional and operational point of view, it is a four layer PNPN three terminals Anode, Cathode, Gate semi controlled device. That is why the name of thyristor consists of first four letters of thyratron tube and last five letters of transistor.

If a thyristor is in the blocking state and a rapidly rising voltage is applied two transistor analogy of scr the device, high currents would flow through the junction capacitors. The two-transistor model is shown in two transistor analogy of scr 4.

SCR-Two Transistor analogy

At the first stage when we apply a gate current I git acts as base current of T 2 transistor i. This is a pnpn thyristor. Although there are many different members are two transistor analogy of scr in analoy family, but silicon controlled rectifiers are so widely used that as if thyristor and SCR become synonymous. An increase of I A which is an increase of I Anaalogy would oc a 1 as shown in figure 4.


It must be noted that a large current through the junction capacitors may cause damage to the device. But we cannot turn it OFF by control signal. The current gain a 1 varies with emitter current I E1 which is two transistor analogy of scr to I A ; and a 2 varies with emitter current I E2 which is equal to I k.

If we bisect it through the dotted line then we will get two transistors i. SCRwhose full form is silicon controlled rectifieris also a well known member of dcr family.

The characteristic of thyristor consists of the characteristic of thyratron tube and characteristic of transistor. A thyristor can be considered as two complementary transistors. Connects Facebook Youtube Videos. If a 1 and a 2 approach unity, the denominator of equation 6 approaches zero and a large value of anode current is produced causing the thyristor to turn on as a two transistor analogy of scr of the application of analofy small gate current.

The emitter current of transistor Q 1 is the anode current I A of the thyristor and collector current I C1 is given by.

What is Thyristor or SCR?