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

The content is copyrighted to www. Here is the explanation using two transistor model of SCR. The capacitance of the pn junctions fwo shown in figure 4.

What is Thyristor or SCR? A typical variation of current gain a with emitter current I E is shown in figure 4. The device has ideal states, i. The current through capacitor C j2 can be expressed two transistor analogy of scr. The increase in values of two transistor analogy of scr a 1 and a 2 would further increase the value of anode current I A which is a regenerative or positive feedback effect.

If the gate current I G is analoyy from zero to some positive value, this will increase the anode current I A as shown by equation 6. The value current then can only be controlled by external resistance of the circuit.

An increase of I A which is an increase of I E1 would increase a 1 as shown in figure 4. A thyristor can be considered as two complementary transistors.


By substituting this valyue aalogy 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. The two-transistor model is shown in figure 4.

But we cannot turn it OFF by control signal. In other words, it can be said, that the characteristic of thyristor is combination of characteristics of thyratron tube and transistor. Related pages Concept of Power Electronics.

Under transient conditions, the capacitances of the two transistor analogy of scr junctions influence the characteristics of the thyristor.

This model is used to demonstrate the regenerative or latching action due to positive feedback in the thyristor. That means we have control upon its turn ON, once it goes to conduction mode, we lose control over it.

Two transistor analogy of scr must be noted that a large current through the junction capacitors may cause damage to the device. This is a pnpn thyristor.

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 result of the application of a small gate current. 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. Now the question is how increasing?

Although there are many different members are available in thyristor family, but silicon controlled rectifiers are so widely used that as if thyristor and SCR become synonymous. One being pnp and the other npn. The current gain a 1 varies with emitter current I E1 which is equal to I A ; and two transistor analogy of scr 2 varies with emitter current I E2 which is equal to I k.

Silicon Controlled Rectifier SCR | Two Transistor Model | Operating Principle

That is why the two transistor analogy of scr of thyristor consists of first four letters of thyratron tube and last five letters of transistor. Similarly, the collector current for transistor Gwo 2 is I C2 where Similarly, the collector current for transistor Q 2 is I C2 where. We can turn it ON by sending a gate current signal between second P layer and cathode. SCRwhose full form is silicon controlled rectifieris also a well known member of thyristor family.

It twk a silicon based semiconductor device, which is used in electrical circuits for switching operation.

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