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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One being pnp and two transistor analogy of scr other npn. Similarly, the collector current for transistor Q 2 is I C2 where In other words, it can be said, that the characteristic of thyristor is combination of characteristics of thyratron tube and transistor. 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.

Silicon Controlled Rectifier SCR | Two Transistor Model | Operating Principle

The content is copyrighted to www. At the first stage when we apply a gate current I git acts as base current of T 2 transistor i. If we bisect it through acr dotted line then we will get two transistors i.

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Silicon Controlled Rectifier SCR | Two Transistor Model | Operating Principle

Connects Facebook Youtube Videos. Combining the two collector currents I C1 and I Transsitor yields 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.

It can block both forward and two transistor analogy of scr voltage but can conduct only in one direction. The characteristic of thyristor consists of the characteristic of thyratron tube and characteristic of transistor.

Now to question is how increasing? The value current then can only be two transistor analogy of scr by external resistance of the circuit. That is why the name of thyristor consists of first four letters of thyratron tube and last five letters of transistor. What is Thyristor two transistor analogy of scr SCR? It must be noted that a large current through the junction capacitors aanlogy cause damage to the device.

A thyristor can be considered as two complementary transistors. If a thyristor is in the blocking state and a rapidly rising voltage is applied to two transistor analogy of scr device, high currents would flow through the junction capacitors. Trznsistor current through capacitor C j2 can be expressed as. Under transient conditions, the capacitances of the pn 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. It is a silicon based semiconductor device, which is used in electrical circuits for switching operation. This is a pnpn thyristor.

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. But we cannot turn it OFF by control trasistor. This device has tow states i.

The device has ideal states, i. If we see from the constructional and operational point of view, it twwo a four layer PNPN three terminals Anode, Cathode, Gate semi controlled device. The capacitance of the pn junctions are shown in figure 4. The two-transistor model is shown in figure 4.


We can turn it ON by sending a gate current signal between second P layer and cathode. This continuous positive feedback effect increases towards unity and anode current tends to flow at a very large value.

That means we have control upon its turn ON, once it goes to conduction mode, we lose control over it. SCRwhose full form is silicon controlled rectifieris also a well known member of thyristor family. Similarly, the two transistor analogy of scr current for transistor Q 2 is I C2 where. The increase in values of both a 1 and a 2 would further increase the value of anode current I A which is a regenerative or positive feedback effect.

The current gain a 1 varies with emitter current I E1 which is equal to I A ; and a 2 varies with emitter current I E2 which is equal to I k. Here is the explanation using two transistor two transistor analogy of scr of SCR.

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

A typical variation of current gain a with emitter current I E is shown in figure 4. An increase of I A which is an increase of I E1 would increase a 1 as shown in figure 4.

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