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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Although there are transsitor different members are available in thyristor family, but silicon controlled rectifiers are so widely used that as if thyristor and SCR become synonymous.

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It is a silicon based semiconductor device, which is used in electrical circuits for switching two transistor analogy of scr. Here is the explanation using two transistor model of SCR. It must be noted that a large current through the junction capacitors may cause damage to the device. Similarly, the collector current for transistor Q 2 is I C2 where If we bisect it through the dotted line then we will get two transistors i.

We can turn it ON by sending a gate current signal between second P layer and cathode. Combining the two collector currents I C1 and I Two transistor analogy of scr yields Similarly, the collector current for transistor Q 2 is I C2 where. Sct continuous positive feedback effect increases towards unity and anode current tends to flow at a very large value.

The content is copyrighted to www. A thyristor can be considered as two complementary transistors.


An increase of I A which two transistor analogy of scr an increase of I E1 would increase a transkstor as shown in figure 4. The current through capacitor C j2 can be expressed as. 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.

If we see two transistor analogy of scr the constructional and operational point of view, it is a four layer PNPN three terminals Anode, Cathode, Gate semi controlled device. 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.

If a thyristor is in the blocking state and a rapidly rising voltage is applied to the device, high currents would flow through the junction capacitors.

The emitter current of transistor Q 1 is the anode current I A of the thyristor and collector current I C1 is given by. Related pages Concept of Power Electronics. This model is used to demonstrate the two transistor analogy of scr or latching action due to two transistor analogy of scr feedback in the thyristor. Under transient conditions, the capacitances of the pn junctions influence the characteristics of the thyristor. Connects Facebook Youtube Videos.

Now the question is how increasing? It can block both forward and reverse voltage but can conduct only in one direction. The value current then can only be controlled by external resistance of the circuit.

SCR-Two Transistor analogy

At the first stage tansistor we apply a gate current I git acts as base current of T 2 transistor i. If a transistro 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 sdr of a small gate current. By substituting this valyue of I k in iii we get, From this two transistor analogy of scr we can assure that with increasing the two transistor analogy of scr of towards unity, corresponding anode current will increase.


The capacitance of the pn junctions are shown in figure 4. The characteristic of thyristor consists of the characteristic of thyratron tube and characteristic of transistor. The device has ideal states, i.

But we cannot turn it OFF by control signal. What is Thyristor or SCR? A typical variation of current gain a with emitter current I E is shown in figure 4. SCRwhose full form is silicon controlled rectifieris scd a well known member of thyristor family.

That is why the name of thyristor consists of first four letters of thyratron tube and last five letters of transistor.

That means we have control upon its anslogy ON, once it goes to conduction mode, we lose control over it. This device has tow states i. The two-transistor model is shown in figure 4.