The thyristor is an electronic switch Semi-conducteur commandable with lighting but not with the extinction.

General information

The thyristor (of the Greek will thura: carry) is an electronics component Semi-conducteur composed of four alternatively doped layers of Silicium positively and negatively. In its structure in layers P-N-P-N the thyristor can be modelled by two Transistor S PNP and NPN.

Sometimes called SCR (English Silicon Controlled To rectify , is “rectifying ordered silicon”), these components are adapted for the piloting of the stages of static inverters of energy such as Redresseur S controlled or Onduleur S.

The thyristors thus hold an important place in the applications of power of the Avionique, the Ferroviaire, the Automobile, the Electrical communication, etc

Operation

Convention receiver:

V_ak, tension of threshold enters the anode and the cathode of the thyristor.

I_ak, running considered as positive when crossing the thyristor of the anode towards cathode.

I_g, running considered as positive when returning on the trigger.

Condition of setting in conduction

1st case (to be avoided): if the thyristor is in a blocked state and the V_ak tension exceeds an elevated level called Tension of reversal , the thyristor becomes busy and without order on the trigger.

2nd case (to be avoided): if the variation of V_ak tension is too fast and that even if the tension is lower than the tension of reversal.

3rd case (traditional order):

• a) the V_ak tension > tension of threshold (some V),
• b) injection of a current positive I_g on the trigger.

Once these two observed conditions the thyristor is busy and behaves like a Diode. The I_ak current crosses the thyristor of the anode towards cathode and its V_ak tension is slightly beyond the tension of threshold (around 1  V for most common)

Condition of maintenance in conduction

The current I_ak must be positive whatever the current of trigger.

One is not then held any more to maintain current of trigger to allow the conduction of the thyristor. This remark is all the more true when the I_ak current is high. When the thyristor is busy its V_ak tension is slightly beyond the tension of threshold (around 1  V for most common).

Condition of blocking of a thyristor

When a thyristor is busy, i.e. more no order of trigger is necessary to allow maintains it state and that the level of the I_ak current is enough important to maintain the polarization of the thyristor, the blocking of the thyristor will intervene only when the current I_ak = 0 .

See too

• Thyristor GTO
• Triac
• MOS controlled thyristor

External bonds

• Thyristor

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