Hi all,

    As promised, here a thyristor circuit made with a NPN and a PNP Silicon transistor.

    It is in fact an equivalent circuit. Lectron has also a thyristor module nr. 2418.

    A thyristor has 3 connections, a Gate, a Cathode and an Anode.

    In our circuit, the lamp is connected to the “Anode”.

    The upper switch is connected via a voltage divider (made of the 4,7k and 1,5k resistors) to the “Gate”.

    The lower switch is connected to the “Cathode” .

    A thyristor is like a switch with remote control.

    When the Gate is grounded, the path between the Anode and the Cathode is open. This means that the light bulb doesn’t lit.

    Once we connect the Gate to a positive voltage, the path between Anode and  Cathode closes and the light bulb is lit.

    When we remove the voltage at the Gate, the path between the Anode and Cathode remains closed.

    Only by disconnecting this path (by pushing on the normally closed lower switch) the thyristor resets at its beginning position.

    The circuit seems somewhat compacter than the one with the Germanium transistor.

    Here is “an open air” circuit of the thyristor.

    A question, why is there a 1,5k resistor in the circuit ?

    After building this circuit, you’ll find out !