A thyristor is an electronic component that opens when a voltage is applied to the gate, and then remains open, regardless of the voltage change across it. To close the thyristor, it is necessary to turn off the power of the controlled circuit.
Instructions
Step 1
In the DC circuit, the thyristor functions as a storage element, similar to an RS flip-flop. To make it work in this mode, assemble a circuit consisting of a 6 V rectified and filtered voltage source, a 6 V and 0.1 A light bulb, and a thyristor. Include it in the open circuit so that the anode is facing the plus of the power supply, and the cathode is facing the light bulb.
Step 2
Immediately after the voltage is applied to the circuit, the light will not glow, since the thyristor is closed. To open it, take a resistor with a resistance of 100 Ohm to 1 kOhm (depending on the type of device) and connect it between the thyristor anode and its control electrode. The light will light up and will continue to light even after removing the resistor.
Step 3
There are two ways to extinguish a light bulb. The first is to connect a jumper between the anode and cathode of the thyristor and then remove it. When the jumper is removed, the light goes out. The second method is to disconnect and then turn on the power source or short-term rupture of the circuit supplied from it.
Step 4
The thyristor behaves completely differently if the power supply contains a rectifier, but does not have a filter and produces a ripple voltage. In this case, the lamp will light up and go out simultaneously with the connection and removal of the resistor between the anode and the control electrode. Please note that the current in the control circuit will be significantly less than in the controlled one. Thus, the thyristor has amplifying properties and allows you to control a powerful load using a low-power switch, at the same time preventing burning of its contacts.
Step 5
Using a thyristor, you can regulate the power in the load by means of pulse-width modulation. For this, the circuit is also powered from a source with a rectifier without a filter. The moments of supply of opening pulses to the control electrode are chosen differently, depending on what average power is required in the load. In fact, it simply turns on at full power at high speed, then turns off completely, but due to inertia, the average power changes smoothly.
Step 6
In practice, in dimmers (dimmers) operating on this principle, not thyristors are usually used, but triacs capable of passing current in both directions. This avoids the use of a rectifier bridge. A neon lamp or a dinistor is used as a threshold element for the sharp opening of the triac, as, for example, in the following diagram:
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