Thyristor power regulator: circuit, operation principle and application

The article describes how the thyristor power controller works, the circuit of which will be presented below

In everyday life very often there is a need to regulate the power of household appliances, such as electric stoves, a soldering iron, boilers and electric heaters, in transport - engine speed, etc. To the aid comes the simplest radio amateur design - a thyristor power controller. It is not difficult to assemble such a device, it can become the first homemade device that will perform the function of adjusting the temperature of the soldering iron tip of a novice ham radio. It is worth noting that ready-made soldering stations with temperature control and other nice functions cost an order of magnitude more than a simple soldering iron. The minimal set of parts allows to assemble a simple thyristor power regulator by mounted mounting.

For information, hinged installation is a way of assembling radio-electronic components without the use of a printed circuit board, and with a good skill it allows you to quickly assemble electronic devices of medium complexity.

You can also order an electronic constructor for a thyristor regulator, and for those who want to understand everything themselves, a diagram will be presented below and the principle of operation explained.

The scope of thyristor regulators

By the way, this is a single-phase thyristor power controller. Such a device can be used to control the power or the number of revolutions. However, first we need to understand the principle of the thyristor, because it will allow us to understand what kind of load it is better to use such a regulator.

How does the thyristor work?

Thyristor is a controlled semiconductor device capable of conducting current in one direction. The word "controlled" is used for a reason, since with its help, unlike a diode, which also conducts a current only to one pole, it is possible to choose the moment when the thyristor starts to conduct a current. Thyristor has three conclusions:

• Anode.
• Cathode.
• Control electrode.

In order for the current to flow through the thyristor, the following conditions must be met: the part must be in the circuit under voltage, a short pulse must be applied to the control electrode. Unlike a transistor, the thyristor control does not require a control signal to be held. At this point, the nuances do not end: the thyristor can be closed by interrupting the current in the circuit, or by forming an anode-cathode reverse voltage. This means that the use of a thyristor in direct current circuits is very specific and often unreasonable, but alternating circuits, for example in such a device as a thyristor power controller, the circuit is constructed in such a way that the condition for closing is provided. Each of the half-waves will close the corresponding thyristor.

You probably do not understand everything? Do not despair - the process of the finished device will be described in detail below.

The scope of thyristor regulators

In which circuits is the thyristor power controller effective? The circuit makes it possible to perfectly adjust the power of the heating devices, that is, to act on the active load. When working with a highly inductive load, the thyristors can simply not be closed, which can lead to the failure of the regulator.

Is it possible to regulate the engine speed?

I think many of the readers saw or used drills, angle grinders, which people call "Bulgarians", and other power tools. You may have noticed that the number of revolutions depends on the depth of the trigger-trigger. This is the element in which such a thyristor power controller (the circuit of which is shown below) is built-in, by means of which the number of revolutions is changed.

Note! Thyristor regulator can not change the speed of induction motors. Thus, the voltage is regulated on the collector motors equipped with a brush assembly.

Scheme of thyristor power controller on one and two thyristors

A typical circuit in order to assemble a thyristor power regulator by one's own hands is shown in the figure below.

The output voltage for this circuit is 15 to 215 volts, in the case of using the specified thyristors installed on the heat sinks, the power is about 1 kW. By the way, the switch with the brightness control is made according to a similar scheme.

If you do not need to fully adjust the voltage and just get at the output from 110 to 220 volts, use this circuit that shows a half-wave power regulator on the thyristor.

How it works?

The information described below is valid for most schemes. The letters will be taken in accordance with the first scheme of the thyristor regulator

Thyristor power controller, the principle of operation of which is based on the phase control of the magnitude of the voltage, also changes the power. This principle is that under normal conditions the load is affected by the AC voltage of the household network, which varies according to the sinusoidal law. Above, when describing the principle of the thyristor, it was said that each thyristor operates in one direction, that is, it controls its half-wave from the sinusoid. What does it mean?

If the thyristor periodically connects the load at a strictly defined moment, the value of the acting voltage will be lower, since part of the voltage (the effective value that "hits" the load) will be less than the network voltage. This phenomenon is illustrated in the graph.

The shaded area is the area of stress, which turned out to be under load. The letter "a" on the horizontal axis indicates the opening time of the thyristor. When the positive half-wave ends and a period with a negative half-wave begins, one of the thyristors closes and the second thyristor opens at the same time.

We'll figure out how our thyristor power controller works specifically

Scheme One

We will say beforehand that instead of the words "positive" and "negative", "first" and "second" (half-wave) will be used.

So, when the first half-wave starts acting on our circuit, the capacities C1 and C2 begin to be charged. The speed of their charge is limited by the potentiometer R5. This element is variable, and with its help the output voltage is set. When the voltage required for the opening of the VS3 diodistor appears on the capacitor C1, the diistor opens and a current flows through it to open the VS1 thyristor. The moment of breakdown of a dynistor is also the point "a" on the graph presented in the previous section of the article. When the value of voltage passes through zero and the circuit is under the second half-wave, the thyristor VS1 closes and the process is repeated anew, only for the second dinistor, thyristor and capacitor. Resistors R3 and R3 serve to limit the control current, and R1 and R2 are used for thermostabilization of the circuit.

The principle of operation of the second circuit is similar, but it controls only one of the half-waves of the alternating voltage. Now, knowing the principle of operation and the circuit, you can assemble or repair the thyristor power regulator with your own hands.

Application regulator in everyday life and safety

It should be said that this scheme does not provide galvanic isolation from the network, therefore there is a danger of electric shock. This means that you should not touch the controls with the hands. It is necessary to use an insulated enclosure. You should design the design of your device so that if possible you can hide it in the adjustable device, find a free space in the case. If the adjustable device is stationary, then in general it makes sense to connect it through a switch with a dimmer control. This solution is partially protected against electric shock, eliminates the need to find a suitable enclosure, has an attractive appearance and is manufactured by an industrial method.