Various terms and signs are often used in diagrams and technical documentation, but not all novice electricians know their meaning. We propose to discuss what power thyristors for welding are, their principle of operation, characteristics and marking of these devices.
What is a thyristor and their types
Many have seen thyristors in the Running Fire garland, this is the simplest example of the described device and how it works. A silicon rectifier or thyristor is very similar to a transistor. This is a multilayer semiconductor device, the main material of which is silicon, most often in a plastic case. Due to the fact that its principle of operation is very similar to a rectification diode (AC rectifiers or dinistors), the designation on the diagrams is often the same - this is considered an analogue of a rectifier.
Photo - Scheme of a garland running fireThere are:
- ABB turn-off thyristors (GTO),
- standard SEMIKRON,
- powerful avalanche type TL-171,
- optocouplers (say, TO 142-12.5-600 or MTOTO 80 module),
- symmetrical TC-106-10,
- low frequency MTTs,
- triac BTA 16-600B or VT for washing machines,
- frequency TBC,
- foreign TPS 08,
- TYN 208.
But at the same time, for high-voltage devices (furnaces, machine tools, other production automation), transistors such as IGBT or IGCT are used.
Photo - Thyristor But, unlike the diode, which is a two-layer (PN) three-layer transistor (PNP, NPN), the thyristor consists of four layers (PNPN) and this semiconductor device contains three p-n junctions. In this case, diode rectifiers become less efficient. This is well demonstrated by the thyristor control circuit, as well as any reference book of electricians (for example, in the library you can read the book by the author Zamyatin for free).
A thyristor is a unidirectional AC converter, meaning it only conducts current in one direction, but unlike a diode, the device can be made to operate as an open circuit switch or as a direct current rectifying diode. In other words, semiconductor thyristors can only operate in the switching mode and cannot be used as amplification devices. The key on the thyristor is not able to go into the closed position by itself.
The silicon controlled rectifier is one of several power semiconductor devices, along with triacs, AC diodes, and unijunction transistors, that can switch from one mode to another very quickly. Such a thyristor is called a fast thyristor. Of course, the class of the device plays a big role here.
Thyristor application
The purpose of thyristors can be very different, for example, a home-made thyristor-based welding inverter, a car charger (thyristor in the power supply) and even a generator are very popular. Due to the fact that the device itself can pass both low-frequency and high-frequency loads, it can also be used for a transformer for welding machines (just such parts are used on their bridge). To control the operation of the part in this case, a voltage regulator on the thyristor is necessary.
Photo - the use of Thyristor instead of LATR Do not forget about the ignition thyristor for motorcycles.
Description of the design and principle of operation
The thyristor consists of three parts: "Anode", "Cathode" and "Input", consisting of three p-n junctions that can switch from "ON" and "OFF" at a very high speed. But at the same time, it can also be switched from the "ON" position with different durations in time, i.e. for several half-cycles, in order to deliver a certain amount of energy to the load. The operation of a thyristor can be better explained by assuming that it will consist of two transistors connected to each other, like a pair of complementary regenerative switches.
The simplest microcircuits show two transistors, which are combined in such a way that the collector current, after the “Start” command, flows to the NPN transistor TR 2 channels directly into the PNP transistor TR 1. At this time, the current from TR 1 enters the channels in the bases of TR 2. These two interconnected transistors are arranged so that the base-emitter receives current from the collector-emitter of the other transistor. This requires parallel placement.
Photo - Thyristor KU221IM Despite all safety measures, the thyristor can involuntarily move from one position to another. This is due to a sharp jump in current, temperature differences and other various factors. Therefore, before you buy a thyristor KU202N, T122 25, T 160, T 10 10, you need to not only check it with a tester (ring), but also familiarize yourself with the operating parameters.
Typical thyristor I-V characteristics
To start a discussion of this complex topic, view the diagram of the thyristor IV-characteristics:
Photo - characteristic of the VAC thyristor - The segment between 0 and (Vvo, IL) fully corresponds to the direct locking of the device;
- In section Vvo, the “ON” position of the thyristor is carried out;
- The segment between the zones (Vin, IL) and (Vn, In) is a transitional position in the on state of the thyristor. It is in this area that the so-called dinistor effect occurs;
- In turn, the points (Vn, In) show on the graph the direct opening of the device;
- Points 0 and Vbr are the section with thyristor blocking;
- This is followed by the segment Vbr - it denotes the reverse breakdown mode.
Naturally, modern high-frequency radio components in the circuit can affect the current-voltage characteristics in an insignificant form (coolers, resistors, relays). Also, symmetrical photothyristors, SMD zener diodes, optothyristors, triode, optocoupler, optoelectronic and other modules may have other CVCs.
Photo - CVC thyristor In addition, please note that in this case, the devices are protected at the load input.
Thyristor test
Before you buy a device, you need to know how to check the thyristor with a multimeter. The measuring device can only be connected to a so-called tester. The scheme by which such a device can be assembled is presented below:
Photo - thyristor tester According to the description, a positive voltage must be applied to the anode, and a negative voltage to the cathode. It is very important to use a value that matches the resolution of the thyristor. The drawing shows resistors with a nominal voltage of 9 to 12 volts, which means that the voltage of the tester is slightly higher than the thyristor. After you have assembled the device, you can begin to check the rectifier. You need to press the button that gives pulse signals to turn it on.
Checking the thyristor is very simple, the opening signal (positive relative to the cathode) is briefly applied to the control electrode with the button. After that, if running lights lit up on the thyristor, then the device is considered inoperative, but powerful devices do not always immediately respond after the load arrives.
Photo - tester circuit for thyristors In addition to checking the device, it is also recommended to use special controllers or a control unit for thyristors and triacs ARIES BOOST or other brands, it works in much the same way as a power regulator on a thyristor. The main difference is a wider range of voltages.
Video: the principle of operation of the thyristor
Specifications
Consider the technical parameters of the thyristor of the KU 202e series. This series presents domestic low-power devices, the main application of which is limited to household appliances: it is used to operate electric furnaces, heaters, etc.
The drawing below shows the pinout and the main parts of the thyristor.
Photo - ku 202 - Set reverse on-state voltage (max) 100 V
- Closed voltage 100 V
- Impulse in the open position - 30 A
- Repetitive pulse open 10 A
- Medium voltage<=1,5 В
- Non-triggering voltage >=0.2 V
- Set current in open position<=4 мА
- Reverse current<=4 мА
- DC trigger current<=200 мА
- Set DC voltage<=7 В
- Turn-on time<=10 мкс
- Shutdown time<=100 мкс
The device turns on within microseconds. If you need to replace the described device, then consult with the sales assistant of the electrical store - he will be able to select an analogue according to the scheme.
Photo - thyristor ku202n The price of a thyristor depends on its brand and characteristics. We recommend buying domestic appliances - they are more durable and have an affordable cost. In spontaneous markets, you can buy a high-quality powerful converter up to hundreds of rubles.