Thyristor is a semiconductor key, the design of which consists of four layers. They have the ability to move from one state to another - from closed to open and vice versa.
The information presented in this article will help to give an exhaustive answer to the question about this device.
- 1 The principle of operation of the thyristor
- 2 Ways to turn on and off the thyristor
- 3 The main types of thyristors
- 4 Protection
- 5 Thyristor application
- 6 Thyristor Limitations
The principle of operation of the thyristor
In the specialized literature this device also carries the name of a single-operation thyristor. This name is due to the fact that the device is not fully manageable. In other words, when receiving a signal from the control object, it can only switch to the on mode. In order to turn off the device, a person will have to perform additional actions, which will lead to a drop in the voltage level to zero.
The operation of this device is based on the use of a force electric field. To switch it from one state to another, a control technology is applied that transmits certain signals. In this case, the current through the thyristor can move only in one direction. In the off state, this device has the ability to withstand both direct and reverse voltage.
Ways to turn on and off the thyristor
The transition to the working state of a standard device of this type is carried out by teaching a current voltage pulse in a certain polarity. On the speed of inclusion and on how it will subsequently work, The following factors influence:
- The nature of the load. The load in this case may be inductive, active, etc.
- Speed increase control pulse.
- The amplitude of the increase control pulse.
- The temperature of the thyristor.
- The magnitude of the load current.
- The level of voltage applied.
Thyristor shutdown can be implemented in some ways:
- Natural shutdown In the technical literature also found such a thing as natural switching - it is similar to natural shutdown.
- Forced shutdown (forced switching).
The natural shutdown of this device is carried out in the process of its functioning in circuits with alternating current, when the current level drops to zero.
Forced shutdown includes a large number of a variety of ways. The most common of these is the following method.
The capacitor, denoted by the Latin letter C, is connected to the key. It should be denoted by S. In this case, the capacitor must be charged before closing.
The main types of thyristors
Currently, there are a considerable number of thyristors, which differ among themselves by their technical characteristics - the speed of operation, methods and processes of control, the directions of the current while in the conductive condition, etc.
Most common types
- Thyristor diode. Such a device is similar to a device that has an anti-parallel diode in the on mode.
- Diode thyristor. Another name is dynistor. A distinctive feature of this device is that the transition to a conducting mode is carried out at the moment when the current level is exceeded.
- Lockable thyristor.
- Symmetric. He also carries the name of a simistor. The design of this device is similar to two devices with anti-parallel diodes while in operation.
- High-speed or inverter. This type of device has the ability to go down in a record short time - from 5 to 50 microseconds.
- Optotiristor. His work is carried out using the light flux.
- Thyristor under field control on the leading electrode.
Thyristors are included in the list of devices that are critical affect the speed change increase direct current. As well as for diodes, and for thyristors the process of flow of reverse current of recovery is characteristic. A sharp change in its speed and falling to zero mark leads to an increased risk of overvoltage.
In addition, overvoltage in the design of this device may occur due to the complete disappearance of voltage in various components of the system, for example, in small inductances of installation.
For the above reasons, in the overwhelming majority of cases, a variety of CFTP schemes are used to ensure reliable protection of these devices. These circuits, when in dynamic mode, help protect the device from the occurrence of unacceptable voltage values.
A reliable means of protection is also varistor application. This device connects to inductive load output points.
In the most general form, the use of such a device as a thyristor can divided into the following groups:
- Power keys. They are alternating voltage switches. One of the main factors that led to the widespread demand for these devices was the low level of power consumption during operation. Power is susceptible to dissipation in switching parts. In the off state, the power loss is almost zero - this is due to the fact that the voltage level in this situation is zero. When in the open state, the thyristor loses a certain amount of power. However, these losses are completely insignificant.
- Threshold devices. The use of a thyristor in these devices is ensured due to the presence of the property to pass current only at a certain voltage value. Most often, these types of devices are used in phase regulators, as well as relaxation generators.
- DC connection. This group uses locking types of devices. They are necessary to interrupt the voltage in the circuit or to turn the device on and off.
- Experimental devices. Their use in this area due to the property to have negative resistance when in a transition mode.
When working with any type of this device, you should follow certain safety guidelines and also be aware of some of the necessary restrictions.
For example, in the case of an inductive load in the operation of such a type of device as a triac. In this situation, the restrictions relate to the rate of change of the voltage level between the two main elements - its anodes and the operating current. To limit the effects of current and overload apply RC chain.