Ⅰ. History of Thyristor
Ⅱ. Characteristics and advantages and disadvantages of thyristor
Ⅲ. Function of Thyristor
Ⅳ. The relationship between thyristor and transistor
Ⅴ. What are the protection measures for the thyristor?
Ⅵ. Working conditions and working principle of thyristor
Ⅶ. Bidirectional Thyristor
Ⅷ.Thyristor-TVS, SCR, TRIAC, DIAC, SIDAC
A thyristor is a semiconductor power device that belongs to the thyristor class of devices. It is an electronic device with amplification and switching characteristics, widely used in power control and electronic frequency conversion and other fields. A thyristor can be regarded as a two-way switch, which can conduct current only under the action of a trigger signal. Once it is turned on, it will maintain a conductive state until the current drops to a certain value.
Thyristors are usually constructed of four layers of semiconductor material (P-N-P-N), where "P" stands for positive (positive polarity) and "N" stands for negative (negative polarity). Its working principle is based on the characteristics of the semiconductor PN junction, by applying a trigger pulse or signal to control the conduction of the device, and then realize the current control.
The first thyristor device became commercially available in 1956. Because thyristors can control relatively large amounts of power and voltage with a small device, they find widespread use in power control, from dimmers and motor speed control to high-voltage DC transmission.
A thyristor is a four-layer three-terminal semiconductor device, each layer consisting of alternating N-type or P-type materials, such as P-N-P-N. The main terminals, labeled anode and cathode, span all four layers. The control terminal, called the gate, is connected to the p-type material near the cathode. (A variant called SCS (Silicon Controlled Switching) brings all four layers out to the terminals.) The operation of a thyristor can be understood as a pair of tightly coupled bipolar junction transistors arranged to act in a self-latching manner.
A thyristor has three states:
1. Forward blocking mode – the direction of voltage application causes the diode to conduct, but the thyristor is not triggered to conduct
2. Reverse blocking mode - apply voltage in the direction that the diode will block
3. Forward conduction mode – the thyristor has been triggered to conduct and will remain in conduction until the forward current drops below a threshold called the holding current.
Ⅰ. History of Thyristor
The emergence of semiconductors became one of the most significant breakthroughs in modern physics in the 20th century, marking the birth of electronics. Due to the actual needs of different fields, semiconductor devices have been rapidly developed into two branches since then. One of the branches is microelectronic devices represented by integrated circuits, which are characterized by low power and integration. Tools for delivery and processing.
The other category is power electronic devices, which are characterized by high power and rapidity. In 1955, General Electric Company of the United States published the world's first silicon rectifier (SR) using silicon single crystal as the semiconductor rectification material. In 1957, it published the world's first silicon controlled rectifier (SCR) for power conversion and control. ).
Due to their advantages of small size, light weight, high efficiency and long life, especially SCR can control large power with small current, semiconductor power electronic devices have successfully entered the field of strong current control from the field of weak current control, high power control field. In the application of the rectifier, the thyristor quickly replaced the mercury rectifier (ignition tube), making the rectifier solid, static and non-contact, and significantly saving energy.
Since the 1960s, ordinary thyristors have successively derived thyristors with various characteristics such as fast thyristors, light-controlled thyristors, asymmetric thyristors, and bidirectional thyristors, forming a huge family of thyristors.
The thyristor itself has two important factors restricting its continued development. One is the lack of control function. Ordinary thyristors are semi-controlled devices. The gate (control pole) can only be used to control its opening but not its shutdown. After it is turned on, the control pole will no longer work. Cut off the power supply, that is, the forward current flowing through the thyristor is less than the holding current. Due to the uncontrollable turn-off characteristics of the thyristor, it must be equipped with a forced commutation circuit composed of inductors, capacitors and auxiliary switching devices, which will increase the size of the device, increase the cost, and the system will be more complicated and the reliability will be reduced. Second, because this type of device is based on a discrete device structure, the turn-on loss is large, and the operating frequency is difficult to increase, which limits its application range.
At the end of the 1970s, as the turn-off thyristor (GTO) became more and more mature, it successfully overcomes the defects of ordinary thyristors, marking the development of power electronic devices from half-controlled devices to fully-controlled devices.
Ⅱ. Characteristics and advantages and disadvantages of thyristor
1. Features:
To turn on the thyristor, one is to apply a forward voltage between its anode A and cathode K, and the other is to input a forward trigger voltage between its control pole G and cathode K. After the thyristor is turned on, the button switch is released, the trigger voltage is removed, and the conduction state is still maintained.
A thyristor is a thyristor-like device that changes from blocking current flow to conducting only when a sufficient trigger voltage is applied. This enables the thyristors to achieve control and regulation of current flow.
A thyristor is bidirectional, which means it can conduct forward current (from anode to cathode) and reverse current (from cathode to anode). This makes thyristors suitable for DC conversion and control of AC power supplies.
The voltage and current characteristics of a thyristor are closely related to its working state and application, including rated voltage, rated current, maximum voltage and current, etc.
Shutdown of the thyristor requires the current to drop to zero or below a lower limit, or an external trigger to disconnect the current. Once the thyristor is turned off, it returns to the blocking state.
Thyristor conduction requires a sufficient excitation voltage. Once the excitation voltage is reached or exceeded, the thyristor will switch from blocking state to conducting state.
2. Advantages:
Controllability: The thyristor can control the conduction of the current through an external trigger signal, so as to realize precise current control and switching operation.
Bidirectional conduction: Thyristors have bidirectional conduction characteristics and can be used for DC conversion and control of AC power.
High power carrying capacity: Thyristors can withstand high current and high voltage, suitable for high power applications such as power control and industrial drives.
High Efficiency: Once turned on, the thyristor has very little conduction loss, making it advantageous in high-efficiency applications.
Fast Switching Speed: Thyristors switch relatively fast and are suitable for applications that require a fast response.
Energy saving: Thyristors can achieve efficient use of energy through current control, especially in motor control and power frequency conversion.
Reliability: Under the right conditions, thyristors have high reliability and long life. They are usually able to work in harsh environments.
3. Disadvantages:
Switching characteristics: Thyristors require an external trigger signal to switch, so auxiliary circuits are required to achieve switching control, which may increase the complexity of the circuit.
Voltage Controlled Gate: Thyristors require a high excitation voltage to control conduction, which may limit their application in some cases.
Shutdown characteristics: Shutdown of the thyristor needs to reduce the current to zero or below the lower limit, or to achieve by external triggering.
Temperature dependence: The performance and characteristics of thyristors are affected by temperature changes.
Current Leakage: Thyristors have a small reverse current leakage in the off state.
Ⅲ. Function of Thyristor
A thyristor has three p-n junctions (named J1, J2, J3 sequentially starting from the anode). When the anode is at positive potential VAK with respect to the cathode and no voltage is applied to the gate, junctions J1 and J3 are forward biased and junction J2 is reverse biased. Since J2 is reverse biased, no conduction (off state) occurs. Now, if VAK increases above the breakdown voltage VBO of the thyristor, an avalanche breakdown occurs in J2 and the thyristor starts to conduct (conduction state).
If a positive potential VG is applied at the gate terminal with respect to the cathode, the breakdown of junction J2 occurs at a lower value of VAK. By choosing an appropriate VG value, the thyristor can be quickly switched to the conduction state.
Once avalanche breakdown occurs, the thyristor continues to conduct regardless of the gate voltage until: (a) the potential VAK is eliminated or (b) the current through the device (anode-cathode) becomes less than the holding current specified by factory. Therefore, VG can be a voltage pulse, such as the voltage output of a UJT relaxation oscillator.
The gate pulse is characterized by a gate trigger voltage (VGT) and a gate trigger current (IGT). The gate trigger current is inversely proportional to the gate pulse width, and it is clear that a minimum gate charge is required to trigger the thyristor.
Thyristor is one of the key devices in power control. It can be used to control the current of high-power loads (such as motors, heating elements, etc.) to achieve precise regulation and control of power.
Thyristors are used in electric furnaces and resistance welding to control the current flow to heating elements for thermostatic control and high-efficiency welding.
Thyristors can be used to convert AC power to DC power. By using thyristors as switches, AC power can be rectified into DC power for use in electronic devices and circuits.
Thyristors can be triggered by light from photosensitive devices and are used to make light-controlled switches, such as light controls, safety devices, etc.
Ⅳ. The relationship between thyristor and transistor
Thyristors work in a very similar way to transistors, but there are subtle differences. When the low trigger current comes from the gate pin, the current will flow from the anode to the cathode, that is, using the low trigger current from the gate pin can control the high current between the anode and the cathode. While the currents controlled here in transistors are usually very low, typically on the milliampere level, in the control of thyristors there can be varying levels of current intensities from milliamps to ampere levels.
The difference between thyristor and transistor:
1. The difference in working principle
Thyristor: A thyristor is a silicon-controlled device, which is usually composed of four layers of semiconductor materials (P-N-P-N structure). A thyristor has a control pole (Gate) and two main poles (Anode anode and Cathode cathode). Its working principle involves triggering a signal to control conduction. When a sufficient positive pulse signal is applied to the control electrode, electrons are injected from the control electrode to the P region, so that the P-N junction region forms a conduction channel, allowing current to flow from the anode to the cathode. Once turned on, the thyristor remains on until the current drops below the holding current. At this time, the thyristor can be disconnected by an external circuit, or the thyristor will be automatically disconnected after the current is reduced to a certain level.
Transistor: A transistor is a semiconductor device used for signal amplification and switching operation, and there are various types such as bipolar junction transistor (BJT) and field effect transistor (FET).
2. Differences in basic structure
Transistors: There are many types of transistors, including bipolar junction transistors (BJTs) and field effect transistors (FETs). BJT includes NPN and PNP types, and FET includes MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and JFET (Junction Field Effect Transistor).
Thyristor: A thyristor is a silicon-controlled device, usually composed of four layers of semiconductor material (P-N-P-N structure).
Ⅴ. What are the protection measures for the thyristor?
Overcurrent Protection: A current limiting circuit is used to ensure that the current to the thyristor does not exceed its rating. This can be accomplished with current sensors, fuses, current limiting resistors, etc.
Reverse voltage protection: To prevent the reverse voltage from exceeding the tolerance range of the thyristor, a reverse diode can be used to maintain it.
Over-temperature protection: The operating temperature of the thyristor should be within a safe range to prevent overheating. The thyristor temperature can be monitored using a thermistor, temperature sensor, etc., and measures can be taken to reduce the temperature, such as heat sinks, fans, etc.
Overvoltage Protection: An overvoltage protection circuit is used to prevent thyristors from being exposed to voltages in excess of their ratings. This can include the use of overvoltage protection circuits, voltage monitors, etc.
Electrostatic protection: When handling and installing thyristors, take appropriate anti-static measures to avoid damage to thyristors caused by electrostatic discharge.
Trigger control: Ensure the stability and accuracy of the trigger signal, avoid false triggering and incomplete triggering, and prevent abnormal conduction.
Current pulse protection: When the thyristor is triggered to conduct, a current pulse may be generated, which may cause interference to other parts. This interference can be reduced by using filters or relays etc.
Ⅵ. Working conditions and working principle of thyristor
1. Working conditions
When a thyristor is subjected to a forward anode voltage, the thyristor will only conduct if the gate is subjected to a forward voltage. At this time, the thyristor is in the forward conduction state, which is the thyristor's thyristor characteristic, that is, the controllable characteristic.
When the thyristor is subjected to the reverse anode voltage, no matter what voltage the gate is subjected to, the thyristor is in a reverse blocking state.
When the thyristor is turned on, as long as there is a certain positive anode voltage, the thyristor remains on regardless of the gate voltage, that is, after the thyristor is turned on, the gate loses its function. The gate only acts as a trigger.
When the thyristor is turned on, when the main circuit voltage (or current) decreases to close to zero, the thyristor turns off.
2. Working principle
One-way thyristor:
The unidirectional thyristor is a PNPN flash layer structure, forming three PN junctions, with three external electrodes: anode, cathode K and control pole G. The one-way thyristor can be equivalent to a composite tube composed of two transistors, PNP and NPN. After a positive voltage is applied across the anode A, the thyristor does not conduct. Only when the trigger voltage is applied to the gate G, VT1 and VT2 are turned on rapidly one after another, and they provide base current to each other to maintain the thyristor on. At this time, even if the trigger voltage on the control electrode is removed, the thyristor remains on, and the thyristor is not turned off until the passing current is less than the holding current of the thyristor.
Triac:
A bidirectional thyristor can be equivalent to two unidirectional thyristors connected in reverse parallel, as shown in Figure 4-47. The bidirectional thyristor can control bidirectional conduction, so the other two electrodes except the control electrode G are no longer divided into anode and cathode, but are called main electrodes T1 and T2. When a trigger voltage is applied to the control electrode G, the bidirectional thyristor is turned on, and the well remains on after the trigger voltage disappears. The current can flow from T1 to T2 through VS2, and from T2 to T1 through VS1. The thyristor turns off when the current is less than the holding current of the thyristor.
Thyristors can be turned off:
After the ordinary unidirectional or bidirectional thyristor is turned on, the control pole will not work. To turn off the thyristor, the power must be cut off so that the forward current flowing through the thyristor is less than the maintenance current I. The feature of the turn-off thyristor is that it can be turned off by the control pole break, overcome the above-mentioned defects. When the turn-off thyristor control pole G is applied with a positive pulse voltage, the thyristor is turned on, and when the control pole G is applied with a negative pulse voltage, the thyristor is turned off.
Ⅶ. Bidirectional Thyristor
A triac is a three-terminal electronic component that conducts current in either direction when triggered. It is a subset of thyristors (similar to relays in that small voltages and currents can control larger voltages and currents) and is related to thyristors (SCRs). Triacs differ from SCRs in that they allow current to flow in both directions, whereas SCRs can only conduct current in one direction. Most triacs can be triggered by applying a positive or negative voltage to the gate (SCRs require a positive voltage). Once triggered, the SCR and triac will continue to conduct even if the gate current stops, until the main current drops below a certain level called the holding current.
The bidirectional nature of triacs makes them convenient switches for alternating current (AC). Additionally, the application of flip-flops with controlled AC phase angles in the main circuit can control the average current flowing into the load (phase control). This is commonly used to control the speed of general motors, dim lights and control electric heaters. Triacs are bipolar devices.
Ⅷ.Thyristor-TVS, SCR, TRIAC, DIAC, SIDAC
It is an electronic device used to protect electronic equipment and circuits from transient overvoltages (such as lightning strikes, electromagnetic pulses, etc.). Its operating principle involves the characteristics of thyristors. A TVS device usually consists of one or more junction thyristors, which are used to limit overvoltage, discharge the overvoltage to ground or other appropriate locations, and thus protect electronic equipment from damage.
It is an important semiconductor device and belongs to a kind of thyristor device. It has a wide range of uses in power control and electronic applications. Thyristors are usually constructed of four layers of semiconductor material (P-N-P-N), forming a PNPN structure. It has three main poles: Anode, Cathode and Gate. The working principle of the thyristor is based on the characteristics of the PNPN structure, and when the trigger signal is applied to the control electrode, it changes from the blocking state to the conducting state.
It is a bidirectional semiconductor device that can control positive and negative alternating currents. TRIAC consists of two PNPN structures forming a bidirectional conduction channel. It has three main pins: MT1 (Master 1), MT2 (Master 2) and G (Gate, control pole). Similar to the thyristor, the work of the TRIAC also involves the characteristics of the PNPN structure and the excitation of the gate.
It is a special type of semiconductor device, which is often used to trigger the control circuit of bidirectional conduction devices (such as TRIAC). A DIAC can be considered as a bidirectional flip-flop, which has two PN junctions that conduct current in both forward and reverse directions. A DIAC usually consists of two interconnected PN structures to form a bidirectional conduction device. It only has two pins, unlike some other devices which have three pins (eg TRIAC). The operation of the DIAC involves breakdown of the PN junction under forward and reverse voltages.
Is a special type of semiconductor device, also known as a voltage-controlled bidirectional switch. Like other devices, SIDACs also have unique characteristics in specific applications. SIDAC is a bidirectional conduction device with two PN junctions. It is somewhat similar to DIAC, but differs in how it works. The operation of the SIDAC involves breakdown of the PN junction under forward and reverse voltages, enabling it to conduct current in both directions.
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