1. Definition of Thyristor (SCR).
Thyristor, also known as SCR, is a high-power semiconductor device consisting of three PN structures.In terms of performance, the thyristor not only has unidirectional conductivity, but also has more valuable controllability than the silicon rectifier element. It only has two states of conduction and off.
2.Purpose.
(1).Advantage.
Thyristor has many advantages, such as: controlling large power with small power, power amplification up to hundreds of thousands of times;The reaction is very fast, turning on and off in microseconds.Non-contact operation, no sparks, no noise;High efficiency, low cost.Therefore, especially in high-power UPS power supply system, thyristor has been widely used in rectifier circuit, static bypass switch, contact-free output switch and other circuits.
（2）Weakness.
static and dynamic overload capacity is poor, easy to be disturbed and misleading.
Thyristors are classified into bolt - shaped, flat - plate and bottom - shaped.
3 .Structure and working principle of ordinary thyristor.
Thyristor is a PNPN four layer three terminal device, there are three PN junction.When analyzing the principle, it can be regarded as consisting of a PNP tube and an NPN tube. Its equivalent diagram is shown in Figure 1 (a), and Figure 1 (b) is the circuit symbol of the thyristor.
4 .Working conditions of thyristors:
When the thyristor is subjected to the reverse anode voltage, the thyristor is in the off short state regardless of the gate voltage and the type of voltage.
When the thyristor is under positive anode voltage, the thyristor is on only if the gate is under positive voltage.
In the conduction case of thyristor, as long as there is a certain positive anode voltage, no matter what the gate voltage is, the thyristor maintains the conduction, that is, after the thyristor conducts, the gate loses its function.
The thyristor is turned off when the main circuit voltage (or current) decreases to near zero in the conduction case.
5.Application of thyristors
(1) Choice of thyristor type: There are many types of thyristors, which should be selected reasonably according to the specific requirements of the application circuit.
If it is used for AC/DC voltage control, controllable rectification, AC voltage regulation, inverter power supply, switch power supply protection circuit, etc., ordinary one-way thyristor can be selected.
If it is used for ac switch, AC voltage regulation, ac motor linear speed regulation, lamps linear dimming and solid state relay, solid state contactor and other circuits, should be selected bidirectional thyristor.
if it is used for ac motor frequency conversion speed regulation, chopper, inverter power supply and various electronic switching circuits, etc., the thyristor can be turned off by the gate pole.
BTG thyristor can be used for sawtooth generator, long time delay device, overvoltage protector and high power transistor trigger circuit, etc.
If it is used for electromagnetic oven, electronic ballast, ultrasonic circuit, superconducting magnetic energy storage system and switching power supply, the reverse thyristor can be selected.
If it is used for photoelectric coupler, optical detector, optical alarm, optical counter, photoelectric logic circuit and operation monitoring circuit of automatic production line, optical thyristor can be selected.
(2).Use of thyristors at low temperatures:
The parameters of power electronic devices, such as thyristors and diodes, are closely related to the environmental conditions in which the chips are placed. When working at high altitude and low temperature, users need to pay attention to reasonable application to ensure the devices work reliably.
Among the factory parameters of thyristors in most domestic enterprises, the blocking voltage, leakage current, DI/DT, DV /dt and other parameters refer to the test values under the rated junction temperature. These parameters can still ensure its performance at low temperature.Gate trigger current and gate trigger voltage are measured at 25℃ and generally decrease with increasing temperature.
When used at high altitude and low temperature, attention should be paid to:
I.Under the condition of -40℃, the triggering current value of thyristor gate will double compared with that at 25℃, and the triggering voltage of thyristor gate will increase by about 30%. Therefore, sufficient strength of thyristor gate triggering current is required to ensure the reliable starting of equipment.This is also the strong trigger we ask users to adopt.It also plays an important role in improving the di/dt performance of the device, reducing the opening time and opening loss, and facilitating the serial and parallel operation of the device.The recommended gate triggering conditions are as follows: the threshold triggering current amplitude IG=10IGT (2-5A, <10A);Gate current uptime TR ≤1 s.
II.Under the condition of high altitude, the heat dissipation capacity of the air-cooled radiator will be reduced, but the lower environmental stability is conducive to the heat dissipation of the device. Therefore, the choice of the device and the radiator should be considered according to the highest possible environmental temperature on the site, and a certain current margin should be left.
III.If the device is started and stopped very frequently and the device is frequently cycled between -35℃ and 125℃, the life and reliability of the device will be increased
It is lower than the normal working time. Please pay attention to it.
The power electronic devices produced by Runau Electronics are very reliable in low temperature and high altitude conditions.
6. Several main technical parameters of thyristor.
1.Forward blocking peak voltage (VPFU)
The peak of the forward voltage that can be repeatedly applied to the device under open control and forward blocking conditions.This voltage is specified as 80% of the positive transition voltage value.
2.Reverse blocking peak voltage (VPRU)
It is the peak value of the reverse voltage that can be repeatedly applied to the device at the control circuit break and rated junction temperature.This voltage is specified at 80% of the maximum reverse test voltage value.
3.Rated forward mean current (IF)
When the ambient temperature is +40C, the device conduction (standard heat dissipation condition) can continuously pass through the power frequency (i.e., the power frequency supplied by the power supply network).Generally, it is 50Hz or 60Hz, and the average value of sinusoidal half-wave current is 50Hz in China.
4.Forward mean pressure drop (UF)
The average voltage drop between the anode and the cathode when the device is running at a rated mean forward current under specified conditions.
5.Maintenance current (IH)
The minimum forward current necessary for the device to maintain the conducting state when the control pole is disconnected.
6.Control pole trigger current (Ig)
When dc voltage of 6V is applied between anode and cathode, the minimum dc current of control pole is required to make thyristor complete conduction.
7.Control pole trigger voltage (Ug)
Refers to the minimum dc voltage applied on the control pole during the transition from blocking to conducting state.
The technical parameters of the thyristor are so specialized that we just use the thyristor and can ignore it.The first principle of the type selection is to consider the working reliability, that is, the allowance of current and voltage must be sufficient, then consider the economy, and finally consider the installation of beautiful volume.The rated voltage of the low-voltage motor is 380V thyristor, 1200V is enough; the rated voltage of the 660V motor should be at least 2200V or above, and the voltage withstand voltage of the 1100V high voltage motor thyristor should be at least 3500V.