SCR is abbreviated as SCR, which is a kind of high-power electrical component, also called thyristor. It has the advantages of small size, high efficiency, good stability, and reliable work. In the automatic control system, it can be used as a high-power drive device to realize the control of high-power equipment with low-power controls. With its emergence, semiconductor technology has moved from the weak current field to the strong current field, and has become a component used in industries, agriculture, transportation, military scientific research, as well as commercial and civilian electrical appliances.
1. Working principle diagram of thyristor
Thyristor has three poles-anode (A), cathode (K) and control pole (G). The die is a four-layer structure composed of P-type conductors and N-type conductors. There are three PN junctions in total. It is very different in structure from a silicon rectifier diode with only one PN junction. The four-layer structure of thyristor and the introduction of the control electrode laid the foundation for its excellent control characteristics of "controlling big by small".
In the application of thyristor, as long as a small current or voltage is added to the control electrode, a large anode current or voltage can be controlled. At present, SCR components with current capacity of several hundred amperes or even thousands of amperes can be manufactured. Generally, SCRs below 5 amperes are called low-power SCRs, and SCRs above 50 amperes are called high-power SCRs.
2. What are the functions of thyristor?
One of the functions of SCR is controlled rectification, which is also the most basic and most important function of SCR. The well-known diode rectifier circuit can only complete the function of rectification, and does not realize controllability, and once the diode is replaced with a silicon controlled rectifier, a controllable rectifier circuit is formed. In a most basic single-phase half-wave controllable rectifier circuit, when the sinusoidal AC voltage is in the positive half cycle, only when the trigger pulse is applied to the control pole, the thyristor will be triggered to conduct, and there will be voltage output on the load. It is possible to further adjust the average value of the output voltage on the load by changing the arrival time of the trigger pulse on the control pole to achieve the effect of controllable rectification.
The second function of SCR is to be used as a non-contact switch, which is often used in automation equipment to replace general-purpose relays. It has the characteristics of no noise and long life.
The third function of the thyristor is to play the role of switching and voltage regulation. It is often used in AC circuits. Because it is triggered at different times, the current passing through it is only a part of its AC cycle, and the voltage passing through it is only the full voltage. Part of it, thus playing a role in regulating the output voltage.
Three. SCR classification
There are two types of SCRs: one-way SCR and two-way SCR. Triac is also called triac, or TRIAC for short. The bidirectional thyristor is structurally equivalent to two unidirectional thyristors connected in reverse, and this thyristor has a bidirectional conduction function. Its on-off state is determined by the control pole G. Adding a positive pulse (or negative pulse) to the control pole G can make it conduct in the forward (or reverse) direction. The advantage of this device is that the control circuit is simple and there is no reverse withstand voltage problem, so it is particularly suitable for use as an AC non-contact switch.
4. What are the main parameters of SCR?
1. Positive blocking peak voltage (VPFU)
It refers to the peak value of the forward voltage that can be repeatedly applied to the device under the conditions of open control and forward blocking. This voltage is specified as 80% of the positive turning voltage value.
2. Peak reverse blocking voltage (VPRU)
It refers to the peak value of the reverse voltage that can be repeatedly applied to the device under the control pole open circuit and the rated junction temperature. This voltage is specified as 80% of the highest reverse test voltage value.
3. Rated forward average current (IF)
When the ambient temperature is +40C, the device conduction (standard heat dissipation conditions) can continuously pass the power frequency (that is, the power frequency supplied by the power supply network. Generally 50Hz or 60Hz, China's stipulated as 50Hz) the average value of the sine half-wave current.
4. Positive average pressure drop (UF)
Under specified conditions, the average value of the voltage drop between the anode and the cathode when the device is supplied with the rated average forward current.
5. Holding current (IH)
When the control pole is off, the minimum forward current necessary for the device to maintain the on-state.
6. Control pole trigger current (Ig)
When a DC voltage of 6V is applied between the anode and the cathode, the minimum control electrode DC current necessary to make the thyristor fully conduct.
7. Control electrode trigger voltage (Ug)
