Analysis of types and applications of silicon controlled rectifiers (SCRs): unidirectional, bidirectional, turn-off and light-controlled types

Introduction: Secret devices in power electronic devices

Silicon-controlled rectifiers (SCRs), also called thyristors, are semiconductor power gadgets with a four-layer three-way junction structure (PNPN). Given that its introduction in the 1950s, SCRs have actually been widely made use of in industrial automation, power systems, home appliance control and other areas because of their high withstand voltage, huge existing bring ability, rapid feedback and simple control. With the advancement of innovation, SCRs have developed right into numerous types, including unidirectional SCRs, bidirectional SCRs (TRIACs), turn-off thyristors (GTOs) and light-controlled thyristors (LTTs). The differences between these types are not only shown in the structure and functioning concept, yet additionally establish their applicability in different application circumstances. This article will start from a technical perspective, combined with specific parameters, to deeply analyze the primary distinctions and common uses of these four SCRs.

Unidirectional SCR: Standard and stable application core

Unidirectional SCR is one of the most standard and common sort of thyristor. Its framework is a four-layer three-junction PNPN arrangement, consisting of 3 electrodes: anode (A), cathode (K) and gateway (G). It just enables existing to flow in one direction (from anode to cathode) and turns on after eviction is caused. When switched on, also if eviction signal is removed, as long as the anode current is more than the holding current (typically much less than 100mA), the SCR continues to be on.

(Thyristor Rectifier)

Unidirectional SCR has solid voltage and present tolerance, with a forward repeated optimal voltage (V DRM) of as much as 6500V and a ranked on-state typical present (ITAV) of up to 5000A. Consequently, it is commonly used in DC electric motor control, commercial heating unit, uninterruptible power supply (UPS) correction components, power conditioning gadgets and other celebrations that call for continual transmission and high power processing. Its benefits are straightforward structure, low cost and high reliability, and it is a core part of several traditional power control systems.

Bidirectional SCR (TRIAC): Ideal for air conditioner control

Unlike unidirectional SCR, bidirectional SCR, likewise referred to as TRIAC, can attain bidirectional conduction in both positive and unfavorable fifty percent cycles. This framework contains 2 anti-parallel SCRs, which allow TRIAC to be caused and turned on any time in the air conditioning cycle without altering the circuit link technique. The in proportion transmission voltage range of TRIAC is usually ± 400 ~ 800V, the optimum load current is about 100A, and the trigger current is less than 50mA.

As a result of the bidirectional conduction qualities of TRIAC, it is particularly ideal for AC dimming and speed control in household devices and consumer electronic devices. For example, devices such as light dimmers, follower controllers, and ac system fan rate regulatory authorities all depend on TRIAC to attain smooth power regulation. On top of that, TRIAC additionally has a reduced driving power need and is suitable for integrated design, so it has actually been extensively used in smart home systems and little appliances. Although the power thickness and changing speed of TRIAC are not comparable to those of new power tools, its inexpensive and convenient usage make it an essential gamer in the area of tiny and moderate power air conditioning control.

Gateway Turn-Off Thyristor (GTO): A high-performance agent of energetic control

Gate Turn-Off Thyristor (GTO) is a high-performance power gadget created on the basis of typical SCR. Unlike average SCR, which can just be turned off passively, GTO can be switched off actively by using a negative pulse present to the gate, hence attaining even more flexible control. This feature makes GTO carry out well in systems that need regular start-stop or fast reaction.

(Thyristor Rectifier)

The technical parameters of GTO show that it has extremely high power managing capacity: the turn-off gain has to do with 4 ~ 5, the optimum operating voltage can reach 6000V, and the optimum operating current is up to 6000A. The turn-on time has to do with 1μs, and the turn-off time is 2 ~ 5μs. These efficiency indications make GTO widely used in high-power situations such as electrical engine grip systems, big inverters, commercial electric motor regularity conversion control, and high-voltage DC transmission systems. Although the drive circuit of GTO is reasonably intricate and has high switching losses, its performance under high power and high dynamic reaction requirements is still irreplaceable.

Light-controlled thyristor (LTT): A reputable option in the high-voltage isolation environment

Light-controlled thyristor (LTT) makes use of optical signals as opposed to electric signals to cause transmission, which is its largest function that distinguishes it from other kinds of SCRs. The optical trigger wavelength of LTT is typically between 850nm and 950nm, the feedback time is gauged in split seconds, and the insulation level can be as high as 100kV or above. This optoelectronic seclusion system significantly enhances the system’s anti-electromagnetic interference capacity and security.

LTT is primarily made use of in ultra-high voltage direct present transmission (UHVDC), power system relay protection tools, electromagnetic compatibility protection in clinical tools, and military radar communication systems etc, which have extremely high requirements for safety and security. As an example, numerous converter terminals in China’s “West-to-East Power Transmission” project have taken on LTT-based converter shutoff modules to guarantee steady operation under very high voltage conditions. Some advanced LTTs can also be integrated with gate control to attain bidirectional conduction or turn-off functions, additionally increasing their application variety and making them an optimal option for fixing high-voltage and high-current control troubles.

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