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

Introduction: Trick gadgets in power electronics

Silicon-controlled rectifiers (SCRs), also known as thyristors, are semiconductor power gadgets with a four-layer three-way junction framework (PNPN). Considering that its introduction in the 1950s, SCRs have actually been widely utilized in commercial automation, power systems, home device control and other areas as a result of their high hold up against voltage, big present bring capability, quick feedback and simple control. With the advancement of innovation, SCRs have actually advanced right into lots of types, consisting of 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 framework and functioning concept, yet also identify their applicability in various application situations. This article will start from a technological perspective, combined with specific parameters, to deeply analyze the primary differences and common uses of these 4 SCRs.

Unidirectional SCR: Standard and secure application core

Unidirectional SCR is the most basic and typical kind of thyristor. Its framework is a four-layer three-junction PNPN plan, including three electrodes: anode (A), cathode (K) and entrance (G). It only permits existing to move in one direction (from anode to cathode) and switches on after the gate is set off. When switched on, also if the gate signal is eliminated, as long as the anode current is higher than the holding current (usually much less than 100mA), the SCR remains on.

(Thyristor Rectifier)

Unidirectional SCR has strong voltage and present resistance, with a forward repetitive optimal voltage (V DRM) of as much as 6500V and a rated on-state typical present (ITAV) of approximately 5000A. Therefore, it is commonly used in DC electric motor control, industrial heating systems, uninterruptible power supply (UPS) rectification components, power conditioning tools and other celebrations that need continuous transmission and high power handling. Its benefits are simple framework, inexpensive and high reliability, and it is a core component of several traditional power control systems.

Bidirectional SCR (TRIAC): Ideal for air conditioning control

Unlike unidirectional SCR, bidirectional SCR, also referred to as TRIAC, can attain bidirectional transmission in both positive and adverse half cycles. This framework contains two anti-parallel SCRs, which enable TRIAC to be set off and activated at any moment in the AC cycle without changing the circuit link approach. The in proportion conduction voltage range of TRIAC is generally ± 400 ~ 800V, the maximum tons current is about 100A, and the trigger current is less than 50mA.

Due to the bidirectional transmission qualities of TRIAC, it is particularly ideal for AC dimming and speed control in household home appliances and consumer electronics. As an example, gadgets such as light dimmers, fan controllers, and ac system follower speed regulatory authorities all count on TRIAC to attain smooth power policy. On top of that, TRIAC additionally has a reduced driving power need and appropriates for integrated style, so it has actually been widely made use of in clever home systems and tiny devices. Although the power density and switching speed of TRIAC are not comparable to those of new power tools, its low cost and hassle-free use make it an essential player in the field of tiny and average power AC control.

Entrance Turn-Off Thyristor (GTO): A high-performance rep of active control

Gateway Turn-Off Thyristor (GTO) is a high-performance power gadget developed on the basis of typical SCR. Unlike ordinary SCR, which can only be switched off passively, GTO can be switched off actively by applying an unfavorable pulse present to eviction, hence accomplishing even more adaptable control. This function makes GTO perform well in systems that need constant start-stop or quick response.

(Thyristor Rectifier)

The technical specifications of GTO show that it has exceptionally high power dealing with capability: the turn-off gain has to do with 4 ~ 5, the optimum operating voltage can get to 6000V, and the maximum operating current depends on 6000A. The turn-on time has to do with 1μs, and the turn-off time is 2 ~ 5μs. These efficiency indications make GTO commonly used in high-power circumstances such as electrical locomotive grip systems, large inverters, commercial electric motor regularity conversion control, and high-voltage DC transmission systems. Although the drive circuit of GTO is relatively complex and has high switching losses, its efficiency under high power and high vibrant feedback demands is still irreplaceable.

Light-controlled thyristor (LTT): A reliable option in the high-voltage isolation atmosphere

Light-controlled thyristor (LTT) uses optical signals instead of electrical signals to set off conduction, which is its greatest attribute that distinguishes it from other sorts of SCRs. The optical trigger wavelength of LTT is typically in between 850nm and 950nm, the response time is gauged in nanoseconds, and the insulation degree can be as high as 100kV or above. This optoelectronic isolation device substantially improves the system’s anti-electromagnetic interference capacity and safety and security.

LTT is primarily made use of in ultra-high voltage straight present transmission (UHVDC), power system relay protection gadgets, electro-magnetic compatibility security in medical devices, and army radar communication systems etc, which have very high requirements for safety and security. For example, lots of converter stations in China’s “West-to-East Power Transmission” task have adopted LTT-based converter valve modules to ensure stable procedure under incredibly high voltage conditions. Some progressed LTTs can additionally be combined with gateway control to achieve bidirectional conduction or turn-off features, even more increasing their application range and making them a suitable selection for resolving high-voltage and high-current control troubles.

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