Introduction: Key gadgets in power electronic devices

Silicon-controlled rectifiers (SCRs), likewise referred to as thyristors, are semiconductor power gadgets with a four-layer three-way junction structure (PNPN). Since its intro in the 1950s, SCRs have actually been extensively made use of in industrial automation, power systems, home device control and other areas as a result of their high withstand voltage, large existing lugging capacity, quick feedback and straightforward control. With the advancement of technology, SCRs have developed into several kinds, consisting of unidirectional SCRs, bidirectional SCRs (TRIACs), turn-off thyristors (GTOs) and light-controlled thyristors (LTTs). The differences between these kinds are not only mirrored in the structure and working concept, however also establish their applicability in different application circumstances. This post will certainly start from a technological viewpoint, combined with specific criteria, to deeply evaluate the primary differences and normal uses of these 4 SCRs.

Unidirectional SCR: Standard and stable application core

Unidirectional SCR is the most standard and common kind of thyristor. Its framework is a four-layer three-junction PNPN plan, consisting of three electrodes: anode (A), cathode (K) and entrance (G). It just enables existing to flow in one instructions (from anode to cathode) and activates after eviction is triggered. When activated, even if the gate signal is eliminated, as long as the anode current is higher than the holding current (generally much less than 100mA), the SCR remains on.

(Thyristor Rectifier)

Unidirectional SCR has strong voltage and current tolerance, with an ahead repetitive top voltage (V DRM) of approximately 6500V and a rated on-state typical existing (ITAV) of as much as 5000A. As a result, it is widely used in DC motor control, industrial heater, uninterruptible power supply (UPS) correction parts, power conditioning devices and other events that need continual conduction and high power processing. Its benefits are basic framework, inexpensive and high integrity, and it is a core element of lots of traditional power control systems.

Bidirectional SCR (TRIAC): Perfect for AC control

Unlike unidirectional SCR, bidirectional SCR, additionally known as TRIAC, can attain bidirectional conduction in both favorable and unfavorable half cycles. This framework contains 2 anti-parallel SCRs, which enable TRIAC to be set off and turned on any time in the AC cycle without changing the circuit link technique. The symmetrical conduction voltage series of TRIAC is normally ± 400 ~ 800V, the optimum lots current has to do with 100A, and the trigger current is less than 50mA.

Due to the bidirectional conduction features of TRIAC, it is particularly ideal for AC dimming and rate control in household home appliances and consumer electronics. As an example, tools such as lamp dimmers, fan controllers, and air conditioning system fan rate regulatory authorities all rely upon TRIAC to accomplish smooth power guideline. In addition, TRIAC also has a reduced driving power requirement and appropriates for integrated layout, so it has been extensively made use of in clever home systems and tiny devices. Although the power density and switching rate of TRIAC are not like those of brand-new power gadgets, its inexpensive and hassle-free usage make it an important player in the field of little and average power a/c control.

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

Gate Turn-Off Thyristor (GTO) is a high-performance power tool developed on the basis of standard SCR. Unlike regular SCR, which can just be turned off passively, GTO can be turned off actively by applying an adverse pulse present to eviction, hence accomplishing even more flexible control. This feature makes GTO execute well in systems that require constant start-stop or fast reaction.

(Thyristor Rectifier)

The technological parameters of GTO reveal that it has extremely high power handling ability: the turn-off gain has to do with 4 ~ 5, the maximum 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 extensively utilized in high-power circumstances such as electric locomotive traction systems, huge inverters, industrial motor frequency conversion control, and high-voltage DC transmission systems. Although the drive circuit of GTO is reasonably complicated and has high switching losses, its efficiency under high power and high dynamic response needs is still irreplaceable.

Light-controlled thyristor (LTT): A dependable choice in the high-voltage isolation environment

Light-controlled thyristor (LTT) uses optical signals rather than electrical signals to set off transmission, which is its biggest feature that distinguishes it from various other sorts of SCRs. The optical trigger wavelength of LTT is normally between 850nm and 950nm, the response time is gauged in milliseconds, and the insulation degree can be as high as 100kV or over. This optoelectronic isolation mechanism greatly boosts the system’s anti-electromagnetic interference capability and safety.

LTT is primarily used in ultra-high voltage direct present transmission (UHVDC), power system relay protection gadgets, electro-magnetic compatibility defense in clinical devices, and military radar communication systems and so on, which have extremely high demands for security and stability. As an example, many converter stations in China’s “West-to-East Power Transmission” job have actually embraced LTT-based converter valve modules to guarantee steady operation under extremely high voltage conditions. Some progressed LTTs can likewise be combined with gateway control to attain bidirectional conduction or turn-off functions, further expanding their application array and making them an optimal selection for fixing high-voltage and high-current control issues.

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