In this article, we work with the most important parameters of SCR which always consider in practice. These parameters are: gate current (IG or sometimes written as IGT), gate voltage (VGT) forward break over voltage (VBO), reverse break down voltage(VDRM), rate current (mostly known as on-state current IT{RMS)) and rate rms voltage (V). Used the SCR datasheet to find these values (pdf).
For example, let us consider the TN12, TS12 and TYNx12 Series from STMicroelectronics. From the SCR datasheets, IT{RMS) parameters is safe to used for driving load current until 12A (rms). The TN12 SCR parameters is shown below. If this SCR is used for rectifier, the maksimum peak inverse voltage (PIV) is equal to 1000 V. It mean that, this SCR can block maksimum reverse voltage until 1000V. Then what about the SCR gate current? The positive low gate current IGT varied from 0.2mA to 15 mA must injected by VGT = 1.5V. So the gate resistance (RG) may varied from 100 Ohm to 7.5 kOhm
Table 1. SCR parameters
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Symbol Value Unit
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IT(RMS) 12 A
VDRM/VRRM 600 to 1000 V
IGT 0.2 to 15 mA
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Source: STMicroelectronics
Note that: Either in sensitive (TS12) or standard (TN12 / TYN) gate triggering levels, the 12 A SCR series is suitable to fit all modes of control, found in applications such as overvoltage crowbar
protection, motor control circuits in power tools and kitchen aids, inrush current limiting circuits,
capacitive discharge ignition and voltage regulation circuits. Available in through-hole or surface-mount packages, they provide an optimized performance in a limited space area.
note: rms= root mean square or effective value .