SCR Full Form

Full Form of SRC

SRC is Silicon Controlled Rectifier or Semiconductor Controlled Rectifier, a four-layer solid-state current-controlling device is known as an SRC or semiconductor-controlled rectifier. General Electric’s commercial name for thyristor types is Silicon controlled rectifier. The silicon-controlled rectifier is primarily helpful in electrical devices that need high-voltages and high-power regulations. As a result, you may use them in processes requiring medium to high Alternating Current power. When you apply gate pulses to an SCR, it conducts like diodes. It comprises semiconductors in four layers that create two different structures: NPNP and PNPN. It also has three terminals and three junctions.

The different stages of SCR

• In the off state of a Silicon-controlled rectifier, the anode receives positive voltages, the gate gets zero voltages, and the cathode receives negative voltages. Hence, the first and third junctions are forward biased, whereas J2 is reverse biased. J2 achieves its avalanche breakdown value and begins to conduct. J1’s resistance is very high below this value, and people, therefore, consider it to be off
• The ON state is achieved by either raising the possible difference between the cathode and anode above the avalanche voltages or providing positive signals to the gate. As soon as the SCR begins to conduct, the gate voltage does not require maintaining the ON state, and the SCR turns off

Triggering/Firing

This technique of ensuring Silicon-controlled rectifier conduction is known as triggering or firing, and it falls among the most prevalent method of latching SCRs in practice. In reality, people often select SCRs with a break overvoltage more significant than the highest voltage predicted from the supply of power, allowing them to be switched on only by a deliberate voltage pulse given to the gates.

Reverse triggering

It’s worth keeping note that you can switch off Silicon-controlled rectifiers directly by connecting their cathode and gate terminals or “reverse-triggering” them with negative voltages (about the cathode) to push the transistor at the lower end into cutoff. Because it entails shunting the collector current of the higher transistor via the base of the transistor at the lower end, I believe this is “occasionally” achievable. This current might be significant, making prompted SCR shut-off problematic at best. A thyristor with Gate-Turn-Off is a version of the SCR that makes this operation more manageable. Even with Gate-Turn-Off, the current needed at the gate to switch it off might be up to 20% of the load current!

Using an Ohmmeter to Check SCR Function

You may use an ohmmeter to conduct a basic test of Silicon-controlled rectifier performance or, at the most miniature terminal identification. Since the connection on the inside between the gate and the cathode is a PN junction (single), a metre with the gate (red test lead) and the cathode (black test lead) should display continuity between these terminals. All additional continuity tests on a Silicon-controlled rectifier will result in an “open” result. It’s essential to remember that this is a reasonably basic test that doesn’t provide a complete picture of the SCR. Even though an SCR gives decent ohmmeter readings, it might still be faulty.

The gate-to-cathode junction voltage signal you obtain from a multimeter with a “diode check” feature may or may not correlate to silicon PN junctions. The junction voltage will be significantly lower in certain circumstances: a few 100ths of a single volt. Some SCRs include a resistor (internal) linked between the cathode and gate, which causes this. This resistor helps to protect the SCR against erroneous triggering caused by sudden voltage spikes, noise, or static discharge of electric pulses.

Conclusion

True rectifiers, SCRs allow just one direction of current to pass through them. As a result, you cannot utilise them to manage full-wave AC power independently. When you replace the diodes in a rectifier circuit with SCRs, a controlled rectifier circuit is formed, with DC power to a load time-proportioned by activating the SCRs at different places along the AC power waveform.