SCR
2. A Deep Dive into Silicon Controlled Rectifiers
The SCR is like that trusty old pickup truck you can always count on. It’s robust, reliable, and gets the job done. It has three terminals: Anode, Cathode, and Gate. The gate is the control terminal; applying a current pulse to the gate triggers the SCR, allowing current to flow from the anode to the cathode. Once triggered, the gate loses control; the SCR remains on until the current through it drops below its holding current. That’s the key characteristic to remember.
Imagine a water slide. You give the first person a little push (the gate current), and they start sliding down (current flow). Once they’re going, you can remove your hand (remove the gate current), but they’ll continue sliding until they reach the bottom (current drops below holding current). Makes sense, right?
Because the gate loses control after triggering, turning off an SCR typically involves interrupting the current flow. This can be done by using a commutation circuit, which essentially forces the current to drop below the holding current. This is a bit like placing a stopper at the bottom of the water slide to stop the flow of sliders. Different commutation techniques exist, each with its own advantages and disadvantages. Some use capacitors and inductors to create a temporary reverse current, while others simply switch off the voltage supply.
SCRs are commonly used in applications where you need to control high-power AC circuits, such as light dimmers, motor speed controllers, and rectifiers. Their ability to handle large currents and voltages makes them ideal for these kinds of applications. They are a simple and effective solution when precise control over the turn-off time isn’t crucial.