Hello everyone, welcome to the ZimZimDIY channel. Today, I will introduce an electronic device called SCR. What is SCR? SCR is an electronic device, a type of semiconductor, short for Silicon-controlled rectifier, which can be translated into Thai as a rectifier circuit controlled by silicon. It will be in the group of thyristors. Thyristors are semiconductor materials that are arranged in 4 or more layers from 2 types of semiconductors, which are P-type semiconductors and N-type semiconductors. When we combine all the semiconductors, we will get 3 junctions or PN junctions. They will connect the upper and lower legs to use. The upper leg will be the A (anode) leg, the lower leg will be the K (cathode) leg, and the other leg will be the G (gatte) leg between the 3rd layer. Is it like a diode? This is the symbol of a diode. And this is the symbol of SCR. Notice that there will be a 3rd leg sticking out, which is usually a diode. In general, it will work or conduct current from connecting the power supply terminals correctly and have a forward bias voltage to it, right? That is, there is a voltage of about 0.3 - 0.7 V for the diode to work. But SCR, even with a voltage of more than 0.7 V, is 110V, 220V, thousands of volts connected across it, it will not conduct current. And instead of working, it is us who feed too high a voltage that may destroy the SCR. It may be damaged. So what makes it different from a diode? The fact that it has too many connections means that no matter which side we switch, it cannot conduct current. Therefore, SCR has one leg that is a specific bias leg, similar to a transistor. But we call it a trigger. The triggering characteristic is to use a resistor to drop the current from the positive voltage to a low value of about 18mA, and it works. When it is triggered Most of the current can flow from leg A to leg K immediately. If you still can't visualize it, SCR is similar to having 2 gears, which is a small gear placed here and a larger gear placed here. When we release the current into the G pipe, the small gear will stimulate the large gear at the A pipe to rotate. Most of the current will flow from the A (anode) terminal to the K (cathode) terminal freely. It will work similarly to what I just mentioned, but in an electrical system. And when it successfully conducts the current, it is considered to have done its job 100% perfectly. And you don't have to trigger the current. We can just put a switch to press and release to stimulate the operation. If we look at the structure of the 3rd layer, while it is conducting the current, the P-type semiconductor will temporarily change to an N-type semiconductor. Therefore, now all 3 layers are the same, which means that the SCR has now become a diode that is conducting the current, but it is a diode with a longer N layer than a general diode. If we use SCR with AC, it will only get half a wave of voltage. But if it is used with DC, it will get a normal positive voltage. So most of them are used with DC work, so it is more suitable. Then, how to stop the current flow? How do we do it? When we trigger the G leg and it conducts current, how do we make it stop working? Actually, there are 3 types. Type 1 is to disconnect the power supply, which may be the positive terminal, and remove it. Type 2 may disconnect the power supply from the negative terminal, and remove it. Type 3 is a direct bypass type, which means there will be a switch that is directly connected from terminal A to terminal K. When we press the switch, most of the current will choose to flow through this switch because there is almost no resistance. This causes the SCR to have insufficient power and return to its original state. Its advantages are: 1. It is a solid state switch device, which does not have any moving parts, which means that there is no contact surface. When there is no contact surface, there is no arc. 2. No loss of current in bias. Note that it will be triggered only once, and all the current will flow. Let's take a look at the real SCR. This one will be number 2N6399, withstands a current of 12A, it is considered one of the most popular models. Speaking of which, it is small, similar to a transistor. If you search the datasheet, pin 1 will be pin K, pin 2 will be pin A, and pin 3 will be pin G. Its body will be connected to pin 2 as pin A as well. I will demonstrate and experiment with the current conduction of the SCR. First, plug the SCR into the photo board. I will use an incandescent light bulb as a load in the circuit. Connect one leg of the bulb to the center leg or the anode leg of the SCR. Then use a 9V battery with a battery terminal. Connect the positive wire to the remaining leg of the bulb. After that, plug the negative wire into pin 1 and use another yellow wire to jump the positive terminal of the battery. We will connect it to the trigger leg and reduce the current with a 500ohm resistor. Now, I will try the trick by touching the resist