Silicon Controlled Switch (SCS)

Silicon Controlled Switch SCS (Silicon Controlled Switch) is also called a four-terminal low-power thyristor. It is a novel, multifunctional semiconductor device. As long as the wiring method is changed, ordinary thyristors (SCR), turn-off thyristors (GTO), reverse conduction thyristors (RCT), complementary N-gate thyristors (NGT), programmable unijunction transistors (PUT), single-junction thyristors, etc. can be formed. Transistor (UJT), in addition to NPN transistor, PNP transistor, Shockley diode (SKD), 3 types of Zener diodes, N-type or P-type negative resistance devices, respectively realizing the circuit functions of more than ten kinds of semiconductor devices . To date, there has never been a device with so many functions. Therefore, it is well-deserved to be hailed as a novel "universal" device. The silicon control switch is a PNPN four-layer, four-terminal device. Its internal structure, equivalent circuit and symbols are shown in Figure 1. The equivalent circuit is composed of NPN transistor (T1) and PNP transistor (T2). The four terminals are anode A, cathode K, anode gate GA, and cathode gate GK. Because its gate trigger current is extremely small (several microamps) and its switching time (tON, toFF) is extremely short, it is equivalent to a high-sensitivity low-power thyristor. The capacity is generally 60V, 0.5A, and most are packaged in metal shells. The tube diameter is 8mm. The pin arrangement sequence is shown in Figure 2. Typical foreign products include 3N58, 3N81, MAS32, 3SF11, etc. The biggest feature of the silicon control switch is that there is a terminal on each layer of PNPN, so it is extremely flexible to use. Under different wiring methods, the circuit functions of the silicon control switch are detailed in Table 1. Among them, Shockley Diode SKD (Shockley Diode) is a four-layer, high-speed, controllable semiconductor rectifier diode. It can be used as a switching diode or trigger and is used in laser pulse generators. In addition to the uses listed in the table, silicon controlled switches can be used as relay drivers, delay circuits, pulse generators, bistable flip-flops, and high-sensitivity level detectors. When using the silicon controlled switch GTO, you need to pay attention to the following points (see Figure 3): First: the A pole is connected to the positive pole of the power supply, and the K pole is connected to the negative pole of the power supply; second: the device is turned on when a negative pulse is applied to the GA pole. The device turns off when a positive pulse is applied; third: the device turns on when a positive pulse is applied to the GK pole, and turns off when a negative pulse is applied. The following introduces the method of using a multimeter to check the silicon control switch 1. Check the unidirectional conductivity of the three PN junctions. Set the multimeter to the R×1k range and measure the forward and reverse resistances between A-GA, GA-GK, and GK-K respectively. The forward resistance should be several thousand ohms to more than ten kiloohms, and the reverse resistance should be infinite, indicating that the PN junction has unidirectional conductivity. 2. To check the reverse conductivity, just short-circuit GA and A, and you can observe the reverse conductivity. But in order to make the effect more obvious, now GK and K are also short-circuited. At this time, there are only two silicon PN junctions of the same polarity connected in parallel between A and K, and the K pole is connected to the positive pole of the PN junction, and the A pole is connected to the PN junction. the negative pole. Therefore, connect the black test lead to the K pole and the red test lead to the A pole. What is measured is the forward resistance, which is about several thousand ohms. This characteristic is called "reverse conduction" (meaning reverse conduction). If the positions of the test leads are exchanged, there will be no reverse conductivity and the resistance will become infinite. 3. To check the triggering ability, first connect the black test lead to the A pole and the red test lead to the K pole. The resistance is infinite, which proves that the device is turned off. Then follow the steps below: (1) Touch the GA pole with the tip of the red test lead, and then disconnect it (but the red test lead is always connected to the A pole), which is equivalent to adding a negative pulse to the GA pole. If the resistance decreases rapidly, it means that The device has trigger capability. (2) Take a black test lead and touch the GK pole, and then disconnect it immediately. This is equivalent to inputting a positive pulse to the GK pole, and the resistance value decreases rapidly, indicating that it has triggering ability. 4. To check the shutdown capability, first use the method introduced above to turn on the device, and then perform the following operations: (1) Touch the GA pole with the tip of a black test lead, and then disconnect it. If the resistance becomes infinite, it proves that the device is turned off, see the figure 4(a). (2) Touch the GK pole with the tip of the red test pen and quickly disconnect it. The resistance is infinite, indicating that the SCS is turned off, see Figure 4(b).