![]() The name Triac stands for triode (three electrode) AC switch. The SCR will continue to conduct after the trigger pulse has ceased, until current through the SCR ceases, at which point it returns to a blocking state. The SCR will conduct with an almost constant voltage drop across it – typically 1.2 Vdc. This trigger pulse will trigger the SCR into conduction and current will pass from A to K. If terminal K is taken positive with respect to A, the SCR is reverse biased and will block current from flowing. If terminal A is taken positive with respect to K, the SCR is forward biased, and will block current flow until terminal G (the gate) receives a positive pulse with respect to K. We can easily control a 500 watt load with standard relays.Īn SCR (silicon controlled rectifier, or thyristor) is a semiconductor switching device, with two power terminals, called the anode (A) and cathode (K) and one control terminal called the gate (G). Relays can handle 10-15 Amperes of current and 110-220 volts. In order to supply them sufficient voltage they are derived through transistors. But some relays coils require more current to switch the output channel. ![]() Small +3 volt and +5 volt relays can directly be controlled trough microcontrollers GPIO(General purpose input/output) pins. Relays can directly be controlled with microcontroller pins. Relay’s comes in many packages such as single pole single through, double pole and double through(DBDT), Single pole double trough(SPST) etc. The path is a straight mechanical connection between wires. A 5 pin relay is shown on left hand side. ![]() Making a path of current flow between common and normally open pin. But when a sufficient voltage is applied across the coil of relay the common pin shorts with the NO(Normally Open) pin. Of current flow between common and normally close line. During ideal state(No Power) the common pin is shorted with the NC(Normally Close) pin. Relays consists of a coil and a NC(Normally Close), NO(Normally Open) and Common line. Relays are mechanical switches that open and close when voltage is applied across its specified pins. Driving heavy loads with Microcontrollers and Transistors. I interfaced the above components in many circuits with different microcontrollers e.g Arduino, Pic, Stm32, 8051, Picaxe, Avr, Atmega, Arm and LPC series etc to control high power loads. The above components can be used with mini computers or development boards such as BeagleBone, Raspberry Pi, Olimex and Xilinx FPGA boards. These electronic components can be interfaced with any vendor of microcontrollers Altera, Atmel, Cypress Semiconductor, Maxim Integrated, EPSON Semiconductor, Freescale Semiconductor, Infineon, Intel, Microchip Technology, National Semiconductor, NXP Semiconductors, Panasonic, Parallax, Silicon Laboratories, Silicon Motion, Sony, STMicroelectronics, Texas Instruments, Toshiba. The upper list starts from low power control electronic component(Transistor) to high power control(SSR-Solid State relay). We can use following electronic components to drive high power loads with microcontrollers. ![]()
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