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 NXP Semiconductors

  • SCR Control Circuit

  • Created: Nov 10, 2014

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This project is an SCR control circuit that uses configurable function gate in regulating the device. SCRs are mainly used in high powered devices that is possibly coupled with high voltage. The 74AUP1G57 provides configurable multiple functions where its output state is determined by eight patterns of 3-bit input. The user can choose the logic functions AND, OR, NAND, NOR, XNOR, inverter, and buffer.In addition, it ensures a very low static and dynamic power consumption across the entire VCC range from 0.8 V to 3.6 V.

In the circuit, input A used to control the current to turn on the SCR while input B will be used to turn off the SCR . When input A is at logic "1″ ,U1 will return to logic "0″. and C1 is charged from a positive light, through R9. The trigger pin through the gate of SCR is U2 while R6 limits the gate current. When the SCR is triggered, it conducts (ON) and hold. The transistor Q1 conducts that will drive the LED to glow. To stop the SCR from conducting, input B should be at logic 1. Moreover, the anode voltage drop across the grounding pin is set to 0V, making the transistor to off along with the LED.

The ability of an SCR to control large currents to a load by means of small gate current makes the device very useful in switching and control applications. SCRs are mainly used in devices where the control of high power, possibly coupled with high voltage, is demanded. Their operation makes them suitable for use in medium to high-voltage AC power control applications, such as lamp dimming, regulators and motor control.