SCR Characteristics
SCR stands for silicon control rectifier. The SCR is a type of semiconductor called a thyristor, which are used to handle large amounts of power. The SCR works as both an on and off switch for the power and can also regulate the amount of power going through the device. A number of characteristics are shared between all silicon control rectifiers. Does this Spark an idea?
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Components
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The SCR has three major components: the anode, the cathode and the gate. The relationship between the anode and the cathode determines whether the SCR is in the forward or reverse mode. The forward mode on the SCR is the on and off switch of the device. The reverse mode allows the most power to flow through the thyristor.
Forward Mode
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Forward mode on the SCR occurs when the anode is positive compared to the cathode. To turn the SCR on from an off state a breakover voltage must be supplied. For example, if the SCR breakover voltage is 100 volts, the SCR will remain off, although the voltage will leaks through the system until the voltage reaches 100 volts. To turn off the SCR, the voltage must be reduced to near zero.
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Reverse Mode
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The reverse mode occurs when the anode is negative with the respect to the cathode. Like the forward mode, a breakover voltage is required to activate the reverse mode of the SCR. Reverse mode, once the breakover voltage is reached, starts a massive conduction also called an avalanche. Once the voltage is reduced under the breakover voltage, the SCR will block current flow through the SCR.
Uses
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SCRs are used in applications where switching between a high-resistance, low-current state and a low-resistance, high-current state is required. For example, SCR are found in appliances within the home and in power conversion in high-voltage transmission lines. SCRs are not used in low-voltage applications because turning on and off and switching the direction of current is slower than in other semiconductors. The SCR can only conduct in one direction, making them impractical in situations that require current to be conducted to and from each device.
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