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How to Identify an SCR in a Circuit

A silicon-controlled rectifier, or SCR, is an electronic component similar to a diode, but with a third terminal, called a gate, in addition to the diode's anode and cathode terminals. The SCR does not conduct in either direction until the gate receives a trigger of electrical current. SCRs, also called thyristors, are used in electric power control devices from dining-room lamp dimmers to power plants generating millions of watts of electricity. As other electronic components such as transistors also have three leads, and because manufacturers produce SCRs with packaging similar to a transistor, you need a schematic to identify these components in a circuit.

Things You'll Need

Circuit schematic diagram

Instructions

- 1
  Examine the circuit schematic diagram. Find a three-terminal component that looks similar to a diode, though with an extra "leg" coming from the center. The symbol for a diode is a solid black equilateral triangle with a horizontal line at the tip. The SCR's symbol has a third line coming from the center.
- 2
  Find the part number printed on the schematic next to the SCR's symbol. For example, it may say "SCR" or "SCR 1." Note the SCR's location on the schematic relative to other components, such as diodes, transistors or capacitors.
- 3
  Examine the component side of the equipment's circuit board for white, silk-screened lettering next to each component that identifies it by type and number. Find the SCR as identified on the schematic. Make sure the device has three terminals; one terminal may be a metal tab or bolt-like outer package.

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