The SCR (Silicon Controlled Rectifier) is called a rectifier because it allows current to flow in only one direction, similar to a diode, thus converting alternating current (AC) to direct current (DC).
Here's a breakdown:
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Unidirectional Conduction: The key characteristic of a rectifier is its ability to permit current flow in one direction only. An SCR, when triggered or "gated" into conduction, acts in precisely this manner. It blocks current flow in the reverse direction, and it allows current to flow in the forward direction only after a gate signal is applied. Once conducting, it will continue to conduct as long as the current through it is above a certain threshold (the holding current) and will continue to act as a rectifier.
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AC to DC Conversion: Rectification is the process of converting alternating current (AC), which flows in both directions, into direct current (DC), which flows in only one direction. Because an SCR can control the timing of forward current flow through its gate terminal, it can be used in sophisticated rectifier circuits (like controlled rectifiers) to regulate the DC output voltage. Without the Gate it would only allow current when the voltage polarity is positive. But, it will still only allow flow in 1 direction.
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Comparison to a Diode: A regular diode is a simple two-terminal device that rectifies based solely on voltage polarity. The SCR adds a third terminal (the gate) which provides control over when the forward conduction can occur. This control element is what sets it apart and is why they are sometimes referred to as controlled rectifiers.
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Solid-State Equivalent of Thyratron: As noted in the provided reference, the SCR is a solid-state equivalent of a thyratron. Thyratrons are gas-filled tubes that also act as switches controlling large amounts of current. Like the SCR, once "fired," the thyratron conducts until the current drops below a certain level. This functional similarity reinforces the SCR's rectifier (and switch) role.
In summary, the SCR's unidirectional current flow, its ability to convert AC to DC (particularly in controlled rectifier circuits), and its historical relation to devices like the thyratron, all contribute to why it is correctly identified as a rectifier. It's more accurately a controlled rectifier, highlighting the gate terminal's importance in regulating conduction.
