Opto-isolators for AC signals contain how many LEDs, and DC circuits contain how many LEDs?

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Multiple Choice

Opto-isolators for AC signals contain how many LEDs, and DC circuits contain how many LEDs?

Explanation:
The input side of an opto-isolator is driven by an LED to generate light for the output side. For AC signals, you need the input to conduct on both halves of the cycle. Since an LED conducts only in one direction, two LEDs are arranged in antiparallel so that during the positive half-cycle one LED conducts and during the negative half-cycle the other conducts. This lets the optocoupler respond to the full AC waveform without exposing a single LED to reverse voltage damage. In DC circuits, the current has a fixed direction, so only one LED is needed to light the optocoupler whenever the DC input is present. Thus, two LEDs for AC and one LED for DC.

The input side of an opto-isolator is driven by an LED to generate light for the output side. For AC signals, you need the input to conduct on both halves of the cycle. Since an LED conducts only in one direction, two LEDs are arranged in antiparallel so that during the positive half-cycle one LED conducts and during the negative half-cycle the other conducts. This lets the optocoupler respond to the full AC waveform without exposing a single LED to reverse voltage damage. In DC circuits, the current has a fixed direction, so only one LED is needed to light the optocoupler whenever the DC input is present. Thus, two LEDs for AC and one LED for DC.

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