In circuits, which component is commonly used to limit current in an LED circuit?

In circuits, which component is commonly used to limit current in an LED circuit?

• A. Open Switch
• B. Thermistor
• C. Resistor
• D. Transformer

Answer: (C)

In LED circuits, keeping the current within safe limits is essential to prevent damage. A resistor in series with the LED provides a simple and effective way to do this because the same current flows through both components, and the resistor drops the extra supply voltage. Using Ohm’s law, the current is determined by I = (V_supply − V_forward_LED) / R. So, by choosing a resistor value, you set the desired LED current. For example, with a 5V supply and an LED that needs about 2V to operate at 20 mA, a resistor of roughly (5 − 2) / 0.02 = 150 ohms works. The resistor also needs a suitable power rating, since P = I^2 × R. Other options aren’t as suitable for steady current limiting in a basic LED setup: an open switch would just cut current off rather than regulate it; a thermistor could vary resistance with temperature and is not a stable current limiter for this purpose; a transformer isn’t used for limiting current in low-voltage DC LED circuits.

In LED circuits, keeping the current within safe limits is essential to prevent damage. A resistor in series with the LED provides a simple and effective way to do this because the same current flows through both components, and the resistor drops the extra supply voltage. Using Ohm’s law, the current is determined by I = (V_supply − V_forward_LED) / R. So, by choosing a resistor value, you set the desired LED current. For example, with a 5V supply and an LED that needs about 2V to operate at 20 mA, a resistor of roughly (5 − 2) / 0.02 = 150 ohms works. The resistor also needs a suitable power rating, since P = I^2 × R.

Other options aren’t as suitable for steady current limiting in a basic LED setup: an open switch would just cut current off rather than regulate it; a thermistor could vary resistance with temperature and is not a stable current limiter for this purpose; a transformer isn’t used for limiting current in low-voltage DC LED circuits.