Question 1:
How does a current-limiting resistor protect an LED, and how can you calculate the appropriate resistor value using Ohm’s Law?
Answer 1:
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A current-limiting resistor protects an LED by restricting the amount of current that can flow through it. LEDs are sensitive to excess current, which can damage or burn them out. Using Ohm’s Law (V = I x R), the resistor value can be calculated by rearranging the formula:
Where:
- VSOURCE is the voltage supplied (for example, 5 V from the ADALM2000)
- VLED is the forward voltage drop of the LED (for example, 1.84 V for a red LED)
- ILED is the desired current (for example, 0.018 A or 18 mA)
By plugging in these values, you get the resistor needed to keep the LED current below its maximum rating.
Question 2:
Why can the current-limiting resistor be placed on either side of the LED and still have the same effect?
Answer 2:
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The current-limiting resistor can be placed either before or after the LED because the resistor limits the current through the entire series circuit. The same current flows through all components in a series circuit. Kirchhoff’s Voltage Law explains this: the sum of voltage drops across all components equals the source voltage. Changing the order of the resistor and LED does not change the total resistance or current, so the LED receives the same current and brightness in either configuration.
See the article: https://www.analog.com/en/resources/analog-dialogue/studentzone/studentzone-december-2025.html