Current Limiter: Level 1

Electricity and Magnetism Level 2

LEDs are one of the most important components for electronics hobbyists. Blake is one of them, but he is a novice. Last night he blew up an LED when he connected the LED directly to his $\SI{12}{\volt}$ battery.

Through some research, he found out that each LED has a recommended maximum voltage $V_\text{max}=3.2\text{ V}$ and maximum current $I_\text{max}=20\text{ mA}.$

Any voltage or current supply above that will damage the LED. That's why a current-limiting resistor is connected in series with the LED. This creates a voltage divider that supplies the recommended voltage and current to the LED.

Now, Blake doesn't want to blow up another of his LEDs.

What should be the resistance of the current-limiting resistor?

\leq 400 \Omega

> 400 \Omega

\geq 440 \Omega

\geq 450 \Omega

1 solution

Muhammad Arifur Rahman
Oct 7, 2018

According to Kirchhoff's Law, voltage in a closed loop should be zero . So, $V=R\times I_{max}+V_{max}$ $=> R=\frac{V-V_{max}}{I_{max}}$ $R=440\Omega$

Now, if the resistance is $>440\Omega$ , the current through the circuit should be $<20mA$ - which is just fine for Blake. That's why the answer is $\boxed{\geq 440\Omega}$

For a detailed explanation, I recommend SparkFun's Tutorial

What was the need to mention kirchhoff's law?

Aryan Gupta - 2 years, 8 months ago

It wasn't that necessary for this simple circuit. But this is a standard approach for solving circuits.

Muhammad Arifur Rahman - 2 years, 8 months ago

Current Limiter: Level 1

1 solution

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