Whether you’re using them for indication, communication, lighting, or just for some added cool factor to a project, all LEDs have one thing in common: they are unable to regulate current. Without a limited current flow, LEDs will eventually fail. Sometimes catastrophically.
The PWM for LEDs for current control is often used when resistors would make it too expensive. Most LEDs have a ability to handle a lot of current for a short period in time. If you average the on/off time the average power rating of the LED is within specs.
Why would you drive an LED without a resistor? Simple, to make your circuit more energy efficient. Should you drive your LED with PWM set to a constant duty cycle (i.e. 5V PWM at 34% duty cycle to achieve an average voltage of 1.7V)? Yes and no.
Favorite 68 Introduction LEDs are all around us: In our phones, our cars and even our homes. Any time something electronic lights up, there's a good chance that an LED is behind it. They come in a huge variety of sizes, shapes, and colors, but no matter what they look like they have one thing in common: they're the bacon of electronics.
The main reason LEDs need resistors is to protect the LED from excessive current which can permanently damage the LED. LEDs have current ratings which indicate the optimal current at which the LED operates effectively.
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why do leds need resistors
