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What's wrong with using diodes to step down voltage for LEDs?

I always hear that using a resistor to regulate current for LEDs is very inefficient, even for the low power 5mm ones
What would using a zener diode as well as resistor do if I wanted to run, say just a handful of 5mm LEDs from 12V?


Thanks

Its not so much the voltage you have to worry about with LEDs, it's the current. Either way you go you will have to have a resistor in line with the LED to limit the current. The voltage going to the LED isn't a big factor if you have a large enough resistor. Adding in a zener isn't going to improve efficiency. If anything it will make it worst. If you want it to be more efficient then use more LEDs so you utilize the full 12V. Most 5mm LEDs have a forward voltage of about 2V so 6 LEDS in series will make use of the full 12V. Can't get much more efficient then that.
AndyGadget4 years ago

You wouldn't gain anything.  The heat dissipation in the zener is calculated the same way as a resistor so the efficiency would be the same.
The best way to increase efficiency is to rapidly pulse the LEDs  (PWM) but this would require a lot more circuitry.
rickharris4 years ago
resistors cost £0.60 per 100!!
iceng4 years ago
Depends on how you use the zener....

In series voltage drop and one resistor per led or
in parallel one power limit resistor and one resistor per led..

A