4 ms·

It has to be a good source of direct current, literally. It has to produce a steady, constant amperage regardless of grid spikes and fluctuations. Given that th

It has to be a good source of direct current, literally. It has to produce a steady, constant amperage regardless of grid spikes and fluctuations. Given that the grid is AC, this requires a relatively complex circuit and more careful engineering than is commonly done for the power supplies inside bulbs. Edit: Sometimes LED current is actually high-current AC with a square waveform, especially with dimmable bulbs. This is fine provided it's well-regulated and protected from spikes.

acchow 8y ago
Can we design an LED that isn't affected by typical city fluctuations and spikes?
- pixl97 8y ago
  If you can, I'm sure someone would pay you a lot of money for the design.
- Itsdijital 8y ago
  I'm not sure where the OP is coming from because any halfway decent LED driver will accept a wide range of voltages, far more than the fluctuations seen on public lines.
  - dreamcompiler 8y ago
    I think he's asking if LEDs themselves can be more tolerant, since the drivers built in to LED bulbs rarely even rise to the level of "halfway decent."
  - Itsdijital 8y ago
    LEDs themselves are very intolerant of voltage (well really current fluctuations, semi-conductors are weird), but that isn't an issue because the driver deals with that and large swings will kill the driver or kill the driver and LED. LED tolerance doesn't really play into the scenario here. It's all about the driver.
jcims 8y ago
This is complicated by the fact that the temperature of the LED materially influences its electronic properties. As a result you generally need to wire them in series rather than in parallel so that the current can’t differentially select the LED of least resistance and cause thermal runaway. Series wiring in turn cranks up the voltage requirements necessary to drive lots of power, requiring more costly components. Oh, forgot to mention, different color LEDs have different forward current requirements, so have fun building a good and cheap driver for 100W RGBW.
- Itsdijital 8y ago
  Sort of, but not really. LEDs can easily be wired in parallel as long as you use resistors to balance them. If you dial in the voltage real tight you can get away with minimal losses in the resistors. If you are really fancy you can use transistors and shunts to actively balance then for even more efficiency. The reason why series is more popular is actually because it is cheaper and(can be) more efficient. It's not uncommon for cheap led lights to just throw 40 leds in series with a dead simple "driver" (read: rectifier, smoothing caps, and a resistor)to run it right off 120V.
  - rahimnathwani 8y ago
    Re: your last sentence, does that mean the whole unit dies as soon as one LED fails?
    - jcims 8y ago
      Not the person you’re replying to, but yes. Series config you lose the circuit if the LED fails open and it shuts the whole string down naturally. Similar issues can affect parallel. If one LED fails open and you don’t adjust the current, you’ll start overdriving the other LEDs and shorten their lives...potentially dramatically. You could add current sense and shut down the board or even adjust current, but then costs go up. Typical LED strips are small serial strings of typically three lights connected in parallel. That way if something goes wrong you knly lose a few lights.

acchow 8y ago

Can we design an LED that isn't affected by typical city fluctuations and spikes?

pixl97 8y ago
If you can, I'm sure someone would pay you a lot of money for the design.
Itsdijital 8y ago
I'm not sure where the OP is coming from because any halfway decent LED driver will accept a wide range of voltages, far more than the fluctuations seen on public lines.
- dreamcompiler 8y ago
  I think he's asking if LEDs themselves can be more tolerant, since the drivers built in to LED bulbs rarely even rise to the level of "halfway decent."
- Itsdijital 8y ago
  LEDs themselves are very intolerant of voltage (well really current fluctuations, semi-conductors are weird), but that isn't an issue because the driver deals with that and large swings will kill the driver or kill the driver and LED. LED tolerance doesn't really play into the scenario here. It's all about the driver.

jcims 8y ago

This is complicated by the fact that the temperature of the LED materially influences its electronic properties. As a result you generally need to wire them in series rather than in parallel so that the current can’t differentially select the LED of least resistance and cause thermal runaway. Series wiring in turn cranks up the voltage requirements necessary to drive lots of power, requiring more costly components. Oh, forgot to mention, different color LEDs have different forward current requirements, so have fun building a good and cheap driver for 100W RGBW.

Itsdijital 8y ago
Sort of, but not really. LEDs can easily be wired in parallel as long as you use resistors to balance them. If you dial in the voltage real tight you can get away with minimal losses in the resistors. If you are really fancy you can use transistors and shunts to actively balance then for even more efficiency. The reason why series is more popular is actually because it is cheaper and(can be) more efficient. It's not uncommon for cheap led lights to just throw 40 leds in series with a dead simple "driver" (read: rectifier, smoothing caps, and a resistor)to run it right off 120V.
- rahimnathwani 8y ago
  Re: your last sentence, does that mean the whole unit dies as soon as one LED fails?
  - jcims 8y ago
    Not the person you’re replying to, but yes. Series config you lose the circuit if the LED fails open and it shuts the whole string down naturally. Similar issues can affect parallel. If one LED fails open and you don’t adjust the current, you’ll start overdriving the other LEDs and shorten their lives...potentially dramatically. You could add current sense and shut down the board or even adjust current, but then costs go up. Typical LED strips are small serial strings of typically three lights connected in parallel. That way if something goes wrong you knly lose a few lights.