Modifying an LED lightpanel for low power - is this possible/feasible?

Forget about it! Unless there is something you are not telling us that causes loss that you can eliminate you are subject to conservation of energy. If you can beat that, you can build a perpetual motion machine, but don't bet your house on that.

Bill

Hello Bill,

Thanks for replying. Novice though, so I may need some more info than that. For example, isn't this something that could operate on the same principle as a typical LED dimmer i.e. with Pulse Width Modulation?

Thanks!

Sure, you could do that and it will use less power, but it will be dimmer too.

Sure! If you will be happy with less light you can do with less power. that is why it is called a dimmer and not a brightener.

Bill

Excellent. As I said, I'm not very conversant with this but it *may* be a reasonable tradeoff - I do not need it to light up a room so it need not be very bright.

Thanks.

Maybe a bit higher. If this sign is going to be visible by moving observers, some flicker might be noticed. If its a computer monitor or TV set, this might be OK.

But it will be dimmer. 25% duty cycle (4 groups alternately lit) will look just as bright as running all the LEDs at 25% of normal current. There is no free lunch.

If you can come up with some grouping that satisfies a fixed brightness requirement, that will work. But what do you do if you want to vary the brightness? Rewire the groups?

Use pulse width modulation (PWM). Vary the duty cycle from 0 to 100% and set it to the desired brightness.

Driving 360 LEDs from a 12 volt supply (directly) means breaking them down into 90 series strings of 4 per string. One way or the other, the total draw will be 2.5 A which can be handled by a MOSFET or IGBT and controlled from a microcontroller or even a 555 variable duty cycle oscillator.

Take a look at the existing LED connections and see how they are connected now. It would be best to adapt your design to this because rewiring 360 LEDs is not a trivial task.

Most of the higher power LED stuff I've seen made to run off 12V uses a boost converter. The losses in the converter end up being a lot less than the losses in all the series resistors that would otherwise be required.

Why a boost converter? Starting at 12V, a buck regulator is much simpler.

Because with a boost converter you can run a long string of LEDs in series with a single resistor. A buck converter is great for 1-3 LEDs, but each individual string requires a separate current limiting resistor.

Charge pump (multiplier)?

Those are used occasionally where small size is the highest priority, backlights for very small LCD screens, LED flashlights, etc, but the inductor type boost converter is more common where space allows the slightly larger components.

Dallas/Maxim has a good selection of LED driver ICs along with many application notes and documentation to help one choose.

And with correctly regulated converter is it possible to get rid of that traditional series resistor. Use a switch more power supply in constant current mode and you can get rid of that traditional current limiting resistor and losses caused by it (constant current power supply does the current limiting).

Sure, but his point is that you still would want a series string to minimizing the number of switchers. This likely means a boost regulator.

|> An engineer friend suggested that I could reduce this by dividing the |> LEDs into "multiplexed" groups and cycling through them (so that only |> one group is on at a time) at high frequency i.e. 75Hz - 100Hz. | | Maybe a bit higher. If this sign is going to be visible by moving | observers, some flicker might be noticed. If its a computer monitor or | TV set, this might be OK.

Maybe a lot higher. I've seen flicker to 200 Hz in LEDs.