LED power consumption how to decrease it

[Nigel Goodwin]

Really I want to MAINTAIN the brightness yet decrase the electric power needed for them, So sorry I am not able to understand you correctly Nigel.

You can't - you're essentially talking about perpetual motion and it's impossible.

If you decrease the power then you decrease the brightness, it doesn't matter how you do that the effect is the same.

 

[MrAl]

Hello guys,


Switching the LED on and off does *NOT* save power over a series resistor solution for the same brightness level. It actually uses more power or produces less light because the LED is operated at the upper part of it's voltage/current curve where the efficiency drops off. It's only a true switching regulator that can save power.

This can be proved several ways, but the simplest is the "averaged AC model" approach, where the turn on and turn off of the switch is regarded as a simple resistor of lower value than a regular series resistor would be. Here we would see the lower values resistor itself drops less voltage, that's true, but it also has to deliver more current if the LED brightness is going to be the same as with the series resistor. And because the LED brightness goes down with increased peak current (not average current) because the efficiency goes down with increased current, we actually end up getting LESS light output from the same average current through the LED !

If we hold the LED to the ridged non realistic spec of having constant efficiency over it's current range, then we see the same brightness and the SAME power wasted as heat in the switch as would be wasted in the series resistor. Hard to believe because the 'switch' has low resistance, much lower than the series resistor, but a full analysis of this circuit shows the truth that they are both equal. Another view is that the PWM is attempting to do a power conversion from that of the power supply to that of the LED, but it is not a true power conversion just a power loss. The only way to get a true power conversion (and possibly higher efficiency) is to include an energy storage element like an inductor (and other required parts).

There are still times when a regular PWM (without energy storage) is beneficial, and that's when the LED is to be dimmed using PWM alone. Then the LED can be dimmed without having to use a heavy duty potentiometer or something like that. But in the case of multiple LED's it seems easier just to switch some off like we had been saying.

Still dont believe it? Do two simulations, one using PWM and one with a series resistor. Find the power lost in the switch and the series resistor and compare.

 

[ronv]

Interesting article:

https://techon.nikkeibp.co.jp/english/NEWS_EN/20080407/150114/

 

[audioguru]

I disagree with the scientists who blasted VOLTAGE pulses to their LEDs instead of controlled CURRENT pulses.

I use PWM to dim my LEDs, not to make them brighter. When the pulse width is half then the average current is half and they looked dimmed.
When the pulse width is less then they look more dimmed. When the pulse width is so narrow that you can barely measure it then the LEDs are extremely dim but can be barely seen in a completely dark room.

 

[MrAl]

Hi,

The study shows a perceived brightness in certain color LED's but unfortunately they seem to have forgotten to do the most important 'color', WHITE. Who cares about blue, green and red

And also, they are showing a difference at 5 percent duty cycle. But at that low duty cycle it would take 20 times the nominal current to get something that might resemble full brightness out of the LED. That exceeds the manufacturers spec's for any white LED i know of. For example that means that a 20ma LED would have to be driven at 400ma peak current, which is way over the max spec. That means the efficiency falls quite a bit so the brightness goes DOWN. I guess there might be some hope for dim lighting or where we could use a lot of LED's to make up for the difference running them at low average current.

So in other words i think it was more a test for further exploration of the the Talbot-Plateau effect rather than for an LED.

 

[Nigel Goodwin]

That exceeds the manufacturers spec's for any white LED i know of. For example that means that a 20ma LED would have to be driven at 400ma peak current, which is way over the max spec.

Your 20mA LED is 20mA AVERAGE - so high current short term pulses aren't a problem, and is of course how multiplexing works. It's common to pulse IR LED's in remote controls at 1 or 2 amps.

The current 'limitation' is (like most devices) based on dissipation (too much and it melts), short term high current pulses allow the die to cool before the next one hits. Obviously you wouldn't pulse at 1 second ON and 399 seconds OFF, as the ON time would be far too long - it must be short enough not to overheat.

 

[audioguru]

I think the very thin bonding wire (for the anode) inside an LED melts before the die melts when the current is high.

A "white" LED is actually a blue LED with a yellowish phosphor on top. True white is made with a combination of red, green and blue LEDs.

 

[MrAl]

Your 20mA LED is 20mA AVERAGE - so high current short term pulses aren't a problem, and is of course how multiplexing works. It's common to pulse IR LED's in remote controls at 1 or 2 amps.

The current 'limitation' is (like most devices) based on dissipation (too much and it melts), short term high current pulses allow the die to cool before the next one hits. Obviously you wouldn't pulse at 1 second ON and 399 seconds OFF, as the ON time would be far too long - it must be short enough not to overheat.

Hello again Nigel,

Well then again you choose to follow some spec's and ignore other spec's. That's entirely up to you and i know other people do that too, but i myself dont ignore any spec's unless i dont mind taking a chance on blowing out one of my parts

I've seen experiments that pump very very high current though LED's too, more than we are talking about here, but there the pulse timing is strictly controlled including the rise and fall times and efforts to reduce ringing.

 

[MrAl]

I think the very thin bonding wire (for the anode) inside an LED melts before the die melts when the current is high.

A "white" LED is actually a blue LED with a yellowish phosphor on top. True white is made with a combination of red, green and blue LEDs.

Hello,

Yes but the human eye reacts differently to white when actually using it to view something. But as long as they were testing other color LEDs they could have easily tested a white one too. From the tests they did do we'd have to extrapolate that the viewer would see a cyan color with a white LED. I'd like to know if that really works out that way.

 

[Nigel Goodwin]

Well then again you choose to follow some spec's and ignore other spec's.

Not at all - the 20mA specification is continuous current, the specification for peak currents is FAR higher, if your manufacturer doesn't list it, then it's the fault of the specifications, not it's use.

 

[BeerBelly]

I wouldn't take these claims too seriously. It is likely bad science looking for more government funding. So many claims are.
Just pay my team and I and we will retest this claim.
I have seen so many of these proposals and they don't even get the spelling right most of the time.

 

[Nigel Goodwin]

I wouldn't take these claims too seriously. It is likely bad science looking for more government funding. So many claims are.
Just pay my team and I and we will retest this claim.
I have seen so many of these proposals and they don't even get the spelling right most of the time.

Perhaps you might try quoting what you're referring to?, your post makes no sense 'as it is'.

 

[ronv]

Seems like there are several thing you could do besides the short pulses that would improve the battery life.
Many manufactures bin there LEDs for output.
Some are just better than others (more output for watt)
Sill others bin for forward voltage drop so you can parallel them better.
Also check where they run for the highest efficiency and run them in the "sweet spot".
All of these of course cost more but it all depends on how important it is to you.

 

[BeerBelly]

Perhaps you might try quoting what you're referring to?, your post makes no sense 'as it is'.

Sorry Nigel
Sometimes we techies have a hard time explaining things

Interesting article:

**broken link removed**

This quote came from post #23

 

[ronv]

There are a few write-ups and patents on the internet about it. Not saying it's the way to go as you would need 10 times as many leds to get the same apparent brightness.