How can i reduce LED's power consumption?

[pranam77]

led power consumption

Hello every one. Wish you all a happy and prosperous New year 2009.
While experimenting with white LED's i tried to run 60 LED's with 6 volts 4.5 ah battery, and connected as given in the schematic. I have assumed each LED has a forward drop of 3.3 volts as i didint get any specifications from the manufacturer. The led's are of China origin. Too the current was guessed to 20 Ma and a resistor of 150 ohm was connected in sieres of all the 60 LED's. Now when connected to the
battery, total consumption came to exactly 1.015 amphere. Mean it will glow for approximately 2.5 to 3 hours on a 4.5 ah battery. My question is, there any way to reduce the total current without reducing the LED brightness so that i can get more running hours with same battery. Can i impliment some driver circuits so that the voltage is raised and the LED's can be connected in seires? May i expect sugesstions, links, schematics or Ideas in this regard?.

 

[dfullmer]

led consumption

Hi happy new year to you also.

Consider how much total light you really need - maybe you can increase the resistance values. You could also duty cycle the current through the LEDs. If you operate at a high enough reprate the eye would not see the pulsing but the overall current draw would be dropped.

Just a couple thoughts. There are some ic made that are specificaly for this type of application. Never used them myself but they made have some tricks up their collective sleves.

good luck

dfullmer

 

[CMOS]

white led power consumption

The only way to reduce consumption is to reduce extra energy wastage which in your case is through resistors which can be done using constant current supply or switching regulator as "dfullmer" mentioned,.

Each resistor here dissipates I*I*R watts of power in the form of heat = 20e-3 * 20e-3 * 150 = 0.06 Watts

Total power dissipated as heat = 0.06 * 60 = 3.6W

So overall you can save upto 3.6W (max. which is more than 50% of the total power your circuit is consuming : V * I = 6 * 1.015 = 6.09 Watts) of energy which is not converted to light using a CC source or switching supply.

Using an efficient current source, you can almost double your battery life.

 

[Audioguru]

power consumption of leds

Pulse-Width-Modulation is used to dim LEDs and light bulbs. Your vision is not a peak detector, it responds slowly to the average current of pulses.
For example, multiplexing pulses the LEDs and then they need much more current to be seen.

 

[pranam77]

led power consumption watts

Thanks dfullmer, CMOS, and Audioguru for your Valuable guidance. It would be helpfull if i get any links or schematics to build a switching supply with Constant current for running the same circuit.

 

[CMOS]

figuring led power draw

To use a constant current source, first of all you need to connect all LEDs in series and Use Boost Constant Current driver like TPS61042. It can generate max 27.5V from 6V source. So you need to split 60 LEDs into 10 group of 6 each (assuming 3.6V LED forward voltage) and connect all groups in parallel. The only problem with this configuration is even if 1 LED blows off, it will take away all the groups because of high current! The ideal way is to use only 1 continuous string of LEDs in series, but you need to find a high voltage boost converter for such purpose.

Here is the datasheet.
https://focus.ti.com/docs/prod/folders/print/tps61042.html

 

[AlBo]

whit led power consumption

Hi pranam77 !

Interesting article about LED driving you will find on

**broken link removed**.


See also application notes on national semi web page.

 

[MCMC]

serial led power

Hello every one. Wish you all a happy and prosperous New year 2009.
While experimenting with white LED's i tried to run 60 LED's with 6 volts 4.5 ah battery, and connected as given in the schematic. I have assumed each LED has a forward drop of 3.3 volts as i didint get any specifications from the manufacturer. The led's are of China origin. Too the current was guessed to 20 Ma and a resistor of 150 ohm was connected in sieres of all the 60 LED's. Now when connected to the
battery, total consumption came to exactly 1.015 amphere. Mean it will glow for approximately 2.5 to 3 hours on a 4.5 ah battery. My question is, there any way to reduce the total current without reducing the LED brightness so that i can get more running hours with same battery. Can i impliment some driver circuits so that the voltage is raised and the LED's can be connected in seires? May i expect sugesstions, links, schematics or Ideas in this regard?.

use a serial parallel circuit

you need a 20 pairs of 3 serial led's (60) total, connect 3 led in serial whit one 15 or 20 ohm resistor (test whit one circuit 3 serial led) and then connect this 20 serial led's circuits in parallel, you have a .02 ma x 20 = 0.4 Amp of current is reduced to half, look the attach.

if you add another battery connect it in serial to make 12 volt, and connect 10 pair of 6 leds in serial whit 30 ohm resistor circuit, the total current drop to .2 amp

 

[pranam77]

6 volt to 12 volt booster circuit diagram

Dear MCMC.
Thanks for the info. The attched picture it is totally black with white triangles. If each one of the white LED's have a forward drop of 3.3 volts how can i connect 3 LED's in sieres for glowing it on 6 volts? May i request you to attach the schematic again?

 

[CMOS]

how to boost current without power lost

use a serial parallel circuit

you need a 20 pairs of 3 serial led's (60) total, connect 3 led in serial whit one 15 or 20 ohm resistor (test whit one circuit 3 serial led) and then connect this 20 serial led's circuits in parallel, you have a .02 ma x 20 = 0.4 Amp of current is reduced to half, look the attach.

if you add another battery connect it in serial to make 12 volt, and connect 10 pair of 6 leds in serial whit 30 ohm resistor circuit, the total current drop to .2 amp

There is still a wastage of 0.02 * 0.02 * 150 * 20 = 1.2 Watts. This is not the most efficient way of driving LEDs for lighting. And as pranam77 mentioned, it is not possible to drive 3 LEDs in series each having forward voltage of 3.3V with a 6V battery!

BTW pranam77, did you take a look at switching LED driver's that I mentioned in my previous post ?

 

[MCMC]

led bulb circuits power consumption calculation

dear pranam77

this is a strange led's because the normally voltage drop is 1.8 to 2 volt, "you assumed each LED has a forward drop of 3.3 volts" test 3 led in serial assumed each led is a voltage of 1.8 or 2 volt whit 20 to 30 ohm resistor.

Added after 31 minutes:

use a serial parallel circuit

you need a 20 pairs of 3 serial led's (60) total, connect 3 led in serial whit one 15 or 20 ohm resistor (test whit one circuit 3 serial led) and then connect this 20 serial led's circuits in parallel, you have a .02 ma x 20 = 0.4 Amp of current is reduced to half, look the attach.

if you add another battery connect it in serial to make 12 volt, and connect 10 pair of 6 leds in serial whit 30 ohm resistor circuit, the total current drop to .2 amp

There is still a wastage of 0.02 * 0.02 * 150 * 20 = 1.2 Watts. This is not the most efficient way of driving LEDs for lighting. And as pranam77 mentioned, it is not possible to drive 3 LEDs in series each having forward voltage of 3.3V with a 6V battery!

BTW pranam77, did you take a look at switching LED driver's that I mentioned in my previous post ?

ooohh you forget the ohm law the current in the serial is the same, 3 led in serial like I suggest = 20ma * 6 volt = .12 watts total power, .04 watts per led and 2.4 watts total, compared to 60 led in parallel that is = to .02 * 60 * 6volt = 7.2watts of power in the circuit used by pranam77.

I never ear of a led of 3.3 voltage or is a special or dual led.

I use this led, look the spec of led in the attach the forward voltage is 1.90 to 2.02 volt and 2.4 V max

 

[Audioguru]

how to reduce led brighteness

I never hear of a led of 3.3 voltage or is a special or dual led.

Low current red LEDs are 1.8V to 2.0V. Old green ones were 2.2V.
New blue, new bright green and white low current LEDs are from 3.2V to 3.6V.

 

[MCMC]

how to drive 20 led from 2.4v

I never hear of a led of 3.3 voltage or is a special or dual led.

Low current red LEDs are 1.8V to 2.0V. Old green ones were 2.2V.
New blue, new bright green and white low current LEDs are from 3.2V to 3.6V.

thanks for information Audioguru, I'm wrong

if the led is 3.3 volt is more easy and $ add another battery in serial, if the situation permit, or use a PWM like you suggest.

mcmc

 

[CMOS]

2.4v led with 12 volt power

ooohh you forget the ohm law the current in the serial is the same, 3 led in serial like I suggest = 20ma * 6 volt = .12 watts total power, .04 watts per led and 2.4 watts total, compared to 60 led in parallel that is = to .02 * 60 * 6volt = 7.2watts of power in the circuit used by pranam77.

I never ear of a led of 3.3 voltage or is a special or dual led.

I use this led, look the spec of led in the attach the forward voltage is 1.90 to 2.02 volt and 2.4 V max

The calculation I showed is based on Ohms law itself!!! which accounts to power lost in the resistors in the form of heat and not the total power consumed by complete circuit! Those are called I²R losses.
And as I said earlier in order to increase battery life, you need to reduce power loss and in this case, only loss that occurs is in the resistors! So get rid of them and use a constant current source instead !

 

[pranam77]

1 led power consumption

Thank you every one for your valuable sugessions and ideas. This is the LED what i use. I am intending to use it for constucting an emergeny light with 6 volts. Sorry for the blur image. It was taken with my cell phone.

 

[fsmyth]

3.3v 20ma led in india

There are a number of suitable PWM drivers at:
**broken link removed**
Pick one with enough current drive for all LED's.

 

[u04f061]

led power consumption ma

Hi pranam77 !

Interesting article about LED driving you will find on

**broken link removed**.


See also application notes on national semi web page.

the link you provided is not working. although i am not the initiator of this thread, but i need this article. can u plz update this link?

 

[mvs sarma]

led reducing power consumption

Thank you every one for your valuable sugessions and ideas. This is the LED what i use. I am intending to use it for constucting an emergeny light with 6 volts. Sorry for the blur image. It was taken with my cell phone.

Hai Pranam77, first decide the forward drop of the LEDs you have on hand. then use the formula [Vcc-(n*Vled)]/.02=the resistance that would be needed.
here N*Vled should be less than the Vcc and if you happen to use battery (being an emergency lamp),the Vcc value should be carefully decided.as fully charged battery would be at 8.4V at least for a short time and discharged battery could go low as 4.8V.

Instead a buck/ boost type converter with current source or pwm would be better.
I still have my own doubts regarding failure mode of LED by pwm pulses of higher voltages.

 

[Audioguru]

consumption led ma

The LEDs I have with a clear lens show how thin is the wire that connects the chip to the pin.
It will be a fuse and will burn out open.

 

[mvs sarma]

can a 4.5 led run on 6 volt

While the wire is thin no doubt, it is too short also. thus it might retain its position. I feel that perhaps it is the junction that fails but not the cat whisker.