Connecting LED

[josey_matt]

hi,
i am a noob and was wonderin how i would go about connecting about 100 LED's together either series or parallel. i am using "AA" batteries to light the LED's. i am putting this tring of LED's around pictures.

thanks much

 

[falcon eys]

Hi
I think if you connected the 100 Led in series you may need a power supply outputting around 200 volt Dc and this is hard
so i suggest to connect them in parallel you may need a power supply with about 2 volt
but take in account the proper amper

 

[Diver300]

You shouldn't connect LEDs in parallel, as each may have a different voltage so will end up with different currents in each.

You should connect the LEDs in groups of about 5 in series. Each group needs a resistor to limit the current. Then you have as many group (each with its resistor) in parallel as you need.

 

[Willbe]

hi,
i am a noob and was wonderin how i would go about connecting about 100 LED's together either series or parallel. i am using "AA" batteries to light the LED's. i am putting this tring of LED's around pictures.

thanks much

What are the specs on your LEDs?
The tradeoff is to have as many in series as you can and still get a relatively narrow tolerance on your expected LED current while being fed from a voltage source, since you probably will not be feeding them from a constant current source.

A voltage source has a source impedance less than 60Ω, and typically <1Ω. A current source has a higher apparent or real source impedance, typically MΩs.

 

[Boncuk]

Here is an easy and effective way to connect LEDs to any power source, even current sources, which is desirable as it involves only one calculation. This is simply the LED forward current.

Because of the high number of LEDs to supply I suggest to purchase a wall wart capable of supplying 15V output voltage at 500mA (includes 100mA safety margin)

Split the 100 LEDs in groups of five LEDs for 20 groups. Connect each group as shown in the schematic. No matter which forward voltage applies to the different colour LEDs the correct voltage will automatically be gained using the correct forward current.

The LM317L (TO92 package) can provide an output current of 100mA. Limiting the current to 20mA ensures safe operation. The output current is calculated as follows: Iout=Vref/Rref, in numbers: 0.02A=1.25 (Vref)/62.5Ω

To calculate for Rref reverse the calculation to be: Rref=Vref/Iout.

The circuit shows two colomns of LEDs with different forward voltages. The output current is almost the same (difference 0.1mA) with identical circuitry.

Boncuk

 

[Willbe]

The LM317L (TO92 package) can provide an output current of 100mA. Limiting the current to 20mA ensures safe operation. The output current is calculated as follows: Iout=Vref/Rref, in numbers: 0.02A=1.25 (Vref)/62.5Ω

Since the LM317s in your diagram are not grounded, can you connect the LM317 input to 170vdc and power up ~80 LEDs at a time? If so, no xformer, only 120vac rms, a 600 v PIV diode bridge and filter cap. A filter cap for this 20 mA would be >30µF@>200v.
If the voltage tolerance on each LED is 0.2v the overall string tolerance is [(80)^0.5] x 0.2v = +/-1.8v (out of 160v, so this leaves 8 to 12 volts for the current source).

 

[Boncuk]

Since the LM317s in your diagram are not grounded, can you connect the LM317 input to 170vdc and power up ~80 LEDs at a time?

I've never tried to connect an LM317L to 170VDC. It is limited to an input voltage of 37VDC. Even not directly grounded the total voltage will have some effect by the ground connection via the LEDs.

You might give it a try. Don't forget to wear protective clothes and goggles.

 

[Ubergeek63]

Since the LM317s in your diagram are not grounded, can you connect the LM317 input to 170vdc and power up ~80 LEDs at a time? If so, no xformer, only 120vac rms, a 600 v PIV diode bridge and filter cap. A filter cap for this 20 mA would be >30µF@>200v.
If the voltage tolerance on each LED is 0.2v the overall string tolerance is [(80)^0.5] x 0.2v = +/-1.8v (out of 160v, so this leaves 8 to 12 volts for the current source).

It would not be a problem were it not for line voltage variation. I would recommend an LM317HV if he insists on using them since normal line levels vary from 141-184V peak-and that is BEFORE you consider abnormal conditions.

 

[Willbe]

I've never tried to connect an LM317L to 170VDC. It is limited to an input voltage of 37VDC. Even not directly grounded the total voltage will have some effect by the ground connection via the LEDs.

You might give it a try. Don't forget to wear protective clothes and goggles.

I think the 37v spec is input to output difference. I'll have to look it up.

Another way is to use a full wave voltage doubler and then you could do 160 LEDs using a current source. The output resistance of one of these doublers may be so high that it is already a current source.

Regarding capacitor input filter design, I'm wading through excerpts from the 1943 paper by O.H. Schade, with the help of a spreadsheet.
Turns out diode and cap filters running off the AC line may need a resistor to limit startup current flow to within the diode's I^2 T rating. For a 1N400x it is 30A (I assume 30A rms half sine pulse) for 8.3mS = ~7 (amp^2)sec.

 

[molocas]

Man, the easy way to connect 100 led´s is take a transformer just for isolating from the line. If you connect 1.25 volts led´s.
Primary 120volts ac , secondary 120 volts ac.
Connect all 100 led´s in series and thats all, one transformer and may be
you just need 100 milliamps each transformer. Use a fuse 1/2 amp in series with leds.
Led´s turn on just 1/2 cycle vac.

I have done this a lot of times.

 

[Sceadwian]

The flicker is horrible molocas, I've even tried full wave rectification (no filter though) and I could still blatantly see the flicker.

 

[bryan]

**broken link removed**

 

[audioguru]

But he wants to power 100 LEDs with little AA battery cells.

1.8V red LEDs at 10mA each is a current of 1A. Two alkaline AA cells in series will power the LEDs for 1 hour and the LEDs will be seen dimming.
If the LEDs are 25mA each then two AA alkaline battery cells can power 100 of them for a few minutes.