# Other Aquarium Forums > Equipment and Accessories > DIY Projects >  Electrical Circuit for DIY LED, need input

## limsteel

Which is better? 

- High Voltage with Low Current
With a bridge ($5) I convert 240Vac to 240Vdc I can power up 63 LED (3.8V per LED) connected in Series at 0.1mA

- Low Voltage with High Current
With a 12Vdc Adapter ($50 - $100), I connect 21 parallel sets of 3 LED (3.8v per LED). but as the connection parallel, I need to supply 21 x 0.1mA... meaning I need 2100mA

Power consumption is the nearly the same Pwr = Voltage x Current = 24Watts

Many advise me against playing with 240Vac to 240Vdc with a bridge. it might be cheap but dangerous. But I can add on more parallel connection anytime I want. 

Using a 12Vdc adapter, on the other hand is more expensive. But don't think it is much safer with 2.1A running round the circuit. Moveover I need to buy more adapters ($50 to $100 for high current) if I need to create a few more sets.

Your advise is greatly appreciated

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## Shadow

LED is current drive, thus it is typically connected in series for uniform brightness.

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## limsteel

*Sorry for the typo... should be 0.1A or 100mA instead of 0.1mA*

Bro, LED need voltage to operate... you can't connect 63 LED in series to a 12Vdc source. 

Let me rephrase my Question. Assuming the resistor value (ohm and wattage) is already known, just want some opinion as to which to choose.

BTW In case anyone want to know what is a bridge. it is used to convert AC to DC

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## Shadow

of course need voltage but the brigness is control by current pass throught it. If you connect it in parallel, some LED might draw more current than the other thus some LED might brighter than the other.

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## limsteel

With the same number of LEDs and the same resistor connected in parallel. the current passing through each parallel connect is same ± v.small % (due to resistor % error, Silver 10% and Gold 5%, temperature also affects the resistance) in theory . 

I have load compare LEDs side by side drawing different current. looking from an angle away from the light path and at a distance with my naked eye, I can't tell the different, until the current gap is big 10mA vs 100mA then i can see significant difference. So it is not a concern.

*DO NOT LOOK DIRECTLY INTO THE HEART OF THE LED WHEN YOU POWER THEM UP*... I remember seeing dark spots for several min when the high power LED light took a direct hit on my eyes!

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## Shadow

Seems you already make up your mind.

For what it worth, You might be interested on Maxim application note:
http://www.maxim-ic.com/appnotes.cfm/an_pk/3256

There was also another article related to LCD backlight using LED, but can't find the link  :Opps:

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## limsteel

> Seems you already make up your mind.
> 
> For what it worth, You might be interested on Maxim application note:
> http://www.maxim-ic.com/appnotes.cfm/an_pk/3256
> 
> There was also another article related to LCD backlight using LED, but can't find the link


No I did not make up my mind, Just disagree with you on the inconsistent brightness issue base on the parallel connection. 

In fact, I am inclined to the direct 240Vac - Diode Bridge - 240Vdc then connect 63LEDs in series then later add on more sets of 63LEDs in parallel when I have the $$$ to spare. 

In case you wanna know where I come up with 63 LEDs, Dealer indicated that each LED need 3.4 to 3.8V to work. Extreme case of 3.8V, i can connect 63 LEDs (MAX) which is in total 239.4V. 

So I need a resistor that can drop the voltage by 0.6V at 100mA. R = V/I
Resistor is 6 Ohms with a power (P = IV) rating of 0.06W. So a cheap 10cents 6Ω ¼W will do the job.

Just need someone to tell me extra facts, e.g *Warning*: Direct 240Vac conversion to 240Vdc, very dangerous, Diode Bridge not stable will explode or something. Or *Advise*: connect ??? way, it is safer and can save money.

Main concern here is, how come people spend $$$$ to buy a step down AD-DC adapter when I can use a $5 Diode bridge for the job.

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## Shadow

If you read the aplication note, from the first figure you will see that at the same forward voltage different LED draw different curent. Nothing you can do about it except screening it. It is due to the variation in semiconductor process. Thus for LED it prefered to drive them with constant current.




> When applying white LEDs for display backlighting or other illumination applications, there are two reasons to drive them with constant current: 
> 1. To avoid violating the Absolute Maximum Current Rating and compromising the reliability. 
> 2. To obtain predictable and matched luminous intensity and chromaticity from each LED.

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## sacy

erm. it is not wise to do series led circuit with so many LED together. u have say u are playing with 240VDC!!! any short on your circuit's it will instantaneously catch fire man!!!  :Flame: don't play play. think u better start from square1. try serial+parallel LED circuit. and the 12VDC/2Amp or more adapter that cost $50 to $100 normally will have overload protection circuit built-in and it is still much safer then the 240VDC/100mA bridge. and normally a 12vdc/2amp adapter w/o overload protection circuit built-in should cost less that $30 buck cause it just a step-down transformer only.and even u really want to do a bridge . 

it not that simple like the diagram u show. u still need to add in some other component ..like diode-|>|-,cap -||- to the circuit to filter always the ripple to make the DC wave to be more stable and noise free .And add in an overload protection circuit.base on the add on of component added to your bridge design, u end up spending more then saving. if w/o all the filter and overload protection circuit, u will have blinking led and every now and then replacing spoil resistor and LED due to the unstable DC voltage that cause by the $5 buck bridge.

just my 2cent  :Angel:

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## Shadow

Agree with that, when you are working with hight voltage you might want to start thinking about safety. Adding fuse for example, in case acidentally shorted.

You might want to take a look on the LED tube that NA sell. If I seeing it correctly it does not even have a diode, just 1big and 3 small resistor to limit the current. It worked because LED is essentially diode, but you might see the 60 Hz flicker.

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## unclerobin

> No I did not make up my mind, Just disagree with you on the inconsistent brightness issue base on the parallel connection. 
> 
> In fact, I am inclined to the direct 240Vac - Diode Bridge - 240Vdc then connect 63LEDs in series then later add on more sets of 63LEDs in parallel when I have the $$$ to spare. 
> 
> In case you wanna know where I come up with 63 LEDs, Dealer indicated that each LED need 3.4 to 3.8V to work. Extreme case of 3.8V, i can connect 63 LEDs (MAX) which is in total 239.4V. 
> 
> So I need a resistor that can drop the voltage by 0.6V at 100mA. R = V/I
> Resistor is 6 Ohms with a power (P = IV) rating of 0.06W. So a cheap 10cents 6Ω ¼W will do the job.
> 
> ...





> erm. it is not wise to do series led circuit with so many LED together. u have say u are playing with 240VDC!!! any short on your circuit's it will instantaneously catch fire man!!! don't play play. think u better start from square1. try serial+parallel LED circuit. and the 12VDC/2Amp or more adapter that cost $50 to $100 normally will have overload protection circuit built-in and it is still much safer then the 240VDC/100mA bridge. and normally a 12vdc/2amp adapter w/o overload protection circuit built-in should cost less that $30 buck cause it just a step-down transformer only.and even u really want to do a bridge . 
> 
> it not that simple like the diagram u show. u still need to add in some other component ..like diode-|>|-,cap -||- to the circuit to filter always the ripple to make the DC wave to be more stable and noise free .And add in an overload protection circuit.base on the add on of component added to your bridge design, u end up spending more then saving. if w/o all the filter and overload protection circuit, u will have blinking led and every now and then replacing spoil resistor and LED due to the unstable DC voltage that cause by the $5 buck bridge.
> 
> just my 2cent


i seconded bro limsteel and sacy, it is not wise to have 63 led light connected in a series circuit, you will have problem trouble shooting a blown bulb just in case any 1 of the led light failed you.

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## Shadow

that very easy, just use multimeter

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## sacy

ya multimeter will do the job ^^.

NA got sell the 240vac T5/T8 LED tube lights?

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## khseah79

just abit of of track.. any idea do any where sell led reflector?? i have seen them at swarovski crystal shops..

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## ghim

63 LEDs won't be very bright. The brightness of the LED can be determined by the DC voltage used. 

I tried the brightness of Vdc powered LED light. The brightness is limited, compared to Vac powered LED light.

NA does sell Vac powered LED tubes.

For the start, you can get those LED spot light from lighting shops. They have variants of Vdc powered and Vac powered. I got a pair of Vac powered LED spot light(12 high-intensity LEDs) for $10 each from a lighting shop at Kelantan Lane. You can check out how it is connected. :Smile: 

Personally, I feel the price of individual LED still very high. Do a search at alibaba website on LED lights, you will be able to see the number of commercially available LED lightings. Maybe you can get some idea from them.

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## Shadow

> just abit of of track.. any idea do any where sell led reflector?? i have seen them at swarovski crystal shops..


swarovski crystal that gonna cost you a bom  :Laughing: 

LED is only shine in one direction, no need reflector at the back.

Usually LED come with build in lens, so you might need diffuser instead  :Opps:  You can buy LED with different viewing angle.

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## limsteel

> erm. it is not wise to do series led circuit with so many LED together. u have say u are playing with 240VDC!!! any short on your circuit's it will instantaneously catch fire man!!! don't play play. think u better start from square1. try serial+parallel LED circuit. and the 12VDC/2Amp or more adapter that cost $50 to $100 normally will have overload protection circuit built-in and it is still much safer then the 240VDC/100mA bridge. and normally a 12vdc/2amp adapter w/o overload protection circuit built-in should cost less that $30 buck cause it just a step-down transformer only.and even u really want to do a bridge . 
> 
> it not that simple like the diagram u show. u still need to add in some other component ..like diode-|>|-,cap -||- to the circuit to filter always the ripple to make the DC wave to be more stable and noise free .And add in an overload protection circuit.base on the add on of component added to your bridge design, u end up spending more then saving. if w/o all the filter and overload protection circuit, u will have blinking led and every now and then replacing spoil resistor and LED due to the unstable DC voltage that cause by the $5 buck bridge.
> 
> just my 2cent


Ah! that the kind of Reply I am looking for... I read the noise created by UPs and Downs for the DC wave. 1 way is to connect with a capacitor but I donno how many F is need to smooth out the ripple effect. The $5 bridge should cover the Diodes portion. As for the over load circuit, 3A fuse?





> Agree with that, when you are working with hight voltage you might want to start thinking about safety. Adding fuse for example, in case acidentally shorted.
> 
> You might want to take a look on the LED tube that NA sell. If I seeing it correctly it does not even have a diode, just 1big and 3 small resistor to limit the current. It worked because LED is essentially diode, but you might see the 60 Hz flicker.


1 "big resistor", it might be the Bridge. Bridge itself is a 4 diode circuit. If no capacitor, then the blink is 60 time a second... don't think our eyes can detect that. but the fluctuation might cause resistor failure as Sacy mentioned.





> 63 LEDs won't be very bright. The brightness of the LED can be determined by the DC voltage used. 
> 
> I tried the brightness of Vdc powered LED light. The brightness is limited, compared to Vac powered LED light.
> 
> NA does sell Vac powered LED tubes.
> 
> For the start, you can get those LED spot light from lighting shops. They have variants of Vdc powered and Vac powered. I got a pair of Vac powered LED spot light(12 high-intensity LEDs) for $10 each from a lighting shop at Kelantan Lane. You can check out how it is connected.
> 
> Personally, I feel the price of individual LED still very high. Do a search at alibaba website on LED lights, you will be able to see the number of commercially available LED lightings. Maybe you can get some idea from them.


12 Volts support 3 LEDs - 240Volts Support 63LEDs what wrong with that? So connecting 63 LED in series will have the same brightness when there is enough voltage to push the current thru.

LEDs are semi conductors, for LED, current can only pass in 1 direction unless the reverse Voltage is high enough to blow it. So there is no such thing as a Vac LEDs. there must be a circuit that convert it to DC.

e.g: 





> just abit of of track.. any idea do any where sell led reflector?? i have seen them at swarovski crystal shops..


Agree with Shadow, LED shine in 1 direction. Depending on the LED you buy... standard LED have a light angle of 20&#176; to 40&#176; (Diffusing lens as Shadow mentioned). some high power ones has light angle of 80&#176;, star LED have light angel of 120&#176; to 160&#176; (this one you need a focusing lens)

So get the right LED for the job... If need Light to cover a large area, use a star LED with wide light angle. If you need to focus the light on something maybe a very light demanding SPS Coral then use once that has 20&#176;-40&#176; light angle.

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## limsteel

Dear Sacy, Just found a common electronic ballast for the Down Light in my house. it step down 240Vac to 12Vac transformer - 60W (COST $10). So now 12Vac, using bridge $5 to convert it to 12Vdc. OK? Safer? 

Still cheaper than using a laptop charger as the driver for the LEDs...  :Razz:  OK I am cheapo! Econ Crisis must cut cost, but CUT is one thing, need to be safe too!

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## Shadow

Pulsing LED will not cause a fatigue/failure. LCD backlight on your mobile phone, PDA or others equipment are driven using PWM. Pulsing it will increase the LCD live also save power. That the beauty about semiconductor.

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## ghim

Apologies on what I wrote that causes the misunderstanding. What I meant is not using 12 DC adaptor, but direct power from AC.

Here is an extract from Wiki:
"Power sources

The voltage versus current characteristics of an LED are much like any diode. Current is approximately an exponential function of voltage, so a small voltage change results in a large change in current. It is therefore important that the power source gives the right voltage.
If the voltage is below the threshold no current will flow and the result is a unlit LED. If the voltage is too high the current will go above the maximum rating, heating and potentially destroying the LED. As the LED heats, its voltage drop decreases, further increasing current. Consequently, LEDs should only be connected directly to constant-voltage sources if special care is taken. Series resistors are a simple way to stabilize the LED current, but wastes energy in the resistor. A constant current regulator is commonly used for high power LEDs. Low drop-out (LDO) constant current regulators also allow the total LED string voltage to be a higher percentage of the power supply voltage, resulting in improved efficiency and reduced power use. Switched-mode power supplys are used in some LED flashlights, stabilizing light output over a wide range of battery voltages and increasing the useful life of the batteries.
Miniature indicator LEDs are normally driven from low voltage DC via a current limiting resistor. Currents of 2 mA, 10 mA and 20 mA are common. Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficiency tends to reduce at low currents[citation needed], but indicators running on 100 μA are still practical. The cost of ultrabright LEDs is higher than that of 2 mA indicator LEDs.
Strings of LEDs are normally operated in series LEDs, with the total LED voltage typically adding up to around two-thirds of the supply voltage, with resistor current control for each string. In disposable coin cell powered keyring type LED lights, the resistance of the cell itself is usually the only current limiting device. The cell should not therefore be replaced with a lower resistance type.
LEDs can be purchased with built in series resistors. These can save printed circuit board space and are especially useful when building prototypes or populating a PCB in a way other than its designers intended. However, the resistor value is set at the time of manufacture, removing one of the key methods of setting the LED's intensity. Alphanumeric LEDs use the same drive strategy as indicator LEDs, the only difference being the larger number of channels, each with its own resistor. Seven-segment and starburst LED arrays are available in both common-anode or common-cathode form."

Below is how the resistors are used on my LED lights:

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## Interestor

Really not feel comfortable with any Vdc above 50  :Opps:

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## mark0308

Hi, another option is to get a switch mode power supply, there are 12VDC, 24VDC and 48VDC on the market, if you buy more unit, you could have the bargain power. A transformer with a rectifier may cause you $10 + $5 but you still have to include your labour cause. Switch mode power supply are more efficient and the price should be around $15 to $25 at Sim Lim Tower. Can check it at Sim Lim.
Best regards
Mark Tan

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## limsteel

Beauty of DIY is cheap with lots of elbow grease  :Grin:  What's the point of spending more than 50&#37; of a off-the-shelf unit? It more professionally done, both internal and aesthetically... 

I can purchase a Computer PSU ranging from 300W to 1KW from SimLim Sq, but no fun! Aiya  :Shocked:  I can as well salvage working PSU from my dead computers! HOW COME I DIDN'T THINK OF THAT  :Shocked:  MOD abit should be able to support a few hundreds high power LED and yet comes with Overload, overheat, surge, etc protection!  :Idea: 

Shall use 4pin Molex and 4pin 12V P4 Adapter

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## sacy

he Led tube light look very simple. but i still not sure are there any regulator hide at the back of the LED. Cause, if u telling me that it is using straight 240VAC power with a simple Rectifier to covert the VAC to VDC. it is dam scary man.

ya. Pc power supply is a good idea. u just need to short pin14 and pin15 to turn on the power supply.

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## sacy

normally a $30 pc power supply will have 3.3vdc at 15amp~20amp max for u to run as many parallel LED circuit as u like. and if u use up the 3.3vdc .. u still got +5vdc at 18amp~24amp max for u to use. ^^

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## limsteel

The shorting of the pin is a drag. I can easily whip a contact switch... But how to turn it on auto without manual intervention.

go old shop and see if I can find a AT PSU easier to connect if you ask me.

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## sacy

that easy. just short pin 14 and pin15 all the way. then use a timer will do.

AC socket <---> Timer <---->power supply

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## limsteel

You sure? Usually when PC hangs, we press the power button for 4 sec++ and the system will shut down. So effectively shorting 14 & 15 meaning the system will power on and then turn off in 4 to 5 sec?

OK tomorrow I go office try my PC  :Razz:  I will hold on to the power button then turn on Power Source... If it turns on and stay on then problem solved...

But how come, you only suggested that I use the 3.3V and 5V connection.. there are so many 12V connection eg. 4pin power for IDE HDD, 4 Pin Power for FDD.

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## sacy

the 4sec thing is be cause it control by the motherboard. cause your power button are connect to motherboard. u can try just unplug all the molex connector from your pc. and make sure all power connector has being remove from the motherboard and device(hdd,cd/dvd rom..ect). then u short the pin 14 and 15 of the 20/24pin atx molex connector. right after u short both pin , u will see the fan from the power supply start running.

haha. 12v also can. but base on the 3.3v u can connect around 120 LED rating at 3.4v/100mA each in parallel. easy right

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## Shadow

> he Led tube light look very simple. but i still not sure are there any regulator hide at the back of the LED. Cause, if u telling me that it is using straight 240VAC power with a simple Rectifier to covert the VAC to VDC. it is dam scary man.
> 
> ya. Pc power supply is a good idea. u just need to short pin14 and pin15 to turn on the power supply.


what so scary about? Your PL or T5 or MH also connected directly to 240V

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## sacy

haha. ya forgot. but AC got sine wave. 0V to 240 to 0V to -240V 
DC straight wave all the way 240V that the killer 

that just me only. not trying to mislead ppl ^^

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## Shadow

actually the killer is the curent. For example electro static discharge, althought it is more than 2000V but it won't kill you because very small current.

However I do agree that in this DIY case a bit more dangerous because it is close to water. without proper insulation 240V might cause hazard to the fish and you.

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## sacy

ya. shadow was right on current kills. Voltage shock u and make your muscle contractions .once your hand grad on to the item that shock u, u better pray hard that u can release your hand fast . before the current can pass thought your body to kills u. it only need around 90~100mA to stop your heart with open wound ... so don't play play!!! Voltage and current are evil brothers.. so that why got P=VI and I=V/R

think we a bit off topic

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## limsteel

Finally know the danger of using 240Vac direct covert to 240Vdc... Options available:

- Computer PSU (Few hundred watts)
Cheapest choice with enough power + safety and able to support many LED. and also support other peripherals like DC fan 

Sacy Thanks for the tip... Should have known that PSU are not smart enough for the 4sec off thingy

- Laptop Charger or transformer adapters (usually < 60W) 
Expensive and limited supported LEDs due to low wattage.

- Down light step down (240Vac to 12Vac) + Bridge + capacitor
Again the electrical circuit part a bit draggy.

Final verdict, Computer PSU is best suited for this application. For a little extra $, it offers power + safety.  :Well done:

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## sacy

u welcome. and remember to insulate all expose wire and solder point on your DIY item.
safety first ^^

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## firethorn

I was going on and on about electrical stuff but I shortened it somewhat. So here's my reply:

You'd be better off with a Huge step down transformer say 12v at 120VA (Should you have enough LEDs to require - in this case - 10 Amps), versus connected straight to the mains with, I assume, a simple resistor to limit the typical 13Amps available on the household mains. 

This would also have the added benefit of decoupling the circuit from the mains which is essential in almost every circuit, especially for safety and the electrical noise you will get if you don't decouple the circuit.

From there you can do your ac-dc rectification with regulation, filtering and smoothing (these last 3 are essential in my opinion, regardless of the use). However, it should still work fine without it. Your house lights flicker on and off about 60 times a second but you don't notice it. The same goes for your TV which 'flickers' around 30 times a second. These of course flicker dues to AC current but the effect is similar with unsmoothed DC.

LEDs are diodes so you will need DC no matter what which brings you back again to an SMPS or a transformer. I once considered the possibility of running LEDs ala a rectifying circuit so unless you want to try this out...

At the end of the day, it would be cheaper for you to just buy it from a store, simply because they have something called mass production so unless there is a feature that you simply must have and is not available in stores, it is not cost-justifiable although it will definitely be fun to do.

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## tawauboy

some info;
a) 240vac bridge rectified gives you ~340vdc peak, not 240vdc. 240vac is a root-mean-square (rms) value.
b) 240vdc is no safer than 240vac
c) >50vdc is considered a high voltage. treat it with care.
d) led is a current driven device so you control the current through it. for a voltage increase of 0.1~0.2v, the led current can increase by 2x.
e) proper led current control requires a series resistor for each string of leds.
f) typical leds (<5mm) have a typical max current rating of 20~100ma. for higher power rating, you'll usually need surface mount devices (smd).

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## limsteel

> some info;
> a) 240vac bridge rectified gives you ~340vdc peak, not 240vdc. 240vac is a root-mean-square (rms) value.
> b) 240vdc is no safer than 240vac
> c) >50vdc is considered a high voltage. treat it with care.
> d) led is a current driven device so you control the current through it. for a voltage increase of 0.1~0.2v, the led current can increase by 2x.
> e) proper led current control requires a series resistor for each string of leds.
> f) typical leds (<5mm) have a typical max current rating of 20~100ma. for higher power rating, you'll usually need surface mount devices (smd).


340VDC peak... would have shorten the life of the whole string of LED.

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## Shadow

not really just put more LED in series  :Grin:

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## limsteel

Yes, that it if I already know the peak is 340V...  :Grin: 

Anyway, I got 10 pieces of 10 3W LED from ebay... 50&#37; cheaper then SimLim Tower. 3W White LED cost $10each...

Intensity Type: 110~120Lm 
Viewing Angle: 120&#176; 
Forward Voltage : 3.3V~3.5V 
Forward Current: 700mA
Colour temperature : 6000k

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## sacy

u need to have heatsink for the 3Wled you bought. it will be hot. without heatsink your 3W led will not last long. ^^

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## limsteel

IS LED DRIVER A MUST FOR HIGH POWER LED? I planning to connect them as if they are normal low current LED setup. 12VDC (Laptop charger with a few Amps) + resistor + LED = Light

I bought 10 x 3W White LED... got the shipment and I tested using a 9V batt with 100Ω... With this I should get around 40mA running through the LED. 2 out of 10 are dead. When I talked to the supplier, they replied they will not replace the LED as I use Batt+resistor to power them. They claimed that this will burn the LED. trying to BS me!

These 3W LED runs on 3.5V and 700mA. How can a mere 40mA killed it! what logic?

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## sacy

9v is too much of voltage for the LED. think it's not the current that kill your led. and batt are raw power. batt cant regulate Constance power.

A led driver is needed if u don't have a good source of power supply. that can produce Constance power. normally a switching power supply will do the job.

If u use a normal 12V step-down adapter, u need the LED driver.

just my 2 cent^^

do remember a 9V batt can kill a human being. if u know the right way.

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## Shadow

Actually should be ok, if there is no resistor than it will kill the LED for sure.

(9V-3.5V)/100 = 55mA

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## limsteel

> Actually should be ok, if there is no resistor than it will kill the LED for sure.
> 
> (9V-3.5V)/100 = 55mA


9V batt is quite old one. Measure with Multimeter only have 7.5V. Hooked it up with 100Ω Resistor measure the current, my multimeter shows ~45mA.

NO WAY this current can blow the LED. Unless I directly connect withour resistor.

Sacy:
How about those Nokia HP Charger... they are use to charge HP should be quite precise since it is used to charge sensitive equipment. I am doing up one to light my Aquarium cabinet.

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## sacy

erm.. Hand phone charger is a simple step-down transformer only. the regulating part are done by hand phone.

humm. if u wan to do . u need 1XLM337 and some other component, to help u make Constance output voltage and current.


and do remember ,power the led at near max rating , don't over power it .^^ like led rating([email protected]) don't power it at 4.5~9v this will cause your LED to draw more Current and Burn the Semi-conductor Chip of your led. unless u got very good heat dissipation device mouth on your led

my 2 cent

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## firethorn

> erm.. Hand phone charger is a simple step-down transformer only. the regulating part are done by hand phone.


I am unsure of where you have obtained this conclusion. A hand phone charger is regulated, smoothed and filtered to some degree.

Perhaps you mean that the "charging circuit" is "usually" in the handphone. i.e. The charger puts out 'smooth' dc but the actual circuitry to charge the battery is within the phone.

Also, it should be noted that not only is a hand phone charger NOT a SIMPLE step-down transformer, it is not even a transformer. It is a SMPS unit.


You are right however to say that a popular choice for a voltage regulator in a DIY electronic circuit would be devices in the LM series such as the LM317 (the 337 is a negative voltage regulator). This is truly only needed if you are DIYing the entire power supply yourself. If you already have a relatively stable DC source (those 'newstar' chargers will NOT cut it) and just want to make minor adjustments, you can use a Zener diode and a resistor to regulate the voltage, for a cheaper and much simpler solution.

The LMxxx series though has a lot of cool features including "overcurrent protection (of the IC)" and can typically handle up to 1.5 Amperes of current. You can also adjust the voltage while the device is running, as compared to the Zener diodes where the voltage is fixed (although with regards to lighting a LED, you shouldn't adjust the LEDs brightness by playing with the voltages. Instead, you should play with the current or if you want, with something known as Pulse-width modulation).

If you do decide to DIY the entire power supply, there are quite a few things you need to know before hand, including converting the AC to DC. It's fun and interesting but it's lengthy to explain, especially if you are new to this. But it is fascinating and relatively easy to learn. Just lengthy to explain, and it's not something you can skip because it involves safety.

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## limsteel

Googling around, I found this Is this as simple as the instruction stated? Power Supply + LM317 + Resistors + LED.

LM317 got a Vdrop of 3V using a 12Vdc power supply, I can only hookup 2 more LED Vf of 3.5 to 3.8. with a Imax of 1.5Amps, at most I can only hookup 2more (parallel) Seem like I gotta buy lots of LM317 If I intend to fully replace my Light set.

As for stable power supply, can Computer PSU be used? Computer are filled with sensitive electronic components. Don't tell me that the MB, Hard Drives, Roms, etc have they own Power Stabiliser...

firethorn:
So if the Charger has a stable Voltage, smooth and steady... Can I forget about the LMXXX. I want to hook up a single 3W LED inside my Cabinet so I can see while I work inside the cabinet like adjust my Sump, moving things around..

Also need to setup Single or Twin 3W LEDs for my 1ft guppy tank no plants. this will be powered on for longer.

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## sacy

oh. the LM337 is a Adjustable Regulators. so u can adj the V/out from 1.2V to 37V (depend on your V/in and (R1/R2)) and the Imax/out is 1.5A (depend on your I/in)

about the hand phone charger. i will confirm again. i will try to get a hand phone charger and open it out to double confirm.^^ 

sorry if i miss lead anyone

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## firethorn

> Googling around, I found this Is this as simple as the instruction stated? Power Supply + LM317 + Resistors + LED.
> 
> LM317 got a Vdrop of 3V using a 12Vdc power supply, I can only hookup 2 more LED Vf of 3.5 to 3.8. with a Imax of 1.5Amps, at most I can only hookup 2more (parallel) Seem like I gotta buy lots of LM317 If I intend to fully replace my Light set.


Once you've got the hang of it it's relatively simple. For power devices, you just have to be mindful at all times of where everything is.

For your situation, you will need to include a transformer, 4 shottky diodes and around 2 capacitors estimated at about 10000uF. This is to 'rectify' the AC to DC. (or you could google 'making an SMPS')

What is the maximum voltage and current rating for your LED?

The LM317 typically has a forward voltage drop of around 1.5V (at least in my uses for them). By putting the LEDs in parallel, you 'spread' the current around while maintaining the same voltage across the LEDs. By putting them in series, you 'spread' the voltage around while maintaining the same current. 

i.e. As a very simple analogy, if you can supply 12Volts and 1Amp and the LEDs need 4 Volts and 200mA. If you put it in series, you divide the voltage meaning you can fit only 12V/4V=3 LEDs in. If you put it in parallel, you can fit in 1Amp/200mA=5 LEDs in.

However, it would be better to use a combination of both so as to maintain the correct voltage(parallel) while keeping the additional component count low(series - LED series only needs 1 regulation circuit per series)

i.e.
4 parallel rows of 10 serials.




> As for stable power supply, can Computer PSU be used? Computer are filled with sensitive electronic components. Don't tell me that the MB, Hard Drives, Roms, etc have they own Power Stabiliser...


You could. I wouldn't say it's perfect but it will work sufficiently. If you have those cheapo brands though I'd suggest you use it only as a last resort.




> firethorn:
> So if the Charger has a stable Voltage, smooth and steady... Can I forget about the LMXXX. I want to hook up a single 3W LED inside my Cabinet so I can see while I work inside the cabinet like adjust my Sump, moving things around..
> 
> Also need to setup Single or Twin 3W LEDs for my 1ft guppy tank no plants. this will be powered on for longer.


If it's smooth, stable and steady, yea you can forget about the regulator. However, do note that the charger was probably not meant for such prolonged high power usage so it could fail in some way which would blow your LED so for a permanent setup, it would be best to add some sort of safety mechanism such as a Fuse or similar device to disconnect the power upon failure. For the first purpose you described though, it seems alright.

At 3Watts(Power) and XVolts, you will need YAmperes. Check out XVolts on your LED. Then use Power=Volts x Ampere to determine how many amps(or milliamps) you will need. Then look at the back of your charger to see if it can supply the needed current.

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## limsteel

I read from the site as linked earlier. Author indicated that LM317 has a Vdrop of 3V. 



> The constant current source has a drop voltage of 3 V, so the supply voltage should always be 3 V higher than the LED voltage and can be up to 37V which is the maximum input voltage of the LM317.


LED I got are rated 3.5 - 3.8V, 700mA ops current.

Using a 12V Computer PSU of better brand:
If 1.5V as you stated then I hookup 3 LEDs in series operating at 3.5V
(3.5 *3 + 1.5 = 12V)
If 3V as the site stated then only 2 LED in series can be connected

So if the calculations given are correct 



> "1,25 volts between ADJ and Vout" Ohm's law says that U/I=R, which means that Voltage divided by Ampere makes resistance.


R = 1.25 / 1.4 (parallel connected to 2 row of LED 700mA for each row) 0.8 to 0.9Ω

I can use 
One 1Ω (>1&#188;W) resulting - 1250mA 
Ten 9Ω connect in parallel to get 0.9Ω (&#188;W each)resulting - 1389mA

Seem like I need to bring out my Bread board and multi meter liao... If PSU not the best power supply then what can I get
(lowest cost / effective, efficient, reliable)

*BTW, I am a Mechanical Eng guy... So don't go too deep in the electronic/electrical term...*

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## sacy

humm. the next best thing is just buy a switching power supply from sim lim tower ^^
something like this--->http://www.haitaik.com/detailshow.asp?ID=227

it should not cost a lot. should be cheap ^^. less headache ^^ just find the right output u need.

but don't go for [email protected]~24A type. it will cos $100~$200 plus

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## limsteel

found this Switching Power unit 12V 5A = 60W $30
12V - connect 7 Parallel 3 LEDs.

Buy 2sets totaling 42LED!

Another 12 to 13.6V at 12Amp @ $52++

with 12Amp I can hookup 17Rows of 3 LEDs. buy 1 set totaling 51 LEDs

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## firethorn

Dang. I went on and on about how it would be more cost effective to get an SMPS for your needs. Then you went and found one. haha..

Check out sim lim towers. I do believe they do sell these units also.

But in the same way customers tend to rely on 'better PSUs brands', be careful with these brands. =)

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## tawauboy

> IS LED DRIVER A MUST FOR HIGH POWER LED? I planning to connect them as if they are normal low current LED setup. 12VDC (Laptop charger with a few Amps) + resistor + LED = Light
> 
> I bought 10 x 3W White LED... got the shipment and I tested using a 9V batt with 100Ω... With this I should get around 40mA running through the LED. 2 out of 10 are dead. When I talked to the supplier, they replied they will not replace the LED as I use Batt+resistor to power them. They claimed that this will burn the LED. trying to BS me!
> 
> These 3W LED runs on 3.5V and 700mA. How can a mere 40mA killed it! what logic?


if you tested the leds with the series resistor, then you will not kill the leds. as long as the current drive is low and very little heat is built-up, you will be fine.
however, if you tested the led at much higher current drive >350ma, the led can be damaged due to heat buildup.

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## tawauboy

> 9v is too much of voltage for the LED. think it's not the current that kill your led. and batt are raw power. batt cant regulate Constance power.
> 
> A led driver is needed if u don't have a good source of power supply. that can produce Constance power. normally a switching power supply will do the job.
> 
> If u use a normal 12V step-down adapter, u need the LED driver.
> 
> just my 2 cent^^
> 
> do remember a 9V batt can kill a human being. if u know the right way.


a direct 9v across the led will damage the led due to overcurrent. however, a 9v battery with a resistor in series with the led will limit the current. this arrangement will not damage the led unless the resistor value is too small (causing a overcurrent) or there is not heatsink for the led (when driven at high current levels).

a led driver is nothing more than a constant current source. like a normal power supply, the constant current source has output current as the main control variable instead voltage for a normal power supply.

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## tawauboy

you can use any type of 12v power supply (smps or linear or pc). smps should be the most compact for a given current rating.

if you plan to run the leds at 700ma, you'll need a series resistor of 2.2 ohm (2 watt) for each string of 3 leds. and you'll need to mount both the leds and resistor on a big heatsink. you can select appropriately sized heatsink by calculating the thermal resistance of the whole system which you are designing.

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## sacy

^^. beware of the hot cable u will get. If u run at near max current on the 12amp supply .

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## limsteel

> ^^. beware of the hot cable u will get. If u run at near max current on the 12amp supply .


I'll use the HiFi Monsta cable, should I run on 12 Amps! Or I can connect parallel to divide the current up.

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## firethorn

If your cable gets hot, you are using the wrong cable. You could divide them up but it will look messy.

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## tawauboy

a wire with conductor diameter of 1mm or more can handle 12a. look for awg18 or smaller.
try to keep the cable length short to reduce cable losses.

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## limsteel

Saw this diagram, what is the transistor doing there?

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## Shadow

What is pin 1, 2, 3? Have not see the spec yet, but my guess is to control the output voltage using PWM. Look like you want to clock/pulse the output.

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## firethorn

That image is misleading. Look at the image of the IC in the link below.
http://en.wikipedia.org/wiki/LM317
On that page:
Pin 1 = +VIn
Pin 2 = +VOut
Pin 3 = +Adjust

The LM317 is a linear device. No pulsing here =)

Use this website to calculate the values if you need. http://diyaudioprojects.com/Technica...age-Regulator/

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## tawauboy

though the pin connections are wrong, the LM317 is connected as a constant current regulator.
the constant current is set by the 'r' value. maximum current is 1.5A.
the transistor is use to dim the led using a pulse width modulated signal.

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## firethorn

Based on the specs to calculate a constant current with a regulated voltage gives me impossible results so yea.. Just be wary of that. I am still unsure if they can both be achieved at the same time with one IC.

Also, the LM317 can output more than 1.5A but it is not recommended. It will need serious heat dissipation. Anything above 1A should also be heat sunk. Note that this is load current. Not current available. i.e. Only if the actual current flowing to the load/device is more than 1A should serious thoughts be given to heat dissipation.

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## solonavi

Just saw this thread, have u guys tried the buckpuck?
http://www.luxeonstar.com/buckpuck-7...leads-p-35.php


JC

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## limsteel

Correct me... but this buck puck function like a LM317. Spec is also quite similar...

an LM317 function between 5V (can't go lower anyway) to 32V.. with a resistor 1.8Ω, I get about 694milliamps... 

ONE LM317 - $1
ONE 1.8Ω (1W) - $0.30

Considering Labor, equipment and material cost to solder the components. Even without calculator, it should be much cheaper!

Unless the buck/puck can be connected directly to our home wall socket, but they still need VDC input so not worth the $$$  :Boo:

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## solonavi

I believe its more than the LM317 + resistor. Cos it can buck and puck the current that is been supplied. For a LM317 + resistor, we need to change the resistor whenever we want to change the current. 

Moreover, I read that hte LM317 can get very hot especially if its been driven at 1000mA and above. If you are going to the LM317 design, not sure if you have seen this. Quite a few nice design been proposed.
http://www.instructables.com/id/Circ...h-Power-LED_s/

Cheers
JC

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