DIY: AC Power Supply for LED

[fido-fido]

diy ac driver led

Hi Everyone,

Could you advise if I can do this for home use:

Maybe I'll try to sketch out a circuit for further question if this is possible. So very briefly, from the AC power supply (240VAC) of our home, connect to a rectifier. And the from there, connect to to transformer to step down the voltage to.....lets say, 5V to operate the LEDsss, many many LEDs

At first thought, without considering others tiny things like the resistors for the LEDs and etc...is this possible?

Here, may I ask how do we know/calculate the number of LEDs that I can light up?

[sorry that I don't have any schematics for now]

 

[~E3016~]

diy 220v led driver

The more led to be displayed is the more current you have to supply, it;s meant that you'll need bigger trafo with have higher rating so the current can supply all those Leds. let's says you connect these Leds in parallel, then the total current to be supplied is the current needed in each led time total LEDs you wanna dispalyed.

one thing you should care about is drop voltage of LED and current capability of LED. Do not over supply the current to the LED, otherwise it'll be burned

 

[fido-fido]

connect transformer 9v outputs in parallel

Hi, thanks for your reply....

I tried asking the shop on the current needed to operate an LED but it seems the seller does not know as well and the LED does not come with any datasheet. May I ask if there is any method to check this?

How do we find out the appropriate resistor value to use here for the LEDs?

 

[Audioguru]

led ac power supply schamatics

Don't buy unknown electronic parts without a datasheet from a "shop". Buy clothes and shoes from a shop.

Buy electronic parts from electronic parts distributor like Digikey in America and Canada or from one of the hundreds of worldwide Farnell offices. The parts are made by good manufacturers and each part has a datasheet.

Most ordinary LEDs have a max allowed current of 30mA but all the spec's are with 20mA. The datasheet will spec the range of forward voltage of the LED which is needed to calculate the current-limiting resistor.
You can guess at the forward voltage from the colour of the LED. 1.8V for red and 3.5V for blue or white.

You don't rectify the 240V mains then feed the resulting pulsing DC to a transformer because a transformer needs an AC sine-wave.
You connect the transformer to the AC mains then rectify the transformer's low voltage AC output.

 

[rikie_rizza]

ac led supply diy

Usually you'll need 100ohm resistor for each led. In this kind of setting, you will get the LED intensity nonuniform because of its differences due tolerance value. the best thing is to use LED driver IC. Another benefit of using LED driver is, you can mix red led with other color.

Why don't you just buy a PS so you can concentrate on your main project such as the LED driving that you want to do.

Don't ever rectify your mains first than transformer. transformer first, than rectify.

 

[tvthang]

1.5vdc power supply diy

To connect many leds in your schematic and to use AC power to supply for which, you can calculate total of voltage of leds after you use a transformer to reduce AC220V downto caculated voltage, you should not use a power resistor which will take more power from your AC source.

 

[jrodgers]

ac led diy ac

Always connect the transformer to the mains, preferably with a fuse in series in the 'Live' line. (Say a 100mA fuse) in addition to the 1A or 3A in the plug. You could rectify the mains, but LED are rectifiers, and provided you use the correct resistors, you will not need any diodes/rectifiers. (LED's are diodes!)

OK, for the maths:

If you use, say a 240V : 9V transformer, then the output voltage will have a peak of 9*SQR(2) = 12.72. In fact, the voltage will be a little more, as the manufacturer wants the voltage to be 12.72pk when the transformer is operating at full current level.

Now, if we wanted to connect a red LED with a forward voltage of 1.8V and a current of 20mA directly to the transformer output then use the following equation:

R=V/I = 9 / 0.02 = 450 Ohms.

You could use 470 ohms from the E12 resistor series.

I used 9 Volts and not 12 in the above calculation as the LED will be 'on' for only half the ac cycle (as it is a diode). Really, the 9V refers to the RMS 'DC' equivalent of the ac power wise. In reality, the diode part of the LED means that it is only on for half this time, and so really would only get equivalent to half the current in the calculation. (10mA RMS), You could probably half the resistor value,

You can connect lots of LED to the output of the transformer like this in parallel. It would be a good idea to connect half one way round and the other half the other way round. This will ensure that the transformer is equally loaded on each half cycle of the AC waveform.

Now, how many can you connect. Well, lets take a real transformer as an example, the RS (rswww.com) Part No: 805--057. This is a 20VA transformer and can deliver a total of 1.1 A on each of its 9V outputs (it has 2 of these.) Connect them in parallel (Do this correctly to avoid a short circuit - if you don't this is when the fuse mentioned above comes in handy! 100mA fuse as according to P=I*V, I at the mains at full output is P/V =20 / 240 = 83mA)

OK, so the transformer can deliver up to 2.2A at 9V. Each LED will pull 20mA from one half cycle of the ac, and another resistor/LED wired the opposite way round will pull 20mA from the other half cycle. Infact, one resistor can supply 2 LED's this way, provided the 2 leds are wired in the opposite direction.

So, 1 resistor, 2 LED's draw 20mA. We can draw 2.2 A from the transformer, so we can have a total of 2.2 / 0.02 = 110 pairs of LED's, which is 220 LED's running from this one transformer.

I will try and make a circuit diagram of this setup an post it soon.

Safety Note: Always be careful when using mains, and if you are unsure about anything, seek help from an experienced engineer! Mains can kill!

Added after 23 minutes:

The schematic from my last post is attached! Sorry for the 'doodle' style, it was quick to make!

 

[Audioguru]

diy mains led

You could rectify the mains, but LED are rectifiers, and provided you use the correct resistors, you will not need any diodes/rectifiers. (LED's are diodes!)

Most LEDs have a max allowed reverse voltage of only 5.0V. The reverse voltage of 12.72V will blow them up without a rectifier.
The LEDs will flicker at 25Hz without a full-wave rectifier.

Infact, one resistor can supply 2 LED's this way, provided the 2 leds are wired in the opposite direction.

Good, then the LEDs limit the reverse voltage. But they still flicker.

 

[upInSmoke]

diy power supply for leds

If you are using many LEDs, you might want to use resister arrays. It will make the assembly neater and easier to build.

 

[FvM]

diy driver led 10a

The LEDs will flicker at 25Hz without a full-wave rectifier

I would expect 50 Hz flicker, actually. This frequency is still perceptible by the human eye to a small degree.

 

[zlatkoMM]

connect led to ac power

Audioguru is 100% in right dont play with this easily!

Added after 29 minutes:

Maby this can work:

 

[Audioguru]

diy ac transformer

Maby this can work:

The transformer's output voltage is too low at only 2.5VAC. The voltage is also too low to connect LEDs in series to reduce the total current.

The 2.5VAC will create a supply of only 1.5VDC/3A which is not enough to light any LED.
If the transformer is 12VAC then the DC is 15V and six 2V red LEDs in series with a 120 ohm resistor will create a current of 25mA.

 

[zlatkoMM]

ac mains led calculation

Voltage is not to low dc after brige is 2.2V x sqr(2) with electrolyte 1000uF is
2.2 x 1.41 = 3.1 V and start volztage for RED Led is 1.6V.So if trafo can deliver
3A max then this circuit work enough.15mA is enough for normal litght.

 

[FvM]

diy ac to dc led driver

Apart from obvious calculation errors in your example, series connection has several advantages and is generally used for LED illumination solutions that can be found in any DIY-shop arround the corner.

 

[Audioguru]

diy ac led

Voltage is not too low dc. After bridge is 2.2V x sqr(2) with electrolyte 1000uF is
2.2 x 1.41 = 3.1 V and start volztage for RED Led is 1.6V.So if trafo can deliver
3A max then this circuit work enough.15mA is enough for normal litght.

The DC voltage is not 3.1V. The rectifier bridge has two diodes in series and if the output current is 3A then the diodes have a peak current of almost 10A and each has a forward voltage drop of 1.0V. Then the DC is only 1.1V when the AC is only 2.2VAC and the DC is only 1.5V when the AC is only 2.5VAC. It is not enough DC voltage to light most LEDs. Many red LEDs need 1.8V to 2.0V.

 

[zlatkoMM]

diy power supply

RED led treshhold voltage is 1.6V in europe. and gretz has 4 diode if you dont know??
after gretz is electrolite wich increase dc voltage for sqr(2) if you dont know???

 

[fido-fido]

diy led power supply schematic

Hi All,

Thank you so much for all the guidance and advice. Maybe give me sometime to find out on some parts and do some other readings .... I'll come back to you guys if I have further questions.

Sorry that I didn't mention earlier, I actually intend to build 6 lamps, standing on 6 short poles, for my garden. Intend to only use a lot of LEDs for one lamp...

Thanks again!