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Current limiting resistor for LEDs.

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RayH

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Further to my previous post ,if I were to connect 115 LEDs in series with 230v ac what current limiting resistor would be required?
Thanking you in aticipation.
Rayh.
 
Just straight to 230ac? no rectifying and smoothing capacitor?
2K2 should do. - Make it a 0.5 watt type

I would at least use a 'seperation' transformer (any1 can tell me the english term?). I mean a 1:1 tranformer to isolate you from mains.
 
I might as well ask it while im thinking of it: Why use an isolation transformer? Youre gonna get fried either way, right?
 
An isolation transformer will offer protection when you only touch the live side of the supply , since you're isolated from ground.

If you touch both sides you're still fried indeed.
 
Unless you say what your LED voltage and desired current is, it is impossible to say what the necessary resistance is.

Even a 1/2W 2.2k resistor reaches its limit at only 33 volts across the resistor. You will likely want to drop more than this across the ballast.

Also I assume you're running this through a full wave bridge rectifier. LEDs do not have a strong or reliable reverse breakdown voltage and it's best never to allow reverse voltage on them.
 
you dont need a current limiting resistor. LED can be power by 2 volts. since there are 115 LED in series 230/115=2V
 
It is always necessary to include a current limiting resistor with LED's. What LED's are you using, what is the forward voltage of the LED's.
I would suggest a rectifer and smoothing capacitor with a high power rated series resistor.
 
An isolation transformer might also serve to limit the available current in case of a fault. Electrical systems and components are designed with this in mind.
 
positive logic said:
Try this! connect 3 LED in series and connect it in 6Vac. If the LED blown then i am wrong.
I think you should be the one paying for the LEDs here. Why don't you run the experiment and then report back to us. :oops:
 
Never drive led without limiting its current, as the proper way to drive led is by current and not voltage!
 
RayH said:
We intend to use a standard cheap Led at 2v 10ma.

If u are directly using AC mains to connect the led, you no need resistors to limit current. The suppressor capicator will limit it. For 10ma, use a 200~220nF, 400V and above suppressor-type capicator. Please refer to your very 1st post for the circuit. This is the easiest way to drive your leds(only 3 components).

Base on your spec to drive 115 leds at 2V should be just nice to fit into that circuit.

Lastly is the same old thing, AC is dangerous.... :twisted:
 
i am sorry! i tried to connect LED by using a step-down x'former. maybe in 230Vac it will not work. Better to use current limiting reistor.
My apology!!
 
positive logic - if you tried running 3 LED's directly off of 6Vac without a current limiting resistor it would work. However it doesn't mean that this is a good technique to use. It is bad practice and the LED's would work for a fraction of the time compared to how long they would work with a current limiting resistor
 
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