# LED flicker and parallel arrays



## Revenant (Mar 17, 2007)

I bought a 10-pack of LED flicker circuits from this guy on ebay cuz I want to make some taper LED candles for my mom for Christmas... well, that and I want to practice some electronics so I can make some haunt stuff lol... anyway... The individual candles will be for the bedroom windows and I'll just use AA batteries for those, but for the picture window candelabra I figured I'd wire it to a transformer so it can plug into the same outlet as the other lights. The specs on the flicker circuits say optimal voltage is 2.6 to 4.5V, and I have a 4.5 wall wart (400 mA) from my old phone... so...

If I use an LED and circuit board for each candle, can I just wire the leads from the wall wart to a gang hub and wire each candle to it?

Also... I was reading about LED's on linear's site and he said you have to use resistors to limit current when you wire up LED's or you'll burn them out, and I don't see any resistors in the pix of the flicker PCBs. These circuits are cheap but I don't want to smoke them wiring them up. I wish I wasn't so ignorant of electronics...


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## Dr Morbius (Sep 21, 2004)

Correct me if I'm wrong...Please...but I think resistors limit voltage, not current. The device in question will draw whatever available current is provided, it's the voltage that will kill the LEDS.


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## Revenant (Mar 17, 2007)

linear said:


> Why do you need a resistor with an LED? The short answer: to limit the current in the LED to a safe value.
> 
> The long answer: LEDs are semiconductors, diodes in particular. The current flowing in an LED is an exponential function of voltage across the LED. The important part about that for you is that a small change in voltage can produce a huge change in current. That is the most important concept of this article. Resistors aren't like that. The current and voltage in a resistor are linearly related. That means that a change in voltage will produce a proportional change in current. Current versus voltage is a straight line for a resistor, but not at all for an LED.


On linear's website he specifically mentions using current-limiting resistors. A description of different kinds of resistors can be found here. This article also explains: "An LED (Light Emitting Diode) is a semiconductor that emits light energy when a current flows through it. Current will only flow one direction, just like a regular diode. There are a few things you need to know about an LED before you use one. First, and most importantly, is that an LED has very low internal resistance. This means that left to itself, an LED will pass so much current that it will burn up. They require an external resistor to limit the current."

To address your observation about current and voltage in this context then, Doc, it's the current that smokes the LEDs; the higher voltage allows way to much current to cross the diode. I'm assuming the flicker circuits are using pulse-width modulation to make the light output ramp up and down, I just don't know if it needs resistance added also.


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## gmacted (Jan 18, 2006)

Resistors drop voltage across their leads and limit current through them. You can think of them like a hose. The greater the resistance, the less water will flow. The greater the amount of ohms (resistors are rated in ohms) the less amount of current will flow. They "resist" the flow of current... that's why they were refered to as "current limiting" resistors. The relationship between voltage, current and resistance is defined by ohms law (V=I*R --> Voltage = Current time Resistance).

To answer your question Revenant, you do not need a "current limiting" resistor if you use this 4.5V walwart. Here's why. The flicker circuits you bought have what I call a "black blob" on the circuit board. This black blob is an epoxy that is covering the IC (Integrated Circuit). This is a very inexpensive way to "package" an IC. Another (and more traditional) way to package an IC is to package it in a plastic shell and add leads (or legs) to it. This is how you would see an IC attached to a printed circuit board.

The IC on the board you bought doesn't have legs, but rather pads to connect to. Their picture is self explanitory. In order to use your walwart, you will need to connect these circuits in parrallel. This means you need to bring +V and -V to each circuit board (I'm not I was very clear here) and use one LED per circuit. I'm not sure how much current each board/IC will draw, but the 400 mA should be fine. Since you are wiring the boards in parallel, they will each draw a certain amount of current from the walwart. You should have more than enough current to power at least 10 circuits.

I hope this helps. Please feel free to ask any other questions you may have.


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