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The circuit is a constant-current source. The current through the l.e.d.s will be about 18mA irrespective of variations in the supply.airbrush said:so would running a series one LED with the correct resistor for 12 volts still work then with a non-regulated adapter as per the schematic?
Morgen said:Yes. If you plan on having 20 LEDs connected, multiply 20 x 20mA to get 400mA. A 12V 500mA adapter will provide enough power with the 555 circuit included. I suggest 470 ohm resistors in series with the LEDs.
If you decide to use a voltage regulator, it can be made with a variable output, making the 555 brightness control circuit is unnecessary.
Morgen said:Simplified, yes. I think the schematic you have is for occasions when a constant voltage must be maintained. You aren't restricted by that.
They turn off at a higher voltage, they turn on at a higher voltage. If one LED has a forward voltage rating of 3.3 volts, it needs that amount of voltage before it will conduct current and turn on. Any less and it stays off. If 2 of those LEDs are in series, the forward voltage required becomes 6.6 volts. >6.6V is on, <6.6 is off.Okay...hmm...you said they will turn "off" at a higher voltage if i create a 2led series. Dont you mean "on"..or am i missing something here? I would probably do as you said...a couple leds in series.
Nothing needs to be changed. More amperage from the adapter means you won't need to connect LEDs in series, which is generally a poor circuit design. You could get by with two in series in a noncritical application though.If bigger adapter might be in order, an 800mA...do i need to change anything if i decide to use that instead? I am trying to get the smallest size wallwart that i can, demension wise, that is why i said a 500mA one.
I suggest you use the datasheet circuit and comments that I posted, and just use the other schematic as a reference.So i can go by the schematic on that link....remove the one resistor...what about the other resistor shown there? do i get rid of the capcitor shown there and put the one mentioned at the input of the regulator instead?
I've never used pots before..you say 500k may be alot of play...that could be fine...if I have 2 or 3 full rotations on it for dimming that is fine.
So the power would be running to three of these setups, would i need to add diodes in there somewhere as well?