Dimmable Led circuit

>>1166109
Leds generally don't 'dim' well. It takes so little to get them to light up, a dimmer wouldn't be very useful

You usually dim LEDs with PWM. A 555 timer with a pot.
http://www.pcbheaven.com/circuitpages/LED_PWM_Dimmer/

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>>1166109
get the voltage range that will put ~1mA to ~20mA thru the led, use that range to find the max/min resistance, put a pot in series with a resistor to get standard values

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>>1166187
Using anons current values here and assuming that OP's circuit is drawing 20mA...
Add a 1K pot in series with the 47 ohm resistor

math:
>What's the voltage across the resistor?
V = IR
Vr = 20mA * 47ohms
Vr = 0.94Volts

>What would the Resistor value need be to get 1mA?
R = V/I
R = 0.94v / 1mA
R = 940 ohms

This solution has better control.
>>1166141

>>1166196
and better efficiency

>>1166196
this.
for LEDs, PWM gives better effiiciency and better linearity.

>>1166217
>better efficiency at higher currents
not even close

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Wire this up op, should work great. Make sure Vcc is around 5v.

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>>1166747
Shit forgot pin numbers

>>1166686
why not?

>>1166906
Because he doesn't know what the fuck he's talking about.

>>1167045
So how about you correct him instead of being an even bigger faggot that all of them combined you argumentative cunt?

Oh, thats right, you have no fucking idea either, do you?

>>1167061
>no u
lol

>>1167082
no really, that shit is fucking cancer on this board, faggots chipping in with condescending four word answers who don't actually have anything in their heads apart from a shot of their dads cum.

this is not /b/. contribute or fuck off you waste of flesh.

>>1167090
>responds with a non contributing response
we gonna keep doing this or?

>>1167092
uhh, im not>>1167061 you dense cunt..

>>1167094
doesn't matter, you're still not contributing

you dense cunt

fwiw pwm would be far more efficient than using a resistor/pot as you're only basically only dissipating the power of the resistance of the switch when it's on (very small). Compare this to the resistor where you'd be constantly dissipating the power (Vr*Ir). Of course if you're using more power on the pwm control than what you'd be losing through R, you'd be better off without it, but tbqh uC's which have tiny power consumption are so readily available that it's basically always more efficient to pwm. Not sure off the top of my head what sort of values we're talking for 555 timer, might be cool to build the two side by side and make some comparisons as an afternoon's project.

>>1167102
Agreed, PWM is actually really efficient at high current draws provided the circuit is designed to be as such, since he wouldn't need to drop high (but not max) currents across the resistors to 'dim' it.
This is where boost topology comes in handy for batteries (since the voltage is barely sufficient to run one or two LEDs) because it can be set to precisely the needed voltage to drop very little current across the resistor and waste the least amouunt of power. Whereas if you're regulating the voltage / current with a linear regulator, that voltage overhead is dropped across the regulator IC (V drop x load current) = power wasted

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>>1166906
observe the graph on the left
you will see a similar curve for pretty much every measured LED

>>1167045
faggot

>>1167358
Do you even Ohm? If you use a resistor to limit the current going through an LED you're loosing V*I^2 watts, notice how the current is squared, that means power loss increases exponentially with current, you'll need a big ass resistor to avoid the thing going on flames. PWM on the other hand uses transistors which remain stone cold and don't waste any power, the power is lost at low brightness settings, and even then it's a fraction of the power of the LED. Since the duty cycle is low the power lost is small.

Maybe if you want the LED to stay very dim all the time then it's reasonable to use a resistor, since the current and hence the power loss will be low, but if you're dealing with high currents and want the LED to be at full brightness the resistor will dissipate a LOT of heat in order to limit the current, and then it's preferable to lose a certain percentage of power at low brightness settings.

>>1167402
if you are at all concerned with efficiency and high luminous output, you're going to make a proper constant current switch mode driver for the LED

you still need to limit the current through the LED with a resistor if you just use a constant voltage source and a transistor driven with PWM, dipshit

>>1167358
What you're showing just proves PWM is better. I dont' see the problem

>>1167571
His picture shows that the LED efficiency goes down as you increase the (peak) current. Which is what happens when using PWM control.

>>1167402
This is also wrong. Lets say you're feeding a 3V led from a 4V source and you want the amount of light the LED produces at 1mA. If you use a plain old series resistor, you'll have a 1k resistor, dissipating 1V*1mA = 1mW.
If you have a PWM running at 0.1% duty cycle and having 1R effective series resistance so that you'll have 1mA/0.1% = 1A pulses, the power dissipation in your switch/resistor/whatever is 1V*1A = 1W during pulses and 0W otherwise. Your average power dissipation is the same 1mW as before.

So, PWM alone does not help you and actually lowers the efficiency due to control circuit losses and reduction of LED efficiency. If you want to improve this, you need to toss the resistor as a current limiting element and use an inductor. That is, you need a proper switching regulator.

That's when you care about the actual light output. Eye response might change something if we are talking about the perceived brightness, though.

>>1167595
I think he might have been the only person thinking about LED efficiency and not voltage drop out efficiency, both over resistors, and over linear ICs