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Topic: A cautionary tale with cheap ebay Voltage Regulators. (Read 12247 times) previous topic - next topic

thepenguin


You're driving a LED based on voltage, then you're making it worse by using a regulator circuit that is specified at +/- 2.5% regulation. Grumpy Mike would kick your butt for doing it that way. There's nothing about a LED V/I curve that suggests anything but eventual failure.


If Grumpy Mike is mad, you know that what you are attempting to do is actually going to work.
If he seems to like it, scrap your design.  There's no hope left for it.

He seems to think that if a butterfly flaps its wings in taiwan, it will damage your arduino (that's not much of an exageration).
Connecting an LED without a resistor will not harm the Arduino, only the LED.  If it is done in short pulses (under 2s), no harm can be done.


cjdelphi

If you supply the correct /regulated/ voltage along with no ripple...


The LED will be fine....  show me a dimly lit led running at 2v (1ma draw), no resistor required!  Resistors are purely in place to protect the led from voltage spikes (current limiting in this case)

polymorph

LED forward voltage drops 2mV per degree Celsius.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - https://tinyurl.com/Technote8
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

Osgeld

#34
Jul 23, 2013, 05:54 am Last Edit: Jul 23, 2013, 05:58 am by Osgeld Reason: 1
and your high powered ones get hot pretty quick, so what do you do

you could be normal and use a current limiting device, or you could make some feedback loop to constantly regulate the voltage as it changes

I work with high powered LED's for a living, its not uncommon to watch them zip on up from 23 to 60-70c, there's almost a volt difference using the general guideline posted above

besides I was responding to the post above, last I checked the arduino outputs 5 volts

cjdelphi

i'm using a 10 watt high powered LED with a TIP31 (68 ohm resistor) and PWM (analogWrite) with no problems at all, i draw around 800ma @ 14.5v using analogWrite(pin,200) (11.6watts) but with good heatsinking which my LED does have ... it's happy to draw around 1.2amps (12v LED)

Osgeld

#36
Jul 23, 2013, 07:21 am Last Edit: Jul 23, 2013, 07:23 am by Osgeld Reason: 1
"it works fine" is not an acceptable answer

whats the voltage drop over time, whats the die temp over time, whats the(true) current draw over time, what is all that in an enclosure, whats your ambient temperature?

and I mean serious time not 5 min and welp its good

I don't care what you do with your 1$ ebay find, but you are only seeing a small part of the picture and preaching it like its the bible

it may work fine for now, it may work fine for a while the point is you dont know and you only want to argue that fact, while people who do have a clue sit here shaking their head

cjdelphi

Do you understand what the role of the power transistor is?....

Unlike a mosfet, the TIP31 is current based, using PWM, you're limiting the current to the LED (EG, same as a resistor)

ughhh, man some people need prozak on here....

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