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Here's a bit more about LED's in case you're confused or just interested. Browse the rest of their site if you have time, there are all sorts of interesting topics , tutorials and tips abundant.
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Looks like a good site for info. The one thing about an LED that you have to remember is that it is not so much an electrical "load" like a light bulb, but more like an electrical switch that closes when the polarity of the voltage is correct. That is why the LED requires a resistor in series. The eresistor is the "load" in the circuit. Without it, we basically have a short circuit and the switch (LED) will burn up... just like a light switch.
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that's somewhat right indeed. They do have a load, be it a very small one, up to 1.5V for a standard led, no resistor is required, but in our situation, with higher voltages on tracks and leds build in as headlights etc, we do need one. The site has resistor info too.
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torikoos Wrote:that's somewhat right indeed. They do have a load, be it a very small one, up to 1.5V for a standard led, no resistor is required, but in our situation, with higher voltages on tracks and leds build in as headlights etc, we do need one. The site has resistor info too.
it has to be said- you should be very careful about using LEDS without a series resistor
I am experimenting ATM with building my own streetlights/trafficlights etc using SMD led's of various types
I have a rather nice dual output variable voltage powersupply with current limiting at my disposal (about 200 bucks worth)
while testing out the various leds I was looking at for traffic lights, I managed to burn out an amber led within about 3 minutes, although the voltage was only 3.6v instead of 3.5v, the current rose from 10ma to 60ma in that .1 of a volt
with even a low value resister it wouldnt have happened (or if i had turned on the current limiting on my power supply)
but having a power source without a series resister that isnt a `current limited' type will damage the leds longterm if its voltage isnt extremely tightly regulated
JFYI
poopsie chicken tush
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boppa Wrote:torikoos Wrote:that's somewhat right indeed. They do have a load, be it a very small one, up to 1.5V for a standard led, no resistor is required, but in our situation, with higher voltages on tracks and leds build in as headlights etc, we do need one. The site has resistor info too.
it has to be said- you should be very careful about using LEDS without a series resistor
I am experimenting ATM with building my own streetlights/trafficlights etc using SMD led's of various types
I have a rather nice dual output variable voltage powersupply with current limiting at my disposal (about 200 bucks worth)
while testing out the various leds I was looking at for traffic lights, I managed to burn out an amber led within about 3 minutes, although the voltage was only 3.6v instead of 3.5v, the current rose from 10ma to 60ma in that .1 of a volt
with even a low value resister it wouldnt have happened (or if i had turned on the current limiting on my power supply)
but having a power source without a series resister that isnt a `current limited' type will damage the leds longterm if its voltage isnt extremely tightly regulated
JFYI
I am learning voltage spikes and reverse voltages are LED killers. Another diode should probably be used to protect the LED from reverse voltages when used as a DC headlight, and a capacitor used to protect against voltage spikes caused from motors.
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very much so- most led suppliers will have a datasheet available that lists things like PIV, forward current, etc etc
( heres my streetlight one...)
<!-- m --><a class="postlink" href="http://docs-asia.origin.electrocomponents.com/webdocs/08d4/0900766b808d44df.pdf">http://docs-asia.origin.electrocomponen ... 8d44df.pdf</a><!-- m -->
that tells anyone who knows how to read it everything they need to know about its electrical behaviour
most dcc supplies are dangerously close to the upper limits (eg something like coach lighting can - even with a full rectifier diode bridge be close to them)
even dc supplies can in the right(or wrong) circumstances be enough to be damaging them- even with a series resitor of the correct value fitted
poopsie chicken tush
