But i want to hook up the LED to a car battery which has high current and voltage.Many LEDs now a days can be wired straight up to a supply. They will not drop more than their 2V forward voltage, or whatever it is and won't let too excessive currents.
Check it out. You could probably find some that you can just hook up.
Many LEDs now a days can be wired straight up to a supply. They will not drop more than their 2V forward voltage, or whatever it is and won't let too excessive currents.
Check it out. You could probably find some that you can just hook up.
http://www.farnell.com/datasheets/59322.pdf
*seinfeld* You are very bad man! Very bad man! */seinfeld*
I'll have nightmares now about the poor OP touching LED after LED directly onto a 12v car battery terminals!
"well they DID work! really bright for about 1 second but now they stopped working... how do I make them start working again?"
The LM78xx series are designed to be simple fixed voltage regulators, only requiring external capacitors to prevent oscillations and stabilize the output voltages. They don't require external resistors. However, they can't be used (practically) as current regulators.Thanks for the info Sgtwookie.
I was exposed to LM78xx all this long.
I dont know abt other regulator especially adjustable one.
But i would like to learn some other regulator to increase my knowledge.
Can you explain to me the difference of LM78xx and LM317 and the benefit using LM317 on this circuit?
The red and blue will look like red and blue, which may get you into trouble with the police. Avoid colors that are used by fire and police vehicles.Actually i want to light up many LEDs.
I want to set up lights under the body near the side skirts,like neon light used in most of NFS Underground cars that looks cool in the night.
And i just thinking to use purple LED but never heard of that colour LED available at the shop.So i want to combine blue and red LED to bring out the purple colour.Is it possible?
Ya,i want to use LED rather than neon because dont want trouble with the police.I think want to use blue only as its very bright.The red and blue will look like red and blue, which may get you into trouble with the police. Avoid colors that are used by fire and police vehicles.
You mean this LM317,doesnt have ground pin?Here is a link to the datasheet:
http://www.national.com/ds/LM/LM117.pdf
See page 2 to determine which terminals do what.
See the schematic on the bottom of page 19 entitled "Precision Current Limiter".
You don't need a potentiometer, just a fixed resistor.
62 Ohms will give you roughly 20mA output.
You cannot use a 78xx type regulator as a substitute for the LM317 for this regulation scheme.
No, it does not. It has IN, OUT, and ADJ. You're thinking of the 78xx/79xx series, which have IN, OUT, and GND.You mean this LM317,doesnt have ground pin?
The cathode of the LED should be connected to ground, and the anode to the ADJ terminal of the LM317.So,the ground should directly connected to the LED?
Just for fun.Why do kids shine blue LEDs on the ground under their cars where they cannot be seen??
Now i understand.Thanks for the info SgtWookie.No, it does not. It has IN, OUT, and ADJ. You're thinking of the 78xx/79xx series, which have IN, OUT, and GND.
The cathode of the LED should be connected to ground, and the anode to the ADJ terminal of the LM317.
Apart from the voltage drop of 5V against the 1.25V for the LM317, they can be used in the exact same way - a 220 Ohm resistor is about right for 23 mA.The LM78xx series are designed to be simple fixed voltage regulators, only requiring external capacitors to prevent oscillations and stabilize the output voltages. They don't require external resistors. However, they can't be used (practically) as current regulators.
Søren;153057 said:Hi,
Lanz <- You can get LEDs in just about every color and you'll get a more even purple if you just went with purple LEDs, rather than red and blue ones. Or you could go for 1W RGB LEDs and dial in whatever color suits your current mood (or make the color based on RPM or speed).
Aside from the LM117 having a broader temperature range, they are basically the same.I had connected the circuit like what Sgtwookie said.
I think this is how it should be connected.
I asume that LM317 and LM117 are the same.
The meter has a very high impedance. The regulator is attempting to source 20mA current from the ADJ terminal, but it can't raise the output voltage high enough.
I had test the circuit with VR and fixed resistor(62 ohm).
No change in the voltage even though when i move the VR knob or 62 ohm resistor.
The voltage still shows 12V when i connect to my car battery.
I dono where is the problem?
But the voltage shows 12V,what will happen if i fix a LED at the output?The meter has a very high impedance. The regulator is attempting to source 20mA current from the ADJ terminal, but it can't raise the output voltage high enough.