LED Basics

[BoostedinSoFla]

I work with and see all types of LED's (marine and residential application) 5 times a week, completely sick of them I tell ya. Lol

 

[ramsack]

I got the same way after working at Friendly's with ice cream. I can't eat it anymore despite it being good. And ALWAYS use sockets for ICs.

Also, I think this thread should be put into the "Electrical and Wiring" section under the Tech Article Archives.

 

[mezzio]

I was always amazed with RGB LEDs and there was a circuit like 15 years ago in a magazine that used a PIC controller to change the colors. This was before semiconductors were small enough to have logic on the same LED die to switch colors.

got any more info on this? I've got a project in mind that's gonna require some color changing LED's and a controller w/ memory... Right now I'm thinking about ripping apart a Glo Shift gauge and stealing the circuit in that... but I'd rather have something more custom. I've got tons of electronic experience, but the last classes I took that dealt with electronics were over 10 years ago, .

 

[Blurred Talon]

Blurred can you take a pic of the back of that perfboard that you soldered for the blinkers? And how did you wire it up from there?



Sent from my SAMSUNG-SGH-I897

I don't have a picture. Basically I just soldered a wire to all the positive legs and all the negative legs at the beginning and end of each series and then those wires go to some 18awg wire which go to my PWM.

So...700 mA at 2.5 volts is still 1.75 watts. Almost twice a 1 watt rating. The only thing saving the resistor could be PWM...so you are cutting corner after corner and spending more (or charging) to achieve it. Isn't 2.5 volts a little low, too, for those LEDs? I was looking at the Marktech P4 LEDs, concave, and the max voltage is 3.0 volts. Just giving them 2.5 is a serious loss in brightness without extending life. I would run 2.95 to them. PWM will save them a little bit. Without PWM I would run 2.8 volts to them. They probably aren't even seeing 2.5 volts because you are using a 12v regulator along with a PWM and other nonsense.

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For anyone interested that is a PWM circuit, probably the cheapest way to make one. PWM circuits are mainly useful in controlling brightness in things that will blend oscillations together, for instance filamented light bulbs or motors. A wirewound potentiometer is the only mechanical device that will dim a light bulb. They get hot and wear out if constantly adjusted, so a PWM circuit is the most useful way to control a light bulb. The filament stays lit after it's shut off so you don't see the pulses like you do with an LED. A PWM circuit is never going to get something to full voltage or none at all since there is always a duty cycle.

Time output (pin 3) is high = 0.693 (R1 + R2) C1
Time output (pin 3) is low = 0.693 (R2) C1

Frequency (Hz) = 1.44 / ((R1+ 2xR2) C1)

Q1 is a PNP transistor, so the LED is going to turn on when pin 3 goes low, so R2 would be the best to be a potentiometer and not R1. For pulsing a negative voltage instead of a positive, use a NPN transistor and focus on R1's value. All values to calculate will be absolute, for instance a 4.7 µF capacitor would be 0.0000047 F.

No it's not to low, it's right in the middle for what these LEDs are rated for, their bin voltage rating is 2.4-2.6V. There is no lost brightness, they are rated for 3500-4800mlm when used within the above voltage @ 70mA. They are plenty bright and are painful to look at even with the lens in front of them.
As for the PWM saving the resistors, I've had them running on my bench power supply with no PWM or Vreg for hours with no problems at all. They are series parallel, so there's 4 in a series with a resistor at the end of each series.
Here's a diagram of my LED turns.

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As for the PWMs, lets agree to disagree. We've both got differences of opinion on the matter and there has been enough information posted in this thread about both ways and people can come to their own conclusions.