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Old 16th February 2003, 11:27 PM   #1
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Default Blue Diode as Power Indicator

As it seems the blue LED is the only way to go for a power indicator, I have a dumb question. I read where others have wrapped a couple of turns around the toriodal power transformer to energize the light.
I just ordered a couple of Lumex "Ultra Super Blue" panel mount LED's for my upcoming projects. My question is how the diode lives with the AC coming off the transformer.
I trust others, but most I have seen work off the DC heaters on tube gear. Can you feed them AC without smoking these 5.00 each jewels?

TIA,
George
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Old 16th February 2003, 11:33 PM   #2
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I have never done this. It's a lot easier to simply
place the LED in series with a resistor between the
+ and - supplies. Makes a nice supply bleed-down
circuit, also.
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Old 16th February 2003, 11:50 PM   #3
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Default it is a diode after all

super blues -- Agilent high lumninosity are less expensive.
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Old 17th February 2003, 12:09 AM   #4
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In my latest Gainclone project it was more convenient for me to wrap 10 extra turns on a toroid for a blue led. I connected it through regular rectifying diode and intensity adjustment resistor. Works fine.
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Old 17th February 2003, 10:22 AM   #5
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Default Blue diode wiring

Thanks for the advice on parts needed. I will wrap wire and measure voltage untill it gets to the proper range.
If there are replacements needed I will look into the Agilent LED's. The blue models are not available locally. But that is what is great about the net!

George
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Old 17th February 2003, 11:17 AM   #6
miguel2 is offline miguel2  Portugal
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I use some turns of bell wire around the toroid to get ~ 8V, a diode after, a cap and the led. The value of the cap controls the intensity of the led.
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Old 18th February 2003, 01:06 AM   #7
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Default I assume this is a shunt cap

Some have metioned a series resistor, you are using a shunt cap for filtering?
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Old 20th February 2003, 05:53 PM   #8
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Cap is for current limiting..... placed in series
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Old 20th February 2003, 09:22 PM   #9
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Beware of the orientation of the elko when placing it in series with a led !
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Old 21st February 2003, 08:10 AM   #10
miguel2 is offline miguel2  Portugal
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I put the cap after a rectifier diode, from the +V to ground. Then it is the blue led. I did it to get some ripple off the line voltage to the blue led. Now that I think of it maybe it is a silly idea, but it works. The bigger the cap the higher the voltage the blue led sees, that is why the cap is controlling the light intensity.
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