Power indicator for transformer enclosure
Nov 26, 2008 at 3:49 AM Thread Starter Post #1 of 20

Navyblue

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What I can think of:

- LED with a simple AC to DC circuit
- Some sort of light bulb

I have space constraint so I'd prefer not to go through the trouble of squeezing the AC to DC circuit into the enclosure.

If I were to use AC to power an LED, would it just blink at 50/60 Hz? Is there anyway of smoothing the blink with a capacitor?

Is there any better way?

Btw, is electronic fluorescent ballast found in screw in CFL a "noisy" device?
 
Nov 26, 2008 at 3:59 AM Post #2 of 20

MN Ham Phones

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An LED will work fine on AC. No blink. No need for "AC to DC circuit...."
You still need a series resistor to limit current regardless if you feed it AC or DC.

Feed it AC from low volt (heater winding) end of a transformer. Don't recommend feeding it AC from line voltage end of transformer.

I don't post often, but suggest you fill us in on what your project is.
 
Nov 26, 2008 at 4:25 AM Post #3 of 20

Navyblue

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Thanks.
smily_headphones1.gif


Glad to hear that. I guess my stupid question prompted you to break your silence. It is for my Beta 22 build. I'll understand if you were to try to dissuade me from doing this.
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Nov 26, 2008 at 7:33 AM Post #6 of 20

Navyblue

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Ok, you guys are confusing me.
biggrin.gif


As Uncle said, many power switch comes with LED, do they work with AC and just need a resistor to work off the mains?

If AC would fry LED in reverse polarity, would having resistors at both ends in series, or having a suitable diode at reverse polarity to shield the wrong end solve the problem?
 
Nov 26, 2008 at 8:06 AM Post #8 of 20

amb

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Some switches have neon bulbs and could work directly off AC. Some have a built-in LED with separate pins for the LED (either with or without an internal current-limit resistor). The assumption is that you'd power the LED with a DC voltage, and those with a built-in resistor must be operated at a specific rated voltage. If you don't have a DC voltage to work with, you could use AC to power the LED, but you should use a diode to block the reverse AC pulses from destroying the LED. The forward pulses are at AC frequency (50Hz or 60Hz depending on your local power standard), and that's fast enough that you won't see it as "blinking". No filtration capacitor is needed. The resistor value must be calculated based on the supply voltage, the desired forward current through the LED, and the LED forward voltage. The diode must be rated higher than the supply voltage with some headroom.

attachment.php

 
Nov 26, 2008 at 12:59 PM Post #9 of 20

Navyblue

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Quote:

Originally Posted by cotdt /img/forum/go_quote.gif
why not just use a standard AC light bulb?


I don't know what is the smallest AC bulb is, but I can't find any that are shorter than an inch, not to mention its extreme uncool factor when used on a non vintage themed build

If I were to mount it outside the case, I could use a lamp shade too and double it as a table lamp.
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Nov 26, 2008 at 1:11 PM Post #10 of 20

Navyblue

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Quote:

Originally Posted by amb /img/forum/go_quote.gif
Some switches have neon bulbs and could work directly off AC. Some have a built-in LED with separate pins for the LED (either with or without an internal current-limit resistor). The assumption is that you'd power the LED with a DC voltage, and those with a built-in resistor must be operated at a specific rated voltage. If you don't have a DC voltage to work with, you could use AC to power the LED, but you should use a diode to block the reverse AC pulses from destroying the LED. The forward pulses are at AC frequency (50Hz or 60Hz depending on your local power standard), and that's fast enough that you won't see it as "blinking". No filtration capacitor is needed. The resistor value must be calculated based on the supply voltage, the desired forward current through the LED, and the LED forward voltage. The diode must be rated higher than the supply voltage with some headroom.

attachment.php



Thanks for going through the trouble to make me a schematic.
smily_headphones1.gif


Would the 1N400x line of diodes be suitable for this purpose? Well may be not the 1N4001. I should be using them off the Sigma 22's transformer secondary, could I just plug the LED and RLED (10k ohms I think) off the board and use them? I guess the values are about right?
 
Nov 26, 2008 at 4:19 PM Post #11 of 20

Pars

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Quote:

Originally Posted by Navyblue /img/forum/go_quote.gif
Thanks for going through the trouble to make me a schematic.
smily_headphones1.gif


Would the 1N400x line of diodes be suitable for this purpose? Well may be not the 1N4001. I should be using them off the Sigma 22's transformer secondary, could I just plug the LED and RLED (10k ohms I think) off the board and use them? I guess the values are about right?



Now you have me confused... your title suggests that you are placing just the transformer in this enclosure? But now you are talking about a sigma22? In that enclosure? If so, of course you use the power LED and RLED of that board and you don't need to mess with what has been discussed.
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