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Old 28th October 2010, 07:00 PM   #1
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Default Simple LED power indicator light circuit?

Can someone help me out with a design of LED power indicator? I'm planning of using it for my diy preamp and would like to make it a simple circuit that can provide a dim indicator light. I looked at one in my Tripp-Lite surge suppressor and this is what I can draw from it. Diode is 1N4004.
Click the image to open in full size.

I only need one LED lamp and am wondering if I need to add or remove anything to make this circuit work for me. Any feedback? Thanks in advance.
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Old 28th October 2010, 09:32 PM   #2
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This page has some info Led circuits page

Or you could always go with the old style neon indicators.
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Old 28th October 2010, 09:53 PM   #3
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That's potentially dangrous - dunno where the base of that MPSA13 is going to, but you are now connecting low voltage control circuitry directly into the mains.

It's much safer & easier to put the indicator lamp/LED on the secondary (low voltage) side of the transformer.
If you put it after the rectifier/power supply, all you need is a single current limiting resistor and the LED itself.
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Old 28th October 2010, 10:07 PM   #4
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Quote:
Originally Posted by Steerpike View Post
That's potentially dangrous - dunno where the base of that MPSA13 is going to, but you are now connecting low voltage control circuitry directly into the mains.

It's much safer & easier to put the indicator lamp/LED on the secondary (low voltage) side of the transformer.
If you put it after the rectifier/power supply, all you need is a single current limiting resistor and the LED itself.
That's what I do , hang it off the heater winding ... I love a blue LED with AC on it ... haunting to look at somehow .... I know the PIV probably isn't high enough, but I've had one on my little SE amp that's been like it for years.
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Old 28th October 2010, 10:08 PM   #5
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Originally Posted by Steerpike View Post
dunno where the base of that MPSA13 is going to, but you are now connecting low voltage control circuitry directly into the mains.
I goes to another MPSA13 for another LED light which the base of that transistor is connected to a resistor and then it's grounded.

Quote:
It's much safer & easier to put the indicator lamp/LED on the secondary (low voltage) side of the transformer.
I do have a secondary that's 12VAC. I could use a smaller resistor than what's shown.

Quote:
If you put it after the rectifier/power supply, all you need is a single current limiting resistor and the LED itself.
This preamp I'm working on has SS rectification in a tightly packed circuit board. I was trying not to touch that area if I can help thus my inquiry. I wouldn't rule it out though. Thanks.
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Old 28th October 2010, 10:24 PM   #6
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Originally Posted by Evenharmonics View Post
I goes to another MPSA13 for another LED light which the base of that transistor is connected to a resistor and then it's grounded.
If you just want an indicator lamp, the transistors seem reduundant.

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I do have a secondary that's 12VAC. I could use a smaller resistor than what's shown.
Much better idea. You should ideally put a diode (such as a 1n4001) directly across the LED, but facing the opposite way. I like this better than a series diode, to prodect the LED from reverse voltage. Then only one quarter-watt series resistor of around 1k-ohm will be required,
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Old 28th October 2010, 11:16 PM   #7
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Much better idea. You should ideally put a diode (such as a 1n4001) directly across the LED, but facing the opposite way. I like this better than a series diode, to prodect the LED from reverse voltage. Then only one quarter-watt series resistor of around 1k-ohm will be required,
Kind of like the one on upper left on the link posted by astouffer?
Click the image to open in full size.
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Old 29th October 2010, 12:27 AM   #8
cbj591 is offline cbj591  United States
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Even - Here are come calculators that may help out.

I used a diode bridge and 100 ohm resistor off the heater supply to give me the correct voltage needed.

Brian

LED Resistor Calculator
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Old 29th October 2010, 12:16 PM   #9
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i would just get some industrial pilot lights . those things rock .
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Old 29th October 2010, 01:05 PM   #10
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Quote:
Originally Posted by Evenharmonics View Post
Kind of like the one on upper left on the link posted by astouffer?

Yes, exactly that circuit. But if you wire it to 12V ac of the transformer secondary, you can omit the capacitor. That is about as simple & safe as you can make it.
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