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.
[IMGDEAD]http://img716.imageshack.us/img716/5553/indicatordesign.jpg[/IMGDEAD]

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.
 
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.
 

Doz

Member
2010-07-28 10:22 am
Sat Down
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.
 
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.

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.

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.
 
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.

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,
 
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?
lineled.gif
 
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,

The circuit is fine as it was and stops reverse current flow which protects the diode. DO NOT USE A 1K RESISTOR or you will have an exploding LED and resistor once mains power is applied. Stick with the 15k.
 
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The circuit is fine as it was and stops reverse current flow which protects the diode. DO NOT USE A 1K RESISTOR or you will have an exploding LED and resistor once mains power is applied. Stick with the 15k.

All along I've been inferring 12VAC - the unused heater winding. 1k is about right, depending on required brightness.
 
Hi. Don't mean to shift the focus from low power supplies but here's a link to an LED circuit powered by the mains. Circuit uses a small value cap rated to handle the mains voltage, a bridge diode and a resistor. The circuit works very well. I built the circuit on small board and have had it continuously powered for at least a couple of months.
 
Seraph's link shows a circuit/method I've seen elsewhere as well.

Hi. Don't mean to shift the focus from low power supplies but here's a link to an LED circuit powered by the mains. Circuit uses a small value cap rated to handle the mains voltage, a bridge diode and a resistor. The circuit works very well. I built the circuit on small board and have had it continuously powered for at least a couple of months.

" ... There have been reports of people getting a rather large 'sting' from this circuit when used as a 'night light' (not its intended purpose!) when uplugging it from the mains. ..."

From the capacitor discharge. My comment, however is the use of the slang "sting". When it comes to AC mains power and electrical safety in general, I much prefer the straightforward language ... in other words it's not a sting, it's a shock.

And a warning is appropriate ... the circuit and all wiring IS connected to AC mains voltage. Considerable care should be taken in layout and keep in mind safety at all times.

If you have something in the parts bin that is appropriate ...it doesn't have to be a large VA value ... a transformer can be used, thus taking the LED driver circuit from the secondary, lower-power side. That won't render it completely safe, but certainly reducing the voltage improves the lethality factor.
 
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DAK808

Member
2012-05-27 7:34 pm
i would just get some industrial pilot lights . those things rock .

Sure there is no doubt that they are foolproof, except, that those big pilots do consume quite a few watts whereas the LED so little. Plus, because they are small you can be quite creative as to where they go. Guys put them in a meter. I have seen some under a tube so that the tube has a different glow. I kinda put them in an out of the way spot which looks cool when it is on.