LED activation from 5v winding?

[daz]

I figured since it was 120v capable that the sides were seperate like 2 spst switches, one for the LED one for power. According the enzo thats not the case tho. He's saying they're the same switch as the marshall style but with a LED instead of neon. So if he's right i can't. I'll have to wait till i get it and make sure. It does make sense they'd use the same switch for auto tho and just change to LED, so hels probably right.

Well, i took the old switch apart and it looks like pedro was right, or at least close. There was no weld issue but same sorta thing, the neon;s lead had broken. It was very tedious fixing it but i have a number of eye loupes and used a 5x loupe and very carefully was able to solder the lead together. Switch works again. I think i'm now qualified to do surgery on insects.

[daz]

Well, that was a lot of work for nothing. Damn thing went out again.

[g1]

Not all for naught, you still have the insect surgery skills.

[daz]

Not all for naught, you still have the insect surgery skills.

Well, i repaired it again but i don't need the aggravation of waiting for it to go bad again be it this one or a new one. So i'm going to do the LED indicator off the 5v supply with a bridge rectifier and a resistor and use a DPDT toggle.

[mozz]

If you want a neon bulb with leads, send me your address in a PM.

[R.G.]

Well, i repaired it again but i don't need the aggravation of waiting for it to go bad again be it this one or a new one. So i'm going to do the LED indicator off the 5v supply with a bridge rectifier and a resistor and use a DPDT toggle.

You don't need a full wave bridge, although that will work. You need an LED, an ordinary diode, and a resistor.

The ordinary diode goes either in series with the LED to keep it from being broken over reversed, or in parallel to keep the reverse voltage down to one diode drop. The resistor limits current in either case.

With a diode in series, the LED turns on once every other half-cycle, and no current flows during the opposite half-cycle. With the diode in anti-parallel, the LED still lights once every other half-cycle, but the diode conducts during the opposite half cycle, so current flows every half cycle.

In both cases, the LED blinks on and off 60 times per second, which is too fast for your eye to see, so it appears to be continuously on.

The full wave bridge will eat two diode drops, about 1.4V, from the available peak current of the 5V winding, and let the LED blink on at a 120Hz rate, which is still faster than the eye can see as a blink, so it will look like it's on continuously too. It will appear brighter because the LED is on twice as much for any given time period, and your eye crudely averages.

A 5V winding will have a peak value of about 7.1V, and losing the 1.4V to the diodes means you have only about 5.67V left for both LED and resistor. That's workable, but the resistor values get small for bigger LED forward voltages, and the current limit is less precise. The shunt diode subtracts no voltage from the LED, so your current limiting resistor has more volts to work with to stabilize current.

[Tom Phillips]

First, you're not using the 5V winding to power a rectifier, right? Because then it would be floating at the rectified high voltage, 400, 500V or so. That would take this idea out of the running entirely...

daz,
I never saw an answer to the above question that Leo asked back in post #3.
Did I miss it?
Tom

[daz]

If you want a neon bulb with leads, send me your address in a PM.

Wow, thanks bud, i DO appreciate the offer. But as i said earlier i was just gonna use a toggle and a LED from a unused 5v winding. And i already got the parts today and installed them. Just haven't wired it up yet but will tonite. After seeing the bulb in that switch i realized theres not enough room for the bulb without it being moved each time you use the switch and that movement is obviously what eventually breaks the solid wire lead. Rather have a quality heavy duty toggle and seperate LED so i don't have to deal with this again.

daz,
I never saw an answer to the above question that Leo asked back in post #3.
Did I miss it?
Tom

No, it's an unused winding. I mentioned that in the original post. The amp is SS rectified.

You don't need a full wave bridge, although that will work. You need an LED, an ordinary diode, and a resistor.

The ordinary diode goes either in series with the LED to keep it from being broken over reversed, or in parallel to keep the reverse voltage down to one diode drop. The resistor limits current in either case.

With a diode in series, the LED turns on once every other half-cycle, and no current flows during the opposite half-cycle. With the diode in anti-parallel, the LED still lights once every other half-cycle, but the diode conducts during the opposite half cycle, so current flows every half cycle.

In both cases, the LED blinks on and off 60 times per second, which is too fast for your eye to see, so it appears to be continuously on.

The full wave bridge will eat two diode drops, about 1.4V, from the available peak current of the 5V winding, and let the LED blink on at a 120Hz rate, which is still faster than the eye can see as a blink, so it will look like it's on continuously too. It will appear brighter because the LED is on twice as much for any given time period, and your eye crudely averages.

A 5V winding will have a peak value of about 7.1V, and losing the 1.4V to the diodes means you have only about 5.67V left for both LED and resistor. That's workable, but the resistor values get small for bigger LED forward voltages, and the current limit is less precise. The shunt diode subtracts no voltage from the LED, so your current limiting resistor has more volts to work with to stabilize current.

Thanks RG, good info. I'll try the single diode but i was under the impression you needed a bridge for a winding with no center tap. Someone even mentioned that earlier. But you know your stuff so that'll make it simpler. Thanks.

[Dave H]

...i was under the impression you needed a bridge for a winding with no center tap.

You don't need a bridge, half wave rectification is good enough for a LED. A LED, diode and 220 ohm resistor all three in series should do it.



Edit: I forgot the switch. It will also need that in series.

[daz]

You don't need a bridge, half wave rectification is good enough for a LED. A LED, diode and 220 ohm resistor all three in series should do it.

[ATTACH=CONFIG]41023[/ATTACH]

Edit: I forgot the switch. It will also need that in series.

I already did just that after RG's post. But i didn't need to wire it to the power switch since the winding powers on and off with power. However, i intend to replace it with a larger LED, maybe one of those ones made specifically as pilot lights with a lens thats about 4 times the size. A single LED is just too small and hard to see as a pilot light.

[R.G.]

If you need more LED light, there are some other possibilities.

One is making the resistor smaller so the peak current in the LED runs up to about, say, 100ma. The LED cools off in the half cycle it's not on.

One simple possibility is to use two LEDs, each with a resistor so one doesn't current-hog. Or N LEDs and resistors. SMD LEDs soldered across a manually-cut slice on a tidbit of PCB stock makes this easy. This can scale up to blinding.

Another is spreading out the conduction time by using a second LED on the other half cycle, or by putting a capacitor across the LED+resistor.

Or using a surplus-house 1W or so LED. These suckers get BRIGHT.

[daz]

Thanks RG, but it's bright enough. (I used a 100ohm) It's just so small, so i want a larger area therefore looking to a LED pilot light that has a large (maybe 20mm) lens to spread out the lighted area instead of that little pinpoint LED. I noticed there are some that are 120v. How the *&%$ do they do that?

If you need more LED light, there are some other possibilities.

One is making the resistor smaller so the peak current in the LED runs up to about, say, 100ma. The LED cools off in the half cycle it's not on.

One simple possibility is to use two LEDs, each with a resistor so one doesn't current-hog. Or N LEDs and resistors. SMD LEDs soldered across a manually-cut slice on a tidbit of PCB stock makes this easy. This can scale up to blinding.

Another is spreading out the conduction time by using a second LED on the other half cycle, or by putting a capacitor across the LED+resistor.

Or using a surplus-house 1W or so LED. These suckers get BRIGHT.

[R.G.]

Ah. OK, gotcha.

There are some electrical solutions. I don't know what mechanical constraints you have to fit.

The beam spread on an LED is a function of where the LED is placed relative to the round lens part at the top and probably other internal trickery. You can mess with width by messing with the plastic lens. I used to file them flat for pretty even illumination over the LED face, but that won't help spread the light much. One could file facets on the top, leaving a point in the middle, and that would probably spread it. But the facets would need polished.

There are some special plexiglas variants intended to spread backlighting for signs and LCDs, but that turns this into a quest for unobtainium.

To me it's tempting to use a fingernail of PCB stock with several SMD LEDs on it. Kind of a mess, but it puts the light where you want it, and some SMD LEDs have wide beam spreads deliberately as they sit.

Maybe look for an LED with wider spread? Mouser lists that kind of thing in their search setup.

[daz]

I was just going to buy one thats sold as a "pilot light". I imagine the way they fill the lens with light is to use a bright white LED but thats a guess.

Ah. OK, gotcha.

There are some electrical solutions. I don't know what mechanical constraints you have to fit.

The beam spread on an LED is a function of where the LED is placed relative to the round lens part at the top and probably other internal trickery. You can mess with width by messing with the plastic lens. I used to file them flat for pretty even illumination over the LED face, but that won't help spread the light much. One could file facets on the top, leaving a point in the middle, and that would probably spread it. But the facets would need polished.

There are some special plexiglas variants intended to spread backlighting for signs and LCDs, but that turns this into a quest for unobtainium.

To me it's tempting to use a fingernail of PCB stock with several SMD LEDs on it. Kind of a mess, but it puts the light where you want it, and some SMD LEDs have wide beam spreads deliberately as they sit.

Maybe look for an LED with wider spread? Mouser lists that kind of thing in their search setup.

[Dave H]

It's a guitar amp and you want it bright so why not do it the traditional way and use a jeweled pilot light running off the 6.3V or 5V winding then you won't need any extra components?