Fading LEDs

You mean a flux capacitor.

audioguru said:

WalMart had a fading LED globe with 3 colors of LEDs. It used a microcontroller and you could see the fading jerk between the steps.
My analog fading 3 colors of LEDs fade smoothly.

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Since we're bragging...
I built several RGB versions based on the Bill Bowden 'Fading-red-eyes' opamp circuit. Very slow, and a much broader spectrum of colors. Still like these the best.

I've got seven tiny13 faders, fade slow and smooth between colors. Basic 7 colors, but good variation in transition. Haven't been using resistors with these, figure off 4.8 volt rechargables and PWM its safe enough. One got wet last week when the huricane passed, haven't messed with it to see if it's okay. These are the easiest to make, burn the chip, solder the LEDs to the pins, power leads, hot glue to diffuse.

audioguru said:

An astable multivibrator using silicon transistors harms the transistors if the supply voltage is more than about 6V which is the absolute max allowed voltage for the reverse emitter-base voltage for a silicon transistor. The emitter-base junctions have avalanche breakdown.

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Howdy,

What you say above is interesting, theoretically, certainly. After having
looked at URL you referenced, I can see what you're talking about.

Empirically, however, I have found that the above theory has never
caused an issue in any of *many* copies of that exact circuit I've built
over the years. Mostly I stick them in cars in/near the dash somewhere
to discourage people from tampering (they see red LEDs flashing back
and forth and hopefully leave it alone). Running at 12V, they run 24/7
for years...

FYI,
Corey

saturn1bguy said:

Howdy,

What you say above is interesting, theoretically, certainly. After having
looked at URL you referenced, I can see what you're talking about.

Empirically, however, I have found that the above theory has never
caused an issue in any of *many* copies of that exact circuit I've built
over the years. Mostly I stick them in cars in/near the dash somewhere
to discourage people from tampering (they see red LEDs flashing back
and forth and hopefully leave it alone). Running at 12V, they run 24/7
for years...

FYI,
Corey

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Here's a quote from Bob Pease:

"This reverse current - even if it's as low as nA or very brief in duration - tends to degrade the low current beta at least on a temporary basis. So in cases where accuracy is important, find a way to avoid reverse-biasing the inputs. Bob Widlar reminded me that the high current beta of a transistor is generally not degraded by this zenering, so if you are hammering the Veb of a transistor in a switch-mode regulator, that will not necessarily do it any harm, nor degrade its high-current beta."

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Some of you may know that Bob Pease and Bob Widlar are (Widlar is dead) two of the most respected analog IC designers in the world. Unfortunately, I haven't seen any empirical data from either of them to corroborate these claims.

Roff said:

Here's a quote from Bob Pease:Some of you may know that Bob Pease and Bob Widlar are (Widlar is dead) two of the most respected analog IC designers in the world. Unfortunately, I haven't seen any empirical data from either of them to corroborate these claims.

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Hello Roff, we meet again You assisted me the other day, thanks
again.

Yes, good ol' Bob Pease, we've spoken several times. He's a generally
nice fellow, very easy going. I enjoy his NSC Reality TV podcasts.
I know of Widlar too, and respect both immensly.

In any case, the 2-transistor astables keep on ticking... (Although I
ought to stick a scope on there to see what I can see in terms of Veb
levels.)

The continuing avalanche breakdown of the emitter-base junction of a transistor might cause its hFE to reduce to 50 from the original 200. But a simple mulivibratpr will keep on oscillating until the hFE drops below maybe 10 (depending on the value of its base resistors).

A high frequency oscillator might destroy its transistors sooner than a very low frequency oscillator.

audioguru said:

The continuing avalanche breakdown of the emitter-base junction of a transistor might cause its hFE to reduce to 50 from the original 200. But a simple mulivibratpr will keep on oscillating until the hFE drops below maybe 10 (depending on the value of its base resistors).

A high frequency oscillator might destroy its transistors sooner than a very low frequency oscillator.

Click to expand...

Thanks for the input, that's good to know. Given that these things have never failed on me, I had never even thought about the Veb issue...

Corey

Here is an "inverter" that has its transistors' emitter-base junctions always avalanching.
The capacitors blow up. The capacitors are backwards too. They even blow up when they are not backwards because the avalanche breakdown current is very high in them.

The author say it produces an output of hundreds of watts but people who built it say 35W at a low voltage.