Power Supply Filter Anatomy

[anotherjim]

Eric, your smoke generator...
http://www.gaugemaster.com/seuthe.html
Smells nicer than carbon film too.

[Kipper4]

This should be fine. Maybe change r13 r14 to something 10x smaller, depending on your application.

Thats similar to what I use all the time.

In a real situation like prolonged reverse polarity to the point something in the circuit burns It would likely be cheaper to replace the entire pcb than start fiddling with the power supply bits.
I know cause one of the first pedals i boxed. Son of screamer got burnt when I gave it to an experienced gigging guitarist who fed it the power supply for a line 6 box.
Gulp.
lesson learned. Put a diagram on the front of the box or at the dc jack. Include documentation warning about expected power supply use. and failure to adhere to this.
It's not idiot proof but it's a disclaimer that makes the user think.
You with me Eric......

[Cozybuilder]

Now move R11 to the other side of D3 so you don't add the current from the LED to the Schottky.

[antonis]

You know Cozy, LEDs are also prone to damage with reverse polarity.. 

Maybe not in that specific case, 'cause reverse voltage drop on LED is about the same with its forward voltage drop but margins aren't so wide..
(i.e. with 12V PS and prolonged reverse voltage applied, LED will be destroyed..)

(after all, about 1.5mA added to 1A shouldn't make any difference, should it..??)

[Cozybuilder]

Good thing it has a CLR to keep the current down, no? Hmm, 2k2 with 9V would allow a max of 4mA, would that blow an LED with the power connected reverse?

[Phoenix]

Good thing it has a CLR to keep the current down, no? Hmm, 2k2 with 9V would allow a max of 4mA, would that blow an LED with the power connected reverse?

It's not the current that'll kill a reverse-biased LED (or any other diode for that matter), but the voltage. Because no current is flowing through under reverse bias conditions (except some small leakage current), the full voltage is across the LED, none is dropped by the current limiting resistor. Vrrm (max reverse voltage) for most standard 3mm or 5mm LED's is 5V, so 9V is really pushing things. You could put an anti-parallel diode alongside it (say a 1N4001 or even a 1N4148/1N914) - that is reverse biased under normal conditions, but if reverse polarity is applied, it'll cap the voltage across the LED to 0.7V. Seems simpler to me just to connect the LED after the series schottky.

[antonis]

@Cozy: I refered to Rich's shematic with 4k7 current limiting rersistor and 2V voltage drop on LED...

[Cozybuilder]

Thank you, I learned something today 

[Kipper4]

Not my schematic. It was in Potl's first post.

[pee-j]

The chemical fuses may take some Seconds to trip.

Transistor death happens much quicker.

All old transistor workers KNOW that transistors always blow to protect the fuses.

I was doing a search as I was right about to order a bunch of multifuses, ptc-s, which I though would be a modern method
of low voltage drop reverse polarity protection...

I was really happy that POTL had brought up the multifuse method!
and of course, as a layman, I couldn't imagine an argument against it...
so thank you very much!! and to all of you, this is such a nutrient rich thread!!