Power Supply Filter Question

[gaussmarkov]

Various power supply choices are being used.  Here's one that has most of the components that I have seen.  

I just put the diode in for completeness. As I understand it, the basic filter is just a 100uF cap across the supply rails (positive to ground).  In addition, I have seen a smaller cap (usu. .1uF) across the supply rails because electrolytics don't actually admit the highest frequencies adequately.  This seems to be particularly important for some fuzzes.  The resistor is less common.  And it makes a big theoretical difference in the filter's behavior.

What do you all prefer to use?  Thanks!

(p.s.  i got some of this info from the power supply discussion in this thread.  thanks especially to jmusser and puretube!)

[Nikolay]

This is good choice
Actually I put the diode before positive pin, not between + and gnd.
"+" than --------|>|-------- than this circuit
            (this is the diode)

I use 220uF for filtering

[gaussmarkov]

This is good choice
Actually I put the diode before positive pin, not between + and gnd.
"+" than --------|>|-------- than this circuit
            (this is the diode)

I use 220uF for filtering

hey, thanks for your input.  it sounds like you are putting the diode in series.  i have seen that arrangement before (e.g., Miss Piggy v5), too.  have you read R.G.'s Polarity Protection article on this stuff?  here's what R.G. says there:

Ok, so reverse polarity is a Bad Thing. How do we prevent it? The standard wisdom is to use a diode. Not much cleverness needed here, and only two ways to do it - series and parallel. A diode hooked in series with the power supply will allow current to pass only in one direction. If you put the diode in the + lead, the diode takes all the voltage drop if the power leads are reversed. The circuit sees essentially no reverse voltage. The problem is that you pay for that protection in voltage. The diode's forward voltage drop is subtracted from every battery, so a fresh 9.5V battery becomes a middle-of-the-road 8.8V to the circuit that it's powering. And the battery "wears out" 0.6 to 0.7V early as well. Still, better than nothing, and you can get special Schottky diodes with 0.4V drops or maybe germanium diodes for 0.3V drops if you work at it.

A cleverer arrangement is to put the diode in parallel with the effect so it's reverse biased by the normal polarity. When the voltage is reversed, the diode conducts heavily and clamps the reverse voltage to no more than one diode drop. You don't even have to pay the diode forward drop in normal operation. Slick, huh?

i have also seen the diode placed after the RC filter, but still to ground.  i have supposed that this doesn't make much difference.

[gaussmarkov]

:idea: i just remembered that runoffgroove.com (rog) was one of my early sources on this.  if you are intersted, see a breadboard power module for integrated circuits where they show the diode after the 100 ohm resistor.  (they also have a voltage divider that i am ignoring.)

[Fuzzy-Train]

Holy bringing up and old thread batman!

I was just wondering if someone can confirm this strip board layout I made for this PS filter. I don't understand schematics that well so...



Thanks in advance for the help.

EDIT: oops the diode in not oriented properly.

[gaussmarkov]

Holy bringing up and old thread batman!

no kidding! 

I was just wondering if someone can confirm this strip board layout I made for this PS filter. I don't understand schematics that well so...



Thanks in advance for the help.

EDIT: oops the diode in not oriented properly.

right, diode is backwards ... and you want to move the "+ to PCB" to a8, after the resistor.

all the best, paul

[Fuzzy-Train]

Thanks a lot man... I also think that the resistor is wrong. It's supposed to 100ohm not 100k right?

Thanks again.

[gaussmarkov]

Thanks a lot man... I also think that the resistor is wrong. It's supposed to 100ohm not 100k right?

Thanks again.

right.  it's just 100 ohms.   good catch.  i didn't even look at the values in your layout.