Working with Power Filtering and Reverse Polarity Protection

[debrad]

Hi PedalPCB friends!

I'm aiming to make a modification to a NON-PedalPCB circuit but I thought I'd check in here...a) to solicit your wisdom and b) to share the discussion with those of you who may grapple with a similar situation down the road.

As shown in the schematic below, the board has a charge pump to boost the 9v input to 18v but the fellow I'm building for wants to run it directly off an 18v input so in my attempt to bypass the charge pump, I'm hoping to get some advice on the components in the power section.



Based on my limited knowledge, it appears that D1 (1N4001) and C2 (220uf electrolytic) form a parallel reverse polarity protection while D2 and D3 (1N5817) form series reverse polarity protection for the 9v input (D2) and the charge pump's 18v output (D3) respectively.

After speaking with the circuit designer, I am still not 100% sure if I should:

• omit D1 + C2 and jumper D2 to leave myself with D3 as the only series reverse polarity protection,
• install D1, C2, and D3 with a jumper replacing D2, or
• do something else entirely.

Can someone please confirm or correct my understanding of this part of the power input and/or provide me with some advice on the best way to proceed with this particular modification?

Thanks so much!

- brad -

 

[Brett]

Omit everything left of D3, jumper D2.

 

[debrad]

Thanks @Brett. I made a quick edit to my original post since I had mistakenly implied OMITTING D2 in my first option rather than replacing it with a jumper as you suggest.

One question I do have with that first option though is the fact that many schematics seem to show a large capacitor to ground FOLLOWING the 1N5187 series diode...is that function being served by C1 and/or C10 in the schematic above?

 

[Brett]

Actually, you can just omit C1 altogether. I didn't catch that when I commented the first time. To answer your question, if C1 and C10 both stayed, the order shouldn't matter since they're both coming off of the same net.

 

[Brett]

Here's the power section from PedalPCB's Blue Breaker build doc:

This example shows a very simplified single IC version of what I think you're trying to achieve.

In your schematic, C22 (100n) is added for additional filtering, commonly found in the power filtering circuit in pedals. I'm not entirely sure that you'll need C30 or C31 in this case either (let someone like @Chuck D. Bones confirm this one for you). Those appear in parallel with R2/R3 and the designer may have placed them there to filter excess charge pump noise.