Capacitors in series for filter design.

[warpie]

Probably this has been discussed before but couldn't find any info.

Is there any drawback in combining 2 caps in series to get the exact value for a filter?
For example if I need a cap value of 75nF can I just connect two 150nF in series just like I would normally do if I wanted 300nF (in parallel)?

thanks
Michael

 

[Apache5]

I think that caps sums capacitance in paralel not in serie... that is, caps works backwards compared to resistors, but Im not sure at all.

Arnau

 

[Kingston]

For example if I need a cap value of 75nF can I just connect two 150nF in series just like I would normally do if I wanted 300nF (in parallel)?

Yes you can. No drawbacks for simple filter usage.

 

[warpie]

I think that caps sums capacitance in paralel not in serie... that is, caps works backwards compared to resistors, but Im not sure at all.

Arnau

Arnau, you are right but I think you misread the post 

For example if I need a cap value of 75nF can I just connect two 150nF in series just like I would normally do if I wanted 300nF (in parallel)?

Yes you can. No drawbacks for simple filter usage.

great! thanks 

 

[Apache5]

Yes, I missread it  ;D you are true! sorry!

Arnau

 

[JohnRoberts]

For a simple filter it should not be a problem other than perhaps noise pickup from longer leads.  Non-capacitance terms like lead inductance and series resistance will increase, but this should be inconsequential.  Voltage sharing across two parts is another concern if each part can't handle the full circuit voltage individually. 

JR

 

[warpie]

Hi John,

thanks for the answer. I think I follow you but please bare with me...

For a simple filter it should not be a problem other than perhaps noise pickup from longer leads

I'll be using wimas on a PCB (LC filter) so I think noise pickup from longer leads will not be an issue (?)

Voltage sharing across two parts is another concern if each part can't handle the full circuit voltage individually.

If I understand correctly this will not be a problem since we are talking for line levels (low voltage) (?)

 

[JohnRoberts]

Hi John,

thanks for the answer. I think I follow you but please bare with me...

Too cold but I will bear with you,,,  ;D

For a simple filter it should not be a problem other than perhaps noise pickup from longer leads

I'll be using wimas on a PCB (LC filter) so I think noise pickup from longer leads will not be an issue (?)

Use your judgement... in any case always keep leads short. 

Voltage sharing across two parts is another concern if each part can't handle the full circuit voltage individually.

If I understand correctly this will not be a problem since we are talking for line levels (low voltage) (?)

thanks
mike

Indeed, if either part can handle full voltages present, no concern about how they will share.

JR

 

[warpie]

cool thanks!
I'll prepare a nice dinner! hhahah  ;D

 

[PRR]

> Is there any drawback

Costs four times as much.

Maybe not four times if voltage rating price-steps are favorable.

Making a 750uFd min-5V from two 1,500uFd 16V is a buck expensive.

For nanoF audio filters in DIY economics, the cost is insignificant.

 

[CJ]

what about face shift for series caps?