Capacitor in Series Connection

[ibwev]

Which is the better method for placing capacitors in a circuit? Should I connect the voltage regulator and both capacitors to the power plane (option 1) or should I connect voltage regulator to each capacitor and then to the power plane (option 2)?


Option 1
View attachment 68030


Option 2
View attachment 68031

 

[kubeek]

Option 2 is better, as it is more similar to an RC filter so the caps do better filtering. Also I would swap C2 and C3 positions.
Anyway, why do you have there the red circles around the cap? Those look like being etched into the copper, which you do not want.

 

[ibwev]

Thanks for the response. The red circles should be yellow as it is part of the silkscreen.

 

[ccurtis]

I think they should be structured more like option 1 (except I don't see how the capacitor pads are connected to the power plane in that image). The reason is that the capacitors are not so much intended to be RC filters as they are charge storage devices to deliver transient current and regulator stability. I'm assuming those capacitors are on the output of the regulator.

 

[KeepItSimpleStupid]

Neither. Just connect the leads direct to the ground plane.

 

[ronsimpson]

I would attach the gnd end of the caps straight to the gnd plain.
Attach the output caps (+) end to the power plain. Do not use traces.
Increase the trace size on all power traces. A thin trace is a resistor and maybe a inductor.

Something is wrong with your parts. (C2,3) The parts appear to have copper (red) in the part. Did you make these?

 

[KeepItSimpleStupid]

BTW, the capacitors look like they are in parallel, not series. Parallel capacitors add.

 

[ibwev]

Something is wrong with your parts. (C2,3) The parts appear to have copper (red) in the part. Did you make these?

I did make these and I put the arc in the wrong layer. It should be in the silk screen. Thanks to ronsimpson, ccurtis, and kubeek for catching that.

Thanks to KeepItSimpleStupid for noticing that the capacitors are in parallel and not series.


I designed the power to the PCB by the videos in the following link
https://www.electro-tech-online.com/threads/power-supply-design-for-beginners.113613/
Those videos show the need of C1, C2, and C3 in the below illustration. The datasheet shows a need of PIC16F690 requiring a 100 n capacitor. Do I need C4 in the illustration or does C3 suffice?

View attachment 68041

 

[KeepItSimpleStupid]

Your going to have to point to the datasheet and the schematic.


I did see a 0.1 uf cap for the POR circuit in a PIC datasheet.

It's customary, to place ceramic caps on the order of 0.1 uf near the power pins of an IC. These are called bypass capacitors. Without going into much detail, they could make a circuit more reliable and emit less RFI. Sometimes as many as three different types of capacitors are paralleled for the bypass function. For bypass caps, it's important to keep the leads as short as possible and as close as you can to the devices.

You don't want to use an electrolytic cap for the 0.1 uf bypass cap. That should usually be ceramic or Tantalum. Check the regulator datasheet.
C3 and I think C4 are bypass caps (If pin #1 of the PIC is power) and should not be a normal electrolytic cap.

 

[ibwev]

I could not find the need of a 100 n capacitor for the pic in the datasheet of PIC16F690. I did find it suggested in other articles (https://www.electro-tech-online.com/threads/resistor-capacitor-and-9v-to-5v-questions.113844/) and tutorials (https://www.electro-tech-online.com/custompdfs/2012/10/PIC_Base_A_1.pdf page 3).

The datasheet of the voltage regulator (https://www.electro-tech-online.com/custompdfs/2012/10/oki-78sr.pdf page 11) Suggest 2 ceramic capacitors. One on the input.

…Murata GRM32 series or a polymer type. Initial suggested capacitor values are 10 to 22 μF, rated at twice the expected maximum input voltage…

Another on the output

…use low-ESR ceramic (Murata GRM32 series) or polymer capacitors. Initial values of 10 to 47 μF may be tried, either single or multiple capacitors in parallel…

The datasheet of the voltage regulator does not mention a bypass capacitor. The video from https://www.electro-tech-online.com/threads/power-supply-design-for-beginners.113613/ suggest using one.

1) Is it wise to use a 100 n bypass capacitor on the output side of the voltage regulator or should I follow the datasheet?

2) Does the attached PCB layout appear to be correct? The supply voltage is 24V and C3 (Digikey 445-4756-ND) is CAP CER 0.1UF 50V 5% RADIAL (through hole) and C1 and C2 (Digikey 490-1891-1-ND) are CAP CER 10UF 50V Y5V 1210 (surface mount)


View attachment 68251

 

[KeepItSimpleStupid]

Bypass caps are sometimes something that is not mentioned on the datasheet. It's basically recommended practice and sometimes very complex, because each type does a different thing. I recently read that on a TI evaluation board they used 6 bypass caps of different types.

1) You will typically have lots of 0.1 uf caps around. Having a pad for a ceramic or poly, but not using them is a better option.

2) I think they look OK.

 

[ccurtis]

I recommend the 100 nF ceramic cap at the output for transient load switching in parallel with 10uF. The key is for the total capacitance not to exceed the 10-47uF range stated in the data sheet. Better to place individual bypass capacitors close to the powered components on the board where they are most needed. The reasonable assumption (and likely what your recommendations here are based before you posted data on your "voltage regulator") is that it is a three terminal linear, regulator. But that is not what you are using. Always follow the manufacturer's data sheet recommendations when in doubt.