Types of Capacitors?

[navjas73]

I'm buying some parts for a project I'm working on, and I'm supposed to buy, among many other things, a 100V, 5mm pitch, C0G 10 pF capacitor. The website I'm using to order parts has many capacitors that fit this description, each with different capacitance tolerances and capacitor case style numbers (and different prices). I was wondering if somebody could help me understand the difference between these parts, and possibly explain why I would need to buy a more expensive capacitor over a different, cheaper one. The more information, the better. Thanks.

 

[davenn]

the type of 10pF capacitor depends on the type of circuit its going into

for example a RF cct would specifically use a disc ceramic
but disc ceramics will be found in audio ccts. its just you would use other types in an RF cct

so what type of cct are you using it in ?

show a link to the parts site you were looking at

Dave

 

[navjas73]

I'm trying to build this actually:
http://openeeg.sourceforge.net/doc/modeeg/modeeg.html
On the bill of materials, it's pretty unspecific as to what capacitors are needed.
I can give you a sample row:
10 pF C0G, package C-5, analog board, 100V, 5mm pitch, C0G.
Newark Electronics Part no: 50N1022.
I went to Newark's website, but the part isn't listed anymore so I can't find them like that.
Unfortunately, it seems like the different capacitors need to be different types. One note says that "its hard to find capacitors like this in through-hole form."
Do you have any advice?

 

[navjas73]

I've researched some more, and decided that I probably want radial components. I have an image of the completed pcb, and all the parts seem to be through-hole parts. Can somebody explain how surface mount capacitors work, and whether I'd need specific measurements to order capacitors of the right size?

 

[navjas73]

Also, I'm supposed to buy a cxtal C0G.

The notes say: The crystal's loading capacitors must be chosen appropriately. Set Cxtal = (Cload - Cstray) * 2
Cload (crystal loading capacitance) is given in the crystal data sheet. Cstray is stray capacitance on the PCB + microcontroller. Estimate Cstray = 3 - 5pF.

But I still have no idea what I'm supposed to get. The crystals all have different frequencies, and on top of that I'm not even sure what load capacitance I'm looking for.

 

[navjas73]

Newark electronics is the parts site.
http://www.newark.com/

 

[Resqueline]

The exact crystal loading capacitance is not crucial, you can miss by -50% to +100% (unless driving a clock), and it'll still work - even if missing with -90% to +300%.
Here's the cheapest (& best) xtal at N.A. I believe 7.37Mz is what you're after, and it needs 18pF so you can use 15pF.
Here is the cheapest 15pF from N.A.
Here is a 10pF 100V.
Newark has got to have one of the better selection engines, and if you look at it you'll see all the SMD sizes available, not that I understand what you'll want with them.

 

[(*steve*)]

navjas73, surface mount components do not have leads on them. So if your printed circuit board has holes to place the component leads through, smd is *not* what you want.

Surface mount technology allows for smaller boards, easier automated pick and place, and much lower profiles.

It also has a number of disadvantages including difficulty of hand soldering, absence of component markings, and some ridiculously small sizes (consider 1/100th of an inch along the LONG side of a rectangular component!)

I'm almost certain that you will want to exclude surface mount devices.

 

[navjas73]

Cool thanks everybody. I think I've got most of it figured out now.

 

[nbw]

The 100pF is probably a little round disc, a ceramic.... and yes - if you need leads, SMT is going to be out