Purpose of cap from power to ground

[Ignoramus26744]

I am curious... On many schematics, there is a cap shown from power to
ground for many chips.

Two questions.

1. Why is it necessary

2. Can I use one cap from power to ground, for the entire circuit.

Thanks
i

 

[John Popelish]

I am curious... On many schematics, there is a cap shown from power to
ground for many chips.

Two questions.

1. Why is it necessary

2. Can I use one cap from power to ground, for the entire circuit.

Thanks
i

There are small, local stores of charge, so that when a chip or
transistor needs a pulse of current from the supply, it doesn't have
to travel through all the inductance of the path back to the supply
main storage capacitor or regulator. You don't need one at every load
in the system, but the higher the rate of change of current needed by
some circuit, the more important it is to have a storage cap nearby.

Remember that such capacitors do not hold the voltage constant, since
the only way to draw charge from them is to have their voltage change.
But they reduce the voltage sag caused by a sudden current increase
or the rise in voltage caused by a sudden current decrease.

 

[ehsjr]

I am curious... On many schematics, there is a cap shown from power to
ground for many chips.

Two questions.

1. Why is it necessary

To bypass electrical noise to ground.

2. Can I use one cap from power to ground, for the entire circuit.

You want to use a cap at each IC.
Ed

 

[Walter Harley]

[...]
Thank you. How about Digikey item P993-ND.

For common components, Mouser is often cheaper than Digikey, and they have
no minimum order.

Jameco is also often cheaper; they have a smaller selection and most of
their components are generic rather than coming from a specific
manufacturer, but for hobby stuff they're a good choice.

 

[Ignoramus26745]

[...]
Thank you. How about Digikey item P993-ND.

For common components, Mouser is often cheaper than Digikey, and they have
no minimum order.

I have very hard times finding stuff in mouser. I am actually building
an order there, right now, centering around a 19 pin Amphenol plug for
the welding foot pedal. Finding common stuff like caps etc, is a big
pain to me. Maybe I am missing some secret.

For example, I could not find that digikey item P993-ND in mouser,
using manufacturer's item number or its variations.

Jameco is also often cheaper; they have a smaller selection and most of
their components are generic rather than coming from a specific
manufacturer, but for hobby stuff they're a good choice.

Yes, I agree with that.

i

 

[Rich Grise]

[...]
Thank you. How about Digikey item P993-ND.

For common components, Mouser is often cheaper than Digikey, and they have
no minimum order.

I have very hard times finding stuff in mouser. I am actually building
an order there, right now, centering around a 19 pin Amphenol plug for
the welding foot pedal. Finding common stuff like caps etc, is a big
pain to me. Maybe I am missing some secret.

http://www.mouser.com/index.cfm?handler=catalog._ShowForm&mode=new
http://dkc1.digikey.com/us/pdf/Current.html
http://www.newark.com/products/browse/index.html

Have Fun!
Rich

 

[John Popelish]

I have very hard times finding stuff in mouser. I am actually building
an order there, right now, centering around a 19 pin Amphenol plug for
the welding foot pedal. Finding common stuff like caps etc, is a big
pain to me. Maybe I am missing some secret.

(snip)

Ask them for a paper catalog. Much easier to browse through than
using the on line search engine.

 

[Walter Harley]

[...] I have very hard times finding stuff in mouser. [...]

As John says, the paper catalog is easier to browse (true for all the big
distributors).

But you shouldn't expect to find the same manufacturers at both Digikey and
Mouser. They carry different product lines. For commodity items like
capacitors, though, both have everything you need.

You can also phone them and talk to the sales reps. They're quite helpful,
and willing to talk to you even for small orders. Both of these companies
got their start working with hobbyists.

 

[Rich Grise]

[...] I have very hard times finding stuff in mouser. [...]

As John says, the paper catalog is easier to browse (true for all the big
distributors).

But you shouldn't expect to find the same manufacturers at both Digikey and
Mouser. They carry different product lines. For commodity items like
capacitors, though, both have everything you need.

You can also phone them and talk to the sales reps. They're quite helpful,
and willing to talk to you even for small orders. Both of these companies
got their start working with hobbyists.

A couple of years ago, I filled out the registration on
http://www.newark.com , and a few weeks later, a salesman called me,
coincidentally just when I needed to order some parts for a project.
The guy opened an account for me on the phone! I ordered about a couple
of hundred bucks' worth of stuff, and they shipped it and sent me a
bill about three weeks later.

I was pleased.

Cheers!
Rich