Author Topic: Component placement on a simple power supply question.  (Read 2565 times)

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Offline Mint.Topic starter

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Component placement on a simple power supply question.
« on: December 15, 2011, 09:35:10 am »
I was thinking about building a power supply recently, and not only do I want to be able to make it, but also to understand how it works. I understand pretty much everything except the component placement part. For example, why does this capacitor as shown in the drawing have to be places so that it touches both 6v and 0v? Why not have it like it is in the second drawing?
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Offline Psi

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Re: Component placement on a simple power supply question.
« Reply #1 on: December 15, 2011, 09:46:08 am »
Because you want the capacitor to charge up from the supply voltage, so you put it across the supply.
You also want the capacitor to be like an alternative source of electricity for your load. So if the main source of electricity drops in voltage for a short time the capacitors electricity can be used for to make up the difference. So you want the capacitor and the supply in parallel.

If you put it in series with the supply it will only charge up from current flowing through the load.
And once it is fully charged no more current will flow. The load would, in effect, not be connected to the supply any more.


A capacitor behaves like a short circuit when its empty and an open circuit when its charged up to the supply voltage.
« Last Edit: December 15, 2011, 09:53:34 am by Psi »
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Offline Mint.Topic starter

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Re: Component placement on a simple power supply question.
« Reply #2 on: December 15, 2011, 09:50:05 am »
I think I get it now. So it's basically connected to 0v so it have somewhere to discharge?
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Offline IanB

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Re: Component placement on a simple power supply question.
« Reply #3 on: December 15, 2011, 09:59:49 am »
The capacitor is acting like a buffer tank if you think in terms of a water flow analogy.

In electrical terms you can think of it like a battery that is acting as a second source of power in parallel with the main supply.
 

Offline M84AB1

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Re: Component placement on a simple power supply question.
« Reply #4 on: December 15, 2011, 10:00:01 am »
Look up Coupling and Decoupling Capacitors.

In the first picture it is used as a decoupling capacitor, converting the 100Hz rectified AC voltage to a DC Voltage. If you were to use it as you drew it in second picture, it would be used as a coupling capacitor. In such configuration you would NOT obtain DC voltage but would merely couple the 100Hz signal across to the next stage.

hope this helps.
 


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