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Author Topic: Basic question about circuits etc.  (Read 1008 times)

sg3

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Basic question about circuits etc.
« on: December 05, 2004, 07:06:16 AM »

Ok, simple question here and one that I have never really grasped.
Does current change when you change what parts are in a circuit or is a set current supplied by the battery or power source?

I never know. So for example.. If I put a LED that draws 20mA, does that mean the current in the whole circuit is 20mA total and if I then replace it with one that draws 40mA the circuit current in 40mA total?
Or is the current defined by the battery.. i.e some batteries pump in 1A?
From my knowledge I think the current depends on the parts you have in the circuit and it will change depnding on those parts.

2nd query...

How do I measure the Voltage and current that my LED's require? Do I just have to look at documentation or is there a way to measure. Without documentation it just seems like a guessing game.

Just 2 queries to settle my mind :)

P.S. I have the ratings etc for the LEDs, but just wondered if there is a way.

Thanks - Jamie
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hollow head

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Basic question about circuits etc.
« Reply #1 on: December 05, 2004, 04:03:06 PM »

Your powersource can only put a max of current out. So you can't get more current then your max.
For changing the parts you're right.
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viridius

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Basic question about circuits etc.
« Reply #2 on: December 05, 2004, 07:57:08 PM »

Most LEDs fall into a narrow range of current consumptions (10-20) mA, but voltages can be anywhere from 1.7 to over 5 volts.  The manufacturer's spec is the only reliable source of information.  Your current source can change the amount of current in a circuit if you try to overload it (eg: drawing more than is permissible from a PSU or trying to draw a lot of current from a battery that isn't designed to provide it), but the choice of components is the greatest factor.
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sg3

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Basic question about circuits etc.
« Reply #3 on: December 06, 2004, 11:26:15 AM »

Thank you, that clears it up. I was wondering about the amp rating on my PSU. It confused me, thinking that the amp output was always that, but now it is max, I understand!
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