Current question

EvilMaro

I have a power suplly board that can give me 12V and 3A.· I know that the max voltage i can have in stamp is 9v right?· As for Current is only a few mA.· I know how to slove the Voltage problem by using a voltage divider circuit as voltage is different in series but how about the current? i mean how can i reduce the amphere from 3A to a few mA that is needed by the board.· Pls advise as i do not want to damage my new stamp board thank.

From
Tony

Franklin

The current will take care of itself. The 3a is just the maximum the PS can supply the device will only use what it needs

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- Stephen

EvilMaro

Thank for the fast reply i am using bs2 and u mean that if bs2 need onli a few mili amphere and my input current is like 4A is ok?· By the way can i ask can the BS2 take in 12V DC directly??

Mike Green

1) Your input current is a few milliamps, not 4A. The 4A is the maximum current that the power supply can provide if needed.

2) Your question about using 12V doesn't have a simple answer. The BS2 itself can handle higher voltages than 9V, but the excess voltage is turned into heat that its regulator has to dissipate. The more current the BS2 has to use (like to drive LEDs or other loads), the more power has to be dissipated. Eventually, the regulator will shut itself off to protect itself and the BS2 won't work until the regulator cools down. Some boards that the BS2 might be plugged into may have their own input voltage limitations (like the development boards). The best thing to do is to have a separate 7.5-9V regulator (like an LM7808 or LM7809) with its own filter capacitors as described in their datasheet to drop the power supply voltage to 8 or 9V and distribute the heat dissipation.

allanlane5

Yes. Saying your supply can supply 4 amps is like saying your car can go 120 miles per hour. The actual current used depends on what your circuit needs, not what your supply can supply.

So you can't "over-current" your BS2, it only gets the current it needs. Now you CAN "over-voltage" your BS2 -- but 12 volts is not an "over-voltage", so that's ok too.

Another analogy is like a water tower. The height of the tower is the 'voltage'. The size of the pipe leaving the tower limits the amount of water ('current') that can leave the tower. If you attach that pipe to a thin hose to water your lawn, it doesn't matter that the tower has LOTS of water in it, the thin hose will only 'conduct' a small amount of water.

Now, if you apply too much pressure ('voltage') to that thin hose, you can blow it out. But as I say, with 12 volts, you're not applying too much voltage, and so the BS2 will only take as much current as it needs.

EvilMaro

k thx alot i now understand what current actual mean. Thank u to all of u

QuattroRS4

Or back to an old College quote "Current is drawn Votlage is applied'

Quattro

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'Necessity is the mother of invention'