Power Supply Question

If I have a 12 V, 2 AMP power supply with 4, 33 Ohm resistors in series then will there be 3 V across each, so that I can put a circuit across 3 of them for 9 V and 2 of them for 6 V?

Only if your circuit draws less than 10mA or so otherwise it will load the potential divider and upset the voltage calculations.
Powering stuff with a potential divider chain is total and utter rubbish. Get a proper regulator.

If I have a 12 V, 2 AMP power supply with 4, 33 Ohm resistors in series then will there be 3 V across each

Yes, you have created a voltage divider of four equal sized resistor so each resistor will 'drop' 25% of the total source voltage.

so that I can put a circuit across 3 of them for 9 V and 2 of them for 6 V?

Depends on what the circuits are. If it's high impedenace then yes. If not then the load resistance of each of the circuits wired to the 9v point and 6 volt point will upset the voltage dividers 'balance' and very different voltage values will be seen at those points. The bottom line is that in practice voltage dividers are not good at providing power for other circuits, that's a job for constant voltage dividers rated for the maximum load current your circuits will draw.

Lefty

Rats that GM fellow beat me to the draw once again. At least our answers agree :smiley:

I have an Arduino and a 4 digit seven segment array that'll need about 540 mA at max.

guitarboy667:
I have an Arduino and a 4 digit seven segment array that'll need about 540 mA at max.

You will have to use voltage regulators for loads like that, not voltage dividers.

Lefty

So just sending 12 V into a 6 V regulator will bring it down to 6 V? Will each component only draw as much current as it needs?

So I can just send the 12V directly to the Arduino and then can I put two 6V regulators in parallel somehow for the digits? Would I need to? The regulator I found says it can only handle 1 A I believe:

guitarboy667:
So just sending 12 V into a 6 V regulator will bring it down to 6 V? Will each component only draw as much current as it needs?

Yes, that is correct. There are a couple capacitors needed for the input and output of each regulator, but they are really the best and simplest solution. You also gain some protection as the regulators will automatically shutdown if they get too hot or if you try and draw more current then they are rated for.

Lefty

guitarboy667:
So I can just send the 12V directly to the Arduino and then can I put two 6V regulators in parallel somehow for the digits?

Yes each regulator would need for it's input terminal to wire to the +12v positive terminal. There are two caps needed for each regulator.

Would I need to? The regulator I found says it can only handle 1 A I believe:
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There are regulators rated for more then 1 amp (just not as common or inexpensive as the 1 amp models), however keep in mind that the total current drawn from all loads (each regulator and the arduino load) must total to equal or less the the rated current of your 2 amp supply.
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How do i know what capacitors to use? In series, right? The regulators themselves don't take any current, right? I was thinking that I'd have the 12+V go directly to the Arduino then through the parallel capacitors and regulators and then to the digits? I thought the digits would take 540 mA at max with all 8's and then the Arduino could have at least 1,460 mA.

The regulator I found says it can only handle 1 A I believe:

And most likely it will only handle that current with a generous heat sink attached.

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Are you sure you want to regulate your voltage to minus six volts?

Don

You're right. Good catch. What's the difference? What would you use the other one for?

I really need the last post I did answered though.

How do i know what capacitors to use?

It will tell you in the data sheet for the regulator you use they are all diffrent . This will be a minimum value.

then through the parallel capacitors

Odd choice of words. If it is parallel then it is across, you can't get any DC through a capacitor.

then the Arduino could have at least 1,460 mA.

You really don't understand current and voltages do you? The arduino is not going to take anything like that much. It takes 30mA by itself and what ever you hang off the 5v line and power directly from the pins. But this can't exceed about 300mA otherwise you over heat the regulator on the arduino. You can't put regulators in parallel the outputs have to go to separate places.

How do i know what capacitors to use?

The data sheet (for any three terminal regulator) has a diagram with some recommendations.

In series, right?

Wrong.

The regulators themselves don't take any current, right?

They need some power to operate, but not a significant amount.

Don

Well it's an Arduino Mega, with about 28 pins filled. I don't pretend to know as much as anyone else here. That's why I'm asking the questions. I found the datasheet that showed the capacitors. It wasn't with the first link I found.

I just have a few questions:
It didn't seem like I could wire the voltage regulators in parallel, but is there anything I could do that doesn't involve finding another voltage regulator since the current one can only handle 1 A? Will it draw more current than it can handle?

Will any of the components fry from too much current or will they only draw what they need?

... but is there anything I could do that doesn't involve finding another voltage regulator since the current one can only handle 1 A?

Look in your data sheet for an example of a 'High Current Voltage Regulator'. These circuits typically use the 78xx regulator along with a substantial transistor to handle the higher currents.

Will any of the components fry from too much current or will they only draw what they need?

The devices that are connected to your power supply (except LEDs) will draw the current that they need. As far as the power supply supply is concerned it will (try to) supply all the current that is required by the devices that are connected to it. If this is more than it's rated current then it will fry.

Don

So figure 22 here:

With this transistor:

?

Thank you for your help!

That looks good. Don't forget that the transistor will need a heat sink. Also check to see if the tab of the transistor is isolated. If it is connected to pin 2, as many are, then you will have take some more precautions.

Don

So is the voltage rating of the capacitor important in this case? What does it mean? Is that the max voltage it's rated for or does it actually build up that difference?

Well I found a 50V radial, so that should be fine, right?