Changing DC voltage

Hi, Tom. The quick answer is, "Use a series resistor".

Here's how it works. Let's say your two volt bulb has a resistance when hot of 2 ohms (view below in fixed font or M$ Notepad):

| | .--------------. | | --------> | | | 1 amp | | | | 2 ohms | +| .-. | --- ( X ) | 2V - '-' | | | | | | | | | | '--------------' | | 2V / 2 ohms = 1 amp | (created by AACircuit v1.28.5 beta 02/06/05

Using Ohm's Law ( I = V / R ), we can infer that when the bulb is hot,

You have seen that, if you connect the 12V battery to the 2V bulb, too much current will go though it, causing it to burn out. We need to add something else to the circuit so the total current going through the bulb remains 1 amp.

That something is a series resistor. Again, using Ohm's law, we can find the total resistance we need:

You can easily see that ? should be 12 ohms. That would mean we have to add a 10 ohm resistor in series to make the total resistance 12 ohms, like this:

| | ___ | .----|___|-----. | | 10 ohms | | | | | | --------> | | | 1 amp | | | | 2 ohms | +| .-. | --- ( X ) | 2V - '-' | | | | | | | | | | '--------------' | | 12V /( 10 ohms + 2 ohms ) = 1 amp | (created by AACircuit v1.28.5 beta 02/06/05

If this isn't just a homework problem, you'd also have to size the resistor properly for the power dissipation.

Good luck Chris

But this is wasteful of energy. In this case only 1/6 of the power f om the battery reaches the bulb.

A better solution would be a switching regulator but why not just use a 12V bulb ?

Where did you find a *2 Volt* light btw ?

Graham

To go from a higher voltage to a lower one there are 2 simple methods. If the current is low and constant then a resistor would do it. A much beter way is a voltage regulator. For currents up to about 1 amp you can use a 3 terminal voltage regulator. Look up a LM7805. I know of some 5 amp regulator ICs. For greater current (up to 50 amps and more) you can use a LM723 IC and a few transistors. The basic circuit has been around for 20 or

Start here and then look at some of the circuit diagrams.

To get a higher DC voltage you usually convert it to an AC voltage , send it to a transformer (which can be part of the DC to AC converter) , then change it back to DC.

This reminds me of the old joke "Y'know, if they'd just hire taller girls those ballerinas wouldn't need to stand on their toes."

bulb

Hi, Graham. It sounds like a homework or science fair question. Considering the time of the year and the way the question is phrased, I was guessing it might be a basic level high school physical science question. Some high school sequences cover electricity toward the end of the second semester.

Let's not scare 'em off too soon. ;-)

Cheers Chris

How do you convert DC to AC?

-- Sincerely, |

------------------------------------------------------------------------

You 'chop' it.

Graham

You use switches to reroute it in alternating directions. Actually, you don't need to actually reverse the direction of current, you can just interrupt it and use inductance and capacitance to work with those changes to generate more voltage.

Here is a tutorial that covers some of the circuit physics involved: