OK, here's a diagram of three different configured transformers. Keep in mind that transformers can have many different configurations. You can have a single secondary, a center tapped secondary, two or more secondaries, each with similar or different voltages.

You also need to rectify that current. You can use two diodes as shown in the second illustration, four diodes as shown in the first and last illustration OR you can use a bridge rectifier (which is the same as the four diode illustration). AND you'll need to filter that output with a capacitor. The best value will be dependent on how much current your circuit draws.

Engineering is HEAVY in math and algebra (which is why I'm not an engineer). It will also serve you to learn Ohms Law (for starters). It's the most basic law out there. Easy to learn and use in a lot of applications. In time you can learn the rest of it. But keep in mind, it IS heavy in math.



And THANKS to Lestraveled for catching my errors. The drawing has been corrected.

 

@cmartinez: Our young engineer doesn't know what amperage he needs. He may actually need more than what he thinks. The links you provided are good links, however, the 12 volt regulator is only rated for half an amp (or 6 watts), and the five volt regulator is rated for 2 amps (10 watts) (see cornycorn, there's that math thing I mentioned).

Cornycorn: I suggest before you spend any money you figure out how much power (wattage) your circuit is going to draw. Otherwise you can be turning your money into smoke. But that's not such a bad thing, as long as you learn from your mistakes. Just don't spend a whole lot of money on smoke.

And those

 

Hello, this is my first post so please bear with me.
I am 12 years old and i am working on a prototype for an invention i have. I will need to turn 24vdc into 12vdc, but i want to use something that:
-will not generate heat
-that is small in size (about an inch)

Thanks!

Any kind of linear regulator will convert the dropped voltage into heat according to VxA=W. That includes dropper resistors and potential dividers.

A buck regulator is the standard solution for what you've asked.

There is a company making SMPSU drop in replacements for the popular 78xx 3-terminal regulators. You'll have to search, I don't recall the details.

 

@Tonyr1084

You have a few errors in post #41.
First, perhaps a typo, the second transformer with a single 24 Vac winding, you have the rectified output at 12 volts. You probably meant 24 volts.

Second, when rectifying and filtering an AC voltage, the resultant DC voltage is 1.414 times the AC voltage, when unloaded. So, all of the 12v outputs should read 17 Vdc and the 24V output should read 34 Vdc.

I know we want to keep it simple for Corn, but it is also good to be accurate.

 

@cmartinez: Our young engineer doesn't know what amperage he needs. He may actually need more than what he thinks. The links you provided are good links, however, the 12 volt regulator is only rated for half an amp (or 6 watts), and the five volt regulator is rated for 2 amps (10 watts) (see cornycorn, there's that math thing I mentioned).

Cornycorn: I suggest before you spend any money you figure out how much power (wattage) your circuit is going to draw. Otherwise you can be turning your money into smoke. But that's not such a bad thing, as long as you learn from your mistakes. Just don't spend a whole lot of money on smoke.

And those

You're right. The 12v regulator is not the one I meant to pick, but rather one that looks exactly like that one from the same brand, capable of delivering 2 amps.
Perhaps this is a good moment for corn to visit the digikey site and do a search for dc to dc converters.

 

@Lestraveled: You're right. I JUST noticed the error on the 24 vac transformer (not tapped). You're absolutely right, it should have been 24 VDC
And to go even further, you're also right about RMS voltages. Yes, the 12 volts WOULD be 16.97 VDC and the 24 volts would be 33.94 VDC.

I'm going to go back and correct those errors. But like I said to CornyCorn, math is the reason I never became an engineer. I don't often think of numbers, just the road to get there from here.

Thanks for pointing out the RMS voltages.

 

@cmartinez: You're right. The 12v regulator is not the one I meant to pick.

Yes, we all make mistakes. I mistakenly called a 24 VAC final DC voltage as +12 when it should have been (incorrectly) +24. Lestraveled alerted me to the error (1.414) which would correctly be 34 VDC. And the 12 volts should have been 17 VDC.

I have to laugh the hardest when I make mistakes. We all make them. And this is probably the main reason why over the years so many times the smoke has leaked out of many a component under my hand.

Gaud I love this website!

 

@cmartinez:
Perhaps this is a good moment for corn to visit the digikey site and do a search for dc to dc converters.

What is wrong with the regulator @CornyCorn picked here?

http://forum.allaboutcircuits.com/threads/how-can-i-convert-24v-to-12v.120870/page-2#post-965696

 

What is wrong with the regulator @CornyCorn picked here?

http://forum.allaboutcircuits.com/threads/how-can-i-convert-24v-to-12v.120870/page-2#post-965696

Let me tell you what's wrong with it:

1. I hadn't seen that post 'till now
2. I've been paying way too much for a DC-DC converter
3. That module is better than the one I suggested in both ripple and accuracy
4. It also has a wider input voltage range
   
5. It has four output ranges instead of just one
6. And most importantly, I now hate myself for not having discovered that thing before

That's what's wrong with that module, you happy?

PS: I'm gonna go buy myself a few pieces of that thing right now, do some testing.

 

Let me tell you what's wrong with it:

1. I hadn't seen that post 'till now
2. I've been paying way too much for a DC-DC converter
3. That module is better than the one I suggested in both ripple and accuracy
4. It also has a wider input voltage range
   
5. It has four output ranges instead of just one
6. And most importantly, I now hate myself for not having discovered that thing before

That's what's wrong with that module, you happy?

PS: I'm gonna go buy myself a few pieces of that thing right now, do some testing.

Have you seen the Jeff Foxworthy show, "are you smarter than a 5th grader?"

This may have been posted in the Jokes thread, too...

 

The LM2596 buck converter boards on ebay, of which two would be needed (one for 12v, one for 5v), are about 1" wide, about 3/4" high, and about 2" long. They are more efficient than 78xx regulators in the sense that they generate less heat to convert the voltage. Their voltage can be adjusted using a trimpot on the board. You could solder pins on them to make connections.

 

This buck converter looks much smaller than the LM2596 converters. Handles up to 3A (though a heat sink may be required for that much). It is also smaller than 1" by 1", and probably less than 1/2" high.

http://www.ebay.com/itm/Mini-MP1584...423493?hash=item2c7e2cc205:g:gv0AAOSwrklVdVaF

 

I suggest you take a look at these two options:

http://www.digikey.com/product-detail/en/V7812W-500/102-2454-ND/2757920
http://www.digikey.com/product-detail/en/V7805-2000/102-2175-ND/2352134

They're kind of expensive, but meet your requirements, I think.

Strange they would pick 7805 and 7812 as a part number for a switching regulator.

 

I found this part some may be interested in. Little out of range for CornyCorns requirements, but may be useful to others.

http://www.readytoflyquads.com/rtf-1v-17v-adjustable-voltage-regulator

It is very small (<1" all sides) and $0.99 each. Can't take credit for finding it, a show I watch called KnowHow used them. That show is a good one for young kids (and adults like me too!) learning about electronics, computers, etc. has a few episodes quad copter heavy but does a good job mixing it up. On YouTube or can find them at twit.tv. The screen savers is also another favorite of mine.

 

Strange they would pick 7805 and 7812 as a part number for a switching regulator.

There is at least one company producing (allegedly) drop in replacements for the 78xx linears.

As the linked page shows, they're a bit bulkier and don't look easy to fit to a heatsink. So they won't "drop in" in every case.

But they are switchers, and in many applications won't require a heatsink.

Elektor magazine published a project to build something very similar in recent years - there may have been a kit with PCB that you can order.

 

I think i finally found something that may work
http://smart-prototyping.com/MP1584...onverter-24V-To-12v-9V-5V-3V-for-Arduino.html

Hi there,
I have DC DC Converter 24v to 12v.
SAKET

 

Everything you dream of could be here: http://www.aliexpress.com/item/Stan...C-Converter-1pc-New-SG053-SZ/32320655374.html
Get two of them, connect each to you 24 volt supply and adjust them to your desired voltage (they are variable) and fire up.
Good luck

 

Have you seen the Jeff Foxworthy show, "are you smarter than a 5th grader?"

This may have been posted in the Jokes thread, too...

Why do people insist on adding annoying background music when posting these videos? I'd rather hear the hot blond no matter how dumb she might be.

 

Everything you dream of could be here: http://www.aliexpress.com/item/Stan...C-Converter-1pc-New-SG053-SZ/32320655374.html
Get two of them, connect each to you 24 volt supply and adjust them to your desired voltage (they are variable) and fire up.
Good luck

How do they do that? The IC is $3 from distribution.

 

How do they do that? The IC is $3 from distribution.

Most likely counterfeit/reject parts.