24vIN to 12V (3A) voltage regulator, without coil? (LM2576 must use a coil?)

the inductor stores energy and is necessary in a switching power supply.

It will not work without it.

The LM2576 needs a coil, period. It's a switching type of regulator and the coil is essential. The MC78T12AC is/was a linear (non-switching) regulator and does not need a coil. Switching types are more efficient in that less power is lost in the regulator circuit. This means less heat to dispose of. A linear regulator like the MC78T12AC has to continuously absorb the difference between the input and output voltages - 12V in this case. Multiply that voltage with the current and you get the amount of power that's converted into heat. At 3A, that's 36W. This requires a massive heatsink, otherwise, the regulator will overheat and burn up in no time.

There are other linear regulators that can do the same job, but the heating issue is always there.

Thanks Pimpom... I didn=B4t know about the difference between the LM2576 and the MC78T12 ... A big heatsink is no problem for me... in fact, I prefer that to the hassle of having to make or obtain a coil...

So what linear regulator with the same specs as the MC78T12 is there, that is currently being produced?.

FC

There are many models from various manufacturers. Here are three examples, all from National Semiconductor:

LM350 - 3A, adjustable voltage (you set the desired output voltage with 2 resistors) LM338 - 5A, same as above LM1084 - 5A, comes in both adjustable and fixed voltage versions.

I checked at Digikey and they're all available. Look up the datasheets on Nat Semi's site or from

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If your purpose is getting a low cost P/S for your new notebook, I recommend to you buy a cheap switching P/S from radio shack. I believe that's most cost efficient and comfortable.

If it's re-using old P/S, to keep it for next chance for 24V device.

If it's re-using old P/S for your new notebook, I want to say that inductors are good reliable industrial products much than you think. Bad efficiency is big disadvantage of using LDO as like 78T12, versus using step down switch as like LM2576. Especially it's wasteful to use a power supply inefficient though PC of low power consumption is used with great pains.

Good Luck, F

dohi

So, you're unwilling to carry around a 5 ounce power supply that was designed to operate the netbook, but you ARE willing to carry around a 5 pound heat sink with a linear regulator that still needs to be plugged into something, the 24V supplies scattered around the house?????

Your question suggests that you don't have a clue. Power supply designers who don't have a clue have a tendency to make a fireball of their $250 netbook. A power supply schematic is trivial... assuming you don't leave out components critical to its operation. The devil is in the details you learn the first few times you build one that blows up and takes out whatever it's powering.

Get yourself some AC power cords and let the end dangle next to your

Hey, I'm not sure any here actually LIKE winding coils, especially toroids - that's probably why they are a cheap-as off-the-shelf commodity for the sort of load you require.

A linear stepdown is going to dissipate bulk power, as others have pointed out. More cost, more weight, the *only* benefit is a slightly lower component count.

It will explode. It needs the inductor for regulation and overload protection.

The "Simple Switcher" series isn't exactly rocket science. Input capacitor, output diode, output coil, output capacitor, and feedback divider. Put the parts on a flatbed scanner, scan, place into photo editor, draw traces connecting the pictures, print traces on blue peel with a laser printer, iron onto a board, peel, etch, add solder paste, drop the parts on it, heat, and you're done. It's all Digikey parts and you don't even need custom software.

I have one inside the handle of a 0-50W LED flashlight with plenty of room to spare:

Try the "Simple Switcher Power Module" line if you don't need much current. LMZ14203H has a built-in coil.

no. it doesn't need a very big inductor.

dunno.

That part can do 3A or 24V input not both at the same time. the max dissibation is 25W (and that's when attached to an "epic" heatsink) which for a drop of 12V in gets you a little over 2A

If you don't want to build a voltage converter buy one.

WOW an amazing discussion.

fcassia,

Have you looked at the data sheet for the LM2576 ??

Its called a "simpler switcher" for a reason.

If you do not know what a "switching regulator" is. please goolge.

Your requirement of 24v - 12V@3A = 36Watts is a lot of power to burn up as heat is a series regulator.

This will require a large heat sink and maybe a fan.

In todays internet age, you could have had an answer and solution within

hamilton

Absolutely not - the LM2576 is a switching / "switchmode" type, which requires an inductor. (Unless abused so badly that it can be improved upon by use of a "linear" [non-switching] regulator.)

MC7812AC is a "linear" voltage regulator. Difference between input voltage and output voltage, multiplied by output current, becomes heat.

Furthermore, 12V voltage difference times 3 amps is 36 watts, more than the 25 watts max power dissipation of MCT78xx. For that matter, 25 watts heat dissipation is the rated max, also max at merely upper 30's degrees C ambient temperature when the combined thermal resistance of heatsink, any heatsink insulator, and preferable- over-lack-thereof "heatsink compound"/"heatsink grease" all add up to a mere 2.4 degrees C per watt.

This gets me in a bad mood to go inductor-less...

LM2576-12 at input voltage up to 27.5-28 voltage, with 3 amp load current (max that LM2576 is up to doing), requires 150 microhenries. Its datasheet

-116 version (fair chance more reliably achieving at least 150 microhenries).

The feedback divider is not even necessary for the 4 fixed-voltage options of LM2576, one of which is 12V.