Dual Voltage Regulator vs Two Separate Regulators

[Veramacor]

Hi all,

I've got a project that requires two different voltage supplies,  coming from one power source.

The voltages are 3.3V  and 5V.   I'm wondering what would be better,  using a single Dual Voltage regulator like the one here:

http://www.infineon.com/dgdl/TLE4476_DS_25%5B1%5D.pdf?folderId=db3a304318f3fe290118f5a433570040&fileId=db3a30431c48a312011c55e0456c0243

or using a one 3.3V Fixed and one 5.5 Fixed.   Has anyone had a need for multiple regulated voltages in their projects?

J

[Waifian]

It would depend on your current requirements along with space requirements I would think. The single dual voltage supply only puts out 350 ma and 450 ma where two single regulators with proper heat sinking will give you about 1.5 amps or more with additional circuitry.
 
Also, if current requirements are really low you could use a zener Diode with the voltage rating and a series resistor.

[Simon]

I expect price and part count would also play a part in your choice

[DJPhil]

I can't answer your question with authority, but I think I know of a resource that might help. I found this pdf on Onsemi's site (be patient, takes a while to load) a while back when I went looking for more info on regulation. It seems like a fairly comprehensive treatment of regulation in general, and I found it very useful in the past. It might not be enough to solve your problem, but it might narrow your scope to a few solutions from an overwhelming selection of parts.

NEC's got a shorter pdf along the same lines. It was a pain to track down, as apparently they've recently merged(!) with Renesas Technology Corporation (who?). Aside from the first page blurb, it seems to be the same document.

Hope that helps.

[Veramacor]

Thanks all for the replies - Good point made about having extra current reserve in case I need it.  It really about saving maybe 5 cents or either way.

J

[EEVblog]

The problem with using a specific dual supply chip like that is that it is likely not a common/defacto industry standard part/pinout. This can often result in supply problems, lack of alternatives choice, production price, and all sorts of other issues.

generally speaking you should try to stick to jellybean parts where possible, unless you have a specific reason to chose a more obscure part like that.

Dave.

[Veramacor]

Ive seen the usb wall adaptors that output 5V at around 500ma.  I could use one of those

http://cgi.ebay.com/USB-Wall-Charger-AC-Adapter-for-Mobile-Cell-Phone-500mA_W0QQitemZ280379010747QQcmdZViewItemQQptZPDA_Accessories?hash=item4147e42ebb

+/- .5V though and probably not very well regulated.  Although a USB jack plug could be used for data transfer if I decide to use a Pic18F (with usb support).

I would still need a 3.3V reg regardless.   Anyone else using USB for power and data transfer to their microcontroller?

J

[Simon]

I'm sure that anyone making a USB pic device that works only when plugged into a USB port will use the port for power unless they need a lot of power or for the device to work "solo"