On Fri, Jan 25, 2002 at 09:46:08PM -0800, Rick Mann wrote:
> I was going to use a voltage regulator from Toko America, what Digi-Key
> listed as a 260 ma 5.5 volt regulator (datasheet:
> http://207.208.84.9/semiconductors/pdf/tk112xxb.pdf).
>
> However, when it arrived and I started looking at the data sheet, it seemed
> to be only a 150 ma regulator. What I'd like to know is, can I safely put
> two of these together, both outputs tied to the same positive (circuit)
> supply rail? Will I then be able to get 300 ma out of the two regulators?

Probably not a good idea. Linear bipolar regulators generally have a "feature"
called thermal runaway. Simply put the hotter it gets, the more current it
draws, making it even hotter. When you parallel once one becomes hotter than
the other, taking all of the current.

>
> If I can't tie them to the same supply rail, can I run some of my components
> off a separate rail? For example, can I have one regulator power the LCD in
> my circuit, and the other regulator power the MCU, but still have output
> pins of the MCU connected to input pins of the LCD, and everyone sharing a
> common ground?

Yes. That should be fine.

>
> As a side question, does anyone know of a 250 - 300 ma 5.5 volt
> surface-mount regulator?

Of course there is the third option: use a pass transistor in parallel with
the regulator. Then when the regulator starts passing too much current the
pass transistor kicks in and delivers the rest. A surface mount low sat
PNP or PMOS power transistor should be able to easily deliver a 1/2 amp.

Hope this gives you some ideas.

BAJ

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu