Is this the most useless voltage regulator ever?

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#1
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I found some of these in a box so I looked them up.  A 5V regulator with a maximum input voltage of 6V ?!?!  What in the world would this be good for?  Maybe it's intended for running 5V circuitry from 4 battery cells?  But even then, four fresh 1.5V batteries puts out at least 6.4V.

 

https://www.mouser.com/datasheet...

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One of a series of chips which were for some time the bane of my life, while I was trying to locate LDO regulators with minimum 'base' current and low noise... There are many many regulators - most at 3.3v or less but one or two at 5v - with a 6v maximum input. It is as if no-one at the chip designer thought one might want to apply them to a 4*cell supply - 6.4v with new alkaline (and staying there for several months on some of our loads) and over 7v with some of the lithium primary cells.

 

I suspect that the less than 5v outputs are in anticipation of a 4.2 lithium cell input, but the 6v in 5v out is inexplicable. And none of the manufacturers we spoke to would even contemplate giving us any certification, even derated, for an over 6.0v input. So we didn't use 'em...

 

Neil

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Seems to be a common limitation of these type of cmos regulators. The likes of Torex and Richtek have similar limitations.

It's a pity though - one gets enticed by the specs of very low dropout, very low quiescent current etc only to find the input voltage is rather restrictive. 

Then there's the little dc/dc switcher chips - many of them top out at 18V.

 

Why can't manufacturers just simply make what we want? It would make my job soooo much easier!

 

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The big sell here is that it is CMOS, so no overhead, no power waste (other than of course, the much larger waste of the voltage drop times load current).

 

So this would be great for a standby setup, where the load is not yet connected & the regulator basically kicks back and sips a few electrons & ponders the universal programmer.

 

 

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The spec sheet you linked to gives an 'Absolute Maximum' of 6.5V, although various behaviours are not guaranteed at that level.  It should at least tolerate 6.4V from a fresh set (maybe not lithiums) for awhile.

 

But more interestingly, it comes in a range of outputs - yet with the same input.  If you wished to make 3.3V out of 5V, it would work very well (which is what I suspect the important point is).  S.

 

Edited to add:  Perhaps they also had in mind that you'd put a diode in the input to prevent against reversed polarity.  Even a Schottky would take your 6.4V down a bit.  S.

Last Edited: Sun. Sep 27, 2020 - 11:53 PM
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They are probably available because they are CHEEEEP. 3.3V LDO has its output set by a (probably trimmed) resistor divider. Just change that divider, and bingo, you have 5.0V out. No other redesign, probably. Cost of the change for the manufacturer has to be really low.

 

Jim

 

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Yes, a universal family is always going to be cheaper... I wonder if they have in mind the multiplicity of rails within current processor setups, where they might be expected to be driven by a regulated 6v?

 

Neil

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The other use for these is in multi-pcb setups, especially where the cards plug into a backplane. The main rails run at a low voltage and you regulate to the operating voltage at the point of use to distribute any heat.

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