Low drop out voltage regulator.

[beanman]

I am currently in the R&D stages of a Altoids tin iPhone charger but the voltage regulator I am using is much to inefficient. If anyone could tip me off on a voltage regulator that takes 9v down to 5v and has a drop out voltage of .7v (but a lower dropout voltage would be better) it would be very much apricated.

-Ben

 

[davenn]

Hi Ben,

Have you googled low drop out regulator ?

there are many to choose from, then look through the data sheets and find one with the lowest dropout voltage

cheers
Dave

 

[beanman]

I have but I have been haveing troubble finding one. Maybie I was being to specific in my searches or something.

 

[(*steve*)]

Try using digikey. Start here. That's 34,000 low drop out regulators to choose from.

 

[Harald Kapp]

Where's the catch?
A low drop regulator is one that can operate at a very low drop out voltage, but the voltage that really drops is the difference between input voltage and output voltage.So in order to regulate 5 V from a 9 V battery the regulator needs to drop 4 V.
Why the need for 0.7V drop out voltage? I guess you want to quench the last drop of juice out of the battery. But a linear regulator (even low drop) is the wrong approach. Depending on the current drawn it will very effectively convert the excess voltage from the battery to heat. In that case a switch mode regulator would be much more efficient.

 

[zalmonox]

Indeed tehre is something about the undestanding of the problem. A low drop-out regulator is a regulator that can potentially use an input voltage very close to the desired output voltage (so close as the low drop-out value).
Ex. if you want 5V on output and your DC-DC has a drop-out of 0.5 it basically means you SHALL power it with at least 5.5V to work.
As much for the model (to get 5 from 9) this is another story. Pay attention with the LDOs ... they will dissipate a lot.
In the case above and for a current of 100mA (not much!) they will dissipate:
(9-5)*1/10 = 0.4 W which is already a lot.
You might want to use a switching regulator in this case.
Look at this on www.Digikey.com
296-12290-2-ND
296-18037-2-ND

Good luck

 

[gorgon]

I am currently in the R&D stages of a Altoids tin iPhone charger but the voltage regulator I am using is much to inefficient. If anyone could tip me off on a voltage regulator that takes 9v down to 5v and has a drop out voltage of .7v (but a lower dropout voltage would be better) it would be very much apricated.

-Ben

You don't say anything about your charging current or the max voltage input range.
The efficiency you have is also not listed.

I stipulated the following:
Vinmax = 12V
Vinmin = 3V
Vout =5V
Ioutmax = 1A

Just for fun I put this into webench designer from TI/NS and came out with the following SEPIC design:
The efficiency of the converter is 80-84%

TOK

 

[Electrobrains]

Hi Ben
Here is a low-cost "super-low-drop circuit":

See the whole article here: "Zero-Drop," 0.5-A Voltage Regulator Costs Under $1