Hello everyone,

For my next project, I'd like to use a capacitor based DC-DC switching regulator to take 7.4v down to 5v. Does anyone know of any good regulators, and can give me some advice about setting them up? I've only been able to find information on using inductors for step-up regulators.

Thanks,
Barnaby

 

You can go for low dropout type 5V regs.

These can take inputs down to almost 6 volts unlike standard types.

Googling low drop out 5V regulators will help

 

Please give me one example of a switched capacitor step-down converter so I can figure out what you want.

Please tell the current you need.

Have you tried national.com for "simple switchers"?
No...wait...they will likely use an inductor.

 

If the input is constant and you have current to play with a simple voltage divider might work.

 

Learn to use the parametric search features on manufacturer websites. This is one product from Texas Instruments: http://focus.ti.com/lit/ds/symlink/ptn78000w.pdf. There may be others at Analog Devices, Maxim IC, Linear Technology, etc.

 

Hi everyone,

Thanks for your feedback.

Please tell the current you need.

Have you tried national.com for "simple switchers"?
No...wait...they will likely use an inductor.

This is going to be supplying an MCU, as well as a few LEDs and some output signals — nothing huge. I could get by with a linear regulator but wanted to try using a switching one. It doesn't matter if it uses an inductor, particularly (they look awesome on PCBs! I haven't had the chance to use one yet).

Learn to use the parametric search features on manufacturer websites.

I am trying, as with all the graphs on datasheets. The problem I have found with parametric search is that they're fab for fine-tuning selection if you already know almost exactly what you want — which in this case, I didn't.

This is one product from Texas Instruments: http://focus.ti.com/lit/ds/symlink/ptn78000w.pdf.

That looks perfect for what I need — thanks a lot!

Cheers,
Barnaby

 

You really should define your projects' power requirements before looking at (a) regulator(s), or you may wind up with too little (frequently happens) or far too much capacity (overkill is expensive and bulky).

 

Now that you say you're open to using an inductor, the most commonly used DC-DC converter controller is the MC34063A. These are used in USB car chargers that you can get at a thrift store for $1.25 or on eBay for $2.50. They expect an input voltage above 10.5 but you can change components to optimize for your voltage.

http://focus.ti.com/lit/ds/symlink/mc34063a.pdf
http://focus.ti.com/lit/an/slva252b/slva252b.pdf