voltage regulator help - ot

[mister_e]

Welcome back Ralph! We miss you!

[docwisdom]

Ralph,
Thanks for the post.
I think you went over my head a little bit with SMPS and SEPIC. Could you throw out a couple specific examples for me, or a website reference?

thanks
-=brian

[NavMicroSystems]

For the SEPIC Converter See: HERE

[docwisdom]

Ralph,
Thanks for the post. I have read the thread and reviewed the schematics. Its quite a large unit, but that is to be expected for 60w. Anyway, could you or anyone else recommend component changes so I can operate from a 4.5 to 7.6 output at 3A?

As I have mentioned in previous posts, I am pretty savvy with analog circuits, but just now getting my feet wet with digital components.

thanks very much

p.s. What is your opinion on switching regulators like the LM2676/2678? Both you & Steve mentioned that they are expensive, but digi-key lists them around $6 each. They are available in variable output versions as well.

[NavMicroSystems]

...Its quite a large unit, but that is to be expected for 60w...

Well, it is even more, it provides a stable 12V output at Input Voltages between 8 and 18 Volts, so it steps up or down at high current (with high efficiency).

Anyway, could you or anyone else recommend component changes so I can operate from a 4.5 to 7.6 output at 3A?

Again there are many ways, of course you can simplify the circuit as you don't need to step up, all you need is a "simple" step down switching regulator.
(Your minimum Input voltage is always higher than the maximum required output voltage)

See the UC3843 Datasheet for design examples.

p.s. What is your opinion on switching regulators like the LM2676/2678? Both you & Steve mentioned that they are expensive, but digi-key lists them around $6 each. They are available in variable output versions as well.

Sure, you could even use an LM2676, that would save some components like the external MOSFET.

I'm using the 2676 in one of my (GSM) designs where part count and PCB space was an issue, but overall this design was more expensive than others.
However, the 2676 is a somewhat expensive but reliable component.

And as mentioned earlier:
if you want efficiency, take special care of the inductors and capacitors you use!

You'll be surprised what increase (or decrease) in efficiency you get by simply changing a capacitor or inductor.

I have spent days with winding my own inductors on different cores to get maximum efficiency over the full Input voltage and output current range.

[Acetronics2]

You'll be surprised what increase (or decrease) in efficiency you get by simply changing a capacitor or inductor.

I have spent days with winding my own inductors on different cores to get maximum efficiency over the full Input voltage and output current range.

Hi, Ralph

you're right ... new design = "some" windings to try !!! I also appreciated your converter.

by the way ... Would you know a replacement part for the MAX 879 ( low power, low voltage Step up/ Step down ) ... ???

It was a jewel for my 4 cells to 5 v applications, but no more produced now ...

Regards

Alain

[docwisdom]

I am in a holding pattern right now until I get my capacitor and inductor specs figured out. I going to go the LM2676 route. I have tried a piece of software by National that figures these values out for you, but it seems to be giving me conflicting information, or just information I dont understand (most likely) Anyway, if anyone is a wizz at this stuff, could I get a recommendation on a purchase list of caps and inductors for these three voltages?

thanks much

[NavMicroSystems]

by the way ... Would you know a replacement part for the MAX 879 ( low power, low voltage Step up/ Step down ) ... ???

It was a jewel for my 4 cells to 5 v applications, but no more produced now ...

How about the MAX 710/711?

ok, it requires a little more space plus an external schottky, but it's efficiency is better.