DC-DC Buck-Boost converter using 555 Timer?

[Jdo300]

Hello All,

I'm working on a project that requires an isolated switching supply that will output 15V from a 9-18V input at up to 2W. I have found the perfect DC-DC converter module for the job from MicroPower Direct but I'm trying to see if it would be possible to build something with similar functionality using a simple 555 timer (or several of them). My understanding is that a buck-boost topology would probably work to get the wide volage input range tha I'm looking for and I'm hoping that I can leverage the 555 timer to my advantage (since I have a whole drawer full of them) to test out my prototype circuit before buying the 'nice' tidy-box module.

Does anyone know of any nifty circuits using 555 timers that can do a buck-boost setup? If not, does anyone know of some bare-bones, simple buck-boost controller ICs out there that don't have lots of external guts hanging out or come in a package that I'd have to view with an electron microscope to solder? I'm looking for the simplest solution just to see if it would be more cost-effective than buying the modules (which cost about $12-15 depending on where you get them from).

Thanks,
Jasson O

 

[MATLABdude]

I don't think it's worth doing from 555s (except, maybe to challenge yourself). You would probably end up with fairly tight current / voltage tolerances, and spend more on parts and tuning than you would for the module itself!

Maxim makes a number of step-up (or step-down) ICs... Look for the 8-pin PDIP (Plastic DIP) or 8-pin CDIP (Ceramic DIP) packages. Bonus: free samples. Still need a few (~half dozen) external components, however:
http://www.maxim-ic.com/

Intersil makes step-up/down converters (but AFAIK, you can't configure one of these so it does both--you'll need two if you expect this situation to occur), also available in DIP packages. They're kinda pricey, however.

TI also makes all of the above. With complete reference designs and calculation charts (reduces the amount of leg-work you need to do). Pretty cheap as well, and with no need for massive inductors.

I'd recommend going to the Digikey website, searching for regulator, choosing DC-DC converters, and then filtering by 8-DIP, and finally company.

 

[berkeman]

You can use the On Semi NCP3065 in its "Sepic" configuration:

http://www.onsemi.com/PowerSolutions/product.do?id=NCP3065

And National Semiconductor has several buck-boost converters:

http://www.national.com/cat/index.cgi?i=i//310

.

 

[slach]

hi all..i need help in designing the buck boost fundamental circuit for solar power.i'm just don't know how to exactly determine the value for capacitor and inductor..here are the parameter that i have
vin> 2-18v
vout> 12v
idc> 3.15A
f> 20kHz

 

[Jdo300]

You may find these pages helpful:

http://web.archive.org/web/20071002...b/design_center/articles/DC-DC/converter.shtm

http://ecee.colorado.edu/~rwe/papers/Encyc.pdf

- Jason O