Buck Converter

Hi Jerry,

Do you already understand the principles behind the design of a buck converter, and you now wish to design one? There are a number of resources on the web. For example, this one explains some of the fundamental principles. And this link leads you to a collection of industry white papers written by various companies.

If you need more info, just let us know.

-e

I have very little understanding of a Buck converter. This is what I was told I need to drop voltage in a project I am working on. I have always had someone else make the things I come up with, and now I would like to do them myself. That being said, I have been doing alot of reading, and have myself more confused than I have ever been.

I'd say someone with 'little understanding' has no chance of making a buck converter.

If you feel you must I'd suggest National Semiconductors have a IC which together will make a switchmode poersupply. I believe the have excellent application notes and a program which will walk you through the design. Try googling 'simple switchers psu' or get onto the National Semiconductor website.

Del

Thank you for your input and info. I have some understanding of electronics, I know more by just putting things together to see what they do. My main problem is I do not know what all the components are in a schematic diagram. I have learned how to make my own circuit boards and how to use some things like resistors even though I have yet to get a handle on how to figure just exactly which ones to use when, I try it untill I get the result I want. What I am tring to do is take 120v AC and reduce it to 12v so I can use the power to charge a unit back up. I still need the 120v in the unit for other reasons.

"What I am tring to do is take 120v AC and reduce it to 12v so I can use the power to charge a unit back up. I still need the 120v in the unit for other reasons."

What's wrong with a transformer, rectifier bridge, capacitor, voltage regulator circuit? In other words, a good ol' linear power supply.

Exactly, and linears are cheap and easy to build - and buy.

Perhaps a better approach for Jerry to take is one of buying an off-the-shelf supply (he didn't mention output current, btw) and put it into service. He can have his cake and eat it too. With the PS in service and doing what he needs, he can then learn about buck converters at his leisure. I might also note that buck converters are not usually used in 120VAC service. Normally they're used to convert a fairly low DC voltage to a lower DC voltage. Say one converting 5V supply on a computer motherboard to one of the lower voltages used by CPU cores. Other kinds of switching supplies take 120VAC inputs, but these are typically are not based on buck converters.

I am not against other methods, however maybe I should have said that size is more inportant. I have 2 rectifiers and they are to big. If I should not be asking questions in here because I do not have the proper knowlage, please let me know and I will be more that respectful and stay out and away. Thank you to everyone who has tried to help.

How big are your rectifiers? How much 12 VDC current do you need? Charging currents range from 1 - 2 amps or less to more than 100 amps (or more) for some systems. Your rectifiers may be large, but they may not need to be physically large.

Give us an idea of the amp-hour capacity of your back-up batteries and the frequency of usage, or something along those lines.

This is the place to go with questions, but to answer some, we need more information. And even if you don't know what questions to ask, or how much more information may be needed, you and we will get to the answer before long.

By the way, high current buck regulators aren't physically small either.

nobody is "too big" to be here, don't put yourself down, loads of others will do that for you but don't let that stop you either.

Unfortunately I know buck all about what you are talking about so I will stay out.

Amen to that!

You are not looking for a buck converter. Those are step down converters for an already DC supply. For this, National Semiconductor has the easy way to go.

You are in fact looking for an off line switcher , google will help you finding some stuff. Try DigiKey, Mouser, Allied Electronics for your purchases. This should be too specialized for the Shack to carry.

All in all, a transformer solution may be the easiest, but the least gratifying to built, if your knowledge of electronics is sufficient.

You have to walk before you run. Ant mains voltage is kinda like a large highway...

Please, don't die.

Hi Jerry,

Here's another tutorial about buck converters.

Best site I found is: www.smps.us/

If small is important, it is possible to 'sniff off' small amounts of power from AC mains through a capacitor/diode arangement. Look at this link.

carefull to get correctly rated capacitors....

Del

Are capacitors not those things that if they are rated wrongly, they give you a house full of smelly confetti and lots of smoke? Or is that if connected up in reverse?

Are capacitors not those things ..

Hey man just don't start asking negative questions.. if the pedants start giving technically correct answers no one will know if it means yes or no.

e.g. The are capacitors NOT those things? Answer is NO because they are those things...oh no I'm confused now

Hang on...if you didn't have the 'not' in the question the answer would be 'Yes'...therefore with the 'not' it must be 'no'

Del

down kitty kitty....

ok lets start again, are capacitors those things that....bla bla bla?

Just wanted to know about the confetti and the smoke realy. I am an engineer with prepensity to mechanical and some minor electrical but hardly any electronics. Still interested in it tho so if you please, humour me

Yup...electrilytics can go with a nice bang..only a few weeks back we had a duff bridge rectifier which put 12AC onto an electrolytic...The cans are designed to rupture ... but...this one didn't, it popped right off, hit this guy square between the eyes leaving a nasty bruise. It hit so hard it bounced 20feet away to the other end of the room!

Ouch!

I saw a 33' diameter x 85' long capacitor at Sandia Labs. The conductors in and out of the thing were 6-inch copper pipes. I'd like to see 'em blow that thing!