Does the Buck-Boost Converter do both?

[Terrano]

Does the Buck-boost converter step-down and step-up voltage?

What I want to do is, if input voltage is above 5V to be steped-down (decrease) to 5V and if input voltage if below 5V to be steped-up (increase) to 5V. Is this possible with the Buck-Boost converter?

Thanks

 

[Optikon]

Does the Buck-boost converter step-down and step-up voltage?

What I want to do is, if input voltage is above 5V to be steped-down (decrease) to 5V and if input voltage if below 5V to be steped-up (increase) to 5V. Is this possible with the Buck-Boost converter?

Thanks

You want SEPIC topology.

 

[hantto]

I made one powersupply that does exactly what you described. I found this page **broken link removed**. I took some model from there (or to be more exact, almost copied the whole thing) and made my own. I also made a 12v and 3.3v output model, easily adjusted with by R5 and R6 and finetrimmed by R13. I made this for my car computer. The efficiency of my version on PCB was about 75%, but I think that it will increase when i finetune the coil leads. This design should be capable of delivering many amps (8 according to the website).

I added a small heatsink to the diode and MOSFET.

 

[Circuit Seeker]

A buck boost converter will either step up or step down dependant on the duty cycle. Use feedback to control the duty cycle and you will be able to keep a well regulated 5V regardless of whether the input voltage is below or above 5V.

 

[evandude]

However it's important to note that a standard buck-boost will invert the voltage... ie - 5 volts in, -5v out. so if you are using it with a battery or isolated (floating) source then you can often get away with it, but if you need a true + to + converter then you'll need a SEPIC or similar topology as others have mentioned.

oh, and hantto, thanks very much for posting that information/website.

as you may have noticed from my recently active thread, I'm trying to build a 12v output DC-DC for my car computer and having a working design to start from (or just use straight up...) is awesome.

 

[williB]

This is an interesting article..
https://www.electro-tech-online.com/custompdfs/2005/04/syncrecapec2005.pdf
It talks about syncronous rectifiers, buck converters ,and the use of common source inductance in each case..and the power savings you can achieve when using common source inductance..

 

[hantto]

However it's important to note that a standard buck-boost will invert the voltage... ie - 5 volts in, -5v out. so if you are using it with a battery or isolated (floating) source then you can often get away with it, but if you need a true + to + converter then you'll need a SEPIC or similar topology as others have mentioned.

oh, and hantto, thanks very much for posting that information/website.

as you may have noticed from my recently active thread, I'm trying to build a 12v output DC-DC for my car computer and having a working design to start from (or just use straight up...) is awesome.

No problem ^^

Here are the EAGLE files, if you find them of any use, and some pictures of my 12v and 5v board. I put two supplies on one board. The gray wire is for shutdown, in case you wonder what it's for.

As you can notice, I haven't yet soldered the coil for the other supply. I might also say that the coils DO sing if you have a big load so one must make them firm with epoxy, harz or someting similar

Edit: I should point out that there are 6 jumpers in my PCB design, just so that potential builders know about it. The jumper to the right supply should be thick, because its the powerlead for the whole right supply.

 

[Terrano]

Circuit Seeker -> "A buck boost converter will either step up or step down dependant on the duty cycle. Use feedback to control the duty cycle and you will be able to keep a well regulated 5V regardless of whether the input voltage is below or above 5V"

If I want to use the Buck-Boost converter to step up or step down the output voltage say 10V depending on the input voltage, I need some circuit that can detect a the level of voltage and reduce or increase the duty cycle accordingly, right?

To make myself more clear:

D = Duty Cycle
Vd = Input voltage
Vo = Output voltage

D = Vo/(Vd + Vo) Where Vo = 10V

So D = 10/(Vd + 10)

From the equation above:

- If input voltage is higher that 10V I need a circuit than can detect that and reduce duty cycle to get 10V output.

- If input voltage is lower than 10V I need a circuit than can detect that and increase duty cycle to get 10V output.

I hope I made myself clear

Thanks

 

[William I. Behen]

An isolated buckboost (Flyback converter) will do the job OK, as will a SEPIC, which is naturally non-inverting. But, both suffer from noisy outputs. A better approach is an isolated Cuk Converter, or a Boost-Buck cascade. See www.boostbuck.com for info!

 

[akula]

i am searching for solution to the project on ac-dc buck boost converter with 15v input & 25v output.

 

[Hero999]

Simple, just add a bridge rectifier and filter capacitor onto the input of the buck-boost converter.