why use a buck converter ? please try to convince me

[TripACT]

Hey all,

as part of the project i'm studying and writing about, i need to justify the use of buck converter topology other than boost or buck-boost.

other than it's functionality, what other major differences there are ?

if i want to supply 10v @ 1A for a 10ohm load, why wont i use a boost ? or buck-boost?

i know that output voltage depends on the duty cycle and the duty cycle relationship varies along with the type of the converter.

yet, i'm sure there are other reason why buck is popular and preferred when using low voltages at high ampers...

please provide me with important reasons

UPDATE: just wanted to note that i'm talking about why picking a buck converter from the three classic options: buck, boost, buck-boost


thanks

gary

 

[goldsmith]

Dear Gary
Hi
It is simple , lets look at advantages and disadvantages of Buck converter together :
Advantages :
1- Easy to implement .
2- low noise at out put .
3- low price , at high powers .
4- compact design .
5- easy to get feed back .
6-cheaper price .
.... etc

And about disadvantages :
1- it has not any isolation between input and out put ( ground isn't safe ) .
2- the 50 Hertz hum ( if the frequency of your power line is 50 HZ ) or 100 HZ hum , can appear at out put ( from ground ) .
3- Step down ( we can't increase the voltage within ) .
... etc
Best Wishes
Goldsmith

 

[TripACT]

yes i know all those..but is there something buck can do and the two other wont?

 

[FvM]

if i want to supply 10v @ 1A for a 10ohm load, why wont i use a boost ? or buck-boost?

No reasonable answer possible without knowing the input voltage range.

 

[goldsmith]

If you see the advantages and disadvantages of each SMPS , you can select one of them according to your requirements .
For example , a boost converter , can't decrease voltage , it just can increase voltage . or a buck boost converter will give you a minus voltage ( your input is positive but out put is negative ) . so i think now you get my meaning .
WE want buck , because it's out put is positive instead of positive input and it can decrease the voltage .
Best Wishes
Goldsmith

 

[TripACT]

No reasonable answer possible without knowing the input voltage range.

voltage ranges from 1v to 41.5v dc

 

[checkmate]

Buck is a step down.
Boost is a step up.
The buck-boost is just a combination of the 2, with more complicated control control and more power FETs.
In other words, it depends on what output voltage you want and what input voltages you have available.

 

[goldsmith]

more power FETs.

Dear checkmate
Hi
Why more power fets ? each buck boost , just has one power mosfet . ( an inductor and a diode and a capacitor and a switch ) isn't it ?
Best regards
Goldsmith

 

[checkmate]

Dear checkmate
Hi
Why more power fets ? each buck boost , just has one power mosfet . ( an inductor and a diode and a capacitor and a switch ) isn't it ?
Best regards
Goldsmith

**broken link removed**
The buck boost is just the combination of the buck and the boost, sharing the same inductor. It needs at least 2 FETs.

 

[goldsmith]

Ok , then you see below , please :

It is derived from professor Marty brown's book .
Respectfully
Goldsmith

 

[FvM]

each buck boost , just has one power mosfet . ( an inductor and a diode and a capacitor and a switch )

If we don't restrict the topology, an universal would be described to have four switches, at least two of it active (transistor) switches. 1 to 42 V input voltage is possible but involving some overhead according to the high maximum input current for 10 W output.

P.S.: goldsmith, you are referring to the special case of inverting buck boost. Not exactly what was asked for.

 

[checkmate]

Ok , then you see below , please :
View attachment 75313
It is derived from professor Marty brown's book .
Respectfully
Goldsmith

Why recommend a negative switcher when the TS is looking for a 10V output?

 

[goldsmith]

Humm . 10 volts ?? what do you mean by that ?

 

[BradtheRad]

The buck type steps down only.

The boost type steps up. The supply V is automatically added to whatever comes through the coil.

The buck-boost is versatile in that you can get less than or greater than the incoming supply. It can invert the polarity of the incoming supply.

There is a fellow promoting a boost-buck converter. He claims it's better than the other 3 types. I believe his website is boostbuck.com.

 

[TripACT]

And yet buck is being used vastly. See on pc motherboards....why won't they use buckboost or boost? They all can provide the cause...arnt they?

 

[FvM]

And yet buck is being used vastly. See on pc motherboards....why won't they use buckboost or boost? They all can provide the cause...arnt they?

In cases, where a basic buck (Vin > Vout) or boost (Vin < Vout) converter can be used, it will be used, because it means less area, cost and losses.

Inverting buck-boost has the advantage of only needing two switches (1 transistor, 1 diode), but 100% of energy has to be stored in the inductor, requiring a larger inductor compared to buck or boost, where voltage difference defines the stored energy. And it's only usable where inversion is wanted/acceptable.

 

[crutschow]

Buck is more often seen because the buck is usually more efficient than a boost circuit, and the input DC voltage is typically higher than the desired circuit voltage. This is because a higher input DC voltage means the input current is smaller for a given power output, thus allowing smaller diodes, smaller wire, etc. for the input power supply.