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non-inverting buck boost converter

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Ahmed Kh

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About buck boost converter in one circuit

Hello
please how can i design the buck-boost circuit
i have been designed as this circuit but the value of (l.r.c) hard to get it

i just want the equation if u have
my project about the variable input from(6-20)v and i have to get 12v output
my regards
Code:
 

Re: About buck boost converter in one circuit

Review Linear LTC3780 datasheet to get an idea about an effective buck-boost topology. Another possible topology is a SEPIC converter.
 

Re: About buck boost converter in one circuit

In addition to what FvM mentions, the Zeta converter, also called inverse SEPIC, is another possibility.

Google SEPIC and Zeta converters; there are lots and lots of good app notes which thoroughly explain their operation.
 

Re: About buck boost converter in one circuit

To let you see how the equations perform...

Click this link to a user-interactive animated simulation of a buck-boost converter.



(Click 'Allow' to load the java applet.)

You can (a) turn power on and off through the coil manually, or (b) observe clock pulses driving the action.

Click the switch to start the cycle. Let up the switch to go on to the second half of the cycle. Soon you'll set up a tempo which outputs the voltage you wish.

Change values at will. Right-click on a component, and select Edit.
 

Re: About buck boost converter in one circuit

FvM said:
Review Linear LTC3780 datasheet to get an idea about an effective buck-boost topology. Another possible topology is a SEPIC converter.
Click to expand...



thanks for your replay but i have do it by my self and i have to used pic micro controller 16f877a to get 2 pwm
sp i have to do that calculation
my regards
 

Re: About buck boost converter in one circuit

Ahmed Kh said:
thanks for your replay but i have do it by my self and i have to used pic micro controller 16f877a to get 2 pwm
sp i have to do that calculation
my regards
Click to expand...

What we are attempting to tell you, is that you must read the available literature to completely understand the mathematical relationships between duty cycle, input voltage, output voltage, switching frequency, load current and component values (most importantly, the inductor).

Only then and not before, you will be able to write some code or select a ready made controller.
 

Re: About buck boost converter in one circuit

as my 2.JPGthanks
actually i read about the calculation but some of equation can not get

- - - Updated - - -

**broken link removed**


from this file i have been used the design but can not get the duty cycle
please need help
my regards
 

Attachments

  • as my.JPG
    as my.JPG
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Re: About buck boost converter in one circuit

The linked paper gives the design equations, but doesn't explain the buck-boost operation principle in detail neither derives the equations. I think your doubts can be subsummed as "I don't know how a buck-boost converter actually works".

The circuit can be reduced either to a basic buck (by closing SW2 continuously) or boost (by closing SW1) converter. So the first step is to understand the operation principles and design equations of both basic converters from text book literature.
 

Re: About buck boost converter in one circuit

FvM said:
The linked paper gives the design equations, but doesn't explain the buck-boost operation principle in detail neither derives the equations. I think your doubts can be subsummed as "I don't know how a buck-boost converter actually works".

The circuit can be reduced either to a basic buck (by closing SW2 continuously) or boost (by closing SW1) converter. So the first step is to understand the operation principles and design equations of both basic converters from text book literature.
Click to expand...


thanks dear
actually i understand how the circuit working , but my problem that calculation of (R,L,C) my simulation circuit.JPG

and have done some equation for (R,L,C) but its not correct because when i put load around 1A
the output voltage will be decrease and i designed the circuit at 2A so that's mean my calculation is not right
my best regards
 

Re: About buck boost converter in one circuit

Ahmed Kh said:
thanks dear
actually i understand how the circuit working , but my problem that calculation of (R,L,C) View attachment 110824

and have done some equation for (R,L,C) but its not correct because when i put load around 1A
the output voltage will be decrease and i designed the circuit at 2A so that's mean my calculation is not right
my best regards
Click to expand...


Hello
i would like to know some information about boost converter when i use full load the out put voltage will be decrease too much and i could not give the switch more pulse
my best regards
 

Re: About buck boost converter in one circuit

Did you use the design equations from the TI application note?
 

Re: About buck boost converter in one circuit

Ahmed Kh said:
i could not give the switch more pulse
Click to expand...

In a boost converter, increasing duty cycle does not necessarily increase output voltage.

You must adjust frequency too. Current must be ON for a sufficiently long time, so that it builds in the inductor.

Then your OFF time must be sufficiently long, while the inductor discharges through the output section.

Also, have you reduced parasitic resistance to a minimum amount? Is your mosfet turning on sufficiently?

i designed the circuit at 2A so that's mean my calculation is not right
Click to expand...

One equation is not enough to describe the operation of a switched-coil converter.

You'll need more than 2A going through it. More like 3 or 4A.

See if your waveforms are similar to those in my simplified simulation. I used your component values, and I assumed a 12V power supply.

4770545300_1414859247.png
 

Re: About buck boost converter in one circuit

To boost voltage, the input supply, storage inductor & switch must supply more input current than the output load demands to satisfy conservation of energy law. .

Therefore, do not exceed the capability of each part. examine Imax and ESR or effective series resistance of each component; supply, switch, inductor, & load.

Normally a boost regulator changes frequency then duty cycle to regulate over a broad range of loads, such that a light loads, it is low pulse rate and pulse width and heavy loads , the opposite.

Imax must not cause the inductor to saturate, otherwise inductance drops quickly, nor have excessive I*R drop from the supply, Rs of coil, RdsOn of switch etc.
 

Re: Boost Converter Design and Output Current Problem

goldsmith said:
Dear recon
Hi
What do you mean by that ?!
And do you know the formula of out put voltage of boost converter ? and how you designed the L and c and what is your frequency ?
I have some doubt about the values . and about the duty cycle .
Best Wishes
Goldsmith
Click to expand...

hello i have problem with my circuit
my circuit is buck-boost converter when the input is low voltage and the load at full the output voltage also is low and if i increase the load resister the output voltage will be increase
i need as output voltage constant even the load is change
my best regards
 

Re: About buck boost converter in one circuit

I'm reviewing your earlier specs. My post #12 does not fit.

Therefore I revised my boost converter simulation. It accepts 6V and steps it up to 12V at 1A.

 

Re: About buck boost converter in one circuit

thanks for replay
i have been used one circuit foe buck-boost converter
i assumed the output voltage 12V and the load resister is 6 ohm mean the current is 2 A
the big problem when i used 6 ohm for load the output is reused too much and if i make the R around 20ohm the voltage will be increase also too much
i want the output voltage as constant even the the load less than 2 A

MY BEST REGARDS
 

Hi...

I am designing a non-inverting buck boost converter which needs to use two mosfet switches with the varying of duty cycle to produce the output 12V with an input voltage from 6-20 and current 2A
Should I be choosing N-Mos or P-Mos as my two switches for my design?
What are the parameters I should look into that matter for my design?
i tried some type of mosfet its working well at buck ,
but at boost converter does not because the output voltage is change with load
i need the output is constant t 12 even the load is less than 2A

Thanks..
 

chuckey said:
Show us your schematic. Have you got any feedback to stabilise the output?, in boost mode the output impedance is much higher (as you have found!!)
Frank
Click to expand...
right now i have not used feedback i just want to reach the 6 v to 12 at 2 A

Capture.JPG
thanks for your replay
 

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