DC/DC Buck/Boost Converter

Hello everyone, I am new here and first post .

So one of my classes this semester wants me to design and build a DC/DC Buck/Boost converter. Personally, I have no idea where to start with this. If someone could provide me with some sort of roadmap to follow, I would very much appreciate it. I am planning to use a MOSFET to act as my switches and a MOSFET driver as well. A question for that, where can I find whether a certain driver would work with the MOSFET I plan to use? I am planning to use an IRFZ44N by the way. Any and all help would be very much appreciated.

Thank you

Is it just one converter, a buck-boost? The kind that produces a negative voltage from a positive supply?
I imagine the purpose is to explore the action as you turn current on and off through an inductor. Observe the output as you change frequency and duty cycle.
It's okay to use a mosfet for switching current on & off, but inductors can produce high-voltage spikes that are liable to destroy components. Have you worked with other types of switched-coil converters?

Hi,

When I design a new circuit then it starts with electrical specifications .... and surely not with a Mosfet.

* specifications (mostly values with units, but also the goals for the design: small in size, low ripple, high efficiency, low cost...)
* look at different manufacturers (or distributors) for integrated solutions.
* look for price and availability (maybe look for alternative ICs)
* read through datasheets
* read through application notes
* maybe read through design examples
* drawing schematic / calculate part values
* designing the PCB layout

But a school project may have a different approch than a commercial design.
* maybe it's part of the "challenge" to use the said Mosfet
* maybe not to use integrated solutions

...we don't know this. Thus it's likely that my list is not suitable for you.

Klaus

Hi,

I'm kind of in a similar place to you re SMPS.

I'd second what Klaus says, and you'll find this as your semester goes on, assuming you have access to teaching material about the circuit in question: the calculated and therefore expected circuit values of voltages, currents, power dissipation, frequency of operation, and other stuff really, all define which components you will be able to use.

After that have fun browsing product parametric search tables on manufacturer's or vendor's websites to find suitable/acceptable re power/speed/price/etc./ + occasional issue of min number per purchase and wondering if you'll ever need another 24 of some obscure component in your life.

Studying how circuit functions and building blocks involved (if not provided, app notes by manufacturers and design notes can be very helpful, even driver datasheets)
Number crunching
COmpensation
Selecting parts (BOM, I think) based on poring over datasheets and perhaps comparing a few
PCB layout
Prototype
End of term report on project which goes towards final grade, no doubt

Other members will know the basic steps to follow you're asking for better than I do.

The best place to get information is in manufacturer data sheets and application notes.

In this case there are tons of off-the-shelf controllers that are designed to support buck-boost topology and a google search will find them.

Even if you don't use the controller IC you can use its data sheet as a good starting point for understanding the application, seeing circuit schematics etc.

Also get yourself a simulation tool, I recommend either LTSpice or PSIM (the free version is good enough for simple stuff). With LTSpice google for a Linear brand buck-boost controller then find it in LTSpice and open up its application circuit. In PSIM I think there will be an example.

here is a buck and a boost in the free ltspice simulator.
Just open them and click run. convert them to .asc first.

also i enclose a buckboost, and one with a gnd'd output

- - - Updated - - -

Naviit.
Please tell, did your teacher tell you that there are things called pwm controllers, that do most of the nitty gritty engineering of an smps for you.
But otherwise, if running those sims you sill dont understand, then please tell me why.

You have to know.
Lenz's law
kirchoffs law.

Start with vin =
vout =

then find duty

decide whether you want ccm or dcm....obviously a buck in ccm means that the average inductor current is the average output current.
a boost in ccm means the average inductor current is the average input current.
Just work it through.
for CCM buck D = (VOUT+VD)/VIN
for ccm boost, (VOUT+VD)/VIN = 1/(1-D)

ton = D.T.

Also, learn the trapezoid equations....for calculating rms of a trapezoid, bacause bucks and boosts are only trapezoid current shapes...even in dcm boost...its two back to back triangles.
And a triangle is a trapezoid with one side zero.
If its dcm boost, then the rms inductor current is the root of the sum of the squares of the individual triangle rms currents....so to speak.

- - - Updated - - -

attached is a flyback smps design file...it shows the type of calculations you do...but best do your own and think it through.....run the sim and it becomes obvious

Anyway, what is the power level?
I have a course in Switch Mode power supplies.....i will send it to you if you PM me an email addresss i will send it to you.
But i like to teach people....do not worry..my course is free.
Give me your spec and i will work you through it.
Or you just tell me where you are getting stuck.
The problem will come if you dont know Lenz's law...V/L = di/dt

Also, if you dont understand that a constant dc current into a capacitor will keep raising the capacitors voltage...then you are going to struggle...but i guess you know that stuff.
Tell me if my learner sims were good enough to get you started.
Remember the assumption you "gernerally" take...that all the AC content of the output current goes through your output capacitance.

Remember that for a buck, if you know A = irms(inductor) and B= i(av)output...then youre capacitor ripple current ACRMS is sqrt(A^2 - B^2)

..dont assume that your tutors want to help you.......universities are only generally interested in the few brill guys that they liek enough to bring into their research...the rest of you can go to "you know where".
Attached is my guide to doing n electronics degree in UK.........the key point it.........you must know what you want to do your final project in...and MUST GET HANDS ON HARDWARE EXPERIENCE IN THE PROJECT IF YOU WANT TO GET A JOB IN THAT AREA!..as the attached reveals

sorry i did not post it..please find

- - - Updated - - -

A question for that, where can I find whether a certain driver would work with the MOSFET I plan to use?

Click to expand...

you need to check there is enough drive current capability (low enough output impedance) to turn your fet on fast enough, and in the consideration of the miller charge too.
To be honest, almost any offtheshelf fet driver will do if its just a low power smps.

But here is best source on fet driveing...

Design And Application Guide
For High Speed MOSFET Gate Drive Circuits
by Laszlo Balogh

www.radio-sensors.se/download/gate-driver2.pdf

Hi,
I think if you going to design buck/boost or any sort of power converter.
First thing you should consider is the input voltage-input current range , output power and current rating because the values of the passive components you will be using will depend on the input and output ratings.
Second thing ,after making sure all passive components you selected are enough for the job ,then you have to make sure to select switches(i.e, mosfets, transistor,diode) that can work efficiently depending on the frequency you will be using for switching and maximum voltage that will be appearing across them.
Third thing, select a proper feedback network for the converter to be able to perform proper voltage regulation. some ideas are either use a micro-controller or error amplifiers to maintain regulation.
It would be good if you consider using dedicated driver ic's for driving switches and you can find them on the website of any IC supplier.

I hope this might help you-Naviit

"This is my first post , so if there's anything wrong in post kindly correct me.I appreciate that."
Hasgle