# Designing a Buck-Boost Converter Circuit

#### darkboii44

Joined Nov 7, 2017
5
Good evening everyone.

I'm new to this forum, would greatly appreciate any help! I'm currently doing an undergraduate degree program in electrical engineering.
I've got a project that requires me to build a buck-boost converter linking certain PV panels to an Arduino UNO Rev 3.

My project requires me to use V and I obtained from the PV panels to power the Arduino. As of now I have no values of the V and I requirements of my panels and Arduino.

May I ask, what formulas or values do I require to calculate the inductances and capacitances that I need in my circuit?

Thank you very much!

#### Øivind Bakke

Joined Aug 22, 2017
12
Hello,

if you can assume that your PV panels deliver a constant voltage (in order to avoid controlling), you have have two parameters to look into:
1. What is your maximal switching frequency
2. What is your maximal input voltage tolerance in the Arduino?

; with U_d2 being the output of the buck-boost-converter(input of the Arduino); Ts=Switching period; D=Duty cycle; R=output resistance;
; U_d1 is the input of the buck-boost-converter;
;

#### darkboii44

Joined Nov 7, 2017
5
Hello,

if you can assume that your PV panels deliver a constant voltage (in order to avoid controlling), you have have two parameters to look into:
1. What is your maximal switching frequency
2. What is your maximal input voltage tolerance in the Arduino?

View attachment 138888; with U_d2 being the output of the buck-boost-converter(input of the Arduino); Ts=Switching period; D=Duty cycle; R=output resistance;
View attachment 138889; U_d1 is the input of the buck-boost-converter;
View attachment 138890;
Good evening!

Thank you so much for the response!

Regarding the parameters, with what considerations do I decide
a) what value should be used for the switching frequency?
b) how do I know how long each period will be?
c) how do I calculate the values of Dbuck and Dboost?

I was surprised to have found so many designs for B-B-Converters (1 / 2 / 4 switches). I'm not really sure what is what now.

Apologies for having so many questions. I have yet to study on buck boost converters and was slapped with a project that requires me to build one from scratch. Have tried researching through IEEE and other websites but it falls into either one of these categories:
1) The circuits designed are based upon current IC chips where some values are given in the spec sheet,
2) The terminologies and symbols used are too advanced and I do not have sufficient time to dwell too deeply into them.

Once again, thank you so much for your response! I really appreciate it.

Cheers and have a good day ahead!

#### Øivind Bakke

Joined Aug 22, 2017
12
Easiest way to construct a buck-boost-converter is with only one switch:
;
You have to set the switching frequency depending on the technical data for the chosen switch. If nothing is specified/chosen, I'd choose a MOSFET with high switching frequency in order to decrease the change of voltage per period, but you can choose what ever you want. Duty cycle of Buck-Boost is one value, whereas 0.5 is U_in=U_out, and the value of this depends on what your input voltage is and what your desired output voltage is, so this have to be defined first. Your period is inverse to frequency (T=1/f). You have to set a few parameters, like switching frequency and input voltage in order to solve the rest. If every parameter is to be chosen by you, pick out reasonable values for each element and you only have to do small amount of computation to have a working Boost-Buck-Converter.

Cheers

#### darkboii44

Joined Nov 7, 2017
5
Easiest way to construct a buck-boost-converter is with only one switch:
View attachment 138907;
You have to set the switching frequency depending on the technical data for the chosen switch. If nothing is specified/chosen, I'd choose a MOSFET with high switching frequency in order to decrease the change of voltage per period, but you can choose what ever you want. Duty cycle of Buck-Boost is one value, whereas 0.5 is U_in=U_out, and the value of this depends on what your input voltage is and what your desired output voltage is, so this have to be defined first. Your period is inverse to frequency (T=1/f). You have to set a few parameters, like switching frequency and input voltage in order to solve the rest. If every parameter is to be chosen by you, pick out reasonable values for each element and you only have to do small amount of computation to have a working Boost-Buck-Converter.

Cheers
Thank you so much for the information! This has really helped me a lot.