Need your help for designing Buck boost converter

[krunalbondre19]

I am in the process of designing a buck-boost converter with the following specifications:

• Input Source: Solar panel rated at 40W peak power (P_p) and 12V.
• Output Voltage: 13V.
• Switching Component: STP75NF75 MOSFET.

I need guidance on determining the appropriate values for the inductor and capacitor for this buck-boost converter. Specifically, I am seeking assistance with:

1. Inductor Value:
   • What is the procedure to calculate the optimal inductance to ensure stable operation and acceptable ripple current?
2. Capacitor Value:
   • How can I determine the suitable capacitance to achieve minimal output voltage ripple?

 

[BradtheRad]

In round numbers your system's throughput is upwards of 3 Amperes (30W / 12V). 4A or 5A is a suitable saturation rating for your inductor. A reasonable value to obtain (or fabricate) is between 300 uH and 1mH.

The buck-boost switches supply On current through it until it ramps up high enough (several Amperes). Then it switches Off current. The inductor goes into propulsive operation, sending current to the output stage. Coil current declines until its time to turn on supply current and start the cycle again.

The source being a PV panel, you'd like to get maximum utilization from it. To achieve this consider building an input filter that pulls constant optimum smooth current from the panel. Another method is to build two or more interleaved converters.

The output capacitor is selected depending on how heavy a load it must carry during each idle cycle.

A voltage regulation circuit changes frequency and/or duty cycle.

--- Updated Sep 19, 2024 ---

Do you have a schematic that you wish to bring to the table? Have you worked previously with switched-coil converters?

 

[FvM]

First step is to choose a buck-boost topology (e.g. inverting, Cuk, four-switch). Not clear at first sight if you are assuming one. Specifying positive in- and output voltage suggests it's not inverting topology.

 

[KlausST]

Hi,

I´d go to a switch mode IC manufacturer site and use their selection tool.
Usually you input all your application specifications and it gives you a list of suitable ICs.
Each IC comes with a datasheet .. and usually with application notes and/or design notes.
They provide all informations you need to know.
Many manufacturers additionally provide online deesign tools to show the schematic and calcualte the necessary part values.

It´s all online, all free, so use it.


Klaus