Buck Boost converter

[Ahmmed Razu]

I am going to start a DC-DC converter project (buck boost chopper) where the input voltage is 12V and output specifications 40V,3A. I do not understand how to build the chopper like how to calculate the inductance, Capacitance and switching frequency, on time, off time.

Please Suggest me.

 

[shaiko]

A good point of start will be writing the electrical equations - begin there...

 

[BradtheRad]

Helpful info with theory of buck-boost operation:



Calculator for component values, and frequency:



Click the thread below and look for my posts about switched-coil converters. They contain links to interactive animated simulations (using Falstad's simulator). These will run on your computer. You can change values by right-clicking, and selecting Edit.

https://www.edaboard.com/threads/268178/

The control circuit (with chopper function) can be made from a couple of op amps, although you would get better performance by using a commercial IC which is designed for the purpose.

 

[Alan69]

Go to ebay. Search lm2577, sort by price, and start looking around. Also do the same for lm2596. These $2 and $3 modules are cheaper than what you can get the parts for. They aren't generally quite 3A at 40V, but to give you an idea on similar. In fact search both 'step up' and then 'boost' with 'module' and 'converter' for both. In fact again, search "DC-DC Converter Boost Power Supply Module 10-32V Step up to 35-60V 120W" and you'll find one for $9. 150W when you're wanting 120W out, so it's pretty close, I'd see if you can find a 200 or 250 watt unit.
12V sounds like like maybe you're working with auto batteries etc, searching around for auto battery type step up converters may also find something..
You probably can't get the parts for less..