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Does anybody know the schematics of these common LM2596 buck converter with current adjustment and buck-boost converters from ebay?

I know I can easily buy it cheap but I like making my own modules for education purposes and also find it fun to make it myself. I basically aim to replicate these modules, learn how they work and see if I can improve them in anyway if possible.

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Link: Buck converter

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Link: Buck-boost converter

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Link: Boost-buck converter

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    \$\begingroup\$ The schematic is the easy part, but a working PCB layout also needs to optimize the current paths for minimal loop size. \$\endgroup\$ – Simon Richter Sep 2 '16 at 15:44
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    \$\begingroup\$ Better than schematic, the datasheet has all the info for you to find the components functions and values by yourself. If its for "educational purposes" as you state, then start from the datasheet, not the middle of the way. \$\endgroup\$ – Wesley Lee Sep 2 '16 at 15:44
  • \$\begingroup\$ The schematics of those charger devices can be found online with google if you search for LM2596 battery charger schematic. \$\endgroup\$ – JRE Sep 2 '16 at 15:48
  • \$\begingroup\$ I have looked and read through the datasheets already, what I'm not really sure is the current limiting circuit used and how did they hook up the buck and boost together? \$\endgroup\$ – Max Sep 2 '16 at 15:51
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    \$\begingroup\$ Well, if you really want to have fun, you could try reverse-engineering them. They seem to be two layer boards. Using a multimeter with good continuity tester function and a loupe you should be able to do it. One problem could be decoding the markings on the tiniest of those SMD parts, but there are sites that can help you with that. Once you have a draft schematic, you could also try to measure resistors and caps (the schematic can tell you if the measurement can be significant or you really have to desolder them to get their actual value). \$\endgroup\$ – Lorenzo Donati -- Codidact.org Sep 2 '16 at 19:10
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The basic circuit comes from National (now TI) datasheet. The application examples show Buck Boost. The CC part relies on LM358 dual OP AMP and LM78L05 voltage regulator. Normally the voltage control loop is in charge. When load current exceeds a value preset by an adjustable divider from LM78L05 5V, the current limiting loop takes over (the voltage sags as required to contain the current. It is achieved by pulling the FB pin above its nominal 1.24V (making LM2577 see excessive voltage i.e. lower the duty cycle)

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Buck Converter: enter image description here

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http://www.ti.com/lit/ds/symlink/lm2596.pdf

Boost Converter: enter image description here

http://www.ti.com/lit/ds/symlink/lm2577.pdf

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  • \$\begingroup\$ By comparing the components on the PCBs in the question, and the schematics above, we can see that they are not the schematics for those PCBs. Therefore this does not answer the specific question which was asked. For example, on the Buck Regulator (top photo) in the question, that PCB has a U2 device and other discrete components, which are not shown in the schematic you included. Your schematics seem to be generic schematics copied from the datasheets, but that does not answer the question which was asked. \$\endgroup\$ – SamGibson Oct 26 '17 at 13:33

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