I was following the circuitry by great Scott for the DIY buck converter here: https://www.youtube.com/watch?v=m8rK9gU30v4 . Created a converter that gives 0-23V on 24V supply.

After this i wanted to add different current limits to this buck converter such as 1/2/3/4/5 Amps for charging different li-ion battery pack. For that i am going to follow this"Traditional method of implementing CC/CV"here:


also have seen this video on adding a current limit to a buck boost converter: https://www.youtube.com/watch?v=8uoo5pAeWZI

with the shunt resistor and all.

Thing is I cannot even understand how is the Traditional method of implementing CC/CV working here and how to approach this software wise.

A more in depth explanation could be quite helpful and any type of suggestions regarding any other way would be highly appreciated.



Current limiting is based on the fact that I = U/R And the easiest way to reduce I (if it exceeds some limit) is to decrease U (voltage) which is what Great Scott is doing in his hacked video and explains it very well.

It is also important to understand how op-amps works, since they are doing all the logic here.

Typical simple DC-DC converter IC is an analog logic device. It knows nothing about what voltage on the exit now, what voltage you want to get or what is the Current and Current limit. All it knows – is FB pin above or below Int. Reference voltage (e.g. 1.25 V) at current tick. If it above reference, e.g. 1.33 V with voltage divider 1:10, which means 13.3 V at output, it reduces duty cycle a little. Next tick it's 1.31 V, reducing duty cycle again, until FB is below 1.25 V (=12.5 V) in which case it will increase duty cycle and than decrease it...dancing around 1.25 V reference.

As did in the video, we just put 3.3V at FB pin (with additional ext. op-amp) when voltage is above some limit, so converter will start to reduce the duty cycle and output voltage each tick, until the current will drop below set limit and our op-amp will dance around this current limit now. This called CC (Constant Current) mode, instead of normal CV (Constant Voltage) mode.

Btw, to indicate CC mode you can simply use current comparator's (op-amp) 3.3V output with a capacitor, resistor and LED.

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    \$\begingroup\$ We seem to have cross-edited. "op-amp" is a contraction of "operational-amplifier" so it doesn't get capitalised. \$\endgroup\$ – Transistor Jul 5 '19 at 12:54

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