# DC-DC buck output voltage

I am designing a DC-DC step-down converter (asynchronous) and I would like to achieve a Li-Po charging with it (18 - 22 V input voltage). My goal is the CC/CV charging but to do this, I need constant voltage (4.2 V) on the output. I have simulated the circuit in MATLAB simulink (with battery model) but I can only measure the battery voltage. I am monitoring the input current/voltage and the output current/voltage too. I am so confused with this now, I have read many topics, articles. Can I achieve CC/CV with asynchronous buck converter?

EDIT:

I have found a CC/CV design for buck: https://e2e.ti.com/blogs_/b/powerhouse/archive/2017/11/24/how-to-design-a-simple-constant-current-constant-voltage-buck-converter

Can I achieve it with asynchronous buck too?

EDIT2:

simulate this circuit – Schematic created using CircuitLab

• Of course! Why would you not? The CC/CV is on a macroscopic scale compared to whether the rectification is synchronous or not. – winny Oct 29 '18 at 11:53
• Thank you! For example if the battery's voltage at 3.8 V, the output of the buck is 3.8 V too? So if I adjust the duty cycle the current changes only (I experienced this while simulating)? – Andrew S. Oct 29 '18 at 12:01
• That's once again a macroscopic effect you are seeing. Please show how you have or are planning to implement your CC/CV control and feedback. In general, for battery chargers you will see the difference apart form efficiency and complexity when it comes to reverse battery voltage protection and operation very close to zero volt. – winny Oct 29 '18 at 13:50
• I have edited my question. This is my current "raw" schematic. – Andrew S. Oct 29 '18 at 14:47
• You could technically cheat on both current and voltage on the input and do MPPT anyway but it should be easier to implement with at least input voltage measurement. Measure your efficiency or model an equivalent resistance and you’ve got UinIin=nUoutIout or UinIin=Iout(1-D*Rdson)*Vout. – winny Oct 29 '18 at 16:39