design buck converter working with solar photovoltaic

[matouk]

Hi all
Please any can give me a hand , I implemented buck converter to use it as power matching between solar photovoltaic ( open circuit voltage is 20 V and operating current is 0.26 A) to electrolyser (operating voltage is 3V and operating current is 3A) . the switching pulses of the buck converter switch is generated manually by other IC circuit so I change the duty cycle manualy . The problem I have is when I adjust the duty cycle at defferint value from 0 to 1 the converter out put voltage is fixed by the load (at electrolyser operating voltage around 3V) but the current doesnot exceed the 0.25A , the converter has effeciency between 65 % to 85%.
if there is further Q I will make it clear.
Thank you very much for your help.

 

[gs611]

Hello, I actually just designed a small buck converter myself (12v -> 5v). The design was pretty simple, 555 timer and P-Channel/N-Channel mosfets to a homemade torroid. I calculated my efficiency to be about the same as yours.

I don't understand what your problem. What do you mean by fixed by the load? Do you mean that the load requires 3 volts to operate?

Daycounter Inc has a nice SMPS converter to get started, check out https://www.daycounter.com/LabBook/BuckConverter/Buck-Converter-Equations.phtml

 

[ark5230]

Hi all
( open circuit voltage is 20 V and operating current is 0.26 A)
to electrolyser
(operating voltage is 3V and operating current is 3A)

The problem I have is when I adjust the duty cycle at defferint value from 0 to 1 the converter out put voltage is fixed by the load (at electrolyser operating voltage around 3V)
but the current doesnot exceed the 0.25A .

The problem is with the maximum current available from the panel you are using, it can provide at most 0.26A and is providing 0.25A, which is not strange. If the current capcity is increased by 12 times (using 12 such panels in parallel), you are done.

 

[Ingenerd]

Did you use a mosfet for your switch? If so did you use a n-channel or p-channel. I am working on a similar project and I want to use a p-channel. The thing is then that the Voc of the pv panel will exceed the maximum Vgs of the mosfet.

 

[dinaa89]

Did you use a mosfet for your switch? If so did you use a n-channel or p-channel. I am working on a similar project and I want to use a p-channel. The thing is then that the Voc of the pv panel will exceed the maximum Vgs of the mosfet.

for a buck converter you must use a n-channel MOSFET so that your voltage gets reduced....however at sometimes Vgs becomes low, so that your MOSFET can not be turned on!