How can i modify XL4016 buck converter for constant volt and current settings

Thread Starter

AttacK

Joined Aug 17, 2020
10
First of all I've just joined you.
Can i ask a question i am making a psu with XL4016 and 24 volt 6.5A SMPS. I measure value of constant volt: for 12 volt i should set pot 3,12 Kohm for 24 volt --> 6,65 Kohm. I shared my schematic. I want to use a two 270 degree normal pot(because they are inexpensive and they can set quickly) one of the pot is approximately 3,25 ohm(I combined 5k pot with 10k resistor.) and the other pot(500 ohm) for fine tuning. In schematic when the switch on rigth position i can adjust 1.2 volt to 12,5 volt. Left position of switch i adjust 12 volt to 24 volt. My question is when i change position of switch on middle position pot circuit will be open. It will be a problem? (Can i use pull up-pull down resistors, if it yes, where i should use it?) I didn't try cut switch wire of number 2. I am afraid of broke my module. Could you help me. I hope i can explain myself. Thank in advance XL4016.png
 

AlbertHall

Joined Jun 4, 2014
10,388
Connect together pins 1 & 2 of the switch. This way the 3k resistor is in circuit and one position of the switch shorts out that resistor, so the converter will always see a valid voltage set resistance.
 

Thread Starter

AttacK

Joined Aug 17, 2020
10
Thank you i am so happy, i couldn't find this solution, its shameful. My second question about set constant current pot. I conncet two pots for set volt because module wants 2 pins, but current pot need 3 pins. How can i use fine tuning pot? Can i use 2 pots like volt pots and how can i connect them?
 

Thread Starter

AttacK

Joined Aug 17, 2020
10
Firstly i don't have it and in my country prices same price with module price. If i can use without multi turn pot like volt adj. i prefer normal pot. Economic issues
 

AlbertHall

Joined Jun 4, 2014
10,388
Without knowing just how the pot connects to the circuit it is difficult to say but a circuit like that below may do the job. You may have to fiddle with the values to suit what you want it to do.
1597673275397.png
 

Thread Starter

AttacK

Joined Aug 17, 2020
10
FIE455SJGGTHK70.png
If you can understand this is a module schematic. I just want to set current with two pots like one pot. I calculated your schematic R eq = 9,33 Kohm. Its good for me. But i can't calculate left pin with middle pin and right pin with middle pin resistance.
If it run like this? --> FİRSTpin-3Kohm-SECONDpin-6,33Kohm-THİRDpin It will be perfect for me. Wait your answer. I will buy something. Thank you for everything.
 

AlbertHall

Joined Jun 4, 2014
10,388
Imagine both pots set in the centre position. Their wipers will be at half voltage. Then if you adjust the fine pot it will, at the limits of its motion, connect a 47k from the wiper of the coarse pot to one of its ends. It will make about a 10% difference to current set point.
 

Thread Starter

AttacK

Joined Aug 17, 2020
10
I understand it and i tried to calculate 3-4 different pot positons.
Generally Resistance of FIRST||MIDDLE + MIDDLE||LAST pin of pots = 9 - 9,33 etc.
I think its accaptable differences. If you think same with me. Thank you for your time. I almost got a PSU with your experiences and your helps.
When i complete my PSU, i will attach photos and schematic for everyone. THANK YOU FOR EVERYTHING! :D
 

Thread Starter

AttacK

Joined Aug 17, 2020
10
Hi, mr Albert i tried your schematic but it doesn't work. Its simple i think i didnt do any mistake. Sometimes i measure (top and bottom pins) 9-8 Kohms sometimes 2-4 Kohms. What can i do?
 

AlbertHall

Joined Jun 4, 2014
10,388
By 'sometimes' do you mean by adjusting the pots you get different resistances, or do you mean without adjusting the pots you sometimes get different resistances?
 

Thread Starter

AttacK

Joined Aug 17, 2020
10
Normally, the same value is always measured on pins 1 and 3 of the pot. The value between 1 and 2 changes. The value between 2 and 3 changes. 1.no pin resistor 2 no pin + 2no pin resistor 3 no pin always remains constant 1 I measured between pins 1 and 3 in your scheme, I can't read a same constant value.
 

AlbertHall

Joined Jun 4, 2014
10,388
Normally, the same value is always measured on pins 1 and 3 of the pot. The value between 1 and 2 changes. The value between 2 and 3 changes.
This sounds exactly as it should be.

1.no pin resistor 2 no pin + 2no pin resistor 3 no pin always remains constant 1 I measured between pins 1 and 3 in your scheme, I can't read a same constant value.
I don't understand what this means, but the resistance between pin 2 and pins 1 and 3 should vary when you adjust the pots.
 
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