Digital Potentiometer and Power Supply

Hi, and thanks for helping me :slight_smile:

I purchased Tusotek Auto DC-DC Constant Current Boost Buck Converter Voltage Regulator 6-35V to 1-35. I am trying to find digitally control the boost buck converter by replacing its 100K potentiometer with a 100K MCP41100 digital potentiometer. I tried using the digital potentiometer with the DC-DC booster and it worked, but the booster does not go as high as with the original mechanical potentiometer. Would you know why I the digital potentiometer is no working as intended? What are the factors I must consider if I want to control boost buck converters with a digital potentiometer?
Specs of the mechanical potentiometer can be found in the following website (scroll down):
http://www.aliexpress.com/item/Trimpot-Trimmer-Potentiometer-3296-W-104-100K-VR-3296W-100K-ohm-Variable-Resistors-100pcs/1596795967.html

Arduino code:

#include <SPI.h>
byte address = 0x11;
int CS= 10;
int i=0;
void setup()
{
pinMode (CS, OUTPUT);
Serial.begin(9600);
SPI.begin();
}

void loop()
{

if (Serial.available()>0)
{
int x = Serial.parseInt();
digitalPotWrite(x);
Serial.println(x);}
}

int digitalPotWrite(int value)
{
digitalWrite(CS, LOW);
SPI.transfer(address);
SPI.transfer(value);
digitalWrite(CS, HIGH);
}

Capture.PNG

If you read the "how to use the forum" stickies you will see how to format and post code and to not cross post.

Simple, because you missed a part in teh datasheet:

Absolute Maximum Ratings
All inputs and outputs w.r.t. VSS............... -0.6V to VDD +1.0V

Aka, if you power it from 5V the max voltage on a pin is 6V. And when you connect it as a voltage divider from the output you try to go above that.

You might want to try this:

Septillion thank you for helping. The link is very helpful. From what I understood from your message, it is not that practical to use digitalpotentiometers to replace potentiometers in boosters. I still couldn't clearly understand why is that so....

Again, thank you

Have a look at the schematic of a DC-DC converter. To set the voltage they all use a voltage divider to a pin on the controller IC. This divider is made with the pot op the print, maybe with an extra series resistor. But when you try to connect a digipot instead you try to connect one of the pins of the digital resistor to the output of the DC-DC. But the datasheet states all resistor pins must stay below Vdd + 1,0V so 6,0V (when you power it from 5,0V). So when you connect a digipot to the output of a DC-DC the output voltage may never be higher then 6,0V otherwise you go out of spec.

thank you!