Open source license: Public Domain
Introduction This is a DC-DC converter module that uses a buck converter (LM2596-ADJ) and a linear regulator (LM317) in cascade in order to obtain a low ripple DC output at fast short circuit response (courtesy of the linear regulator) and a moderate efficiency (courtesy of the buck converter acting as a tracking pre-regulator). An arduino uno, an ADS1115 module and an LCD display are used to display the output voltage, current and power. Tinkercad link: https://www.tinkercad.com/things/dAnySuxN8RZ (LTspice simulation .asc file available in the attachments section below) (Arduino code available in the attachments section)
Working The power supply module is designed to output 1.25V-20V at a maximum current of 250mA. The output of the power supply module is varied using a 10kΩ trimmer. The ‘tracking’ functionality is achieved by modifying the feedback network of the buck converter with the help of a PNP transistor and a TL431 IC. This ensures that the output of the buck converter is always 3V higher than the output of the linear regulator for the entire output voltage range. A 2.2Ω current sense resistor and an NPN transistor are used to set a maximum current limit of 250mA. The output current, in the event of an overload or short circuit, is limited to that value. This ensures that the power supply is not damaged due to overload. Pushbuttons are used for two functionalities: one toggles the output on or off and the other switches the reading on the display from current to power or vice-versa. The pushbuttons send an interrupt to the Arduino, which then runs an ISR to perform the above functionalities.
Result By combining a switch-mode and linear voltage regulator, it is seen that the power supply module provides a low-noise output at a moderate efficiency. The LCD display shows all important measurements (current, voltage and power) in an easy-to-understand layout that is very convenient for the user.
(This project was not fully completed due to the pandemic.)
Short circuit test
Full load pre-regulator waveform
Short circuit response
Short circuit to normal response
Output Ripple - Buck converter (top) vs linear regulator (bottom) Short circuit response