PBL Sem 5 - Buck-Linear Voltage Regulator

1 year ago


Open source license: Public Domain

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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.)

Full Load DMM measurements.jpeg

Short circuit test

Short Circuit DMM measurements.jpg



Full load pre-regulator waveform Full Load PreRegulator Waveforms.png

Short circuit response Short Circuit Response.png

Short circuit to normal response Short Circuit to Normal Operation.png

LTspice simulation

Screenshot 61.pngScreenshot 63.png Output Ripple - Buck converter (top) vs linear regulator (bottom) Screenshot 64.png Short circuit response Screenshot 65.pngScreenshot 66.png

TinkerCAD simulation

Screenshot 146.pngScreenshot 147.pngScreenshot 148.png



ID Name Designator Quantity
1 10u C1,C4,C6 3
2 100n C2,C7,C8 3
3 100u C3,C5 2
4 100n C9,C10 2
5 1N5819 D1 1
6 1N4148 D2 1
7 33u L1 1
8 Ammeter PB1,PB2 2
9 2N3904 Q1 1
10 2N3906 Q3 1
11 560R R1,R7 2
12 100R R2 1
13 100k R3,R8 2
14 5.6k R4 1
15 2.2R R5 1
16 1k LOAD,R6,R13 3
17 4.7k R9 1
18 10k RP1 1
19 LM317AT U1 1
20 TL431 U2 1
21 LM2596-ADJ U3 1
22 LM78L05 U5 1
23 Arduino Uno U6 1
24 LCD-16X2 (JHD162A) U7 1
25 ADS1115 Module U8 1
26 32V VIN 1



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