40V-30A Adjustable Switching Power Supply

2022-10-02 | By Hesam Moshiri

License: Attribution-NonCommercial-ShareAlike Power Supplies

A DC-to-DC converter is one of the most commonly used circuit topologies in electronics, especially in power supply applications. There are three main types of DC-to-DC converters (non-isolated): Buck, Boost, and Buck-Boost. Sometimes a buck converter is also called a step-down converter and a boost converter is also called a step-up converter. A buck converter reduces/steps down the input voltage while increasing the output current.

In this article/video, I introduced an adjustable buck converter circuit that can deliver up to 30A and handle up to 40V at the input. The output voltage is adjustable from 3V to 37.5V. Several PCB design rules were followed to enhance output stabilization and current handling, also to reduce the radiated emission, and noise figure.

To design the schematic and PCB, I used Altium Designer 22, I tested the current handling, output stability, and noise figure using the Siglent SDL1020X-E DC load, Siglent SDM3045X multimeter, and Siglent SDS2102X Plus oscilloscope. Just build one and have fun!

YouTube: https://www.youtube.com/watch?v=xyNHRRr3blo

Specifications

Input Voltage: 6-40VDC
Output Current: 30A (max continuous, See text)
Output Voltage: 3-37.5VDC Adjustable
Output Noise: 50mVpp, 4mVrms (18A load-20MHz)

A. Circuit Analysis

Figure 1 shows the schematic diagram of the device. As it is clear, the main components of the circuit are IC1:UC3843 [1] and IC2:IR2104 [2]. I used Altium Designer [3] to draw the schematic.

dc to dc buck converter

Figure 1

Schematic diagram of the 40V-30A Adjustable Power Supply (Buck Converter)

IC1 is the controller chip. I used UC3843 because it works effectively with 12V which is a suitable supply voltage for the Mosfet driver chip (IC2) as well. R1 and C5 define the switching frequency which is around 117KHz. R2, C3, and C4 build an RC low pass filter to reduce the supply noise as much as possible.

P1 is a 2-Pin XH connector for the 12V supply voltage (regulated) and C1 and C2 are used to reduce the noise. R3 is used to limit the current to D1 which is a 3mm RED LED.

IC2 is the famous IR2104 Mosfet driver chip that drives Q1 and Q2 in a half-bridge configuration. R5 and R9 were used to limit the current. C12 and C13 are decoupling capacitors. C6, C7, C8, and C9 are mandatory capacitors and have been used the remove the input voltage ripple and noises. These noises could appear especially when the input source has to deliver high currents instantly.

Be careful input voltage is NOT identical to the supply voltage. The supply voltage is fixed at 12V; however, the input voltage could be anything between 6V to 40V, however, both supplies (supply and input) share a common ground.

The rest of the circuit is the common buck converter configuration. Since the switching part is a half-bridge circuit, using a diode is not mandatory. P2 and P3 are INPUT and OUTPUT connectors. L2 and C21 … C25 build an LC filter to reduce the output noises as much as possible. R6 is a 10K multiturn potentiometer that builds a feedback path to IC1 to stabilize the output voltage.

B. L1 and L2 Inductors

The core of the L1 and L2 inductors is a green-blue toroid iron powder core (Figure 2).

B-1. Specifications of the L1 core

1. Outer diameter: 51mm

2. Inner diameter: 24mm

3. Ring height: 22.5mm

4. Inductance of the inductor (no current): 80uH(minimum)

B-2. Specifications of the L2 core

1. Outer diameter: 33mm

2. Inner diameter: 19.5mm

3. Ring height: 11.2mm

4. Inductance of the inductor (no current): 10uH

switching power supply

Figure 2

The color and shape of the L1 and L2 toroid iron powder cores

C. PCB Layout

Figure 3 shows the PCB layout of the design. It’s a two layers PCB board and I’ve used a mixture of SMD and through-hole components to design the layout. Figure 4 shows the assembly drawings of the board.

dc to dc buck converter low noise

Figure 3

PCB layout of the 30A-40V DC to DC buck converter

adjustable switching power supply

Figure 4

Assembly drawings of the PCB board

D. Assembly and Test

Figure 5 shows the assembled PCB board. If you don’t have time to find and purchase the components and solder, you can just order it assembled (without inductors). Please prepare a regulated 12V supply and connect it to the P1 connector. The ground of the 12V supply and the Input voltage (P2 connector) is identical.

adjustable dc to dc converter

Figure 5

Assembled PCB board of the 30A-40V adjustable switching power supply (DC to DC buck converter)

There are two main tests for power supplies: regulation and output noise. I used Siglent SDL1020X-E DC load, Siglent SDS2102X Plus oscilloscope, and Siglent SDM3045X multimeter to perform the tests. My setup allowed me to test the supply up to 18A (please watch the YouTube video). At 18A, the power supply (buck converter) only showed around 0.12V or 120mV voltage drop which is quite good! A big portion of this drop is because of using an LC filter. I prefer to have significantly lower noise at the output and tolerate a little bit of voltage drop. Figure 6 shows the test setup which applies the 18A load.

adjustable dc to dc buck conveter circuit

Figure 6

Welcome to my test bench! DC Load applies an 18A load

To measure the output noise, I activated the power analysis feature of the SDS2102X Plus oscilloscope and prepared the probe (please watch the YouTube video). Figures 7 and 8 show the output noise, under no load and 18A load!

siglent sds2000x plus

Figure 7

Output noise (no load) of the 40V-30A Switching Power Supply (DC to DC Buck Converter)

variable dc to dc buck converter circuit

Figure 8

Output noise (18A load) of the 40V-30A Switching Power Supply (DC to DC Buck Converter)

To use the power supply in high currents (above 20), don’t forget to cool down the inductors and Mosfets. The easiest method is to use a 12V fan and mount it on the top of the board and enclosure. It dissipates the heat of both inductors and Mosfets. Also, don’t forget to strengthen the PCB using solder and copper wires. I have exposed some copper areas exactly for this purpose.

E. Bill of Materials

Figure 9 shows the bill of materials for the project.

dc to dc buck converter