A DC-to-DC converter is one of the most widely used circuit topologies in electronics, particularly in power supply applications. There are three primary types of non-isolated DC-to-DC converters: Buck, Boost, and Buck-Boost. A buck converter is sometimes referred to as a step-down converter, whereas a boost converter is known as a step-up converter. A buck converter steps down the input voltage while increasing the output current.

In this article/video, I present an adjustable buck converter circuit capable of delivering up to 30A and handling input voltages of up to 40V. The output voltage is adjustable from 3V to 37.5V. Several PCB design principles were applied to optimize output stability, improve current handling, and minimize radiated emissions and noise levels.

For designing the schematic and PCB, I used Altium Designer 22 and the Octopart electronic search engine to quickly gather information on the required components. To obtain high-quality fabricated boards, I sent the Gerber files to WellCircuits and tested the current handling, output stability, and noise performance using the Siglent SDL1020X-E DC load, Siglent SDM3045X multimeter, and Siglent SDS2102X Plus oscilloscope. Feel free to build one yourself and enjoy!

Specifications

Input Voltage: 6-40VDC
Output Current: 30A (maximum continuous, refer to the text)
Output Voltage: 3-37.5VDC (Adjustable)
Output Noise: 50mVpp, 4mVrms (at 18A load, 20MHz bandwidth)

Download the Gerber files or directly order high-quality power supply boards

To order a fully assembled PCB board (free shipping), please contact: info@wellcircuits.com

A. Circuit Analysis

Figure 1 presents the schematic diagram of the device. As shown, the main components of the circuit are IC1: UC3843 [1] and IC2: IR2104 [2]. I used Altium Designer [3] to create the schematic.

Figure 1

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

IC1 is the controller chip. I selected UC3843 because it operates efficiently at 12V, which is also a suitable supply voltage for the MOSFET driver IC (IC2). R1 and C5 set the switching frequency to approximately 117kHz. R2, C3, and C4 form an RC low-pass filter to minimize supply noise.

P1 is a 2-pin XH connector for the 12V regulated supply, and C1 and C2 help reduce noise. R3 limits the current to D1, a 3mm red LED.

IC2 is the well-known IR2104 MOSFET driver chip that drives Q1 and Q2 in a half-bridge configuration. R5 and R9 limit the current, while C12 and C13 serve as decoupling capacitors. C6, C7, C8, and C9 are essential capacitors to reduce input voltage ripple and noise, particularly when the input source needs to supply high currents rapidly.

Note that the input voltage is NOT the same as the supply voltage. The supply voltage is fixed at 12V, but the input voltage can range from 6V to 40V. However, both supplies share a common ground.

The rest of the circuit follows the typical buck converter design. As the switching section uses a half-bridge circuit, a diode is not strictly necessary. P2 and P3 are the input and output connectors, respectively. L2 and capacitors C21 to C25 form an LC filter to minimize output noise. R6 is a 10K multiturn potentiometer used to create a feedback path to IC1, ensuring stable output voltage.

B. L1 and L2 Inductors

The core material of the L1 and L2 inductors is a green-blue toroidal 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 (no current): 80µH (minimum)

B-2. Specifications of the L2 core

1. Outer diameter: 33mm

2. Inner diameter: 19.5mm

3. Ring height: 11.2mm

4. Inductance (no current): 10µH

Figure 2

Appearance of the L1 and L2 toroidal iron powder cores

C. PCB Layout

Figure 3 illustrates the PCB layout of the design. It is a double-layer PCB, and a combination of SMD and through-hole components were used for the layout. Figure 4 displays the assembly drawings of the board.

Figure 3

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

Figure 4

Assembly drawings of the PCB board

D. Assembly and Testing

Figure 5 shows the assembled PCB board. If you lack the time to source components and solder them, you can simply order the fully assembled board (without inductors). Ensure you have a regulated 12V supply connected to the P1 connector. The ground of the 12V supply and the input voltage (P2 connector) should be common.

Figure 5

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

The primary tests for power supplies are regulation and output noise. I used the Siglent SDL1020X-E DC load, Siglent SDS2102X Plus oscilloscope, and Siglent SDM3045X multimeter to conduct these tests. My setup allowed testing up to 18A (as shown in the YouTube video). At 18A, the power supply (buck