DC-to-DC buck converters are widely used in various electronic devices. This article/video introduces three common types of non-isolated DC-to-DC converters: Buck, Boost, and Buck-Boost, with the Buck converter being the most frequently used. In this post, I present a compact buck converter board that supports input voltages ranging from 8V to 95V and provides a stable 5V at 1A output.

The controller chip used in this design is the MP9486. This high-frequency chip is known to be somewhat sensitive, and some users have reported instability issues. However, after implementing a few modifications to the circuit, I can confidently say that this design, whether in its circuit, PCB, or assembled form, will operate reliably. The circuit maintains stable regulation within the specified input voltage range and efficiently handles the maximum output current.

For the schematic and PCB design, I used Altium Designer 23. I shared the project with my colleague via Altium 365’s secure cloud platform for collaborative feedback and edits. The Octopart component search engine was instrumental in sourcing component information and generating the Bill of Materials (BOM). To ensure high-quality production, I submitted the Gerber files to Wellcircuits for board fabrication.

I tested the circuit under various input voltages, output currents, stability conditions, and noise levels. These tests were performed using the Siglent SDL1020X-E DC load, SDM3045M multimeter, and SDS2102X Plus oscilloscope.

I am confident that this circuit meets the requirements for a compact, high-voltage buck converter solution.

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Specifications

Input Voltage: 8-95VDC (continuous), up to 98-100V (short duration)

Output Current: 950mA (maximum continuous)

Output Voltage: 5V (Fixed)

Output Noise: 38mVp-p (Min), 78mVp-p (Max)

Circuit Analysis

Figure 1 shows the schematic diagram of the device. The heart of the circuit is the MP9486 buck converter chip [1].

Figure 1

Schematic diagram of the 100V to 5V DC-to-DC Buck converter

C2, C3, and C4 are input decoupling capacitors designed to minimize input voltage noise. C4 is a 2.2uF capacitor placed as close as possible to U1. The MP9486 is a high-voltage, step-down switching regulator capable of delivering up to 1A of continuous current. It integrates a high-side, high-voltage MOSFET with a current limit of 2.5A, and supports an input range of 4.5V to 100V, making it suitable for automotive, industrial, and lighting applications. The chip employs hysteretic voltage-mode control for fast response and MPS’s proprietary feedback control system to minimize external components. Its switching frequency can reach up to 1MHz, contributing to a compact design. Thermal shutdown and short-circuit protection ensure reliable operation, while a quiescent current of 170μA allows use in battery-powered applications. The MP9486 is available in an SOIC-8 package with an exposed pad.

C1 is a bypass capacitor, and D1 and L1 are essential components for the buck converter. D1 is the SS110 Schottky diode [2], and L1 is a TDK 33µH inductor [3]. C5 and C6 are output capacitors that stabilize the output and reduce noise. In the first revision, I initially used MLCC-type capacitors for the output, which caused instability and erratic behavior in the chip. Replacing them with electrolytic capacitors resolved the issue. While tantalum capacitors are not required, using electrolytic ones works effectively for this design.

R2 is the load resistor to stabilize the output, and D2 [4] indicates the correct operation and output voltage level. C7, R3, and R4 are components in the feedback control loop.

PCB Layout

Figure 2 displays the PCB layout of the design. It is a compact two-layer board with all components in SMD form. Figure 3 presents the assembly drawings.

Figure 2

PCB layout of the 100V to 5V DC-to-DC Buck converter

Figure 3

Assembly drawings of the 100V to 5V DC-to-DC Buck converter

Assembly and Testing

Figure 4 shows the assembled prototype (first revision) of the board after all tests were completed. If you don’t have the time or resources to source components and solder them yourself, you can easily order the pre-assembled board.

Figure 4

First revision of the assembled PCB

I conducted a series of tests on the board, all of which were successful. You can watch the YouTube video for detailed testing information. Below are the noise measurements for various input and load conditions: Figure 5: 8V input, no load; Figure 6: 30V input, no load; Figure 7: 8V input, maximum load; Figure 8: 30V input, maximum load. The oscilloscope used was the Siglent SDS2102X Plus.