By Hesam Moshiri, Anson Bao

A power supply is a crucial tool in any electronics lab. The TPS54202 is an efficient 2A synchronous buck converter with a wide 28V input voltage range and low EMI, making it suitable for a variety of applications. These features make the TPS54202 an excellent choice for constructing a high-performance power supply.

To minimize noise and ensure optimal performance, I implemented several input and output filters, along with a range of PCB design techniques. The chip operates at a switching frequency of 500 kHz and includes internal loop compensation. Setting up the power supply is simple—just connect the input to a step-down AC transformer (e.g., 220V to 15V) and adjust the output voltage to your desired level using a multiturn potentiometer.

For the schematic and PCB design, I used Altium Designer 23 and shared the project with my peers for feedback via Altium-365. The Octopart component search engine proved indispensable for quickly sourcing components and generating the Bill of Materials (BOM). To ensure high-quality board fabrication, I sent the Gerber files to Wellcircuits for production.

I tested the circuit’s output noise and load step response using the Siglent SDS2102X Plus oscilloscope and Siglent SDL1020X-E DC load. I am confident that this circuit will meet your needs for a compact, efficient power supply that delivers reliable performance for your electronics projects.

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Specifications

Input Voltage: 20V AC Max

Output Voltage: 0.6V DC to VTR-1

Output Current: 2A, Max Continuous

Output Noise (No Load): 3mV(rms), 16mV(p-p)

Output Noise (Max Load): 6mV(rms), 30mV(p-p)

Voltage Drop (Max Load): 100mV

Circuit Analysis

Figure 1 shows the schematic diagram of the adjustable switching power supply. The core component of the circuit is the TPS54202 chip [1], REG.

Figure 1

Schematic diagram of the adjustable switching power supply (Altium)

C2 [2], C3 [2], C4, and C5 function as input capacitors to reduce noise. It’s important to consider the placement order of these capacitors, with the smallest one placed closest to the controller chip. Notably, this controller chip does not require a buck converter diode. Additionally, L1 is a 22μH inductor [3], and its saturation current must exceed 2A.

R2 is a 5K multiturn potentiometer [4] used to adjust the output voltage. Similar to the input capacitors, the output capacitors (C6, C7, C8 [2], C9 [2]) are positioned to reduce output noise. FB is a ferrite bead, and together with C10 [2], they form a low-pass filter to further suppress high-frequency noise.

P1 and P2 are 2.5mm male XH connectors. D1 through D4 are SS34 [5] Schottky diodes that form a bridge rectifier to rectify the AC input voltage. The forward voltage drop of these diodes should not exceed 0.5V.

PCB Layout

Figure 2 illustrates the PCB layout of the adjustable switching power supply project. It is a double-layer PCB with all surface-mount components. Refer to the accompanying YouTube video for a demonstration of the PCB design techniques used. Figure 3 shows the assembly drawings.

Figure 2

PCB layout of the adjustable low EMI Switching Power Supply project (Altium)

Figure 3

Assembly drawings of the adjustable low EMI Switching Power Supply project

Assembly and Test

Figure 4 shows the assembled PCB board. Soldering the TPS54202 (REG) can be tricky, and I used a microscope for this task, but it’s certainly possible to do it by hand. If you prefer to skip the soldering process, you can order the board pre-assembled.

Figure 4

Assembled PCB board for the adjustable Switching Power Supply project

Figure 5 shows the connection diagram for the power supply.

Figure 5

Connection diagram of the power supply

Figure 6 illustrates the output noise of the power supply with no load, as measured using the Power Analysis feature of the Siglent SDS2102X Plus oscilloscope. Figure 7 shows the output noise under maximum load (2A). If these noise levels are not satisfactory, it’s worth noting the significant input ripple at the controller input, which is shown in Figure 8. Finally, Figure 9 presents the results of the step response test. For this test, I set the DC load to generate a 0.2A to 1.9A periodic current pulse and examined the output voltage for stability, recovery time, and ringing. As you can see, the power supply performs well and recovers quickly. Keep in mind that the output noise/ripple should not be confused with instability in the step response.

Figure 6

Output noise of the adjustable low EMI switching power supply project (no load)

Figure 7

Output noise of the adjustable switching power supply project (max load, 2A)