The DC-to-DC buck converter is a popular topology and circuit widely used in electronic devices. A buck converter lowers the input voltage while increasing the output current. In this article/video, I have discussed a DC-to-DC buck converter that can be effectively used as a switching power supply. The output voltage and current can be adjusted: 1.25V to 30V and from 10mA to 6A (continuous). The power supply supports constant voltage (CV) and constant current (CC) features. Two LED lights show the status of CV and CC. The circuit is compact and both sides of the PCB have been used to mount the components. For schematic design and PCB I used Altium Designer 21, as well as SamacSys component libraries (Altium Extension) to install missing schematic symbols/PCB footprints. For high quality PCB boards, I sent Gerbers to PCBWay. To test the circuit, I used the power analysis feature of the Siglent SDS2102X Plus (or SDS1104X-E) oscilloscope, Siglent SDL1020X-E DC Load, and Siglent SDM3045X multimeter. Let’s get started! Specifications Input voltage: 8V to 35V DC Output voltage: 1.25V to 32V DC Output current (continuous): 10mA to 6A Output current (short term): 7A to 8A Output noise (no load) ): 6 mV (9 mVp-p) Output noise (6-A load): 7 mVrms (85 mVp-p) Output noise (6-A load, 16P average): 50 mVp-p Efficiency: What Up to 96% Circuit analysis Figure 1 shows a schematic diagram of the shunt power supply (DC to DC buck converter). The diagram has three main parts: a buck converter, a feedback loop, and an op-amp regulator. Figure 1: The schematic diagram of the PSI adjustable switching power supply is the XL4016 controller chip 1 and the main component of the buck converter; D2 is MBR20100 Schottky diode2; The L2 is a 47-µH, 10-A inductor. C3 – C9 is used to reduce I/O noise. R2 is a 20K multicycle potentiometer (trimmer) that provides a feedback path to the controller chip for adjusting the output voltage. C1 is used to reduce noise on the feedback path. R1 is just a 0-R resistor used as a connection on the PCB board. R4 is the shunt resistor made of two 0.1-R and 5 W resistors. These two resistors are connected in parallel to make one 0.05-R, 10-W resistor. IC2 is a TS4264 3 linear regulator chip that provides a fixed 5-V supply rail. C15 is used to reduce regulator output noise. IC1 is an MCP6002 op amp4 that is used to amplify the voltage of a small shunt resistor to excite the feedback pin of the PS1. D1 provides a feedback path to PS1. The MCP6002 chip provides two practical amplifiers. The first op amp is configured as a non-inverting amplifier and the second op is configured as a comparator to feed the D3 and D4 LEDs (CC, CC). R5 and C11-C13 create a low-pass RC filter to reduce the supply noise to IC1. R9 and C14 also build an RC low-pass filter to remove shunt noise. C10 is also used to reduce speaker noise. PCB layout Figure 2 shows the PCB layout of the variable switching power supply board. It’s a two-layer PCB board and a combination of SMD and through-hole components were used to make it as compact as possible. Figure 2: PCB layout for the adjustable switching power supply I used Altium Designer5 software to design the schematic and the PCB. I didn’t have the schematic symbols, PCB footprints, and 3D models for many of the components on this project. So instead of wasting my time designing component libraries from scratch and increasing the risk of errors and mismatches, I used the free, IPC-branded SamacSys component libraries and imported them directly into an Altium PCB project using the SamacSys Altium plugin. 6 SamacSys provides plug-ins for the majority of CAD electronic design software, 7 not only for Altium Designer. Figure 3 shows the CAD software for the supported electronic design. Specifically, I used the SamacSys libraries for PS1, 8 IC1, 9 IC2, 10 and D2.11 and another option is to download the component libraries from componentearchengine.com and import them manually. Figure 3 shows the components identified in the SamacSys Altium plug-in. Figure 3: Components selected in the SamacSys Altium plugin Assembly and testing Figure 4 shows the panel assembled from the top and bottom view. As can be seen, both sides of the PCB were used to mount the components. The high current-carrying tracks are partially covered by the welding mask. These tracks must be reinforced with solder wire and/or copper (tin). Figure 4: Combined PCB board (top and bottom view) Output noise I used the power analysis feature of the Siglent SDS2102X Plus oscilloscope to measure the output noise. You can use the cheaper Siglent SDS1104X-E oscilloscope and then repeat the experiment without any problem; However, the Plus is a role model device. The first test is to check the output noise of the power supply when there is no load. For this, I have to remove the ground wire of the oscilloscope probe, remove the probe head, and put a ground spring on the head (Fig. 5). Also, enable the 20MHz bandwidth limit for the input channel and put the probe on X10. Figure 5: Prepare the oscilloscope to measure the noise of the power source and then place the tip of the probe directly on the output of the power source. Figure 6 shows the no-load power supply output noise. Figure 6: Adjustable switching power supply output noise (no load, bandwidth limit 20MHz) The best choice for building accurate DC loads is a commercial DC load, such as Siglent SDL1020X-E.14 This device ensures load stability and accuracy in a variety of From modes, such as CC, CV, CP, CR, etc. The CC mode on the SDL1020X-E is limited to 5A, so let’s test the output noise under 5-a load now. Figure 7 shows the power supply output noise under 5-A load. You can look at DC load monitors and oscilloscopes. Figure 7: Adjustable switching power supply output noise (5-A load, CC mode, 20MHz bandwidth limit) To test the output noise under a 6-A (maximum continuous) load, I set the DC load to a constant of resistance (CR) ) and the value of the resistor changed to read 6 A at the output of the power supply. Figure 8 shows the output noise under 6-A load. Figure 8: Tunable switching power source output (6-A load, CR mode, 20MHz bandwidth limit) Figure 9 shows the power source output noise (load 6-A) after applying 16-point average using the math function ( brown waveform). Figure 9: Adjustable switching power supply output noise (6-A load, CR mode, 20MHz bandwidth limit, 16P average) CC modulation There are two ways to set the power supply constant current limit: using a DC load or using a device Multi 15 Both methods are easy to implement. Just watch the YouTube video. Bill of Materials Figure 10 shows the Bill of Materials for the projects. Please note that I did not include the L1 and the heatsink in the bill of materials for the assembly. Ensure that the limiting/embedded inductor (ferrite core) can handle at least 10 A (47 µH). The hole diameter of the agitator pads is 1.3 mm. Figure 10: Bill of Materials for the adjustable switching power supply References Source: https://www.pcbway.com/blog/technology/0_30V__0_7A_Adjustable_Switching_Power_Supply.html 1XL4016 Datasheet: http://www.xlsemi.com/datasheet/xl4016% 20datasheet .pdf 2MBR20100 Datasheet: https://www.diodes.com/assets/Datasheets/MBR20100C.pdf 3TS4264 Datasheet: https://www.mouser.com/datasheet/2/395/TS4264_D15-1142598.pdf 4MCP6002 Sheet Data: https://componentsearchengine.com/Datasheets/2/MCP6002T-I_SN.pdf 5Altium Designer: https://www.altium.com/yt/myvanitar 6SamacSys Altium plugin: https://www.samacsys.com/altium -designer – help library 7 SamacSys extensions supported: https://www.samacsys.com/pcb-part-libraries 8XL4016 Schematic symbol, PCB fingerprint, 3D model: https://componentsearchengine.com/part-view/XL4016/ XLSEMI 9MCP6002 schematic symbol, PCB fingerprint, 3D model: https://componentsearchengine.com/search?term=mcp6002 10TS4264 Schematic symbol, PCB fingerprint, 3D model: https://componentsearchengine.com/elemente a rchengine.com/part-view/TS4264CW50%20RPG/Taiwan%20Semiconductor 11MBR20100 Schematic symbols, PCB fingerprint, 3D model: https://componentsearchengine.com/part-view/MBR20100CT-G1/Diodes%20Inc. 12 Siglent SDS2102X Plus oscilloscope: https://siglentna.com/digital-oscilloscopes/sds2000xp/ 13 Siglent SDS1104X-E oscilloscope: https://siglentna.com/digital-oscilloscopes/sds1000x-e-series-super-phosphor 14 Download SDL2010X-E DC: https://siglentna.com/dc-electronic-load/sdl1000x/ 15Siglent SDM3045X Multimeter: https://siglentna.com/digital-multimeters/sdm3045x-digital-multimeter/.
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