Low Noise Adjustable Power Supply (30V-4A, CC-CV)

[hesam_m]

Power supplies are one of the most popular topics in electronics. There are two major types of regulated power supply: linear and switching. Both power supply types introduce some advantages and disadvantages, however, a linear power supply offers better line and load regulation figures and it handles lower noise at the output, specifically when the power supply is adjustable and the output is under load; although its efficiency is lower than a switching power supply. In this article/video, I introduced an adjustable 30V-4A linear power supply that provides constant voltage and constant current adjustment. The output noise of the power supply is low and has measured using the power analysis feature of the Siglent SDS2102X Plus oscilloscope. All component packages are through-hole, so you don’t need any special tool for soldering. Let’s get started!

Specifications
Input Voltage (max): 35V [30V, max-tested]
Output Voltage (min): 1.28V
Output Voltage (max-tested): 27.35V [28.9Vin, no load, 25C]
Output Current: 1.1mA to 4A(max continous)
Output Noise (no load): 6-7mVpp
Output Noise (1A load): 6-7mVpp
Output Noise (2A load): 8-10mVpp

YouTube: 30V-4A Adjustable Power Supply Circuit [CV, CC] - YouTube

References
Article: 30V-4A Adjustable Power Supply (CC-CV) - Technology - PCBway
[1]: LM338 datasheet: https://www.mouser.com/datasheet/2/405/lm338-440432.pdf
[2]: IRLZ44 datasheet: https://www.vishay.com/docs/91328/sihlz44.pdf
[3]: LM358 datasheet: https://www.mouser.com/datasheet/2/308/lm358-d-299970.pdf
[4]: 78L09 datasheet: https://www.jameco.com/Jameco/Products/ProdDS/192225.pdf
[5]: LM358 schematic symbol, PCB footprint, 3D model: [LM358N/NOPB footprint, schematic symbol and 3D model by Texas Instruments](Component Search Engine - Free access to schematic symbols, PCB footprints and 3D models Instruments)
[6]: 78L09 schematic symbol, PCB footprint, 3D model: [Component Search Engine - Free access to schematic symbols, PCB footprints and 3D models](Component Search Engine - Free access to schematic symbols, PCB footprints and 3D models Semiconductor)
[7]: LM338 schematic symbol, PCB footprint, 3D model: [Component Search Engine - Free access to schematic symbols, PCB footprints and 3D models](Component Search Engine - Free access to schematic symbols, PCB footprints and 3D models Instruments)
[8]: IRLZ44 schematic symbol, PCB footprint, 3D model: Component Search Engine - Free access to schematic symbols, PCB footprints and 3D models
[9]: Electronic designing CAD software plugins: Library Loader help - SamacSys
[10]: Altium Designer plugin: Altium Designer PCB Library - FREE - Footprints - Symbols - 3D Models
[11]: Siglent SDS2102x Plus oscilloscope: https://www.siglenteu.com/digital-oscilloscopes/sds2000xp

[septillion]

First thought was "damn, those resistors are close to the caps!" But 1,1Ω @ 4A is 4,4W so they probably don't get hot. 16,7W in three 10W resistors which will get reasonable hot. Nice and simple design

The heat sinks on the other hand don't seem capable of dissipating the worst case 140W by a long shot... Doubt you can ever dissipate >100W in a LM338 at all. So drawing a working region might be a nice addition.

[hesam_m]

Thanks for your comment. Please watch the video completely. I have increased that distance in the last revision of the PCB board. I have talked about the heatsink also

However, W = R*I^2 so the dissipation would be 1.1 * 16 = 17.6W

[septillion]

Oops, let's say it was a tough day...

Watched Okay, scanned the video. Think it's a good beginners video (good job!) but just to long for me as engineer. But I do think the heat sink part deserves a lot more attention (and testing). Especial because you state "Output Current: 1.1mA to 4A(max continous)" And I already doubt it will handle 4A @5V (Vin = 35V) for over 30 seconds...

[hesam_m]

I don't know if this is a beginner project or not, I did not have bigger heatsinks near me, so I did some tests with these. anyone who wants to get higher current simply can use bigger ones same as bench power supplies. The datasheet of the regulator says 5A continuously, so I kept it lower with this attention that the user knows about temperature ... etc. in commercial supplies, there are some relays that switch to different input voltages to keep the in/out voltage difference low and prevent stress on the regulator. I let the users do and think about these themselves.

[septillion]

Mm, with the amount of detail and explanation you give you made this a beginner project Don't get me wrong, that's not bad at all! But after all the explaining I think thermals turned into an elephant in the room that beginners will just not see. So you don't need to go in depth if you don't want to, but at least make it more clear. Especially if you state "continuous".

[hesam_m]

septillion:
Mm, with the amount of detail and explanation you give you made this a beginner project Don't get me wrong, that's not bad at all! But after all the explaining I think thermals turned into an elephant in the room that beginners will just not see. So you don't need to go in depth if you don't want to, but at least make it more clear. Especially if you state "continuous".

Sure, I'll talk about these, most likely in the next video. Thank you for commenting and reminding me. and you are right, beginners may not notice this until the room fills up with smoke. an experienced user can himself design a circuit, or at least he knows what he does.

[hesam_m]

A tip: As I mentioned in the video, in the last revision of the PCB board (which is available for you), the distance between electrolytic capacitors and the power resistors has been increased, however, if you still have concerns about this, you can use 470uF-50V capacitors instead of 1000uf-50V capacitors which are smaller in diameter.