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ELECTRICAL
Smart Power Supply
Complexity: Medium
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I designed my first lab power supply more than 10 years ago, which operated under continuous load in the University’s Photometric Laboratory for two years. It provided an extremely stable output for the official testing of 100 pieces of high-performance OSRAM Dragon Power LEDs for 1500 operating hours. I designed the circuit for months and did tons of complicated calculations during that time.
Its main components were the popular 2N3055 power transistors and its output could be loaded with DC 33V and 6A. The passive and active cooling systems of the transistors were oversized to provide a highly stable linear output.
At that time, there were no cheap power supply modules on the market like now. So I produced the printed circuit board at home using a laser printer and iron-III-chloride corrosive acid. I didn't take a picture of this, but luckily I photographed the freshly made printed circuit board from another power supply.
I recently needed a reliable and smart power supply to test high-performance devices like the 48V MPPT solar chargers. For me, the main aspects were to have a DC 50V output and a 0.5kVA load capacity. So I was looking for a smart and compact solution that requires little storage space.
Pretty soon I found an excellent 50V programmable power supply module with a maximum load capacity of 20A.
I would like to emphasize that with these parameters we are talking about a power class of 1 kW, which is not such a negligible factor. Due to the mass production of such cheap Lab PSU (Power Supply Unit) modules, there is no longer a need for home-printed circuit board production.
Luckily, I had a 450VA toroidal transformer in perfect condition with 2 x 40V secondary output, which is an excellent choice for such a task. It is a rather large and heavy, low-frequency soft iron core transformer with two symmetrical secondary coils.
In the present case, since there are two perfectly identical secondary coils with the same winding direction, I have the possibility to connect them. I had to be careful because the identical terminals of the two secondary coils had to be connected in parallel to get the 40V output and not the 80V in series mode.
In the next quick and easy step, I designed the bridge rectifier circuit with buffer capacitors, where the capacitance determines the pulsation of the output DC voltage. Fortunately, the input limit voltage of the power supply module is DC 60V because the output voltage of the bridge rectifier circuit I use is √2 * 40V = 56,568V after the buffer capacitor.
Don't forget that this is only true for AC 230V, but the mains voltage also fluctuates by ±10%. By the way, this power supply operates from an automatic AC 230V output voltage regulator in my workshop, which provides a stable pure sinusoidal AC waveform.
The last step of this project was the assembly, where touch protection and heat dissipation aspects had to be considered. I highlighted the last two factors because I chose my solution and not a prefabricated finished instrument box.
For me, all the parts must be perfectly in place in the electrical wiring box, as this concept ensures easy and quick maintenance. The thickness of the properly sized wires in the picture also shows the robust dimensions.
The control panel has an informative OLED display with adjustable brightness that shows the actual voltage, current, and power values. Its buttons and dial are smooth and precise, and I think they're pretty ergonomic, too.
I can appreciate this smart display because I have already built a voltage measuring circuit from LED panels for another power supply. It was not a super easy task, as that solution required a lot of effort at that time, and the galvanic isolation of the measuring module had to be ensured for accurate measurement.
It is especially useful for me that it can store up to 10 predefined voltage and current value groups for efficient work. It is worth mentioning the values ​​can be set at any time, which is a fairly user-friendly feature.
I can say in summary that this compact device was born with minimal creativity and time, and I'm satisfied with its capabilities so far. In my opinion, as far as safe use is concerned, PSU modules with a load capacity of 5 - 10A should not be operated without supervision.
Specifications
Output voltage range: 0.01 - 50.00V
Output current range: 0.01 - 9.00A
Output voltage resolution: 0.01V
Output current resolution: 0.01A
Output Voltage Accuracy: ± (0.5% + 1 digit)
Output Current accuracy: ± (0.5% + 2 digits)
Thank You for reading this article.
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