5A Lab Power Supply With Digital Readout

  
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A used 250VA power transformer that was removed from equipment a couple of weeks ago. The transformer has a dual 10V AC output and a few auxiliary voltage outputs. The 10V winding is rated at 10A, I thought it would be perfect for a high current power supply project. For this particular build, I used the reference design for LM338 5A adjustable linear regulator as the base. Rather than designing
5A Lab Power Supply With Digital Readout - schematic

digitally controlled voltage adjustment circuitry (e. g. via DAC), I decided to just use the simple resistor-potentiometer voltage control mechanism and add the digital voltage/current monitoring portion. Here are some of my thoughts behind this reasoning: By adding the digital voltage adjustment functionality via the three terminal regulator`s Adj pin, we would have increased the complexity of the control loop. In a power supply, the reliability of the control loop is essential to the stability of the output voltage. If the Adj pin somehow becomes floated due to circuit malfunction, the result could be disastrous as the input voltage would be applied directly to the load. Also the stability and the accuracy of the external reference affect the accuracy and the ripple rejection of the power supply as well. This must be taken in to consideration when using a DAC or PWM circuitry to drive the linear regulator`s Adj pin. Last but not least, since the output voltage of the linear voltage regulator would essentially be controlled by the MCU, adequate filtering and monitoring (e. g. via watchdog timer) as well as careful designing of the board layout are usually needed for the MCU circuitry to work reliably. Given the above thoughts, I decided to keep the core circuitry as simple as possible using the reference design and using the MCU only for current and voltage measurements. That said, if you intend to build a digitally...



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