Story
My power supply allows for setting both voltage and current limits using rotary encoders, features a 3.5" touchscreen LCD display, and offers remote control via a 2.4GHz RFM75 module (the same one I used in my Energy meter project). Voltage can be adjusted within a 0-35V range, and the current limit from 0-7A. The adjustment step for voltage and current can be set on the display – 10mV, 100mV, 1V for voltage, and 1mA, 10mA, 100mA for current.
In addition to voltage and current, the display shows load resistance, power consumption, charge in ampere-hours, and energy in watt-hours. Measured data can also be displayed in graph format.
The power supply comprises a toroidal transformer and three PCBs, with their functions illustrated in a simplified block diagram.
From a circuitry standpoint, the power supply is designed as a linear analog system with two control loops regulated by a 16-bit DAC AD5663 (initially, a 12-bit DAC LTC2632 was used, and the new DAC is wired in). A 16-bit ADC LTC1865 is used to measure voltage and current. Both the ADC and DAC communicate with the MCU via an optically isolated SPI bus. As error amplifiers, I used OPA140 operational amplifiers, whose outputs are merged through diodes to control MJE15030A power transistors in a Darlington configuration with BDW93 and BC846. To minimize thermal losses on the transistors, a toroidal transformer with four windings was used, which switches according to the set output voltage.
The output current is measured as the voltage drop across a 10-milliohm resistor, which is further amplified by an OPA228 operational amplifier with a gain of 50. An IC REF5040, providing a 4.096V output, is used as the voltage reference for both ADC and DAC.
The power supply is controlled by a PIC32MM0256GPM028 microcontroller, with firmware written entirely in C (including graphic libraries) in the MPLAB X environment. Eagle CAD was used for PCB design, and the enclosure was created in Fusion 360.
