This project is a simple linear bench power supply with adjustable voltage and current. It is meant to be a learning experience, putting ideas of circuit design, feedback, stability into practice building a complete practical power supply. I have intentionally avoided using a 3 terminal regulator or purpose built chip and instead implemented the feedback for voltage and current using a couple of opamps. The idea is for this to be a practical final product while giving pactice implementing some basic circuits.

Specs:

• 0-30V
• 0-2A
• separate fixed 5V output
• Display of setpoint and measured current and voltage

Beyond this, everything is kept as simple as possible with no additional features to compliacate the design. The display is a 20×4 character LCD controlled by an Arduino which reads the currents and voltages. The voltage and current are set by 2 pots on the front panel. There is no data logging or serial comms, although this could be added later if desired with an update to the arduino firmware.

The design is fairly simple and uses a single npn darlington transistor as the main pass transistor in a common collector configuration. This provides current gain but no voltage gain, which is provided by a small signal npn transistor in a  common emitter configuration. The current and voltage feedback loops are controlled by two opamps which compare the measured output values with setpoints generated by two potentiates on the front panel which are driven by a 5V reference.The output voltage is sampled via a 6:1 votlage divider (converts the 0-30V output to a 0-5V signal) and the current is sampled by measuring the voltage drop over a 100mOhm resistor in series with the output. Everything is mapped down to the 0-5V range so that they can be directly measured with an arduino using the 5V rail as the reference voltage.There is additional circuitry for the mains rectification, the transformer tap select and a 7805 5V regulator which provides the reference voltage, powers some of the chips and is routed to the front panel to provide a fixed 5V output.