Programmable Dual Channel DC Power Supply

This project involved the design and construction of a programmable, dual-channel DC power supply. Each channel is independently capable of being set from 0.00 to 30.00V with a resolution of 1.25mV. Current limiting may be set from 0.000 to 5.000A with a high-side measurement resolution of 0.15mA. Display resolution via the LCD is 10mV and 1mA. Full floating-point precision is available via a remote PC connection. Specification overview: Number of channels: 2 (optional expansion up to 4 with larger LCD) Voltage range : 0.00 - 30.00V Voltage set resolution: 10mV Voltage measurement resolution: 1.25mV Current limit: 0.000 - 5.000A Current set resolution: 1mA Current measurement resolution: 0.15mA Noise: Measured 8mVpp at 5V no load and 120mVpp when sourcing 3 Amps. The design is modular featuring a COTS AC-DC converter for efficiency with a dedicated micro-controller PCB and separate power supply PCBs for each channel. This minimizes noise between channels as well as improving reliability and maintainability. Each board is wired using a star-ground methodology. Right-click to open larger images.

Micro-controller board PIC 18F4550 with interfaces for 16x2 LCD, 6 switch keypad, rotary encoder, I2C DAC, I2C current/voltage monitor, PC UART & USB, PWM buzzer, internal EEPROM, ICP.

Power supply module LM2596 switching regulator with low pass filter. Separate low-noise linear 5V regulator for MCP4725 DAC and INA226 high side power monitor. This module interfaces with the micro-controller board via I2C. Two of these boards are used with different I2C address configurations.

Keypad A simple keypad that allows the user to control various settings. Interfaces directly to the micro-controller board via GPIO pins. Standard through-hole 6x6 tactile switches are used with push-on plastic knobs.

Rotary encoder A simple rotary encoder allows the voltage and current settings to be adjusted up and down. The rate of change varies depending on the cursor position with steps ranging from 10mV/1mA to 10V/1A per step. Pressing and holding the encoder button locks all keys preventing inadvertent adjustment.

Software features Instantaneous display of both voltage and current for each channel. Over-current alarm indicated on LCD plus audible buzzer sound. Save settings in EEPROM which will be restored at power on. Enable/disable outputs without turning the entire unit off. Locate cursor on any digit allowing convenient adjustment of settings. Lock the rotary encoder and keypad so adjustments cannot be made inadvertently. Remote control via USB port on PC. This allows for programmable voltage waveforms in addition to real-time logging of both voltage and current. These screenshots shows how a remote PC connection can be used to generate programmable voltages and demonstrates a typical example of logging voltage and current to a file.

PC serial protocol: 19200, N81 To enable/disable real-time logging of all parameters, send 'L'. To set voltage or current parameters, each command from the PC must comprise of 6 characters: channel mode value1 value2 value3 value4 channel must be either A or B mode must be either V or I value is a decimal representing the actual voltage or current Range of voltage values is 0000 to 3000 (30.00V) Range of current values is 0000 to 5000 (5.000A) eg: AV1234 - sets channel A voltage to 12.34V AI2345 - sets channel A current to 2.345A BV0200 - sets channel B voltage to 2.00V BI1234 - sets channel B current to 1.234A

Construction

Internal view from the front	Internal view from the rear
Proof of concept prototype - top	Proof of concept prototype - bottom
Milling the front panel on my homemade CNC mill	Turning the LCD and keypad standoffs on my lathe