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DCLoad

DCLoad drawing

Introduction

DCLoad is a versatile electronic load designed for testing and evaluating power supplies and batteries

Features

  • Dual channel 60V 5A programmable electronic load
  • Multiple operation modes
    • Constant Current
    • Constant Voltage
    • Constant Power
    • Constant Resistance
  • 60W per channel / 120W total
  • Optional 4 wire voltage sensing
  • Parallel channel operation for higher power via internal relay
  • Data recording with internal microSD card
  • Remote control via USB or Cloud
  • Quiet at all power levels with silent operation below 10W


Simple clamshell enclosure


Mixed-signal

DCLoad combines the quick response of analog controls with the flexibility of digital control.

Constant-Current control is done entirely in the analog Op-Amp error amplifier with the setpoint generated directly with the built-in STM32G0B1 DAC

More advanced modes like constant-power and constant-voltage are implemented in software running in a 500Hz control loop on the FreeRTOS powered STM32.

Safety features like over/under voltage, overcurrent, MOSFET SOA tracking, and thermal protection are implemented to ensure safe operation.

Real-time current trim and calibration are handled digitally, allowing for precise adjustments and flexibility in operation.

Full analog control loop was simulated in LTspice to ensure stability in all operating conditions.



Components

  • STM32G0B1 microcontroller for main control
  • ESP32 CYD as the display, data recorder and wireless module
  • OPA2189 OpAmp as the error amplifier
  • 2x OPA2188 as current and voltage differential amplifiers
  • 2x IRPF260N MOSFET as the pass transistors - chosen for low-cost and older planar technology
  • Arctic P8 Max PWM 80mm fan
  • DS18B20 temperature sensor
  • Omron G5LE-14-5VDC relay
  • MT3608 boost converter for 12V MOSFET gate drive and fan


Thermal design

Pushing 100+ watts requires consideration of thermal design of the entire device - the shape of the heatsink dictated the entire design from PCB layout to enclosure.

Wind tunnel thermal design pushes air through the heatsink from front and the top of the device to the rear


Microcontroller is actively modeling the MOSFET temperatures based on the power dissipation, ambient temperature and temperature of the heatsink

This allows for dynamic adjustment of fan speed based on real-time thermal conditions or in critical cases derating the power/shutting down the device completely

The chosen fan is Arctic P8 Max PWM 80mm fan - it provides high static pressure, good acoustics and PWM control from 0 to 5000 RPM



Connected design

DCLoad is a part of my sowa.systems cloud platform - the onboard ESP32 handles cloud communication and data logging.

You can view the recorded charts, update firmware remotely and view real-time data via websocket anywhere.

Last updated on 2026-09-02