Every programmable DC electronic load offers four core operating modes — Constant Current (CC), Constant Voltage (CV), Constant Resistance (CR), and Constant Power (CP) — and the ActionPower ATLAS series supports all four across its 2kW to 60kW module range. Choosing the wrong mode for a given test doesn't just produce inconvenient results; it can produce results that look valid but don't actually represent how the DUT behaves in real operation.
What Each Mode Actually Does
Constant Current (CC) holds the load's current draw fixed regardless of the voltage the DUT presents. This is the default mode for most power supply and battery discharge testing.
Constant Voltage (CV) holds the load's terminal voltage fixed, drawing whatever current is needed to keep the DUT at that voltage.
Constant Resistance (CR) makes the load behave like a fixed resistor — current drawn is proportional to whatever voltage the DUT presents.
Constant Power (CP) holds power draw fixed, with current automatically adjusting as voltage changes to maintain that power level.
Matching Mode to Test Objective
| Test objective | Correct mode | Why |
|---|---|---|
| Battery discharge curve characterisation | CC | Fixed current lets you plot voltage sag vs. state of charge cleanly |
| Power supply load regulation test | CC or CR | CC for spec compliance testing; CR for realistic transient response |
| DUT with internal constant-power behaviour | CP | Matches the actual load signature the real downstream device presents |
| Resistive/heating-element load simulation | CR | Current scales with voltage the way a physical resistor would |
Why Getting This Wrong Produces Misleading Data
A common mistake is running battery discharge tests in CR mode when CC was the intended test. Because CR mode's current draw falls as the battery's voltage sags during discharge, the resulting capacity figure doesn't match what the battery would deliver under a genuine fixed-current discharge.
Dynamic Mode Operation
The ATLAS series supports dynamic/transient testing within any of the four static modes. With 20μs response time and 500kHz sampling, transient load steps can be resolved cleanly even for fast-switching DUT behaviour.
Specification Checklist
- Identify what the real downstream load actually does and match the load mode to that
- Confirm the standard or test method specifies a mode explicitly
- For transient testing, confirm the load's response time and sampling rate are fast enough for your DUT
- When paralleling modules, confirm mode behaviour is consistent across the parallel bank
Finch Electronic Solutions — Melbourne, Australia
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