Power supply datasheets lead with kilowatts, volts, and amps. Ripple and noise specifications get far less attention but cause far more measurement problems. A supply that's perfectly sized on power and voltage but specified loosely on ripple can quietly corrupt every measurement downstream, without ever throwing a fault.
What Ripple and Noise Actually Are
Ripple is the periodic AC component riding on top of the intended DC output, typically originating from the supply's own switching frequency. It's usually specified as peak-to-peak or RMS millivolts.
Noise is the broader, less periodic component — switching transients, EMI coupling, and high-frequency content. The CORTEX DC series specifies ripple at under 25mV RMS for lower-voltage models (40–80V) and under 200mV RMS at the high end (800–2000V).
Why It Matters More Than Most People Expect
It directly corrupts sensitive measurements. Precision analogue/RF characterisation and instrumentation calibration pick up the supply's ripple as if it were part of the DUT's behaviour.
It affects battery and cell-level test validity. Ripple superimposed on charge/discharge current shows up as noise in derived measurements like internal resistance and capacity.
It can trigger false protection behaviour in the DUT. Some devices respond to supply noise as if it were a genuine line disturbance, producing test failures unrelated to actual DUT design margins.
It compounds in multi-stage or parallel systems. When supplies are paralleled for higher power, ripple from each unit doesn't necessarily average out and can add constructively.
Voltage and Current Accuracy — The Related, Equally Overlooked Spec
- Voltage accuracy (CORTEX specifies ±0.02% F.S.) determines how close output is to the programmed setpoint.
- Current stability (±10 ppm over 8 hours on ZETA-series units) determines drift over the duration of a long test.
- Load and line regulation (±0.01% F.S. on CORTEX DC) determine how much output shifts with load changes or mains variation.
Matching Specification to Application
| Application | What to specify |
|---|---|
| Precision analogue/RF circuit characterisation | Lowest available ripple figure |
| Battery cell formation and cycling | Low ripple + high current stability |
| General production-line power supply test | Standard CORTEX-class spec, ripple secondary |
| Long-duration accelerated life testing | Prioritise line/load regulation over peak ripple |
| Parallel/multi-module high-power systems | Confirm parallel-mode ripple specification explicitly |
A Practical Check Before Committing to a Spec
If ripple and noise genuinely matter, ask for the manufacturer's actual measurement methodology, not just the headline figure — ripple specs are sensitive to measurement bandwidth, probe grounding, and load condition. Two supplies quoting the same figure under different test conditions aren't necessarily equivalent in practice.