A high precision DC power supply maintains output voltage within ±0.05% accuracy and noise below 1mVrms. Key specifications include:
- Accuracy: ±0.05% or better (vs ±0.5% for standard supplies)
- PARD (noise): <1mVrms (vs 5-50mVrms for switching supplies)
- Resolution: 1mV or finer
- Temperature coefficient: <50ppm/°C
This guide explains how to evaluate these specifications for lab and industrial applications[1].
01.The "Resolution vs. Accuracy" Trap
One of the most common misconceptions in power supply selection is bridging Display Resolution with True Accuracy.
- DisplayThe smallest change in voltage/current the front panel can show (e.g., 1mV).
- ProgramThe smallest change the DAC (Digital-to-Analog Converter) can execute.
- OutputThe maximum deviation of the actual output from the programmed value.
Case Study
Consider a 30V/5A supply labeled as "High Precision" because it has a 4-digit display (10.00V). If its accuracy specification is ±(0.5% + 20mV), at a 10V setting, the actual output could legitimately drift between 9.93V and 10.07V.
For a sensitive MEMS sensor requiring 10.0V ±10mV, this "precision" supply is technically out of spec, despite its granular display.
True High Precision sources (often termed "Source Meter Units" or SMUs in the <100W class) typically offer accuracies better than 0.05%. For higher power (>1kW) industrial DC sources, a specification of 0.1% is the gold standard for "precision."
02.Linear vs. Switching: The Noise Spectrum
The topology of the power stage is the primary determinant of Output Ripple & Noise (PARD).
1. Linear Topology
THE QUIET STANDARD
- PARD: < 350 μVrms
- Noise: Low freq (50/60Hz)
- Use Case: Analog, Audio, ADC/DAC
2. Switching Topology
THE MODERN WORKHORSE
- PARD: 10 mVrms
- Noise: Switching spikes (200kHz)
- Benefit: High Efficiency / Low Weight
For high-power applications (>1kW), demanding "Linear-level noise" is often physically impractical. Instead, engineers should focus on Recovery Time and Stability.
03.The Hidden Spec: Transient Recovery Time
In dynamic loading scenarios (e.g., an MCU waking up from sleep), the power supply must react to the sudden current demand (ΔI).
| Metric | Standard Grade | Precision Grade |
|---|---|---|
| Recovery Time (50% Load Step) | > 2 ms | < 50 μs |
| V Drop Risk | High (Brown-out) | Minimal |
04.The Power Density Factor
In modern engineering labs, real estate is premium. The "Rack Efficiency" metric (Watts per cubic centimeter) has become a secondary specification for precision supplies.
Traditional Linear supplies offer 0.05 W/cm³. Modern Precision Switching supplies push this to 0.5 W/cm³ — a 10x improvement. This allows a 1500W precision source to fit into a 1U rack height, enabling higher channel density for burn-in and validation racks.
05.Strategic Sourcing
Selecting the right instrument is a balance of pure metrology vs. practical power delivery.
For ongoing R&D, engaging with a dedicated manufacturer ensures you get units with the correct control loop architecture (e.g., CV priority vs CC priority) for your specific DUT.
06.Conclusion
Not every load needs a precision source. A DC fan motor is indifferent to 100mV of ripple. However, for:
- Semiconductor characterization
- Aerospace sensor calibration
- Optical transceiver testing
The cost of "Precision" (Stability > 0.1%, Noise < 5mV) is a mandatory investment in data integrity.
Frequently Asked Questions
What is the difference between accuracy and resolution?
Resolution is the smallest change the display can show (e.g., 1mV).Accuracy is how close the actual output is to the set value (e.g., ±0.05%).
A power supply can have 1mV resolution but ±50mV accuracy—the display shows 10.000V, but the actual output might be 9.950V[2].
Is switching noise a problem for high power applications?
For loads >1kW, switching noise (typically 5-50mVrms) is usually acceptable because:
- High-power loads are less sensitive to noise
- Recovery time and stability matter more than noise floor
- Linear supplies at this power level are impractical (weight, cost, heat)
Exception: If you're powering precision instrumentation, use a linear post-regulator.
When should I choose a linear power supply?
Choose linear if:
- You need <350μVrms noise (e.g., 24-bit ADC testing)
- You require <50μs transient recovery
- You're working in a shielded RF environment
Otherwise, a high-quality switching supply is more practical[3].
What is PARD and why does it matter?
PARD (Periodic and Random Deviation) is the AC signal superimposed on the DC output. It includes:
- Ripple: Periodic noise related to line frequency (50/60Hz) or switching frequency
- Random noise: High-frequency spikes that are harder to filter
For precision applications (ADC testing, sensor calibration), PARD must be <1mVrms. For general lab use, 5-10mVrms is acceptable.
How much current headroom do I need?
Rule of thumb: Buy a power supply rated for 150-200% of your peak current requirement.
Example: If your load draws 5A peak, buy a 10A supply. This prevents:
- Overcurrent protection trips during startup transients
- Voltage droop under load
- Thermal stress on the supply