How to Choose a Triple Output DC Power Supply
A definitive overview to selecting the right programmable bench power supply for your R&D lab, avoiding common pitfalls, and getting the best value for your budget.
Whether you are testing a complex mixed-signal PCB, characterizing an operational amplifier, or building an Automated Test Equipment (ATE) rack, a triple output DC power supply is the beating heart of your bench. But with prices ranging from $200 to over $3,000, how do you know what you actually need?
1. Linear vs. Switching: The Noise Factor
The first decision is the underlying topology. Switching power supplies (SMPS) are lightweight, highly efficient, and can deliver massive current. However, they inherently generate high-frequency switching noise.
Linear power supplies, on the other hand, use heavy transformers and linear regulators. They are less efficient and heavier, but they provide ultra-cleanpower with extremely low ripple and noise (often < 1mVrms).
The Verdict:
If you are doing RF design, audio engineering, or precision analog sensor testing, you must use a linear supply. If you are just powering motors, LEDs, or digital logic, a high-quality switching supply is perfectly fine.
2. Resolution and Display Precision
A common mistake is buying a power supply with a 3-digit display (e.g., 5.00V / 1.20A). In modern electronics, especially IoT devices with deep sleep modes, you often need to measure quiescent currents in the milliamp or microamp range.
- 3-Digit Displays:Resolution is typically 10mV / 10mA. Not precise enough for modern low-power electronics.
- 4-Digit Displays:Resolution drops to 1mV / 1mA (or better). This is the standard you should aim for. The eTM-DM series features 4-digit precision across all models.
3. Galvanic Isolation & Tracking Modes
A "true" triple output supply isn't just three independent power supplies stuffed into one box. The channels must be galvanically isolated (floating), meaning they don't share a common ground internally unless you explicitly wire them that way.
Furthermore, look for Internal Tracking Modes. This allows you to internally connect CH1 and CH2 in series (to double the voltage or create a bipolar +/- supply) or in parallel (to double the current) without messy external jumper wires.
4. PC Connectivity (SCPI / Automation)
If you ever plan to automate your testing using Python, LabVIEW, or MATLAB, you need a programmable supply. Look for standard interfaces:
- USB: Standard for single-bench setups.
- RS232/RS485: Excellent for industrial environments and long cable runs.
- LAN (LXI): Best for distributed ATE racks.
The Smart Choice: eTM-DM Series
Historically, getting a 4-digit, programmable, triple output supply meant spending over $1,500 on legacy brands like Keysight or Rigol. The eTM-DM Series disrupts this by offering lab-grade precision starting at just $449.
Legacy Brands (e.g., Rigol DP832)
- ✗ High MSRP ($500 - $1000+)
- ✗ Often charge extra to "unlock" high resolution
- ✗ Bulky, outdated interfaces
- ✓ Good brand recognition
eTM-DM Series
- ✓ Unbeatable Price (Starting at $449)
- ✓ 4-Digit Precision included standard
- ✓ CV/CC Auto Conversion
- ✓ RS232/485/USB Ready
How to Choose FAQ
What is the difference between a linear and switching power supply?
Linear power supplies provide ultra-clean power with very low noise, ideal for sensitive analog circuits. Switching power supplies are more efficient, lighter, and can deliver higher current, but generate more high-frequency noise.
Why do I need a 4-digit display on my power supply?
A 4-digit display provides 1mV/1mA resolution, which is essential for accurately measuring the low quiescent currents of modern electronics, such as IoT devices in deep sleep modes.
What does galvanic isolation mean in a power supply?
Galvanic isolation means the output channels are electrically separated from each other and from earth ground. This allows you to connect channels in series or parallel without creating short circuits.
Are programmable power supplies worth the extra cost?
If you plan to automate testing, log data, or integrate the supply into an ATE rack, a programmable supply with USB, RS232, or LAN interfaces is absolutely essential and worth the investment.