Introduction
In high-precision electrical engineering, ensuring that your load receives the exact voltage it requires is vital. As current flows through output cables, a natural voltage drop occurs over the distance. To combat this, many advanced Switching Power Supplies (S.P.S.) feature a Remote Sensing function, which monitors the voltage right at the load and dynamically compensates for any loss along the lines.
While Remote Sensing is incredibly effective, it is a highly sensitive feedback loop. Incorrect implementation can introduce noise, cause voltage instability, or even lead to system failure. Here is what you need to know to set up Remote Sensing safely and effectively.
Best Practices for Remote Sensing Implementation
To maintain a clean signal and prevent the power supply from over-compensating due to external interference, follow these two critical design rules:
1. Noise Mitigation & Proper Wiring
Because the sensing lines carry a low-voltage feedback signal, they are highly susceptible to Electromagnetic Interference (EMI).
- Use Twisted Pairs: Always use twisted-pair wires for the sensing lines. Connect the +S (Positive Sense) terminal directly to the positive terminal of the load, and the -S (Negative Sense) terminal to the negative terminal of the load.
- Maintain Separation: Keep your sensing wires physically isolated and routed away from the main AC input cables and heavy DC output cables to avoid inductive noise coupling.
2. Handling Dynamic Loads (Above 1 kHz)
When your application involves a dynamic load—where the current rapidly pulses at a frequency above 1 kHz—the rapid shifts can confuse the power supply's feedback loop, leading to voltage oscillations.
To stabilize the system, you must add a filtering capacitor at the output end right where the Remote Sensing wires connect. The selected capacitor must meet two strict parameters:
- Sufficient Ripple Current Rating: The capacitor's Rated Ripple Current must be at least 0.2 times greater than the power supply's maximum output current (Iripple>=0.2 x Iout).
- Voltage Headroom: The capacitor's Rated Voltage must be comfortably higher than the power supply's maximum output voltage to prevent component degradation.
Application Scenario: Precision LED Testing Rig
Imagine a manufacturing test bench where high-power LED modules are rapidly pulsed at 2 kHz for quality control testing. Because the test cables are long, the voltage drops significantly by the time it reaches the LEDs.
If you use standard Remote Sensing wires without modification, the 2 kHz pulsing load will inject high-frequency noise into the sensitive +S and -S feedback loop. The power supply will try to fight this noise, resulting in voltage overshoot that could blow the LEDs.
The Solution: By twisting the +S and -S wires, routing them away from the main power cables, and placing a properly rated capacitor right at the test fixture terminal, the high-frequency ripple is filtered out. The power supply receives a clean feedback signal, ensuring perfectly stable voltage delivery during rapid testing pulses.
Conclusion
The Remote Sensing function is an indispensable tool for achieving tight voltage regulation over long distances. However, because it acts as a sensitive direct line to the power supply’s brain, it must be treated with care. By using twisted-pair wiring, keeping lines clear of power cables, and adding appropriate capacitors for dynamic loads, you can guarantee a rock-solid, noise-free power system.
If you have any technical issues, feel free to contact our team at contact@wellforces.co.nz. We provide professional support and a wide range of solutions.
