Catches of Kelvin or 4 Wires Operation

Let’s face it, there’s no free meal, there are prices to pay if Kelvin or 4 Wires operations were to be used

1.       4 wires operation supplies are generally more costly, you pay more $$$ for this feature.

2.       2 additional wires are needed to sense the voltage

3.       There’s limitation on how much voltage the supply can source, if max voltage it is capable is 15V, and there’s 10V drop across the cables, which means only 5V is available across the load

4.       It works by sensing what is at the voltage across the load and adjust itself – which means it is a feedback control loop, and there’s limitation on how fast it can adjust itself, or how stable it can be. When very fast current transient occurs, capacitor across load is generally required.

Why do we need Kelvin or 4 Wires operation?

In short, that’s because all interconnect has resistance, for sure some amount of voltage will drop across the cables, causing less than desire voltage level at load end.

Why 4 wires or kelvin operation is the solution? See the diagram below, since there’s no voltage drop across the sense wires, the source see what the actual voltage across the load, and can adjust accordingly.