Floating node
A node with no conductive path to ground stops the solver. Here is how to find one and what to do about it.
Britt Espinosa
Last Update 15 dagen geleden
A node with nowhere for current to go gives the solver an equation it cannot balance. CircuitSim names floating nodes in several messages, and the underlying engine text uses the same phrase in technical details.
Where the phrase turns up
In the steps for The simulation stopped making progress:
Check for floating nodes, extreme component values, and ideal switching loops.
In the steps for the warning The live simulation may be stalled:
Otherwise stop the simulation, check the circuit for floating nodes or extreme values, and run it again.
And in the technical details behind Missing ground reference, where the engine reports a floating node or no DC path to ground.
What counts as floating
A node qualifies when nothing gives it a resistive path back to the reference. Common shapes:
- A pin left unwired, so the net attached to it has one member
- A stage coupled only through capacitors, which block DC entirely
- A transformer secondary or an optocoupler output, isolated on purpose
- A net label placed once, which names a net without joining it to anything
- The junction between two ideal switches that are both open at time zero
Fixes, in order of how often they apply
Connect the pin. Open the Info panel and check the Status tab for a warning shaped like this one, which names the component and every pin involved:
U1 has unconnected pins: A, B.
Its steps are to show the component in the schematic, then connect each listed pin or mark pins that are intentionally unused with a No connection marker. Press Q to place that marker.
Give an isolated section a reference. Connect a high value resistor, such as 1 GΩ, from the isolated section to ground. The current through it is negligible, and the solver gets the path it needs.
Add a bleed path around a capacitor. A high value resistor in parallel with a coupling capacitor, or from the coupled node to ground, does the same job for a DC blocked stage.
Check your net labels. The schematic status list warns when a net label is not attached to a wire or pin, and again when a label is placed once and therefore connects nothing. Both warnings offer Show in schematic so you can select the label directly.
When a probe is the floating part
A probe on a dangling wire produces no data, and the netlist warnings say so:
A probe is not connected to a usable circuit branch and will not produce results.
Move the probe onto a branch that carries current, or onto a node that has a path to ground.
If the circuit still will not solve
Delete or disconnect one section at a time and run after each change. The section whose removal lets the run complete contains the floating node. If nothing isolates it, copy the technical details from the issue in the Status tab and send them to support with the circuit name.