KiCad ERC: Input Power Pin Not Driven By Any Output Power Pins

Diagnostic signature

Input Power pin not driven by any Output Power pins

An Electrical Rules Check (ERC) diagnostic emitted when a component's power input pin connects to a net without an active power output source. This frequently occurs when power routes through passive components or generic connectors.

What it means

In KiCad's Schematic Editor (Eeschema), every symbol pin is assigned an electrical type, such as 'Power input', 'Power output', or 'Passive'. The Electrical Rules Check (ERC) algorithm evaluates these types across all nets to ensure safe and complete connectivity. This diagnostic indicates that a pin designated as a 'Power input' (like VCC, VDD, or GND on an integrated circuit) is present on a net, but the schematic compiler cannot locate a corresponding 'Power output' pin driving that same net. To the ERC engine, the net appears electrically unpowered, meaning the physical component might lack a required voltage source.

Why it happens

The ERC engine strictly analyzes pin types and does not automatically infer power flow through connectors or intermediary components. If a power net originates from a generic board connector, its pins are typically typed as 'Passive' rather than 'Power output'. Similarly, if power is intentionally routed through a switch, fuse, ferrite bead, or inductor, the component provides passive pins, which severs the logical power trace from the original source. Because the engine cannot traverse passive components to find a valid 'Power output', it flags the downstream 'Power input' pins as un-driven.

Minimal reproduction

(kicad_sch (version 20230121) (symbol (lib_id "Connector:Conn_01x02") (at 100 100 0) (unit 1)) (symbol (lib_id "Amplifier_Operational:LM321") (at 150 100 0) (unit 1)) (wire (pts (xy 100 100) (xy 150 100))))

How to fix it

Designate the isolated power net as an active power source by attaching a PWR_FLAG symbol, or modify the source component's pin type to 'Power output'.

```KiCad Schematic
(kicad_sch (version 20230121) (symbol (lib_id "Connector:Conn_01x02") (at 100 100 0) (unit 1)) (symbol (lib_id "Amplifier_Operational:LM321") (at 150 100 0) (unit 1)) (symbol (lib_id "power:PWR_FLAG") (at 125 110 0) (unit 1)) (wire (pts (xy 100 100) (xy 150 100))) (wire (pts (xy 125 110) (xy 125 100))))
```

Step 1

• Open the schematic and locate the net triggering the ERC violation.

Step 2

• If the net is powered by a generic connector or routed through a passive component, open the 'Add Power Symbol' dialog.

Step 3

• Search for the 'PWR_FLAG' symbol from the power library and place it on the schematic.

Step 4

• Connect the PWR_FLAG explicitly to the un-driven power net.

Step 5

• Re-run the ERC to confirm the 'Power input' pin is now successfully driven.

Upstream references

Getting Started in KiCad: Electrical Rules Check

Schematic Editor: Power Pins and Power Flags