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analyze-power-nets

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Analyzes KiCad PCB files to identify power nets by looking up component datasheets via AI. Use when you need to determine which nets are power/ground nets and what track widths to use, especially when KiCad pintype annotations are missing or unreliable.

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Source SKILL.md: https://github.com/drandyhaas/KiCadRoutingTools/blob/HEAD/.claude/skills/analyze-power-nets/SKILL.md

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Analyze Power Nets

When this skill is invoked, perform a full AI-powered analysis of the PCB to identify power nets and recommend track widths.

Step 1: Load and Extract Components

from analyze_power_paths import (
    analyze_pcb, get_components_needing_analysis, classify_component,
    trace_power_paths, get_power_net_recommendations, format_analysis_report,
    ComponentRole
)

components, pcb_data = analyze_pcb("path/to/file.kicad_pcb")
unknown = get_components_needing_analysis(components)

Step 2: Auto-Classify Obvious Components

These are already handled automatically - no AI needed:

PrefixRoleReason
R (resistor)SHUNTPull-ups, voltage dividers
C (capacitor)SHUNTDecoupling caps
L (inductor)PASS_THROUGHSeries filter element
FB (ferrite bead)PASS_THROUGHSeries filter element
F (fuse)PASS_THROUGHSeries protection
LEDCURRENT_SINKConsumes current
SW (switch)PASS_THROUGHPower switching

Step 3: AI Analysis for Unknown Components

For each component in the unknown list, you MUST:

3a. Identify What It Is

Use WebSearch to look up the component:

WebSearch: "<part_value> <footprint_hint> datasheet"

Examples:

  • "DB9 connector pinout" - Is it signal or power?
  • "1N4004 diode datasheet" - Rectifier vs signal diode
  • "3906 transistor datasheet" - Power switch or signal amp?
  • "LT1129 regulator datasheet" - Voltage regulator specs
  • "MCF5213 power consumption" - IC current requirements

3b. Determine Its Role

Based on the datasheet/search results, classify as:

RoleCriteria
POWER_SOURCESupplies current to the board: power jacks, battery connectors, regulator outputs, USB power inputs
CURRENT_SINKConsumes significant current: ICs, MCUs, CPLDs, FPGAs, motor drivers, high-power LEDs
PASS_THROUGHCurrent flows through it: power switches, transistors used as switches, protection diodes in series
SHUNTBranches off the power path: ESD protection diodes, TVS diodes, signal connectors

3c. Estimate Current Rating

From the datasheet, find:

  • For ICs: Total supply current (ICC, IDD)
  • For regulators: Maximum output current
  • For connectors: Expected load current

3d. Apply Classification

classify_component(components, 'J201', ComponentRole.POWER_SOURCE,
                   current_rating_ma=1000,
                   notes="DC barrel jack - main power input")

Step 4: Key Components to Analyze

Focus AI analysis on these component types:

Power Input Connectors (J*, P*, TB*, CN*)

  • Question: Is this a power input or signal connector?
  • Look for: Connection to power nets, barrel jack footprints, terminal blocks
  • Classify as: POWER_SOURCE if it brings power onto the board

Diodes (D* followed by digit)

  • Question: Protection diode, rectifier, or LED?
  • Look for: Part number (1N4004 = rectifier, BAT54 = Schottky, LED = LED)
  • Classify as:
    • SHUNT if reverse protection (cathode to power, anode to GND)
    • PASS_THROUGH if series rectifier in power path
    • CURRENT_SINK if LED

Transistors (Q*)

  • Question: Power switch or signal amplifier?
  • Look for: Connections to power nets, gate/base drive signals
  • Classify as: PASS_THROUGH if switching power, SHUNT if signal

ICs (U*)

  • Question: How much current does it consume?
  • Look for: ICC/IDD in datasheet, number of I/O pins
  • Classify as: CURRENT_SINK with appropriate current rating
  • Note: Regulators are auto-detected by power_out pins

Voltage Regulators (VR*, or U* with regulator part number)

  • Question: What is the maximum output current?
  • Look for: Output current spec in datasheet
  • Classify as: POWER_SOURCE with max output current

Step 5: Trace Power Paths

After classifying all components:

paths = trace_power_paths(pcb_data, components)
recommendations = get_power_net_recommendations(pcb_data, components, paths)

Step 6: Generate Report

print(format_analysis_report(pcb_data, components, paths, recommendations))

Provide the user with:

  1. Summary of component classifications
  2. Traced power paths showing current flow
  3. Recommended power nets and track widths
  4. Ready-to-use --power-nets command line arguments

Example Analysis Session

When analyzing a board like kit-dev-coldfire-xilinx_5213:

  1. J201 (JACK_2P): WebSearch "DC barrel jack 2.1mm" → POWER_SOURCE, 1000mA
  2. TB201 (CONN_2): Terminal block on same net as J201 → POWER_SOURCE, 1000mA
  3. D201 (1N4004): WebSearch "1N4004 datasheet" → Rectifier, but connected cathode-to-power → SHUNT (reverse protection)
  4. Q101 (3906): WebSearch "2N3906 PNP transistor" → Emitter on +3.3V → PASS_THROUGH (power switch)
  5. U102 (MCF5213): WebSearch "MCF5213 power consumption" → CURRENT_SINK, 200mA
  6. U301 (XCR3256): WebSearch "XCR3256 CPLD power" → CURRENT_SINK, 150mA

Output Format

## Power Net Analysis for board.kicad_pcb

### AI-Classified Components
| Ref | Value | Role | Current | Notes |
|-----|-------|------|---------|-------|
| J201 | JACK_2P | POWER_SOURCE | 1000mA | DC power input |
| U102 | MCF5213 | CURRENT_SINK | 200mA | ColdFire MCU |

### Power Paths Traced
  TB201 (power input) → SW_ONOFF201 → F201 → VR201 → +3.3V → U102 (MCU)

### Recommended Power Nets
| Net | Width | Reason |
|-----|-------|--------|
| Net-(TB201-P1) | 0.5mm | Power input path |
| Net-(F201-Pad1) | 0.5mm | After fuse |
| +3.3V | 0.5mm | Main rail, 500mA total |
| /VDDPLL | 0.3mm | PLL supply, 10mA |

### Routing Command
--power-nets "GND" "+3.3V" "/VDDPLL" "/VCCA" "Net-(TB201-P1)" --power-nets-widths 0.5 0.5 0.3 0.3 0.5

Important Notes

  1. Do not rely on component reference prefixes for ICs, connectors, or transistors - always look up the actual part
  2. Check net connections - a connector on a power net is likely a power connector
  3. Trace upstream - if a component feeds into a known power net, its input is also a power net
  4. Ground nets are always power nets - include GND, GNDA, AGND, VSS, etc.