Transistor Similarity Calculator Skill

Guidance for working with TransistorSimilarityCalculator in the lib-electronic-components library.

For metadata-driven similarity architecture, see /similarity-metadata:

SpecImportance levels (CRITICAL, HIGH, MEDIUM, LOW, OPTIONAL)
ToleranceRule types (exactMatch, percentageTolerance, minimumRequired, etc.)
SimilarityProfile contexts (DESIGN_PHASE, REPLACEMENT, COST_OPTIMIZATION, etc.)
Calculator integration patterns and gotchas

Overview

The TransistorSimilarityCalculator compares bipolar junction transistors (BJTs) based on:

Equivalent groups - Known interchangeable parts
Polarity - NPN vs PNP (must match)
Family/series - BC, 2N, PN, etc.

Applicable Types

ComponentType.TRANSISTOR
ComponentType.TRANSISTOR_NXP
ComponentType.TRANSISTOR_VISHAY
// Any type starting with "TRANSISTOR_"

Note: Does NOT apply to MOSFETs - use MosfetSimilarityCalculator for those.

Similarity Thresholds

HIGH_SIMILARITY = 0.9;   // Equivalent parts
MEDIUM_SIMILARITY = 0.7; // Same family, compatible
LOW_SIMILARITY = 0.3;    // Same category, different specs or polarity

Equivalent Groups

The calculator knows these equivalent groups:

| Group | Members | |-------|---------| | 2N2222 family | 2N2222, 2N2222A, PN2222, PN2222A | | 2N3904 family | 2N3904, PN3904 | | 2N3906 family | 2N3906, PN3906 | | 2N2907 family | 2N2907, 2N2907A, PN2907, PN2907A | | BC547 family | BC547, BC547A, BC547B, BC547C | | BC557 family | BC557, BC557A, BC557B, BC557C |

Polarity Rules

NPN and PNP transistors always return LOW_SIMILARITY (0.3)

| Comparison | Result | |------------|--------| | 2N2222 (NPN) vs PN2222 (NPN) | 0.9 (equivalent) | | 2N2222 (NPN) vs 2N2907 (PNP) | 0.3 (different polarity) | | 2N3904 (NPN) vs 2N3906 (PNP) | 0.3 (complementary pair, different polarity) |

Suffix Handling

The calculator ignores common suffixes:

-T, -TR, -TA (tape/reel packaging)
A, B, C (grade suffixes on BC series)

calculator.calculateSimilarity("2N2222", "2N2222-T", registry);
// Returns 0.9 (same transistor, different packaging)

calculator.calculateSimilarity("2n2222", "2N2222", registry);
// Returns 0.9 (case insensitive)

Test Examples

// Equivalent parts
calculator.calculateSimilarity("2N2222", "PN2222", registry);
// Returns 0.9

// Same part with variant
calculator.calculateSimilarity("2N2222", "2N2222A", registry);
// Returns 0.9

// NPN vs PNP
calculator.calculateSimilarity("2N2222", "2N2907", registry);
// Returns 0.3

// Different families
calculator.calculateSimilarity("2N2222", "BC547", registry);
// Returns 0.3

// Non-transistor parts
calculator.calculateSimilarity("LM358", "MC1458", registry);
// Returns 0.0

Implementation Notes

Returns 0.0 for non-transistor MPNs
Returns 0.0 for mixed transistor/non-transistor comparison
Symmetry: sim(A,B) == sim(B,A)

Learnings & Quirks

Part Number Patterns

2N prefix: JEDEC standard (2N2222, 2N3904, etc.)
PN prefix: Often equivalent to 2N (PN2222 ≈ 2N2222)
BC prefix: European standard (BC547, BC557)
MPS prefix: Motorola/ON Semi (MPS2222A ≈ 2N2222A)

Complementary Pairs

2N3904 (NPN) / 2N3906 (PNP)
BC547 (NPN) / BC557 (PNP)
These are designed to work together but are NOT equivalent