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name: similarity-transistor description: Use when working with transistor similarity calculations - comparing BJT MPNs, understanding NPN/PNP polarity matching, equivalent groups like 2N2222/PN2222, or transistor-specific similarity logic.

Transistor Similarity Calculator Skill

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

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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

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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

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

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

Similarity Thresholds

CopyHIGH_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:

Polarity Rules

NPN and PNP transistors always return LOW_SIMILARITY (0.3)

Suffix Handling

The calculator ignores common suffixes:

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

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

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

Test Examples

Copy// 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)

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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