Resistor

Resistor #

The fundamental passive component that opposes electric current flow. Breadpad’s resistor model includes temperature coefficients and tolerance for comprehensive circuit analysis.

Basic Properties #

  • Terminals: 2 (Start and End)
  • SPICE Designation: R
  • Default Value: User-specified in Ohms (Ω)

Key Parameters #

Primary Parameter #

  • Resistance: The opposition to current flow, measured in Ohms (Ω)
    • Supports values from milliohms (mΩ) to gigaohms (GΩ)
    • Automatically formatted with SI prefixes (e.g., 10kΩ, 2.2MΩ)

Temperature Coefficients #

  • TC1: First-order temperature coefficient (ppm/°C)

    • Typical values: ±50 to ±200 ppm/°C for precision resistors
    • Default: 0 (temperature independent)

  • TC2: Second-order temperature coefficient (ppm/°C²)

    • Usually much smaller than TC1
    • Default: 0 (no second-order effects)

Temperature-dependent resistance is calculated as:

R(T) = R₀ × (1 + TC1×(T-T₀) + TC2×(T-T₀)²)

Tolerance (Premium Feature) #

  • Tolerance: Manufacturing variation as percentage
    • Common values: 1%, 5%, 10%, 20%
    • Used in Monte Carlo analysis with Gaussian distribution
    • 6-sigma approach: 99.7% of values within ±tolerance

SPICE Netlist Format #

Basic resistor:

R1 node1 node2 1k

With temperature coefficients:

R1 node1 node2 1k TC1=50e-6 TC2=0

With tolerance (Monte Carlo):

R1 node1 node2 {1k*(1+gauss(0,0.05/3,6))}

Common Applications #

Pull-up/Pull-down Resistors #

  • Digital circuits: 1kΩ - 10kΩ
  • Weak pull-ups: 47kΩ - 100kΩ

Current Limiting #

  • LED circuits: 220Ω - 1kΩ
  • Base resistors (BJT): 1kΩ - 10kΩ

Voltage Dividers #

  • Signal attenuation
  • Reference voltage generation
  • Level shifting

Biasing Networks #

  • Transistor biasing
  • Op-amp circuits
  • Filter networks

Power Rating Considerations #

While Breadpad doesn’t explicitly model power ratings, consider:

  • P = I²R = V²/R
  • Common ratings: 1/8W, 1/4W, 1/2W, 1W
  • Derate by 50% for reliability

Resistor Types and Their Models #

Carbon Film #

  • TC1: ±200 to ±500 ppm/°C
  • Tolerance: 5%
  • General purpose

Metal Film #

  • TC1: ±50 to ±100 ppm/°C
  • Tolerance: 1%
  • Precision applications

Wire Wound #

  • TC1: ±20 ppm/°C
  • Tolerance: 0.1% - 1%
  • High power, precision

SMD Thick Film #

  • TC1: ±100 to ±200 ppm/°C
  • Tolerance: 1% - 5%
  • Most common in modern circuits

Tips for Simulation #

  1. Convergence: Very small resistors (<1mΩ) or very large (>1GΩ) can cause convergence issues
  2. Temperature Sweeps: Use TC1/TC2 for realistic temperature analysis
  3. Monte Carlo: Set tolerance for statistical analysis of circuit variations
  4. Parasitic Resistance: Add small resistors (0.01-0.1Ω) to model PCB traces and connections

See Also #