Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

Early voltage magnitude (V)

Required number input.

Bias VCE (V)

Required number input.

Collector current at bias (A)

Required number input.

Estimate small-signal BJT output resistance from Early voltage magnitude, bias VCE, and collector current at that bias. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Small-signal output resistance (Ω)

The resulting small-signal output resistance returned as a number.

• BJT calculations using a fixed current gain or junction drop are operating-point approximations. Gain, Early effect, saturation voltage, leakage, temperature, frequency, bias network loading, and safe operating area vary by device and conditions.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

• BJT Early Voltage Effect

  Estimate collector current at a new collector-emitter voltage using the linear Early-effect model at fixed base drive.

• I2C Pullup Min

  Compute the minimum I2C pull-up resistance from VDD, the maximum output low voltage, and the sink current.

• Opamp Short Circuit Power

  Estimate output-stage dissipation during an op-amp short to ground as supply-to-short voltage magnitude times the measured short-circuit current; this is not total device power.