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.

Optical Watts (W)

Required number input.

Responsivity Amperes Per Watt (A/W)

Required number input.

Current Gain

Required number input.

Approximate phototransistor collector current from incident optical power, photodiode responsivity and transistor current gain. 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]

Collector Amperes (A)

The resulting collector amperes returned as a number.

• Photodiode and phototransistor current depend on wavelength, optical power at the active area, responsivity, bias, gain, temperature, dark current, bandwidth, and load. Shot noise, amplifier noise, saturation, and optical coupling are separate design constraints.
• 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.

• PIN Responsivity

  Calculate a PIN photodiode's measured electrical responsivity from dark-subtracted photocurrent and incident optical power.

• Detector Noise Equivalent Power

  Detector noise-equivalent optical power for 1 Hz bandwidth from input-referred current-noise density and responsivity.

• APD Gain

  Calculate avalanche photodiode current multiplication from multiplied photocurrent and unity-gain primary photocurrent after dark-current subtraction.