All phototransistors are based on a photodiode as the photon-to-current converter but include an emitter diffusion creating an npn transistor. The current produced by the photodiode is increased by the hFE of the transistor structure yielding light currents in the milliamp to tens of milliamps. However, the speed-of-response of the photodiode is compromised by the transistor structure with the internal base resistance and the base-collector capacitance (rb-b’ CC) time constant being the primary driver.
Phototransistors have been a primary sensor for decades and continue to be the sensor-of-choice when speed is not of primary importance, but there is need for significant output light current.
- Click on part number for datasheet.
- Radiation source is a 940nm IRED. VCE=5V.
- Measured at IC=100mA.
- Acceptance angle at half power points.
- Measured under dark conditions, VCE=10V.
- A dark condition exists when further irradiation shielding does not reduce ID
- Radiation source is a 850nm IRED. VCE=5V.
- Radiation source is a 660nm LED. VCE=5V.