Phototransistors

A phototransistor is a semiconductor device that converts light into electrical signals. Its core structure is a PN or PIN junction. When light of a specific wavelength strikes the semiconductor material, the photons excite electron-hole pairs, generating a photocurrent under the action of a built-in electric field. Unlike conventional transistors, its collector current is directly controlled by light intensity, amplifying the photoelectric signal.

 

1. What are the Key Characteristics of Phototransistors?

Spectral Response Range: Visible light (400-700nm) and infrared light (700-1100nm).

 

Dark Current: Leakage current in the absence of light (typically <1nA).

 

Response Time: Rise/Fall Time (High-Speed Models Can Reach Nanoseconds).

 

Current Gain (β): The ratio of collector to base current under illumination (typically 100-1000).

 

2. What are the Types of Phototransistors?

Type	Structural Features	Applicable Scenarios
NPN	Base region receives light	general-purpose photodetection
PNP	Emitter photosensitive design	low-power devices
Darlington	Dual-transistor cascade	amplifying weak light signals

 

3. What are the Typical Applications of Phototransistors?

Industrial Automation: Photoelectric Encoders, Object Detection Sensors.

 

Consumer Electronics: Ambient Light Sensing (e.g., Mobile Phone Screen Brightness Adjustment).

 

Security Systems: Infrared Remote Control Receivers, Smoke Detectors.

 

Medical Equipment: Optical Signal Acquisition in Pulse Oximeters.

 

4. Selection and Usage Recommendations for Phototransistors

Matching the Light Source Wavelength with the Device Spectral Response Curve;

 

Considering Dark Current Drift in High-Temperature Environments;

 

Selecting a Package with Low Junction Capacitance for High-Speed Applications;

 

Anti-Static Design (ESD Sensitivity Typically <200V).