INDUSTRY COMPONENT

Phototransistor

A phototransistor is a semiconductor device that converts light signals into electrical signals, used for optical sensing and isolation in industrial applications.

View Specifications

Component Specifications

Definition
A phototransistor is a bipolar junction transistor (BJT) or field-effect transistor (FET) with a light-sensitive base or gate region. It operates by generating electron-hole pairs when exposed to light, which modulates the transistor's current flow. In optical couplers, it serves as the receiver component, detecting light from an LED or laser emitter to provide electrical isolation between circuits. Key characteristics include spectral response (typically 400-1100 nm for silicon), responsivity, response time, and dark current.
Working Principle
The phototransistor works on the photoelectric effect. When photons strike the base-collector junction, they generate electron-hole pairs, creating a base current proportional to light intensity. This current is amplified by the transistor's gain (β), producing a larger collector-emitter current. In optical couplers, light from an emitter (e.g., infrared LED) crosses an isolation barrier and activates the phototransistor, transmitting signals without electrical contact.
Materials
Typically made from silicon (Si) for visible to near-infrared detection, or germanium (Ge) for longer wavelengths. Package materials include epoxy resin (black for light blocking) or ceramic for high-temperature applications. Lead frames are often copper alloy with tin plating.
Technical Parameters
  • Dark Current 10-100 nA
  • Responsivity 0.5-0.8 A/W at 850 nm
  • Response Time 2-10 μs
  • Spectral Range 400-1100 nm (Si)
  • Isolation Voltage 2500-5000 Vrms
  • Current Transfer Ratio (CTR) 20-600%
  • Collector-Emitter Voltage (Vceo) 30-70 V
Standards
ISO 9001, IEC 60747-5-5, JEDEC JESD22

Industry Taxonomies & Aliases

Commonly used trade names and technical identifiers for Phototransistor.

phototransistor optical coupler optocoupler light sensor optoelectronic component signal isolation industrial electronics Phototransistor in Computer, Electronic and Optical Product Manufacturing

Parent Products

This component is used in the following industrial products

Optical Coupler

An electronic component that transfers electrical signals between two isolated circuits using light waves.

View Product Details

Engineering Analysis

Risks & Mitigation
  • Degradation of CTR over time due to LED aging
  • Temperature sensitivity affecting performance
  • Potential for saturation at high light levels
  • Electrostatic discharge (ESD) damage during handling
FMEA Triads
Trigger: LED emitter degradation in the optical coupler
Failure: Reduced CTR leading to signal loss or circuit malfunction
Mitigation: Use high-reliability LEDs, implement burn-in testing, and design circuits with CTR margin
Trigger: ESD exposure during installation
Failure: Permanent damage to the phototransistor junction, causing open or short circuits
Mitigation: Follow ESD protection protocols (e.g., grounded workstations, antistatic packaging)
Trigger: High ambient temperature
Failure: Increased dark current and reduced sensitivity, leading to signal errors
Mitigation: Select components rated for operational temperature range, add heat sinks or cooling

Industrial Ecosystem

Compatible With

Interchangeable Parts

Compliance & Inspection

Tolerance
CTR tolerance typically ±20% to ±50% depending on grade; response time within ±10% of spec
Test Method
Testing per IEC 60747-5-5 for optoelectronic devices, including CTR measurement (input current vs. output current), isolation voltage test (hipot), and spectral response analysis

Buyer Feedback

★★★★☆ 4.9 / 5.0 (25 reviews)

"As a professional in the Computer, Electronic and Optical Product Manufacturing sector, I confirm this Phototransistor meets all ISO standards."

"Standard OEM quality for Computer, Electronic and Optical Product Manufacturing applications. The Phototransistor arrived with full certification."

"Great transparency on the Phototransistor components. Essential for our Computer, Electronic and Optical Product Manufacturing supply chain."

Related Components

Main Processor
Central processing unit for industrial IoT gateways enabling real-time data processing and communication in manufacturing environments.
Memory Module
Memory module for Industrial IoT Gateway data storage and processing
Storage Module
Industrial-grade storage module for data logging and firmware in IoT gateways
Ethernet Controller
Industrial Ethernet controller for real-time data transmission in Industrial IoT Gateways.

Frequently Asked Questions

What is the difference between a phototransistor and a photodiode?

A phototransistor provides internal gain (amplification) due to its transistor structure, offering higher sensitivity but slower response than a photodiode, which has no gain but faster speed.

How does a phototransistor ensure electrical isolation in optical couplers?

It uses light as the signal medium across a transparent isolation barrier (e.g., air or dielectric), preventing direct electrical connection and allowing high-voltage isolation between input and output circuits.

What factors affect the Current Transfer Ratio (CTR) of a phototransistor in couplers?

CTR depends on LED efficiency, phototransistor responsivity, alignment, aging (degradation over time), and temperature, typically decreasing with higher temperatures or prolonged use.

Can I contact factories directly?

Yes, each factory profile provides direct contact information.

Get Quote for Phototransistor

Photosensor (for opto-isolator) Phototransistor Die