Photosensor (for opto-isolator): Dark Current 10-100 nA

Component Specifications

Definition

A photosensor is a semiconductor-based electronic component designed to detect and convert light signals into electrical signals. In opto-isolator applications, it serves as the receiver element, typically paired with an infrared LED emitter. When light from the emitter strikes the photosensor, it generates a photocurrent that modulates the output circuit, enabling signal transmission while maintaining complete electrical isolation between input and output sides. This component is critical for noise reduction, voltage level shifting, and protection against voltage spikes in industrial control systems.

Working Principle

The photosensor operates on the photoelectric effect, where incident photons (typically infrared light from an LED) excite electrons in the semiconductor material (commonly silicon-based phototransistors or photodiodes). This generates a photocurrent proportional to the light intensity. In opto-isolators, this current is amplified to drive the output circuit, creating an electrically isolated replica of the input signal. Key parameters include response time, spectral sensitivity (centered around 850-950 nm for IR), and current transfer ratio (CTR).

Materials

Semiconductor substrate: Silicon (Si) for photodiodes/phototransistors; Encapsulation: Epoxy resin or silicone for optical coupling and protection; Lead frame: Copper alloy with tin plating; Optical window: Clear epoxy or glass for light transmission.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Dark Current	10-100 nA
Package Type	DIP-4, DIP-6, SOP-4
Response Time	3-20 μs
Isolation Voltage	2500-5000 Vrms
Spectral Sensitivity	850-950 nm (Infrared)
Operating Temperature	-40°C to +100°C
Current Transfer Ratio (CTR)	20-600%

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 9001, IEC 60747-5-5, JEDEC JESD22

Parent Products

This component is used in the following industrial products

Opto-isolator / Relay

An electronic component that provides electrical isolation and signal switching between circuits in I/O modules.

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Engineering Analysis

Risks & Mitigation

CTR degradation over time due to LED aging
Contamination of optical path reducing sensitivity
Thermal runaway in high-temperature environments
ESD damage during handling
Misalignment during assembly causing signal loss

FMEA Triads

Trigger: LED emitter degradation in opto-isolator
Failure: Decreased CTR leading to signal loss
Mitigation: Use components with matched aging characteristics; implement periodic CTR testing; design circuits with 30-50% CTR margin

Trigger: Moisture ingress into package
Failure: Internal condensation scattering light, reducing sensitivity
Mitigation: Select epoxy-encapsulated components with IP67 equivalent sealing; control humidity in storage/assembly

Trigger: Excessive operating temperature
Failure: Thermal damage to semiconductor junction
Mitigation: Adhere to temperature specifications; add heat sinking if needed; monitor ambient temperature in enclosure

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

CTR: ±20% typical batch variation; Response time: ±15%; Isolation voltage: +0/-10% test tolerance

Test Method

IEC 60747-5-5 for optoelectronic isolation; JEDEC JESD22 for environmental reliability; In-circuit CTR measurement at 5mA/5V; Hi-pot testing at 1.2x rated isolation voltage

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Photosensor (for opto-isolator)

Manufacturer profiles associated with Photosensor (for opto-isolator).

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the difference between a phototransistor and photodiode photosensor in opto-isolators?

Phototransistors provide higher gain and sensitivity but slower response (10-20 μs), ideal for DC/low-frequency signals. Photodiodes offer faster response (1-5 μs) but lower output, suitable for high-speed digital applications. Selection depends on speed vs. sensitivity requirements.

How does temperature affect photosensor performance in industrial environments?

Temperature impacts CTR (typically decreasing by 0.5%/°C above 25°C) and dark current (doubling every 10°C rise). Industrial-grade components use temperature-compensated designs and wide operating ranges (-40°C to +100°C) for stability.

Can photosensors be replaced without recalibrating the opto-isolator system?

Generally yes if specifications match, particularly CTR, response time, and package. However, batch variations may require minor circuit adjustments. Always verify compatibility with manufacturer datasheets.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Photosensor (for opto-isolator)