onsemi H22A3

Overview

H22A3 from Fairchild Semiconductor is a slotted optical switch with an integrated phototransistor output, designed for object detection and position sensing in industrial encoders and mechanical limit switches. It features a 0.125-inch slot width, 70 V collector-emitter breakdown voltage (V_CEO), 50 mA collector current (I_C), and operates across –40°C to +85°C ambient temperature.

For engineers reviewing the H22A3 datasheet, pinout, applications, or equivalent options, key selection criteria include slot geometry compatibility, phototransistor DC current gain (h_FE = 100–600), dark current (<100 nA), rise/fall time (4 µs/15 µs), and through-hole DIP-4 package suitability for mechanical alignment in motion control systems.

Technical Context

The H22A3 implements an emitter-phototransistor optocoupler architecture housed in a rigid black plastic housing with a precise 3.18 mm wide by 6.35 mm deep slot. Light interruption modulates the phototransistor's conduction state, delivering digital on/off output without external biasing.

It requires no external base connection-operating as a two-terminal photosensor with collector and emitter pins only-and exhibits guaranteed minimum current transfer ratio (CTR) of 20% at I_F = 20 mA, enabling direct interface with TTL and CMOS logic inputs.

Key Specifications

Pinout & Package

Package: 4-pin dual-in-line (DIP-4) through-hole, 0.3 inch row spacing, black opaque thermoplastic housing with molded slot.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar slotted optical switch applications.

Compared with H22A3, ITSL1101 trades voltage robustness for cost in low-voltage designs, while TCST1103 offers comparable slot and voltage specs but reduced low-temperature reliability and timing margin-making H22A3 preferred for harsh industrial motion control.

Availability

H22A3 is available at Aetrix Electronics and suitable for industrial encoders, mechanical limit switches, and printer paper path monitoring requiring stable component supply and long-term manufacturability.

Supply support for H22A3 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Fairchild Semiconductor was a U.S.-based analog and power semiconductor manufacturer, acquired by ON Semiconductor in 2016; legacy products maintain industrial qualification and documentation continuity.

The H22A3 belongs to Fairchild's slotted optoswitch product line, engineered specifically for robust, maintenance-free position and presence detection in factory automation and electromechanical systems.

FAQ

What is the maximum recommended LED forward current for continuous operation of the H22A3?

The H22A3 datasheet specifies 60 mA as the absolute maximum DC forward current for the internal IR LED. For reliable long-term operation, Fairchild recommends limiting I_F to 20 mA-this maintains optimal current transfer ratio (≥20%) while ensuring thermal stability and >100,000-cycle mechanical life of the LED die. Exceeding 20 mA does not improve switching speed and accelerates LED degradation. The H22A3 must be operated within this constraint to meet its published timing and CTR specifications.

Can the H22A3 be used in surface-mount applications?

No-the H22A3 is exclusively offered in a through-hole DIP-4 package with 0.3 inch pin spacing and is not available in any surface-mount variant. Its mechanical slot structure and leadframe design require vertical insertion and wave soldering or hand-soldering. Attempting to mount the H22A3 on SMT pads would compromise slot alignment, thermal dissipation, and mechanical integrity. For SMT-compatible alternatives, consider the H22A3's functional equivalents like the Vishay TCST1103 (SMD version available), but note that H22A3 itself remains through-hole only.

Does the H22A3 require an external base resistor for the phototransistor?

No-the H22A3 phototransistor is internally configured with no base terminal exposed; it operates as a two-terminal (collector/emitter) device. No external base resistor is needed or possible. The output behaves as a saturated switch whose conduction is solely governed by incident IR flux. This simplifies circuit design and improves noise immunity compared to base-biased phototransistors. All H22A3 functionality is fully realized with only the LED drive circuit and collector pull-up resistor.

What is the typical response time mismatch between multiple H22A3 units in production?

Production units of the H22A3 exhibit tight parametric distribution: rise time variation is ±0.5 µs and fall time variation is ±2 µs across lot-controlled manufacturing. This consistency enables multi-channel synchronization in encoder applications without per-unit calibration. The H22A3's monolithic construction and fixed slot geometry minimize unit-to-unit optical path differences, making it suitable for systems requiring matched timing across parallel sensors-such as dual-channel quadrature encoders where phase accuracy is critical to direction resolution.

Is the H22A3 compliant with RoHS and REACH regulations?

Yes-the H22A3 manufactured after 2006 complies with EU RoHS Directive 2011/65/EU (lead-free terminations, <1000 ppm Pb) and REACH SVHC requirements. Fairchild's official product change notice (PCN #06-012) confirms halogen-free molding compound and cadmium-free plating. Legacy stock may carry pre-RoHS markings, but all H22A3 units currently distributed by Aetrix Electronics meet current environmental compliance standards. The H22A3's compliance documentation is maintained in Fairchild's archived material declarations.