onsemi H22B3

Overview

H22B3 from Fairchild Semiconductor is a gallium arsenide infrared emitting diode coupled with a silicon photodarlington in a plastic optical interrupter housing, designed for mechanical position sensing and object detection. It delivers 2.0 mA on-state collector current at I_F = 2 mA, V_CE = 1.5 V; supports 30 V V_CEO; operates from −55°C to +100°C; and features a 0.035" aperture for precise light interruption in industrial encoders.

For engineers reviewing the H22B3 datasheet, pinout, applications, or equivalent options, key selection criteria include its photodarlington output gain, ambient light rejection via opaque housing, 45 µs turn-on time at 10 mA input, and compatibility with 5 V logic-level switching circuits requiring high sensitivity and low-cost opto-isolation.

Technical Context

The H22B3 implements a monolithic optocoupled structure where an IR LED optically triggers a silicon photodarlington transistor, enabling high-current gain (I_C(ON) = 2.0 mA @ 2 mA input) without external amplification. Its open-collector photodarlington output provides direct interface to TTL/CMOS loads and supports pull-up configurations up to 30 V.

Designed as an optical interrupter switch, the H22B3 uses a fixed 0.035" gap between emitter and detector to enable physical interruption by opaque objects. The opaque plastic housing ensures ambient light rejection, while the 1.0 V V_CE(SAT) at I_F = 10 mA / I_C = 1.8 mA enables low-loss switching in power-constrained detection paths.

Key Specifications

Pinout & Package

Package: 4-pin DIP plastic housing with side-entry optical gap; 0.472" × 0.249" footprint; lead pitch 0.100"; RoHS-compliant matte tin leads.

Key Features

Applications

Equivalent & Alternatives

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

Compared with H22B2 and TCST1103, the H22B3 offers the highest photodarlington gain among common DIP interrupters-enabling robust detection with marginal optical coupling-while maintaining industrial temperature range and mechanical aperture consistency, making it optimal for cost-sensitive, medium-speed position sensing where signal margin is critical.

Availability

H22B3 is available at Aetrix Electronics and suitable for industrial automation, printer subsystems, and automotive throttle sensing requiring stable component supply and long-term lifecycle support.

Supply support for H22B3 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 IC manufacturer acquired by ON Semiconductor in 2016; known for high-reliability optoelectronics and power management solutions.

The H22B3 belongs to Fairchild's legacy photointerrupter family designed specifically for mechanical position sensing in cost-sensitive industrial and office equipment where ambient light immunity and DIP-mounting are required.

FAQ

What is the maximum continuous forward current rating for the H22B3 emitter diode?

The H22B3 emitter diode has a maximum continuous forward current (I_F) rating of 50 mA at T_A = 25°C. Derating is required above 25°C at 1.67 mW/°C. Typical operating current is 2–10 mA to achieve specified I_C(ON) performance while ensuring long-term LED lifetime. Exceeding 50 mA risks irreversible degradation of the GaAs IR emitter in the H22B3.

Can the H22B3 be used with a 3.3 V microcontroller I/O pin directly driving the LED?

Yes, the H22B3 can be driven by a 3.3 V microcontroller I/O pin using a series current-limiting resistor. With V_F ≤ 1.7 V at 60 mA, a 220 Ω resistor limits I_F to ~7.3 mA at 3.3 V - well within the H22B3's 2–10 mA recommended range for reliable I_C(ON) output. Ensure the MCU pin can source ≥10 mA continuously; otherwise, use a buffer transistor for the H22B3 LED drive.

What is the dark current (I_CEO) specification for the H22B3 photodarlington at 25°C?

The H22B3 photodarlington exhibits a maximum collector-to-emitter leakage current (I_CEO) of 100 nA at V_CE = 25 V and T_A = 25°C. This low dark current ensures clean OFF-state logic levels in high-impedance pull-up configurations and supports reliable detection in low-duty-cycle monitoring applications. I_CEO increases with temperature but remains <10 µA up to +100°C per datasheet Figure 4.

Does the H22B3 require external base connection for the photodarlington?

No, the H22B3 photodarlington is internally connected in Darlington configuration with no external base terminal - only Collector (Pin 3) and Emitter (Pin 4) are accessible. This simplifies PCB layout and eliminates base biasing complexity. The device operates as a two-terminal photosensitive switch: apply V_CC to collector via pull-up resistor, tie emitter to GND, and read logic state at collector.

How does the H22B3 aperture size affect mechanical design integration?

The H22B3 features a fixed 0.035" (0.89 mm) optical gap, which defines the minimum detectable object thickness and sets mechanical tolerance requirements for shutter flags or encoder wheels. Designers must ensure moving elements fully bridge this gap during interruption and maintain ±0.005" lateral alignment to avoid partial beam exposure. This aperture dimension is standardized across the H22B1–H22B3 family and directly impacts resolution in position-sensing applications using the H22B3.