ST40

Overview

The Littelfuse ST40 is a bidirectional DIAC (Diode for Alternating Current) belonging to the HTxxx, HTMxxx, and STxxx series. It serves as a standard trigger device for thyristors and triacs in phase control circuits. The component utilizes a DO-214 surface-mount package with high-quality plastic encapsulation and bonded die attachment. Key electrical characteristics include a breakover voltage range of 35V to 45V and a maximum breakover current of 15 μA. It operates within a junction temperature range of -40°C to +125°C and supports a pulse on-state current of up to 2A under specific conditions.

Feature Summary

• Bidirectional triggering capability for symmetric AC applications
• High-quality plastic encapsulation with bonded die attachment
• Glass-passivated junctions for long-term reliability
• Lead-free and RoHS compliant construction

Applications

• Lamp dimming circuits
• Universal motor speed control systems
• Heat control applications
• Solid state ballast lighting controls

Procurement Notes

Verify the exact part number suffix against official Littelfuse documentation to confirm packaging options such as bulk or tape-and-reel configurations. Ensure that the selected variant meets the required breakover voltage symmetry specifications for your specific circuit design. Cross-reference the DO-214 package dimensions with your PCB footprint requirements before finalizing procurement.

Selection Notes

Select the ST40 based on its 35V to 45V breakover voltage range suitable for triggering triacs in standard AC phase control applications. Consider the DO-214 surface-mount package for automated assembly processes. Evaluate the thermal resistance and power dissipation limits relative to the ambient operating temperature to ensure reliable performance within the specified -40°C to +125°C junction temperature range.

Part Context

The ST40 is part of the broader HT/HTM/ST series of standard bidirectional DIAC triggers manufactured by Littelfuse's Teccor brand. This series provides a comprehensive range of breakover voltages from 27V to 70V across various packages including DO-35, MINIMELF, and DO-214. These devices are designed to offer reliable switching characteristics for industrial and consumer electronics requiring precise phase control.

Replacement Considerations

Compatible substitutes within the same family include ST32, ST34B, ST35, ST36A, ST36B, and ST60, which share the DO-214 package but differ in breakover voltage ranges. Ensure the replacement maintains the required VBO symmetry and current handling capabilities for the specific application.

FAQ

What is the breakover voltage range for the ST40?

The ST40 has a minimum breakover voltage of 35V and a maximum breakover voltage of 45V.

What package type does the ST40 use?

The ST40 uses the DO-214 surface-mount package.

Is the ST40 RoHS compliant?

Yes, the ST40 is RoHS compliant and lead-free.