ST34B

Overview

The Littelfuse ST34B is a standard bidirectional DIAC trigger device belonging to the HTxxx, HTMxxx, and STxxx series. It operates within a breakover voltage range of 32V (minimum) to 36V (maximum). The component utilizes a DO-214 surface-mount package with high-quality fused junctions and white wafer size selections for reliable performance. It features a maximum breakover current of 15 μA at 50/60Hz sine wave conditions and supports an operating junction temperature range from -40°C to +125°C. The device provides symmetrical triggering characteristics suitable for phase control applications.

Feature Summary

• Bidirectional full-wave thyristor structure enabling triggering in either polarity when applied voltage exceeds the breakover threshold.
• High-quality fused junctions combined with white wafer size selections to ensure robust operation and resistance to junction contamination.
• DO-214 surface-mount package design featuring high-volume, low-cost manufacturing capabilities and simple flow-through layout compatibility.

Applications

• Phase control circuits for lamp dimming systems
• Universal motor speed control applications
• Heat control circuitry
• Solid state ballast lighting controls

Procurement Notes

Verify the specific ordering suffix against the manufacturer's official documentation to confirm the exact packaging configuration. The datasheet indicates that the 'RP' suffix denotes tape and reel packing, while a blank suffix typically signifies bulk packaging. Ensure the selected variant matches the required assembly method for your production line before finalizing procurement orders.

Selection Notes

Select the ST34B based on the required breakover voltage symmetry and the physical footprint constraints of the printed circuit board. The DO-214 package offers a compact solution compared to through-hole alternatives. Confirm that the application's peak on-state current requirements remain within the absolute maximum ratings defined in the electrical characteristics table to prevent thermal damage during operation.

Part Context

The ST34B is part of the broader HTxxx, HTMxxx, and STxxx family of standard bidirectional DIAC triggers manufactured by Littelfuse. This series encompasses various voltage ranges from 27V to 70V across different package types including MINIMELF, DO-35, and DO-214. These devices are engineered to provide consistent triggering characteristics for AC switching and phase control applications requiring noise immunity.

Replacement Considerations

Compatible substitutes within the same series include the ST32B, ST35, ST36A, and ST40. When replacing the ST34B, verify that the alternative part number maintains the required breakover voltage range and fits the existing DO-214 footprint without modifying the PCB layout or soldering parameters.

FAQ

What is the breakover voltage symmetry specification for the ST34B?

The breakover voltage symmetry (ΔVBO) is specified as a maximum of 2V when measuring the difference between positive and negative breakover voltages.

How does the ST34B handle repetitive surge currents?

The device is rated for a pulse on-state current (ITRM) of 2A under test conditions of 120 pulses per second with a pulse width of 10 μs at an ambient temperature of 40°C or lower.

What is the typical switching time for this DIAC?

The typical switching time is 900 nanoseconds, measured at the peak current (IPK) across a 20 Ω resistor.