STMicroelectronics ACST12-7ST

Overview

ACST12-7ST from STMicroelectronics is a transient-protected AC power switch integrating a 12 A RMS TRIAC with overvoltage crowbar clamping (VCL = 850 V) and low gate trigger current (IGT < 10 mA). It operates up to 700 V repetitive peak off-state voltage, delivers 1.5 V on-state voltage at 17 A, and sustains 2 kV line surge per IEC 61000-4-5 - enabling direct MCU-driven static switching of universal drum motors in washing machines without external snubbers or TVS.

For engineers reviewing the ACST12-7ST datasheet, ACST12-7ST pinout, ACST12-7ST application, or ACST12-7ST equivalent, this device serves as a self-protected, high-dV/dt (200 V/µs min) AC mains switch for appliance motor control where gate drive simplicity, surge resilience, and thermal reliability under inductive turn-off stress are critical selection criteria.

Technical Context

The ACST12-7ST combines a planar TRIAC structure with an integrated high-voltage clamping element that activates during transients exceeding VCL, diverting energy either via clamping or controlled crowbar conduction (<10 ms). Its low IGT enables direct 3.3 V/5 V MCU interface using only a series gate resistor.

It exhibits static dV/dt immunity of ≥200 V/µs at 125 °C and critical di/dt immunity ≥5.3 A/ms without snubber, supporting robust commutation of inductive loads like compressor windings and universal motors under fast line transients per IEC 61000-4-4 and IEC 61000-4-5.

Key Specifications

Pinout & Package

ACST12-7ST uses the TO-220AB package (3-pin, insulated tab), with pin 1 = Gate (G), pin 2 = Main Terminal 1 / Output (OUT), pin 3 = Main Terminal 2 / Common (COM). The tab is electrically connected to MT2 (COM) and must be isolated from heatsink unless referenced to system COM.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar AC power switching applications.

Compared with ACST12-7CT, the -7ST offers superior MCU compatibility via lower IGT; compared with BTB12-700CW, it eliminates snubber design complexity and guarantees IEC 61000-4-5 compliance out-of-the-box - making it optimal for next-generation appliance control where integration and certification time matter.

Availability

ACST12-7ST is available at Aetrix Electronics and suitable for washing machine motor control, refrigerator compressor switching, air conditioner fan regulation, and industrial HVAC blower activation requiring stable component supply across high-volume consumer appliance production.

Supply support for ACST12-7ST 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, digital, and mixed-signal ICs for automotive, industrial, and consumer markets.

The ACST12 series belongs to ST's ASD (Application-Specific Discrete) portfolio, engineered specifically for robust AC mains switching in home appliances and industrial controls - prioritizing integrated surge protection, thermal resilience, and simplified gate drive.

FAQ

Does ACST12-7ST require a heatsink for 12 A continuous operation?

Yes - at 12 A RMS, junction temperature rise depends on thermal resistance. With Rth(j-c) = 1.5 °C/W and case temperature limited to 104 °C, a heatsink maintaining Tc ≤ 104 °C is mandatory. Free-air operation supports only ~2 A; derating curves in Figure 3 confirm 12 A requires active heatsinking.

Can ACST12-7ST replace a standard TRIAC in an existing design without layout changes?

Yes, if the existing design uses TO-220AB and references MT2 (COM) to system common. Pinout matches standard TRIACs (G, MT1, MT2), but note: ACST12-7ST's COM pin is internally tied to the insulated tab, requiring electrical isolation from heatsink unless heatsink is grounded to COM - unlike many standard TRIACs with floating tabs.

What is the maximum surge energy the integrated crowbar can handle?

The device withstands ≥10 repetitive 2 kV surges per IEC 61000-4-5 (1.2/50 µs voltage wave, 8/20 µs current wave) with load limiting current. Energy absorption is load-dependent: for resistive loads, clamping dominates; for inductive loads, crowbar conduction dissipates energy through the load. VCL = 850 V defines the clamping threshold.

Is ACST12-7ST compliant with RoHS and REACH regulations?

Yes - ACST12-7ST is supplied in ST's ECOPACK® package with lead-free second-level interconnect, compliant with RoHS Directive 2011/65/EU and REACH Regulation (EC) No. 1907/2006. Full material declarations and compliance documentation are available via ST's quality portal.