STMicroelectronics ACST8-8CT

Overview

ACST8-8CT from STMicroelectronics is an overvoltage-protected AC power switch based on ASD™ triac technology, designed for bidirectional AC line switching in induction motor drives. It delivers 8A RMS on-state current at 90°C case temperature, withstands ±800V repetitive peak off-state voltage, features snubberless turn-off commutation (dI/dt)_c ≥ 4.5 A/ms, and operates reliably in washing machine bi-rotational motor control.

For engineers reviewing the ACST8-8CT datasheet, ACST8-8CT pinout, ACST8-8CT application, or ACST8-8CT equivalent, this device is selected for robust AC static switching in appliance motor control where high dV/dt immunity (>750 V/µs), avalanche clamping, and IEC61000-4-5 transient compliance are critical design requirements.

Technical Context

The ACST8-8CT integrates a planar triac structure with monolithically embedded high-voltage clamping to absorb inductive turn-off energy and suppress line transients. Its gate triggering current is ≤30 mA at 25°C, and it sustains static dV/dt >750 V/µs at 125°C junction temperature without spurious turn-on.

It supports full-cycle ON/OFF and phase-angle control modes for medium-power inductive loads. The device achieves safe breakover under 2 kV non-repetitive line surges per IEC61000-4-5, eliminating need for external MOVs or RC snubbers in compliant designs.

Key Specifications

Pinout & Package

ACST8-8CT uses the TO-220AB package: insulated tab, 3-pin vertical mount, lead-free plating, 2.3 g mass, UL94 V0 epoxy. Thermal resistance junction-to-case is 2.5 °C/W for full-cycle conduction.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ACST8-8CFP and ACST8-8CG, the ACST8-8CT offers optimal balance of thermal performance (2.5 °C/W), through-hole mechanical robustness, and cost-effective manual or semi-automated assembly-making it preferred for mid-volume appliance control boards requiring field-serviceable replacement.

Availability

ACST8-8CT is available at Aetrix Electronics and suitable for washing machine motor control, refrigerator compressor switching, and air conditioning fan drive applications requiring stable component supply across multi-year appliance production cycles.

Supply support for ACST8-8CT 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, power, MCU, and sensor solutions for automotive, industrial, and consumer markets.

The ACST8 series belongs to ST's ASD™ AC Switch family, engineered specifically for robust, snubberless AC static switching in white goods motor control-prioritizing surge ruggedness, thermal stability, and long-term reliability over general-purpose triac performance.

FAQ

What is the maximum allowable junction temperature for continuous operation?

The ACST8-8CT has an operating junction temperature range of –40°C to +125°C. For continuous 8A RMS conduction, thermal design must ensure T_j does not exceed 125°C, typically achieved with TO-220AB tab mounted to ≥10 cm² copper area or small heatsink yielding ≤2.5 °C/W total thermal resistance.

Does ACST8-8CT require a heat sink in typical appliance applications?

At 8A RMS and T_CASE = 90°C, the device dissipates ~1.2 W in conduction. With R_th(j-c) = 2.5 °C/W and R_th(c-a) ≈ 30 °C/W on 5 cm² copper, junction temperature stays below 110°C-so a dedicated heatsink is optional. However, for sustained high-temperature ambient conditions (>60°C), a minimal clip-on heatsink is recommended.

Can ACST8-8CT replace a standard triac in existing designs?

Yes, but only if the existing triac is gate-triggered with negative current and shares the same COM–G–OUT pinout. Unlike conventional triacs, ACST8-8CT requires no snubber for inductive loads and provides built-in overvoltage clamping-so external protection components may be removed, but gate drive circuitry must match its ≤30 mA I_GT requirement.

How does the device handle fast capacitor discharge events in bidirectional motor circuits?

The ACST8-8CT withstands fast capacitor discharge via its 100 A/µs turn-on dI/dt rating and integrated clamping. In bidirectional motor setups, a 14 µH series inductor and 1.2 Ω resistor limit discharge current to within ITSM = 85 A (16.7 ms), providing two-fold safety margin per ST's application guidance-preventing destructive latch-up during phase-capacitor transients.