ACS108 Equivalent: A Complete Guide to ACS108 Variants and Drop-In Alternatives

If you're searching for an ACS108 equivalent, you've likely run into a situation where your go-to part is out of stock, or you need to evaluate whether a related variant better fits your design constraints. The ACS108 family from STMicroelectronics covers sensitive-gate triacs and overvoltage-protected AC switches in a small-load AC control range. With multiple voltage grades (600 V vs. 800 V), current ratings, package options (TO-92 vs. SOT-223), and two distinct device architectures (triac vs. AC switch), choosing the right variant — or a compatible alternative — requires a clear understanding of the differences.

This article compares all major ACS108 variants side by side, explains the design implications of each parameter, and tells you exactly which part to reach for based on your application.

Quick Comparison Table: ACS108 Variants

Part Number	Architecture	VDRM	IT(RMS)	IGT	Package	Notes
ACS108-6SA	Sensitive-Gate Triac	600 V	450 mA	5 mA	TO-92	Through-hole, standard grade
ACS108-6SA-AP	Sensitive-Gate Triac	600 V	450 mA	10 mA	TO-92	AEC-Q101 automotive grade
ACS108-6SA-TR	Sensitive-Gate Triac	600 V	450 mA	10 mA	TO-92	Tape-and-reel for automated assembly
ACS108-6SN-TR	Sensitive-Gate Triac	600 V	800 mA	10 mA	SOT-223	SMD, higher current in same voltage grade
ACS108-8SA-AP	Overvoltage-Protected AC Switch	800 V	800 mA	10 mA	TO-92	Built-in overvoltage clamp, automotive
ACS108-8SA-TR	Overvoltage-Protected AC Switch	800 V	800 mA	10 mA	TO-92	T/R packing, OVP architecture
ACS108-8SN-TR	Sensitive-Gate Triac	800 V	800 mA	10 mA	SOT-223	SMD, 800 V grade

Detailed Analysis

1. Voltage Rating: 600 V vs. 800 V

The ACS108 family splits cleanly into two voltage grades.

The 600 V variants (ACS108-6xx) are designed for 120 VAC mains applications, and with a 600 V repetitive peak off-state voltage (VDRM), they provide roughly 2× safety margin over the 270 V peak found on a 120 VAC line. European 230 VAC lines peak at approximately 325 V, which still falls within the 600 V rating — but leaves less headroom against transients and inductive kickback. If your application involves a noisy industrial 230 VAC supply, inductive loads, or voltage spikes from motor switching, the 600 V parts are marginal.

The 800 V variants (ACS108-8xx) raise the blocking voltage to 800 V, giving comfortable margin on 230 VAC networks worldwide and in environments with common industrial transients up to IEC 61000-4-5 surge levels. For residential 230 VAC appliance control, smart plugs, or HVAC fan controls, the 800 V grade is the safer default even if it costs slightly more.

Rule of thumb: Use 600 V parts only for well-regulated 120 VAC or protected 230 VAC designs. Default to 800 V for any new design targeting global markets or industrial installations.

2. Current Rating: 450 mA vs. 800 mA

The ACS108 targets small-load AC switching, not the multi-ampere motor or heater territory of larger triacs. Within the family, current ratings split as follows:

• ACS108-6SA / ACS108-6SA-AP / ACS108-6SA-TR: 450 mA RMS maximum. Suited for loads under ~50 W on 120 VAC (lamp dimmers, relay coil control, small transformer loads).
• All other variants: 800 mA RMS. Covers up to ~180 W on 230 VAC — adequate for LED drivers, small fans, and solenoid valve control.

The SOT-223 package variants (ACS108-6SN-TR and ACS108-8SN-TR) benefit from the exposed pad on the SOT-223 package, which transfers heat to the PCB copper plane. This means that even at 800 mA, the junction temperature stays manageable in most designs with a modest copper pour, without needing an external heatsink.

3. Architecture: Sensitive-Gate Triac vs. Overvoltage-Protected AC Switch

This is the most important architectural difference in the ACS108 family, and it is frequently misunderstood.

Standard Sensitive-Gate Triacs (ACS108-6SA family and ACS108-8SN-TR) are classical two-terminal power devices controlled by a third gate terminal. "Sensitive gate" means the gate trigger current (IGT) is low — 5 to 10 mA — so a microcontroller GPIO or an optocoupler with a small-current LED can drive the gate directly without a buffer stage. This is the core appeal of the ACS108 series versus larger, less sensitive triacs.

Overvoltage-Protected AC Switch architecture (ACS108-8SA-AP and ACS108-8SA-TR) is a fundamentally different device. It integrates a voltage sensing circuit and a unidirectional thyristor pair that clamps the anode voltage at approximately 800 V. If the line voltage tries to exceed the clamp threshold — due to a surge, an inductive spike, or a lightning-induced transient — the internal protection circuit conducts and absorbs the excess energy before it can damage downstream components. This makes the OVP AC switch significantly more robust in the field without requiring external TVS diodes or varistors.

The trade-off: the OVP variants have slightly higher on-state voltage and are not pure bidirectional triacs. If your circuit depends on precise zero-crossing switching in both half-cycles, verify the OVP architecture is compatible with your control algorithm.

4. Package Options: TO-92 vs. SOT-223

The package choice affects PCB layout, thermal performance, and manufacturing process.

TO-92 (through-hole, D-Pak-style 3-lead) is the original package for the ACS108 series. It is easy to hand-solder, widely available in tape-and-reel or bulk, and permits basic heatsinking via lead bending or a clip. The drawback is that it consumes vertical board space and does not contribute to copper-plane heat spreading.

SOT-223 is a 4-pin surface-mount package with a large exposed tab (connected to the MT2 anode) that bonds to the PCB. For reflow-assembled boards, SOT-223 allows the ACS108 to benefit from the full copper plane as a heat spreader — this matters at 800 mA loads where power dissipation approaches the package limit. SOT-223 also shrinks the footprint and allows fully automated SMT assembly without a through-hole step.

For mixed-technology boards where you are inserting a few through-hole components anyway, the TO-92 variants are perfectly fine. For fully SMD designs or high-volume automated production, prefer ACS108-6SN-TR or ACS108-8SN-TR.

5. Tape-and-Reel and Automotive Grades

The -TR suffix denotes tape-and-reel packaging for pick-and-place machines. The -AP suffix (Automotive Pack) indicates AEC-Q101 qualification, which requires extended temperature range testing, additional burn-in, and stricter ESD handling. For consumer and industrial designs, the standard and -TR variants are sufficient. For automotive body electronics (seat heaters, mirror defrost, door actuators), source the -AP qualified parts.

Use Case Recommendations

Choose ACS108-6SA or ACS108-6SA-TR when…

• Your design targets a 120 VAC North American market only.
• The load draws under 450 mA RMS (small lamps, relays, low-power transformers).
• You are prototyping or need through-hole components for a low-volume PCB.
• BOM cost is the primary constraint and voltage margin is less critical.

Choose ACS108-6SN-TR or ACS108-8SN-TR when…

• You need surface-mount assembly (fully SMD board).
• The load current is closer to 800 mA.
• Thermal performance on the board is important (SOT-223 pad helps).
• 800 V headroom is needed (use -8SN-TR for global 230 VAC designs).

Choose ACS108-8SA-AP or ACS108-8SA-TR when…

• You are designing for 230 VAC global markets, especially industrial or outdoor environments.
• Inductive or motor loads are involved — the integrated OVP clamp replaces external TVS components.
• The application requires automotive qualification (-AP) or high-reliability industrial certification.
• Simplifying BOM protection circuitry is worth the slightly higher unit cost.

Choose ACS108-6SA-AP when…

• You need automotive qualification on a 120 VAC circuit (e.g., EV onboard charger auxiliary controls in North American markets).

Frequently Asked Questions

Q: Can I drop in an ACS108-8 part as a direct equivalent for an ACS108-6 part?

Yes, in most cases. The 800 V variants share the same gate trigger current (IGT ~10 mA), similar on-state voltage, and the same footprint within the same package family (TO-92 or SOT-223). The only differences are the higher blocking voltage (which adds margin, not constraints) and the OVP architecture on the -8SA parts. Review your gate drive circuit compatibility with the OVP architecture if using -8SA variants as substitutes.

Q: What is the main advantage of the ACS108 over a standard BT136 or MAC97 triac?

The ACS108 features a very low gate trigger current (5–10 mA vs. 25–50 mA for standard triacs), which allows direct microcontroller or optocoupler drive without a buffer transistor. This simplifies circuit design and reduces component count. The compact TO-92 and SOT-223 packages also save significant board space compared to TO-220 or TO-92 packages used in higher-current triacs.

Q: Where can I source ACS108 variants reliably, including difficult-to-find tape-and-reel grades?

FindMyChip connects you to 200+ verified distributors globally, including Shenzhen-based IC trading houses with competitive pricing on tape-and-reel lots. You can search for ACS108 variants on FindMyChip and submit a multi-line RFQ to compare pricing across distributors simultaneously. All suppliers are vetted through a 5-point authentication process to minimize counterfeit risk.

Conclusion

The ACS108 family offers a tightly focused set of variants designed for sensitive-gate AC switching in small-load applications. The key decision points are: voltage grade (600 V for 120 VAC, 800 V for 230 VAC or noisy environments), current rating (450 mA or 800 mA), package (TO-92 for through-hole prototyping, SOT-223 for SMD volume production), and architecture (standard triac vs. overvoltage-protected AC switch for transient-rich environments).

For sourcing assistance across all ACS108 grades and packaging options, request a quote on FindMyChip to access competitive pricing from verified distributors.