STL73-AP - 400V 1.5A NPN Power Transistor | STMicroelectronics
MPN: STL73-AP ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.62 | $0.62 |
| 10 | $0.55 | $5.50 |
| 100 | $0.42 | $42.00 |
| 500 | $0.32 | $160.00 |
| 1,000 | $0.24 | $240.00 |
| 5,000 | $0.18 | $900.00 |
STL73-AP Overview
A BJT (bipolar junction transistor) is a three-terminal semiconductor device that amplifies current or switches signals using both electron and hole charge carriers. Within the broader semiconductor hierarchy, the BJT sits as a sibling technology to MOSFETs and IGBTs in the discrete-transistor family, while within STMicroelectronics' portfolio the STL73 belongs to the medium-voltage fast-switching NPN power transistor group, engineered using the company's Multi-Epitaxial Planar process to combine high switching speed with 400V breakdown capability.
Key features of the STL73-AP include a 400V VCEO rating that comfortably supports 110V/220V offline-derived rails after rectification, a 1.5A continuous collector current suitable for relay coils, solenoid drivers, and small motor windings, and a 1100 mW power dissipation envelope that allows sustained operation without an external heatsink in typical low-duty-cycle use. The device operates across an extended -65°C to +150°C junction temperature range, ensuring reliability in automotive underhood, industrial, and consumer environments.
The Multi-Epitaxial Planar architecture provides a balanced trade-off between breakdown voltage, current handling, and switching speed, which is why the part is specified for fast-switching applications rather than pure RF or precision linear use. Compared with a generic 400V small-signal transistor, the STL73-AP offers substantially higher collector current and dissipation, and its TO-92 form factor preserves drop-in compatibility with legacy through-hole designs that would otherwise require a footprint change.
Typical applications include line-powered switch-mode power supply (SMPS) auxiliary circuits, electronic ballast control stages, LED driver buck/boost stages, solenoid and relay drivers, and general-purpose medium-voltage amplifiers. The combination of 400V breakdown and 1.5A current also suits the part for use as a driver transistor for higher-power devices such as MOSFETs or TRIACs in offline control circuits.
When designing with the STL73-AP, derate power dissipation to 600-700 mW in most TO-92 layouts without a copper heatsink pad, since the TO-92 package has a thermal resistance of approximately 200 C/W to ambient. Always observe safe operating area limits when switching inductive loads, and add a flyback or snubber diode across any inductive load to protect the collector-base junction from reverse breakdown transients.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet alone, giving engineers a single reference for sourcing, substitution, and layout guidance.
Drop-in alternatives for STL73-AP — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
STL73
✅ Drop-In📋 Reference alternative (not in catalog)
STL73D
✅ Drop-In📋 Reference alternative (not in catalog)
STL73D-AP
✅ Drop-In📋 Reference alternative (not in catalog)
STL72
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
MPSA42
✅ Drop-In📋 Reference alternative (not in catalog)
STL73-AP Maximum Ratings & Electrical Characteristics
| Transistor Type | NPN Bipolar Junction Transistor (BJT) |
| Configuration | Single |
| Collector-Emitter Voltage (Vceo) | 400 V |
| Continuous Collector Current (IC) | 1.5 A |
| Maximum Power Dissipation (Ptot) | 1100 mW (1.1 W) |
| Operating Temperature Range | -65 C to +150 C |
| Package | TO-92 (formed leads, through-hole) |
| Mounting Type | Through-Hole |
| Number of Pins | 3 |
| Technology | Multi-Epitaxial Planar |
| MSL Level | Not Applicable (through-hole) |
| RoHS Status | Compliant |
STL73-AP Pin Configuration
| Pin 1 | Emitter — Emitter terminal (E) |
| Pin 2 | Collector — Collector terminal (C) |
| Pin 3 | Base — Base terminal (B) |
Typical Applications
STL73-AP is suitable for 7 applications: Offline SMPS Auxiliary Circuit, Relay and Solenoid Driver, Electronic Ballast Control Stage, LED Driver Buck/Boost Stage, Linear Amplifier / Driver Stage, MOSFET / TRIAC Gate Driver, Automotive 12V/48V Subsystem Switch.
Offline SMPS Auxiliary Circuit
The STL73-AP's 400 V VCEO rating and 1.5 A continuous collector current make it well-suited for offline switch-mode power supply auxiliary circuits such as startup transistors, linear regulators, and housekeeping supplies. In a typical 110/220 V AC-derived design, the part operates from a rectified 300 V DC bus and switches at low frequencies (under 100 kHz), where its Multi-Epitaxial Planar architecture provides fast turn-off without requiring a MOSFET gate driver. Power dissipation at 1.1 W is sufficient for housekeeping duties without a heatsink, while the 400 V breakdown gives substantial headroom above rectified-line peaks.
Recommended
Relay and Solenoid Driver
The STL73-AP's 1.5 A collector current comfortably drives automotive and industrial relays, solenoids, and small DC motor windings. With a 400 V VCEO, the part tolerates the high flyback voltages generated when an inductive load is de-energized, although an external flyback diode is still recommended for reliability. Its TO-92 package is well matched to through-hole relay-driver boards in industrial-control enclosures, where the part can switch loads up to several hundred milliamps continuous at 24-48 V DC without thermal stress.
Recommended
Electronic Ballast Control Stage
In fluorescent and HID electronic ballast designs, the STL73-AP functions as a fast-switching NPN transistor in the oscillator or driver section. The 400 V breakdown handles the high-voltage resonant tank voltages, while the Multi-Epitaxial Planar process delivers the switching speed needed for 30-50 kHz resonant operation. Its 1.5 A current capability drives the gate or base of a power MOSFET or IGBT in the main switching stage, providing a cost-effective interface between low-power control logic and the high-voltage power section.
Recommended
LED Driver Buck/Boost Stage
The STL73-AP can serve as the switching element in linear or buck-derived LED driver circuits operating from rectified mains or 48 V industrial rails. With a 400 V VCEO, the part tolerates voltage transients on poorly regulated industrial supplies, and its 1.5 A continuous current drives LED strings up to several watts. Although less efficient than a dedicated LED driver IC, this BJT-based approach offers BOM simplicity and excellent thermal stability when paired with a current-sense resistor and op-amp feedback loop.
Recommended
Linear Amplifier / Driver Stage
With its 400 V VCEO and 1.1 W dissipation, the STL73-AP can be used as a linear amplifier or driver in audio, instrumentation, or transducer excitation circuits where higher voltage swings are needed. The extended -65 C to +150 C operating temperature range supports automotive underhood and industrial deployments. Its NPN polarity and EBC TO-92 pinout are compatible with common driver-circuit topologies, including emitter-follower buffers and common-emitter amplifiers driving piezo transducers or small solenoids.
Recommended
MOSFET / TRIAC Gate Driver
The STL73-AP is well suited to driving the gate of a power MOSFET or the gate of a TRIAC in offline-control applications. Its 1.5 A collector current provides ample base-drive to rapidly charge and discharge the gate capacitance of medium-size MOSFETs, while the 400 V VCEO ensures the driver transistor itself can survive the high-side or low-side switching transients. This configuration is common in motor-control boards, dimmer circuits, and solid-state relay front ends where the STL73-AP acts as the interface between low-power control logic and the main switching device.
Recommended
Automotive 12V/48V Subsystem Switch
In automotive subsystems - including 12 V body controllers, 48 V mild-hybrid auxiliaries, and aftermarket accessory drivers - the STL73-AP serves as a low-side switch for relays, lamps, and small motors. The 400 V VCEO provides enormous headroom over 12 V/48 V rails, ensuring robustness against load-dump and jump-start transients. The TO-92 package, while not AEC-Q100 qualified, is widely accepted in non-safety automotive applications where cost dominates over formal qualification.
Recommended
Recommended Products Summary
Engineering reference data for STL73-AP — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | STL73 | STL73D | STL73D-AP | STL72 | MPSA42 |
|---|---|---|---|---|---|---|
| Brand | STMicroelectronics | STMicroelectronics | STMicroelectronics | STMicroelectronics | STMicroelectronics | onsemi |
| Package | TO-92 | TO-92 - same | TO-92 - same | TO-92 - same | TO-92 - same | TO-92 - same |
| Transistor Type | NPN BJT | NPN BJT | NPN BJT | NPN BJT | NPN BJT | NPN BJT |
| VCEO (V) | 400 V | 400 V | 400 V | 400 V | 300 V (approx, lower) | 300 V |
| Continuous IC (A) | 1.5 A | 1.5 A | 1.5 A | 1.5 A | 1.0 A (approx, lower) | 0.5 A |
| Ptot Max (mW) | 1100 mW | 1100 mW | 1500 mW | 1500 mW | 1100 mW (approx) | 625 mW |
| Operating Temperature | -65 C to +150 C | -65 C to +150 C | -65 C to +150 C | -65 C to +150 C | -65 C to +150 C (typical) | -55 C to +150 C |
| Mounting Type | Through-Hole | Through-Hole | Through-Hole | Through-Hole | Through-Hole | Through-Hole |
| Approx. Unit Price (qty 100) | 0.42 USD | Similar | Slightly higher | Slightly higher | Lower | Comparable |
Key Differentiators
- Higher power dissipation than the legacy MPSA42 (vs MPSA42)
- Same die and ratings as the STL73 non-AP variant (vs STL73)
- Lower dissipation than the higher-power STL73D (vs STL73D)
Design Notes
Estimated: at 25 C ambient in a standard TO-92 PCB layout (no copper heatsink pad), the STL73-AP should be derated to roughly 600-700 mW. With the TO-92 thermal resistance of approximately 200 C/W to ambient, dissipating 1.1 W would push junction temperature close to the 150 C maximum. For continuous high-current switching, add at least 100 mm^2 of copper pour around the collector lead, or use the higher-rated STL73D variant (1500 mW Ptot) if the design must stay in TO-92.
Do not confuse the STL73-AP pinout with Toshiba 2SC-series TO-92 parts that use CBE (Collector-Base-Emitter) ordering instead of EBC. Always confirm the pinout by referring to the STMicroelectronics datasheet before PCB layout, especially when migrating a design across brands. Reverse-pinout mistakes typically destroy the device within seconds of power-up due to Vbe forward bias on the wrong pin pair.
Keep the base-drive trace short and direct, with a small (10-100 ohm) base resistor to limit peak base current during turn-off. When switching inductive loads, place a flyback diode (e.g., 1N4007 or equivalent fast-recovery diode) directly across the inductive load with short leads to suppress the flyback voltage that can otherwise exceed the 400 V VCEO rating and avalanche the transistor.
Estimated: in a typical low-side switch application driving a 24 V relay coil (resistance approximately 200 ohm), the STL73-AP conducts approximately 120 mA continuously and dissipates roughly 24 V * 0.12 A = 2.9 W if used as a linear pass element - far exceeding its rating. Always operate the part in saturated switching mode (Vce < 1 V) for relay/solenoid drivers, never in linear mode, to keep dissipation within the 1.1 W envelope.
Compliance Information
RoHS and lead-free confirmed per STMicroelectronics product page. Not AEC-Q100 qualified - select a different part for safety-critical automotive applications. Halogen-free status not explicitly stated in verified data.
