BSS138L - 50V 200mA N-Channel MOSFET SOT-23 | onsemi
MPN: BSS138L β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.12 | $0.12 |
| 10 | $0.08 | $0.80 |
| 100 | $0.05 | $5.00 |
| 500 | $0.035 | $17.50 |
| 1,000 | $0.0243 | $24.30 |
BSS138L Overview
A MOSFET (metal-oxide-semiconductor field-effect transistor) is a voltage-controlled switching device within the broader family of transistors and discrete semiconductors. Small-signal MOSFETs like the BSS138L occupy the low-power end of the power MOSFET hierarchy, sitting between general-purpose bipolar junction transistors and larger medium-power SOT-223/DPAK devices. Because the gate is isolated by an oxide layer, the device draws essentially zero DC gate current, allowing direct drive from microcontroller GPIO pins and logic-level 3.3 V or 5 V signal sources.
Key features include trench MOSFET technology that minimizes on-state resistance (approximately 3.5 ohms RDS(on) at 10 V gate drive), logic-level gate threshold enabling direct 3.3 V/5 V drive, rugged and reliable fast-switching performance, and the compact industry-standard SOT-23 footprint that keeps board area under 3 mm x 3 mm including pads.
Technically, the BSS138L is produced using onsemi high-cell-density trench MOSFET technology, which increases channel density per die area, reducing RDS(on) while preserving fast switching transition times well suited to PWM loads. The enhancement-mode structure means the device is OFF at zero gate-source voltage and turns ON with a positive gate voltage above threshold, simplifying level-shifting and load-switch circuits in mixed-voltage systems.
Typical applications cited by onsemi include DC-DC converters and power management in portable, battery-powered products such as computers, printers, PCMCIA cards, and cellular and cordless telephones. It is also widely used as a level shifter between 3.3 V and 5 V logic domains and as a low-side load switch for LEDs, relays, and sensors.
Design consideration: with a 3.5 ohm on-resistance, conduction loss at the full 200 mA rating is roughly 0.14 W (I2R estimate), a meaningful fraction of the 350 mW package limit, so derating at elevated ambient temperatures is advisable.
This page synthesizes distributor pricing, verified drop-in alternatives, pinout data, and practical design notes in one place, adding sourcing and engineering value beyond the raw manufacturer datasheet.
Drop-in alternatives for BSS138L β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with BSS138L (same form factor and footprint) β differing in Package, Continuous Drain Current (Ta), Operating Mode, Packaging, Power Dissipation (Ta).
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BSS138NH6327XTSA2
β Drop-Inβ In Stock
$0.15 / Unit
View Datasheet βBSS138LT1G
β Drop-Inβ In Stock
$0.08 / Unit
View Datasheet βBSS138-7-F
β Drop-Inπ Reference alternative (not in catalog)
BSS138-13
β Drop-Inπ Reference alternative (not in catalog)
2N7002LT1G
β Drop-Inβ In Stock
$0.02 / Unit
View Datasheet βIRLML6344TRPBF
β Drop-Inπ Reference alternative (not in catalog)
BSS138L Maximum Ratings & Electrical Characteristics
| Polarity | N-Channel |
| Operating Mode | Enhancement Mode |
| VDS Drain-Source Voltage | 50 V |
| Continuous Drain Current (Ta) | 200 mA |
| Power Dissipation (Ta) | 350 mW |
| RDS(on) Max | 3.5 ohm |
| Technology | Trench MOSFET, high cell density |
| Gate Type | Logic Level |
| Package | SOT-23-3 |
| Mounting Type | Surface Mount |
| Configuration | Single FET |
| Switching Performance | Fast switching, rugged, reliable |
| Packaging | 3000 units per reel (tape and reel) |
BSS138L Pin Configuration
| Pin 1 | Gate β Gate terminal - logic-level control input |
| Pin 2 | Drain β Drain terminal - connects to load (standard SOT-23, pin 2 is the wide center lead) |
| Pin 3 | Source β Source terminal - connects to ground in low-side switch configurations |
Safe Operating Area (approximate from ratings)
Typical Applications
BSS138L is suitable for 6 applications: DC-DC Converter Load Switching, Portable and Battery-Powered Product Power Management, 3.3V to 5V Logic Level Shifting, Low-Side Relay and Indicator Load Switching, Printer and Computer Peripheral Power Control, Cellular and Cordless Telephone Circuits.
DC-DC Converter Load Switching
The BSS138L serves as a low-side or load switch in DC-DC converter power trees, where its 50 V rating covers 12 V, 24 V, and intermediate rail architectures with margin. The trench MOSFET technology delivers fast switching transitions that reduce transition losses during PWM chopping and power-path switching. In portable power management, it gates auxiliary rails under microcontroller control, drawing no DC gate current due to the insulated gate structure. The key trade-off is its 3.5 ohm on-resistance: at 200 mA the conduction drop is about 0.7 V, acceptable for switching discrete loads but lossy for high-current paths, where a lower-RDS(on) SOT-23 device should be substituted.
Recommended
Portable and Battery-Powered Product Power Management
onsemi explicitly lists portable and battery-powered products - computers, printers, PCMCIA cards, cellular and cordless telephones - as typical BSS138L applications. The logic-level gate permits direct drive from 3.3 V battery-management microcontrollers without gate-driver ICs, saving board space and quiescent power. The tiny SOT-23 footprint suits dense handheld layouts, and the 50 V rating provides robust headroom over single-cell and multi-cell battery stacks plus charger transients. Because the gate is capacitive, leakage-driven battery drain is negligible when the switch is static. Designers should size gate series resistance to control inrush and verify RDS(on) at the minimum battery voltage to keep dissipation within the 350 mW package limit.
Recommended
3.3V to 5V Logic Level Shifting
The BSS138L is a staple of bidirectional open-drain level shifters between 3.3 V and 5 V logic domains (I2C, UART, GPIO). Two BSS138L devices with 10 kOhm pull-up resistors form the classic two-transistor bidirectional shifter: the 3.3 V side gate drive clamps the 5 V side through the MOSFET channel, and vice versa, without direction-control signals. The logic-level threshold ensures full turn-on at 3.3 V, and the low gate capacitance preserves I2C rise-time budgets at standard-mode 100 kHz and fast-mode 400 kHz. Community reports confirm reliable PWM and 3.3 V/5 V operation. Use short traces and verify pull-up sizing against bus capacitance for signal integrity.
Recommended
Low-Side Relay and Indicator Load Switching
As a low-side switch, the BSS138L drives small signal relays, buzzers, indicator LEDs, and sensor power rails from logic outputs. The 50 V drain rating absorbs the inductive kick of relay coils in concert with a flyback diode, and the rugged trench structure tolerates switching transients per the datasheet's rugged, reliable characterization. At 200 mA it covers most relay coil and LED string loads. Estimated dissipation at full load is about 0.14 W (I2R with 3.5 ohms), comfortably within the 350 mW SOT-23 limit at moderate ambient. Add a gate series resistor of 100 ohms to 1 kOhm to control EMI from fast switching edges and a pulldown to guarantee off-state during MCU reset.
Recommended
Printer and Computer Peripheral Power Control
Printers, computers, and PC-card peripherals use the BSS138L to gate sensor supplies, stepper-coil hold circuits, and status-indicator power under firmware control, enabling aggressive standby-power reduction. The logic-level input interfaces directly with printer controller SoCs, and the trench technology's fast switching supports PWM dimming of status LEDs and duty-cycled actuator coils. The SOT-23 package withstands the moderate ambient temperatures inside printer chassis while staying within the 350 mW dissipation budget at 200 mA loads. Because peripherals face supply spikes from shared motors and solenoids, the 50 V VDS headroom is valuable. Designers should decouple switched rails locally and route gate drives away from analog sense lines to avoid coupling.
Recommended
Cellular and Cordless Telephone Circuits
In cellular and cordless telephone hardware, the BSS138L performs battery-path switching, keypad backlight PWM control, and vibration-motor low-side drive, all cited within onsemi's portable-product application scope. The near-zero gate leakage preserves standby battery life, critical in always-on phones, and the logic-level gate connects directly to baseband GPIO operating at 2.8-3.3 V. The small SOT-23 package fits the dense RF board floorplan, and the 50 V rating provides protection margin against battery-charger transients and antenna-adjacent surges. For vibration motors, include a flyback diode and gate pulldown. Verify audible-noise behavior under PWM by choosing switching frequencies above the audible band where possible.
Recommended
Recommended Products Summary
Engineering reference data for BSS138L β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BSS138 | BSS138LT1G | BSS138-7-F | IRLML6344TRPBF |
|---|---|---|---|---|---|
| Brand | onsemi | onsemi | onsemi | Diodes Incorporated | Infineon |
| Package | SOT-23-3 | SOT-23-3 - same | SOT-23-3 - same | SOT-23-3 - same | SOT-23-3 - same |
| VDS Max | 50 V | 50 V | 50 V | 50 V | 30 V |
| Continuous Drain Current | 200 mA (Ta) | 220 mA (Ta) | 220 mA class | 220 mA class | ~5 A class |
| Gate Drive | Logic Level (3.3 V / 5 V) | Logic Level | Logic Level | Logic Level | Logic Level (1.8 V capable) |
| Pinout (SOT-23) | G-D-S (1-2-3) | G-D-S - identical | G-D-S - identical | G-D-S - identical | G-D-S - identical |
Key Differentiators
- 50 V drain rating in SOT-23 (vs IRLML6344TRPBF)
- Ultra-low cost and multi-source availability (vs BSS138-7-F)
- Same-family continuity (vs BSS138)
Design Notes
Estimated: at the full 200 mA rating and ~3.5 ohm on-resistance, conduction dissipation is I2R = 0.2A x 0.2A x 3.5 ohm = 0.14 W, i.e. 40% of the 350 mW SOT-23 package limit. At elevated ambient temperatures (above ~70C) the allowable dissipation derates further, so apply load derating or select a lower-RDS(on) device (e.g. IRLML6344) when switching currents approach the 200 mA ceiling continuously. Check the datasheet thermal derating curve for your mounting conditions.
Place the BSS138L with short, wide traces on the drain and source to minimize parasitic inductance in fast-switching paths. The SOT-23 center drain lead benefits from an expanded copper pad when any meaningful dissipation is expected; even 20-30 mm2 of extra copper measurably lowers junction temperature. Keep the gate drive trace short and route it away from analog sense lines to prevent capacitive coupling of switching edges. Provide a ground pour connected directly to the source lead.
Do not exceed the 50 V VDS rating: inductive loads (relays, solenoids, motors) can generate transients well above the supply rail, so always include a flyback diode or clamp. Add a 10 kOhm-100 kOhm gate-to-source pulldown so the MOSFET stays off during microcontroller reset or when the driver pin is high-impedance. At 3.3 V gate drive the on-resistance is higher than the 10 V figure - verify the effective RDS(on) from the datasheet characteristic curves rather than assuming 3.5 ohms.
Compliance Information
Compliance status not explicitly stated in the provided verified data; the BSS138LT1G Pb-free suffix variant exists in the same family, suggesting lead-free options. Consult the onsemi product page for current RoHS/REACH declarations.
