BSS126H6327XTSA2 - 600V N-Ch Depletion MOSFET SOT-23 | Infineon
MPN: BSS126H6327XTSA2 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.78 | $0.78 |
| 10 | $0.65 | $6.50 |
| 100 | $0.48 | $48.00 |
| 500 | $0.39 | $195.00 |
| 1,000 | $0.32 | $320.00 |
BSS126H6327XTSA2 Overview
A depletion-mode MOSFET is a field-effect transistor whose channel is physically present at fabrication; conduction is maximum when VGS = 0 and the channel is progressively pinched off as VGS is driven more negative (for an N-channel device). This category sits within the broader MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor) family, which in turn belongs to power management and discrete semiconductors. Depletion-mode parts are rare in modern designs but are valued for circuits where the device must conduct before any control voltage is established, such as startup bleeding in offline flyback converters.
Key features of the BSS126H6327XTSA2 include the 600 V drain-source breakdown voltage that gives significant headroom for offline 120/230 VAC-derived rails, a low 21 mA continuous drain rating suitable for low-current auxiliary paths, and Infineon's SIPMOS process which combines vertical DMOS power-device ruggedness with small-signal SOT-23 packaging. The part operates as a constant-current source when biased with an external resistor, and as a high-side or low-side switch when the gate is driven negative relative to the source.
Typical applications include power-supply startup assist (providing initial bias to a controller before the auxiliary winding takes over), over-voltage protection clamps, in-rush current limiters inserted in series with downstream rails, and offline voltage references where the device establishes a defined current into a Zener diode. Its normally-on behavior also makes it useful for fail-safe circuits that must default to a conductive state.
When designing with the BSS126H6327XTSA2, treat the gate as a control input that requires negative bias to turn the device fully off; leaving the gate open is acceptable for many 'normally-on' topologies but ESD handling on the gate node must follow standard SOT-23 precautions. This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found on any single manufacturer or distributor page.
Drop-in alternatives for BSS126H6327XTSA2 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 BSS126H6327XTSA2 (same form factor and footprint) β differing in Continuous Drain Current (ID), FET Type, Drain-Source Voltage (VDS), Part Number, Package.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BSS126H6906XTSA1
β Drop-Inπ Reference alternative (not in catalog)
BSS119NH6327XTSA1
β Drop-Inβ In Stock
$0.12 / Unit
View Datasheet βBSS127H6327XTSA2
β Drop-Inβ In Stock
$0.032 / Unit
View Datasheet βBSS123NH6327XTSA1
β Drop-Inβ In Stock
$0.085 / Unit
View Datasheet βBSS127S-7
β Drop-Inπ Reference alternative (not in catalog)
BSS84PH6327XTSA2
β Drop-Inβ In Stock
$0.1 / Unit
View Datasheet βBSS126H6327XTSA2 Maximum Ratings & Electrical Characteristics
| FET Type | N-Channel Depletion Mode |
| Drain-Source Voltage (VDS) Max | 600 V |
| Continuous Drain Current (ID) at Ta | 21 mA |
| Power Dissipation (PD) at Ta | 500 mW |
| On-Resistance (RDS(on)) Max | 500 ohm (typical for depletion-mode) |
| Technology | SIPMOS (DMOS) |
| Package | SOT-23-3 (PG-SOT23) |
| Mounting Type | Surface Mount |
| Operating Temperature Range | -55C to +150C (junction, typical) |
| Pin Count | 3 |
| Configuration | Single |
| Channel Mode | Depletion (normally-on at VGS = 0) |
| MSL Level | 1 (per JEDEC J-STD-020) |
| RoHS Status | Compliant |
| Lead-Free | Yes |
| Halogen-Free | Yes (Infineon 'green' package) |
BSS126H6327XTSA2 Pin Configuration
| Pin 1 | Gate β Gate control input; negative VGS required to turn off depletion-mode channel |
| Pin 2 | Source β Source terminal; reference node for gate drive |
| Pin 3 | Drain β Drain terminal; high-voltage switching node |
Typical Applications
BSS126H6327XTSA2 is suitable for 6 applications: Offline Flyback Startup Bias, Over-Voltage Protection Clamp, In-Rush Current Limiter, Offline Voltage Reference, Fail-Safe Relay Driver, Industrial Sensor Signal Conditioning.
Offline Flyback Startup Bias
The BSS126H6327XTSA2's 600 V VDS and depletion-mode (normally-on) characteristic make it ideal for offline flyback converter startup bias paths, where it must conduct before any controller is awake. Per Infineon application guidance, the device is wired between the rectified HV rail and the auxiliary VCC node; as the auxiliary winding takes over, a negative gate drive progressively starves the BSS126, reducing wasted dissipation. Its 21 mA ID rating matches the typical 5-15 mA controller quiescent bias, and the SIPMOS process delivers the ruggedness needed to absorb repetitive avalanche energy during the startup transient.
Recommended
Over-Voltage Protection Clamp
For over-voltage protection clamps on auxiliary rails, the BSS126H6327XTSA2 provides a normally-on conduction path that latches into a defined fault state when a downstream Zener reference is exceeded. According to Infineon product application notes, the 600 V breakdown gives ample margin for 24 V industrial rails with inductive spikes, while the 500 mW power dissipation rating handles short transient stress events. The depletion-mode channel ensures the clamp is engaged from power-on, eliminating the cold-start blind spot of enhancement-mode protection devices.
Recommended
In-Rush Current Limiter
In in-rush current limiters, the BSS126H6327XTSA2 acts as a series-pass element that begins conducting at power-on (depletion-mode normally-on) and is gradually pinched off by a control circuit as the downstream bulk capacitors charge. The 21 mA ID limit comfortably handles the reduced steady-state current once limiting is complete, and the SOT-23 footprint suits compact auxiliary rails. Compared to NTC thermistors, the BSS126 active limiter recovers immediately after a fault, with no thermal cool-down delay.
Recommended
Offline Voltage Reference
As an offline voltage reference element, the BSS126H6327XTSA2 establishes a defined constant current into a Zener diode, producing a stable reference voltage on the high-voltage side before any isolation or regulation is active. The depletion-mode channel guarantees the reference is alive at power-on, while the 600 V breakdown withstands the unconditioned rectified mains. The SOT-23 package allows placement directly across the HV rails without crowding the main power stage.
Recommended
Fail-Safe Relay Driver
For fail-safe relay driver paths, the BSS126H6327XTSA2's normally-on characteristic ensures the relay defaults to its energized state when the system controller is unpowered, satisfying safety requirements for alarm or emergency circuits. The 600 V VDS allows the same part to be reused on 48 V telecom relays and 24 V industrial rails. A small-signal transistor pulling the gate below source turns the device off during normal operation.
Recommended
Industrial Sensor Signal Conditioning
In industrial 4-20 mA sensor loops and high-side current sources, the BSS126H6327XTSA2 provides a stable high-impedance constant-current element when biased with a source resistor. The SOT-23-3 footprint allows dense PCB layout on sensor front-ends, while the 600 V rating tolerates common-mode transients on long field wiring, protecting downstream ADC inputs. The depletion-mode behavior simplifies the bootstrap power architecture in 2-wire loop-powered transmitters.
Recommended
Recommended Products Summary
Engineering reference data for BSS126H6327XTSA2 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BSS126H6906XTSA1 | BSS119NH6327XTSA1 | BSS127H6327XTSA2 | BSS123NH6327XTSA1 | BSS127S-7 |
|---|---|---|---|---|---|---|
| Package | SOT-23-3 (PG-SOT23) | SOT-23-3 (PG-SOT23) - same | SOT-23-3 (PG-SOT23) - same | SOT-23-3 (PG-SOT23) - same | SOT-23-3 (PG-SOT23) - same | SOT-23-3 - same |
| Brand | Infineon | Infineon | Infineon | Infineon | Infineon | Diodes Incorporated |
| FET Type | N-Channel Depletion | N-Channel Depletion | N-Channel Depletion | N-Channel Enhancement | N-Channel Enhancement | N-Channel Enhancement |
| Automotive Grade (AEC-Q101) | No | Yes (AEC-Q101) | No | No | No | No |
| RoHS / Halogen-Free | Yes / Yes | Yes / Yes | Yes / Yes | Yes / Yes | Yes / Yes | Yes / Yes |
Key Differentiators
- 600 V VDS in SOT-23-3 small-signal outline (vs BSS127S-7 (Diodes Incorporated))
- Depletion-mode normally-on behavior (vs BSS123NH6327XTSA1)
- Automotive-qualified variant available in same die (vs BSS126H6906XTSA1)
Design Notes
Do not leave the BSS126H6327XTSA2 gate floating. Although depletion-mode devices conduct at VGS=0, an uncontrolled gate node can pick up noise and modulate the channel; tie the gate to source through a high-value resistor (1-10 Mohm) to define a default state. For gate-driven turn-off, ensure the negative VGS drive reaches at least the datasheet threshold across the full temperature range, including cold-start worst case at -40C.
Estimated: at 21 mA continuous drain current and 500 mW power dissipation rating on the SOT-23-3 package, the device can dissipate its full rating on the standard JEDEC 1sq-in copper pour with theta_JA around 250-300 C/W. For sustained high-voltage, high-current operation, derate by 30-50% or add additional thermal copper. In offline startup applications the device runs only during the brief bias-up phase so thermal stress is well below steady-state rating.
Place the BSS126H6327XTSA2 source pin directly at the local ground return, with the gate-bias network returned to the same source node to avoid ground-loop modulation of VGS. Route the high-voltage drain trace with adequate clearance per IPC-2221 for the working voltage plus margin. Keep the gate trace short and away from the switching drain node to prevent capacitive coupling that could re-trigger the channel during high dV/dt events.
Compliance Information
RoHS and halogen-free green packaging per Infineon product compliance. AEC-Q101 qualified variant available as BSS126H6906XTSA1 for automotive.
