BC817-40 - 45V 500mA NPN Transistor SOT-23 | Nexperia
MPN: BC817-40 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.08 | $0.08 |
| 10 | $0.06 | $0.60 |
| 100 | $0.04 | $4.00 |
| 500 | $0.03 | $15.00 |
| 1,000 | $0.025 | $25.00 |
| 3,000 | $0.018 | $54.00 |
BC817-40 Overview
An NPN BJT is a three-terminal semiconductor device in which a small base current controls a much larger collector current; it belongs to the bipolar transistor family within discrete semiconductors. The BC817 series occupies the medium-power small-signal segment - more current than a BC847 (100 mA) yet in the same miniature SOT-23 footprint, sitting between signal-level transistors and dedicated switching MOSFETs.
Key features include a transition frequency (fT) of 100 MHz, VCEO of 45 V, VCBO of 50 V, VEBO of 5 V, and a low collector-emitter saturation voltage typically below 700 mV at 500 mA. The complementary PNP counterpart is the BC807-40, which uses an identical pinout with reversed polarity, enabling paired push-pull output stages in audio and DC-DC converter circuits.
The device is built using an epitaxial planar die process in a SOT-23 (TO-236AB) package, the industry-standard 3-pin surface-mount outline measuring approximately 2.9 mm x 1.3 mm with a JEDEC TO-236 registration. The plastic encapsulation carries an MSL-1 moisture sensitivity rating, allowing direct reflow without prior bake-out.
Typical applications include switching circuits, AF driver stages, generic interface level-shifters, MOSFET gate drivers, relay/solenoid drivers, and DC-DC converter synchronised rectifiers. The -40 hFE bin is especially useful where high gain is needed without cascading a second transistor.
When designing with the BC817-40, place a base series resistor to limit base current during turn-off transients, and respect the 310 mW power dissipation limit at 25 C by derating approximately 2.5 mW per degree Celsius above that point.
This page consolidates distributor pricing, pin-compatible drop-in alternatives, and application guidance not found in the standalone datasheet.
Drop-in alternatives for BC817-40 — 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 BC817-40 (same form factor and footprint) — differing in Package, Continuous Collector Current (IC), Transistor Type, MSL Level, Operating Junction Temperature.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
BC817-40,215
✅ Drop-In✓ In Stock
$0.05 / Unit
View Datasheet →BC817-40-7-F
✅ Drop-In📋 Reference alternative (not in catalog)
BC817-40-TP
✅ Drop-In📋 Reference alternative (not in catalog)
MMBTA06
✅ Drop-In📋 Reference alternative (not in catalog)
BCW66H
✅ Drop-In📋 Reference alternative (not in catalog)
MMBTA05
✅ Drop-In📋 Reference alternative (not in catalog)
BCX19
✅ Drop-In📋 Reference alternative (not in catalog)
BC817-40 Maximum Ratings & Electrical Characteristics
| Transistor Type | NPN Bipolar Junction Transistor (BJT) |
| Package | SOT-23 (TO-236AB), 3 pins |
| Collector-Emitter Voltage (Vceo) | 45 V |
| Collector-Base Voltage (Vcbo) | 50 V |
| Emitter-Base Voltage (Vebo) | 5 V |
| Continuous Collector Current (IC) | 500 mA |
| Total Power Dissipation (Ptot) | 310 mW |
| DC Current Gain (hFE) - -40 bin | 250 to 600 (at 100 mA, 1 V) |
| Transition Frequency (ft) | 100 MHz |
| Collector-Emitter Saturation Voltage (VCEsat) | 700 mV max (at 500 mA, 50 mA base) |
| Operating Junction Temperature | -65 C to +150 C |
| Mounting Type | Surface Mount |
| MSL Level | 1 |
| RoHS Status | Compliant |
| Complementary PNP Part | BC807-40 |
BC817-40 Pin Configuration
| Pin 1 | Base — Control input; base current modulates collector current |
| Pin 2 | Emitter — Current returns to ground or low-side reference |
| Pin 3 | Collector — Connects to load or supply rail (load-side for low-side switching) |
Typical Applications
BC817-40 is suitable for 6 applications: Relay and Solenoid Driver, LED Driver and Indicator Switch, Logic Level Shifter (3.3V to 12V/24V), MOSFET Gate Driver Pre-Driver, AF Amplifier Driver Stage, Synchronous Rectifier in DC-DC Converters.
Relay and Solenoid Driver
The BC817-40's 500 mA continuous collector current comfortably exceeds the 70 to 150 mA typical pull-in current of signal relays, making it a textbook low-side switch for 5 V/12 V/24 V coil drive. The 45 V VCEO provides 2x headroom over a 24 V rail, and the 250 hFE minimum lets a 3.3 V GPIO deliver 10 mA into the base to fully saturate the device. Place a 1N4148 flyback diode across the coil; this is critical because the inductive kick otherwise destroys the transistor.
Recommended
LED Driver and Indicator Switch
The BC817-40 is widely used as a low-side switch for LED strings up to 500 mA total current. With a typical hFE of 400 and 1.5 mA base current, the transistor saturates at ~100 mV VCEsat, dissipating minimal power and avoiding the need for a driver MOSFET. The 45 V VCEO also supports high-side switching of multi-LED backlight chains driven from a 12 V or 24 V rail.
Recommended
Logic Level Shifter (3.3V to 12V/24V)
The BC817-40 is a classic level translator between 3.3 V microcontroller GPIO and 5 V, 12 V, or 24 V peripheral rails. With 45 V VCEO and a 250 hFE minimum, the transistor interfaces cleanly from low-voltage CMOS logic to industrial bus voltages. The 100 MHz fT ensures edge transitions remain sub-microsecond, suitable for SPI, I2C, and UART re-buffering into RS-485/RS-232 transceivers.
Recommended
MOSFET Gate Driver Pre-Driver
In DC-DC converters and motor drives, the BC817-40 acts as a totem-pole pre-driver for power MOSFET gates that require 10 to 50 nC of gate charge. The 500 mA collector current and 100 MHz fT easily deliver the peak gate-drive current during switching transitions, while the SOT-23 footprint keeps the driver compact. Pair with a complementary BC807-40 (PNP) for symmetric push-pull drive.
Recommended
AF Amplifier Driver Stage
The BC817-40's 100 MHz transition frequency and 250 to 600 hFE range make it suitable as a small-signal AF pre-amplifier or driver stage in audio circuits. The -40 bin provides high sensitivity, enabling the stage to drive headphones, small speakers through a complementary pair, or buffer line-level signals into a power amplifier input. The 45 V VCEO allows operation from +/-15 V rails.
Recommended
Synchronous Rectifier in DC-DC Converters
In low-power buck converters below 500 mA output, the BC817-40 can be used as a synchronous rectifier (low-side switch) replacing a Schottky diode for improved efficiency. With 700 mV VCEsat max at full load, conduction loss is roughly half that of an equivalent Schottky. The fast 100 MHz fT minimises dead-time losses when paired with a complementary high-side switch in continuous-conduction mode.
Recommended
Recommended Products Summary
Engineering reference data for BC817-40 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BC817-40,215 | BC817-40-7-F | BC817-40-TP | MMBTA06 | BCW66H |
|---|---|---|---|---|---|---|
| Package | SOT-23 (TO-236AB) | SOT-23 (TO-236AB) - same | SOT-23 (TO-236AB) - same | SOT-23 (TO-236AB) - same | SOT-23 (TO-236AB) - same | SOT-23 (TO-236AB) - same |
| Brand | Nexperia | Nexperia | Diodes Incorporated | MCC | onsemi | Nexperia |
| VCEO (Collector-Emitter Voltage) | 45 V | 45 V | 45 V | 45 V | 80 V | 45 V |
| Continuous Collector Current (IC) | 500 mA | 500 mA | 500 mA | 500 mA | 500 mA | 800 mA |
| DC Current Gain (hFE) - Min | 250 | 250 | 250 | 250 | 100 | 250 |
| Transition Frequency (fT) | 100 MHz | 100 MHz | 100 MHz | 100 MHz | 100 MHz | 100 MHz |
| Power Dissipation (Ptot) | 310 mW | 310 mW | 310 mW | 310 mW | 350 mW | 350 mW |
| Polarity | NPN | NPN | NPN | NPN | NPN | NPN |
| Qty-1 Unit Price (USD) | $0.08 | $0.08 | $0.07 | $0.04 | $0.05 | $0.09 |
Key Differentiators
- Highest hFE bin in the BC817 family (vs BC817-25)
- Industry-standard 45 V/500 mA envelope (vs MMBTA06)
- Multi-source second-source availability (vs Proprietary transistors)
Design Notes
Estimated: At maximum ratings of 500 mA collector current and 45 V VCEO, instantaneous power could theoretically reach 22.5 W, but the 310 mW continuous dissipation limit (at 25 C ambient, with no heatsink) bounds real-world operation. Derate by approximately 2.5 mW per degree Celsius above 25 C - at 100 C ambient the limit drops to ~187 mW. For switching applications at 100 mA or less, thermal performance is rarely an issue; for sustained 300 to 500 mA loads use a copper pour of at least 1 cm squared on the collector pad.
Three recurring pitfalls with the BC817-40: (1) forgetting the flyback diode across inductive loads - a relay coil without a 1N4148 across it can produce 100+V transients that exceed the 45 V VCEO and destroy the transistor; (2) driving the base with insufficient current - designs assuming hFE = 600 may saturate but those targeting the minimum hFE = 250 must supply at least IC/250 base current; (3) confusing pinout - on the SOT-23 outline, the base is pin 1, emitter pin 2, collector pin 3, which differs from some larger packages (TO-92 has C-B-E order).
SOT-23 thermal performance depends almost entirely on the copper pad connected to pin 3 (collector). For sustained loads above 200 mA, expand the collector pad to at least 25 mm squared of 2 oz copper on both PCB layers stitched with thermal vias. Place the base series resistor within 5 mm of pin 1 to minimise parasitic inductance that can cause ringing during fast transients.
Compliance Information
RoHS and REACH compliant per Nexperia product page. Not AEC-Q100 qualified for automotive - consult the manufacturer's automotive-grade portfolio if required. Lead-free reflow-compatible per JEDEC J-STD-020.
