Infineon BC817-40E6327: Technical Specifications and Application Circuit Design
The Infineon BC817-40E6327 is a widely adopted general-purpose NPN bipolar junction transistor (BJT) housed in a compact SOT-23 surface-mount device (SMD) package. Its excellent switching and amplification capabilities, combined with its small form factor, make it a fundamental component in modern electronic design, particularly in consumer electronics, automotive modules, and signal processing circuits.
Technical Specifications
The BC817-40E6327 is part of a family of transistors, with the "-40" suffix denoting its specific DC current gain (hFE) classification. Its key electrical characteristics are as follows:
Polarity: NPN Bipolar Junction Transistor (BJT)
Package: SOT-23, a 3-pin miniature surface-mount package ideal for high-density PCB designs.
Collector-Emitter Voltage (VCEO): 45 V. This defines the maximum voltage that can be applied between the collector and emitter with the base open.
Collector Current (IC): 500 mA (max). The maximum continuous current that can flow through the collector.
DC Current Gain (hFE): This is a critical parameter. The "-40" variant offers a gain range of 250 to 600 at a collector current of 2 mA and a collector-emitter voltage of 5 V.
Power Dissipation (Ptot): 350 mW at an ambient temperature of 25°C.
Transition Frequency (fT): 100 MHz (typical). This indicates its effectiveness in amplifying high-frequency signals.
These specifications highlight the transistor's suitability for low-power amplification and fast switching applications.
Application Circuit Design
Two primary use cases for the BC817-40E6327 are as a switch and as an amplifier.
1. Low-Side Switch Circuit
A very common application is using the transistor as a switch to control a load (e.g., an LED, relay, or motor) with a microcontroller (MCU) or logic circuit.
Circuit Operation: The load is connected between the positive supply voltage (Vcc) and the transistor's collector pin. The emitter is connected to ground. A current-limiting base resistor (Rbase) is connected between the MCU's digital output pin and the base of the transistor.
Design Calculations: The key is to ensure the transistor is driven into saturation (fully ON) when the MCU output is high (e.g., 3.3V or 5V).
The base current (Ib) required for saturation is calculated as: `Ib > Ic(sat) / hFE(min)`. For example, to switch a 100 mA load (Ic) with a minimum hFE of 250, the required Ib is > 0.4 mA.
The base resistor value is then calculated using Ohm's Law: `Rbase = (VMCU - Vbe) / Ib`. Where VMCU is the MCU's output high voltage (e.g., 3.3V) and Vbe is the base-emitter voltage (typically 0.7V for silicon transistors). A resistor value between 1kΩ and 10kΩ is often suitable for many low-current applications.
2. Common-Emitter Amplifier
The BC817-40E6327 can also be configured to amplify small AC signals.
Circuit Operation: The design involves setting a DC operating point (quiescent point) through a voltage divider network (R1 and R2) on the base, an emitter resistor (Re) for stability, and a collector resistor (Rc) to develop the output voltage. A small AC input signal is coupled to the base via a capacitor. The amplified, inverted output signal is taken from the collector and coupled through another capacitor to remove the DC bias.
Design Considerations: The values of R1, R2, Rc, and Re are chosen to set the transistor's operating point within its active region, ensuring linear amplification without distortion. The voltage gain (Av) of this stage is approximately `Av ≈ - Rc / Re`.
In all circuits, it is crucial to review the absolute maximum ratings from the datasheet to avoid damaging the device through over-current or over-voltage conditions.
ICGOODFIND summarizes that the Infineon BC817-40E6327 is a highly reliable and cost-effective NPN transistor offering a robust combination of medium voltage handling, good current gain, and high transition frequency. Its SOT-23 package makes it indispensable for space-constrained designs. Its primary value lies in its versatility, serving as the fundamental building block for digital switching and small-signal amplification in countless commercial and industrial electronic products.
Keywords: NPN Transistor, SOT-23, Switching Circuit, Small-Signal Amplification, DC Current Gain (hFE)
