Infineon BC817K-16: Key Specifications and Application Circuit Design
The Infineon BC817K-16 is a widely used NPN bipolar junction transistor (BJT) housed in a compact SOT-23 surface-mount package. It is part of a family of general-purpose transistors designed for amplification and switching applications, offering a robust combination of performance and reliability for modern electronic designs.
Key Specifications
The BC817K-16 is characterized by several critical parameters that define its operational limits and ideal use cases:
Collector-Emitter Voltage (VCE): 45 V. This specifies the maximum voltage that can be applied between the collector and emitter while the transistor is in its off state.
Collector Current (IC): 500 mA. This is the maximum continuous current that can flow through the collector terminal.
DC Current Gain (hFE): This parameter, which indicates the transistor's amplification capability, is classified by a suffix. The "-16" suffix denotes a gain group of 100 - 250 at a collector current of 2 mA and VCE of 5 V, making it suitable for both switching and low-signal amplification.
Power Dissipation (Ptot): 250 mW at an ambient temperature of 25°C. This is the maximum power the device can dissipate without exceeding its junction temperature limit.
Transition Frequency (fT): 100 MHz minimum. This high frequency indicates the transistor's capability to amplify signals effectively into the VHF range.
Application Circuit Design: A Simple Switch
One of the most common applications for the BC817K-16 is as a low-side switch to control a load, such as an LED, a relay, or a small motor. The design principles for such a circuit are straightforward but crucial for reliable operation.
Circuit Components:
Transistor: Infineon BC817K-16 (Q1)
Microcontroller (MCU) or logic gate output providing a control signal (e.g., 3.3V or 5V)
Load (L): e.g., an LED with a series current-limiting resistor (R_LED)
Base Resistor (R_B): Critical for limiting base current.
Protection Diode (D1): A flyback diode (e.g., 1N4148) is essential if the load is inductive (like a relay coil) to protect the transistor from voltage spikes during turn-off.
Design Calculations:
The primary design goal is to drive the transistor into saturation, ensuring minimal voltage drop (VCE(sat)) between collector and emitter when on, thus minimizing power loss.
1. Determine Collector Current (IC): This is defined by the load. For an LED, IC might be 20 mA.
2. Calculate Base Resistor (R_B): The value of RB is calculated to provide sufficient base current (IB) to saturate the transistor. A common rule of thumb is to ensure IB is at least IC / 10 for guaranteed saturation, considering the lowest hFE in its range.
Formula: `R_B = (V_{MCU} - V_{BE}) / I_B`
Where:
VMCU = Microcontroller output voltage (e.g., 3.3V)
VBE = Base-Emitter voltage (typically 0.7 V)
IB = Base current (IC / 10)
Example Calculation:
For IC = 20 mA and VMCU = 3.3V:
IB = 20 mA / 10 = 2 mA
RB = (3.3V - 0.7V) / 0.002 A = 1.6V / 0.002A = 800 Ω (A standard value like 820 Ω or 1 kΩ would be suitable).
This simple circuit leverages the BC817K-16's high current gain and low saturation voltage to efficiently interface a low-power control signal with a higher-power load.
The Infineon BC817K-16 is an exceptionally versatile and cost-effective NPN transistor, perfectly suited for a vast array of general-purpose switching and amplification tasks in consumer electronics, automotive modules, and industrial control systems. Its well-defined characteristics and SMT package make it a fundamental building block for modern PCB design.
Keywords: NPN Transistor, Switching Circuit, Saturation, Current Gain, SOT-23
