Comprehensive Exploration of BC547 Transistor: Advantages, Uses, Specifications and Working Status
21 December 2023
Ⅱ. What are the advantages of BC547 transistor?
Ⅲ. BC547 application circuit
Ⅴ. Working status of BC547 transistor
Ⅵ. Absolute maximum ratings of BC547
Ⅶ. What are the limitations of BC547 in high-frequency applications?
BC547 is a commonly used NPN-type triode with high current amplification and small saturation voltage drop. It is commonly used in electronic devices such as audio amplifiers, oscillators and switching circuits. In this article, we will introduce the specifications and operating status of the BC547 triode and discuss why it is such a popular electronic component.
The BC547, a standard NPN junction transistor, is a product manufactured by Fairchild and falls under the circuit protection category. With a button-top mounting style, it boasts dimensions of 5.2 mm in length, 4.19 mm in width, and 5.33 mm in height. This transistor is designed to withstand a broad operating temperature range, from -65°C to 150°C, ensuring its applicability in diverse environments. Housed in a TO-92-3 package and offered in bulk packaging, the BC547 is a versatile component suitable for various electronic applications. Featuring a maximum gain current of 800A, its primary functions revolve around amplification and switching tasks. The combination of its compact design, wide temperature tolerance, and reliable performance make the BC547 a valuable choice for electronic circuitry requiring precision and efficiency.
Replacements and equivalents:
• BC337
• BC548
• BC639
• 2N2222
• 2N3904
• 2N4401
• 2SC1815
• KSP2222A
• Low noise: The BC547 transistor exhibits an exceptionally low noise figure, contributing to the minimization of electronic circuit noise.
• High stability: Its characteristics are very stable and it can work under different temperatures and voltages.
• Fast switching: Due to its structure and material properties, it can switch circuits quickly.
• High amplification: BC547 has a very high amplification, which allows it to amplify weak signals into observable signals.
• Easy to get: Due to its wide range of applications, BC547 transistor is very easy to get and can be purchased in various electronic component stores.
The circuit diagram of using BC547 ON/OFF touch switch is shown below. When power is supplied to the circuit, the relay will be in OFF mode, at which time the base of the Q3 transistor will be at a high level to maintain its cutoff state. When the S2 switch is turned on, the Q4 transistor starts to conduct and the relay "L3" can be latched. If the S1 switch is pressed for a few moments, the Q3 base is pulled high and the L2LED will turn off. When switch S1 is opened, the circuit operates in the home position because the base of transistor Q3 is still held high and the L2 LED will blink to indicate that the power supply is on. And the Q4 transistor conducts due to its collector voltage through the R8 resistor. Relay L3 will remain off in all cases.
• Manufacturer: Onsemi / Fairchild
• Packaging: Bulk
• Package / Case: TO-92-3
• Transistor Polarity: NPN
• Configuration: Single
• Technology: Si
• Power Dissipation: 500 mW
• Continuous Collector Current: 100 mA
• Operating Temperature: -65°C to 150°C
• Mounting Style: Through Hole
• Product Category: Bipolar Transistors - BJT
BC547 transistor works in three regions, including amplification region, saturation region and cut-off region. These three parts constitute the typical working area of BC547 transistor.
1. Amplification region
The amplification region is located between the cut-off region and saturation region. In the active region, the transistor emitter junction is forward biased and the collector junction is reverse biased. In this case, the collector current is β times the base current, i.e., IC = βIB.
• I C = collector current
• β = current amplification factor
• I B = base current
So the collector current increases in proportion to the base current.
2. Saturation region
In this region, the transistor works like a short circuit. The collector and emitter currents are maximum in this region. In the saturation region, both the emitter and collector junctions are forward biased. In other words, the transistor operates as a closed switch or a short circuit carrying maximum current, which means: IC = IE
• I C = collector current
• I E = emitter current
3. Cut-off region
In this region, the transistor is used as open switch or open circuit. The collector and emitter currents and the base circuit are zero in this region. In the cut-off region, both the emitter and collector junctions are reverse biased. In this region, the collector, emitter and base currents are zero, which gives IC = IE = IB = 0.
• I C = collector current
• I E = emitter current
• IB = base current
Examine the electrical properties of the BC547 by reviewing the specifications provided by the device manufacturer. These parameters are typically listed right after the limit values. The specifications include a specific column (test conditions) that denotes the values used during the manufacturer's testing of the equipment. Generally, these tests are carried out at ambient temperatures that do not exceed 25 degrees Celsius.
1. Nonlinear distortion: In high frequency applications, due to the nonlinear characteristics of BC547, it may introduce some distortion, affecting the accurate amplification and transmission of signals.
2. Power capacity limitation: BC547 triode has limited power capacity. When the power is too high, it is easy to cause damage to the triode. In high-frequency applications, due to the large amplitude of the signal, so we need to pay special attention to the power capacity limit.
3. Frequency response limitation: The internal capacitance and inductance of the BC547 triode impact its frequency response. Excessive frequency can induce oscillations in these components, leading to impaired triode functionality. Consequently, the triode's frequency response is constrained in high-frequency applications.
4. Noise performance: In high-frequency applications, due to the high frequency of the signal, it is susceptible to the influence of noise. the BC547 triode's noise performance is poor, and it is easy to introduce additional noise, which affects the quality of signal transmission.
5. Low cut-off frequency: The cut-off frequency of BC547 is relatively low, usually in the range of tens of MHz. In high-frequency applications, especially in frequency bands exceeding the cut-off frequency, its performance may become unstable or unreliable.
Frequently Asked Questions
1. What is BC547 used for?
BC547 is usually used for current amplifier, quick switching and pulse-width modulation (PWM). Therefore, if you need to control the speed of a motor or actuator in some of your projects, you can simply use this transistor to achieve it.
2. What is the gain of BC547?
The maximum current gain of BC547 is 800mA. Collector-Emitter Voltage is 65V. Collector-Base Voltage is 80V.
3. Is BC547 a NPN or PNP transistor?
BC547 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin.
4. Why is it called BC547?
BC547 is a name registered under the Pro-Electron numbering system. The Pro Electron system is the European type designation and registration system for active components, such as electronic tubes and cathode ray tubes, semiconductors, liquid crystal displays, sensor devices, etc.
5. Can I use BC547 instead of S8050?
Also, there are other alternatives to the S8050, also belonging to the NPN transistors package type. Electrical engineering professionals can thus use them in place of the S8050. They include the MPSA42, 2N3055, 2N3906, 2N2369, and BC547.
