What is a BC558 Transistor?

The BC558 is a PNP transistor, meaning that it has a positive-negative-positive semiconductor layer structure. It is a general-purpose transistor suitable for low-power amplification and switching applications. The BC558 is part of the BC5xx series of transistors, which are known for their reliability and performance.

Key Features of the BC558 Transistor

• PNP polarity
• Low collector-emitter saturation voltage
• High current gain
• Good switching characteristics
• TO-92 package

BC558 Transistor Pinout and Pin Configuration

The BC558 transistor comes in a TO-92 package, which has three pins: emitter (E), base (B), and collector (C). The pinout and pin configuration of the BC558 are as follows:

Pin	Symbol	Description
1	E	Emitter
2	B	Base
3	C	Collector

BC558 Transistor Specifications

Absolute Maximum Ratings

Parameter	Symbol	Value	Unit
Collector-Base Voltage	VCBO	-30	V
Collector-Emitter Voltage	VCEO	-30	V
Emitter-Base Voltage	VEBO	-5	V
Collector Current (DC)	IC	-100	mA
Collector Current (Pulse)	ICP	-200	mA
Total Power Dissipation (TA ≤ 25°C)	Ptot	625	mW
Operating and Storage Junction Temperature Range	Tj, Tstg	-55 to +150	°C

Electrical Characteristics (T_A = 25°C unless otherwise specified)

Parameter	Symbol	Test Conditions	Min	Typ	Max	Unit
Collector-Base Breakdown Voltage	VCBO	IC = -10 μA, IE = 0	-30	–	–	V
Collector-Emitter Breakdown Voltage	VCEO	IC = -1 mA, IB = 0	-30	–	–	V
Emitter-Base Breakdown Voltage	VEBO	IE = -10 μA, IC = 0	-5	–	–	V
Collector Cutoff Current	ICBO	VCB = -30 V, IE = 0	–	–	-100	nA
Emitter Cutoff Current	IEBO	VEB = -5 V, IC = 0	–	–	-100	nA
DC Current Gain	hFE	VCE = -5 V, IC = -10 mA	110	–	800	–
Collector-Emitter Saturation Voltage	VCE(sat)	IC = -10 mA, IB = -1 mA	–	-250	-600	mV
Base-Emitter Saturation Voltage	VBE(sat)	IC = -10 mA, IB = -1 mA	–	-900	–	mV
Transition Frequency	fT	VCE = -5 V, IC = -10 mA, f = 100 MHz	100	–	–	MHz
Collector Capacitance	Cob	VCB = -10 V, IE = 0, f = 1 MHz	–	4	8	pF
Noise Figure	NF	VCE = -5 V, IC = -100 μA, RS = 2 kΩ, f = 1 kHz	–	4	–	dB

BC558 Transistor Applications

The BC558 transistor finds use in a wide range of applications, including:

1. Low-power amplification
2. Switching circuits
3. Inverters and converters
4. Audio amplifiers
5. Oscillators
6. Voltage regulators
7. Motor control circuits
8. Logic gates
9. Sensors and transducers
10. Microcontroller interfaces

BC558 Transistor Circuit Examples

Simple LED Driver Circuit

This circuit demonstrates the use of a BC558 transistor as a simple LED driver. The transistor is used as a switch to control the LED’s on/off state based on the input signal applied to the base.

Common Emitter Amplifier

The BC558 transistor can be used in a common emitter amplifier configuration to amplify small signals. This circuit provides voltage gain and can be used in various low-power amplification applications.

Frequently Asked Questions (FAQ)

1. What is the difference between BC558 and BC557 transistors?
   The main difference between BC558 and BC557 transistors is their current gain (h_FE). The BC558 has a higher current gain range (110 to 800) compared to the BC557 (110 to 220). Other than that, they share similar characteristics and pinouts.

2. Can I replace a BC558 transistor with another PNP transistor?
   In most cases, you can replace a BC558 transistor with another PNP transistor with similar specifications, such as the BC557 or 2N3906. However, it’s essential to compare the datasheets and ensure that the key parameters, such as voltage ratings, current gain, and package type, are compatible with your application.

3. How do I test a BC558 transistor?
   To test a BC558 transistor, you can use a multimeter to measure the resistance between the pins. Set the multimeter to the diode test mode and follow these steps:

4. Connect the red probe to the base (B) and the black probe to the emitter (E). The multimeter should display a voltage drop of approximately 0.7 V for a forward-biased PN junction.
5. Connect the red probe to the base (B) and the black probe to the collector (C). The multimeter should display a voltage drop of approximately 0.7 V for a forward-biased PN junction.

6. Reverse the probes for both tests. The multimeter should display an open circuit (OL) or a very high resistance, indicating a reverse-biased PN junction.

7. What is the maximum power dissipation of the BC558 transistor?
   The maximum power dissipation of the BC558 transistor is 625 mW at an ambient temperature of 25°C. However, this value decreases with increasing temperature. It’s important to ensure proper heat dissipation and maintain the junction temperature within the specified range to avoid damaging the transistor.

8. Can I use a BC558 transistor for high-frequency applications?
   The BC558 transistor has a transition frequency (f_T) of 100 MHz, which is suitable for low to medium-frequency applications. For high-frequency applications, it’s recommended to use transistors specifically designed for such purposes, like RF transistors or those with higher transition frequencies.

Conclusion

The BC558 transistor is a versatile PNP bipolar junction transistor widely used in low-power amplification and switching applications. Its key features include high current gain, low saturation voltage, and good switching characteristics. Understanding the pinout, specifications, and applications of the BC558 transistor is essential for effectively using it in electronic circuits.

When designing circuits with the BC558 transistor, it’s crucial to consider factors such as power dissipation, heat management, and operating conditions to ensure reliable performance and longevity. By following the datasheets and application notes, engineers and hobbyists can harness the full potential of the BC558 transistor in their projects.

As with any electronic component, proper handling, storage, and PCB layout techniques should be employed to minimize the risk of damage and ensure optimal performance. With its wide availability and proven track record, the BC558 transistor remains a popular choice for a broad range of electronic applications.