General Purpose Transistors and Their Uses

Transistors are one of the very important components used in electronic circuit constructions. Transistors can be found almost everywhere; from simple relay driver circuits to complicated motherboard circuits. In reality, your microcontrollers and microprocessors are nothing more than a collection of many transistors synthesized to do a collective operation.

A transistor is a semiconductor device having three terminals that are used to amplify or switch electronic signals. These devices are commonly classified as Bipolar Junction Transistors (BJT) and Field Effect Transistors (FET), allowing for the development of radios, computers, calculators, and other electronic gadgets that you use today.

 

Bipolar Junction Transistor

BJT stands for Bipolar Junction Transistor, it is a solid-state current-controlled device that can be used to electronically switch a circuit. BJT is a three-terminal device having an Emitter, Collector, and Base pin.  The current flow between the emitter and collector is regulated by the amount of current applied to the base terminal.  The BJT is made up of three layers of semiconductor materials: two P-type parts and one N-type part if it's a PNP transistor, and two N-type regions and one P-type region if it's an NPN transistor. The collector and emitter terminals are mounted on the two outer layers, while the base terminal is fixed at the center layer.

 

Bipolar junction transistor

 

 

Symbol of BJT Transistors

The difference between the symbol of PNP and NPN transistors is the arrow at the emitter end.  The arrow represents the direction of current flow in the transistor; in a PNP transistor, current flows from the emitter to the base, whereas in an NPN transistor, current flows from the base to the emitter.

 

Symbol of bipolar junction transistor

 

 

FET

Field-effect transistor, which is generally referred to as a MOSFET (metal-oxide-semiconductor field-effect transistor) and is made up of three pins: gate, source, and drain. It works slightly differently than BJTs due to its different pin construction. A FET is made up of a semiconductor channel with electrodes called the drain and source on either end.  The gate is a control electrode that is placed very close to the channel so that its electric charge is able to affect the channel.

The gate of the FET regulates the flow of carriers (electrons or holes) flowing from the source to the drain. This is done by adjusting the size and shape of the conductive channel.

 

Symbol Of FET

The FET is a three-terminal device with a Drain (D), Source (S), and gate (G). 

Symbol of Field effect transistor

 

 

VI Characteristics

VI characteristics of transistor

 

General Purpose Transistor

General-purpose silicon transistors, best suited for usage in audio amplifier driver stages and tape recorder low noise input stages. Signal processing circuits in television receivers, as well as hi-fi amplifiers. General-purpose transistors can be utilized in a wide range of applications, but they are most commonly used to condition control signals in low-power applications. 

 

 

BC638 (General Purpose PNP Transistor)

The BC638 is a PNP transistor with a VCE of -60V and a continuous collector current of 1A in a TO-92 package. This transistor can be used in moderately high voltage switching applications. The BC638 transistor is a very versatile device that can be used in a wide range of applications. This transistor can be used to switch relatively high voltage devices, such as a pre or mid amplifier stage of a power amplifier. A power amplifier typically operates at 60 to 120 volts DC.

BC638 transistor

When this transistor is biased, it can allow a maximum current of 1A to flow across the CE(Collector-Emitter) Junction; this is known as the saturation state of the transistor and driving a load that consumes more current than 1A may permanently damage the device. During the design process, keep in mind that this device's maximum dissipation is 1W, and any power higher than that can destroy it.

 

BC488 (General Purpose PNP Transistor) 

The BC488 is a PNP transistor with a VCE of -60V and a collector current of -1000mA or -1A in a TO-92 package. It can be used as a signal switching transistor for small signals. It has a low base voltage of 4V. When you need a basic switching device for low-power loads, the BC488 is a good choice. Because the component is inexpensive and simple to use, it is ideal for use as a random switching device. The BC488 transistor can also be used as a basic power amplifier, which can be utilized to boost low-power signals.

BC488 transistor

When this transistor is biased, it can allow a maximum current of 1000mA over the CE(Collector-Emitter) Junction; this is known as the saturation state of the transistor, and applying a load that consumes more current than 1000mA may destroy the device in this state. As you may know, a transistor is a current-controlled device, thus when the base current is removed, the transistor turns off completely. At this point, the transistor is in its Cut-off Region, and no current flows through the C-E junction.

 

 

2N4400 (General Purpose NPN Transistor)

2N4400 transistor

 

The 2N4400 is an NPN transistor with a VCE of 100V and a constant collector current of 1A in a TO-92 package. The 2N4400 transistor is a highly versatile device that can be used in a wide range of applications. This transistor can be used to switch relatively high voltage devices, such as a small DC-DC converter or the pre or mid amplifier stage of a power amplifier (power amplifiers typically require 45 to 60 DC). This gadget is inexpensive and simple to use, making it the best choice for a random switching device.

 

application circuit of 2N4400 transistor

 

BC490 (General Purpose High Current PNP Transistors)

The BC490 is a PNP transistor with a VCE of -80V and a continuous collector current of -1A DC in a TO-92 package. With this characteristic and 625mW total power dissipation, this transistor can be used in moderately high voltage switching applications.

BC490 transistor

The BC490 can be utilized in a variety of applications. This transistor can be used to switch devices with a moderately high voltage.  the transistor is cheap and simple to use, it is ideally suited for switching applications.

The BC490 transistor has a gain of 40 to 160, which determines the transistor's amplification capacity. The maximum current that can be passed through this transistor is 1.5A, which, is when combined with the gain value, makes this transistor a perfect choice for moderate-high voltage application.

 

 

2N3053 (General Purpose NPN Transistor)

The 2N3053 is a Silicon NPN transistor in a TO-39 metal can package. This case is designed primarily for amplifier and switching applications. This device has a high breakdown voltage, a low leakage current, low capacity, and beta that is useful over a wide current range.

2N3053 Transistor

 

2N3053 is an NPN transistor, the collector and emitter will remain open when no power is applied to the base (Reverse Biased). When a positive voltage is provided to the transistor's base, a small amount of current begins to flow from the base to the emitter, and the transistor reaches it's on state. This transistor's maximum gain is 50, which determines the device's amplification factor. The maximum base current is limited to 15mA  more than that can damage the device. This collector-emitter current is 700mA; any current greater than this could harm the device. This transistor has a 5W rating and can be used in a variety of applications.

 

2N3053 transistor application circuit

 

2N4402 (General Purpose PNP Transistor)

The 2N4402 is a PNP silicon transistor that is used in general-purpose amplifiers and switches. The VCE of this transistor is 40V, and the continuous collector current is 600mA. It can be used as a signal switching transistor for small signals. It also has a low 5-volt base voltage.

2N4402 transistor
 
2N4402 transistor application circuit

 

When you need a simple switching device for low power loads, the 2N4402 is a good choice. The 2N4402 can also be used as a basic power amplifier, which can be utilized to boost low-power signals. The gain of the 2N4402 transistor ranges from 20 to 150. This value determines the transistor's amplification capacity; the maximum current that can be passed through it is 200mA, which, when combined with the gain value, makes this transistor an excellent choice for a preamplifier in an audio amplifier.

 

FORMULAS

BASE BIAS

Base bias transistor formula

 

COLLECTOR FEEDBACK BIAS

Collector feedback bias transistor formula

 

EMMITER BIAS

emitter bias transistor formula

 

 DIFFERENCE

Diode BC638 BC488 2N4400 BC490 2N3053 2N4402
Type PNP PNP NPN PNP NPN NPN
Package TO-92 TO-92 TO-92 SOT23-3 TO-39 TO-92
Max. DC current gain (hFE) 160 400 150 400 50 150
Collector Current 1A -1000mA 600mA 1A 700mA 600mA
Emitter base Voltage (VBE) -5V -4V 6V -4V 5V 5V
Base Current (IB) -100mA -50mA 50mA 50mA 15mA 50mA
Collector base Voltage VCB 50V -60V 60V -80V 80V 45V
Transition Frequency 100MHz 150MHz 200MHz 150MHz >100MHz 100MHz
Collector Dissipation 1W 0.625W 625mW 0.625W 5W 0.3W
Collector Capacitance 20pF 9pF 30pF 9pF <15pF 8.5pF
Max. Operating Temperature 150 °C 150 °C 150 °C 150 °C 200 °C 175 °C

 

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