BD139 Transistor Equivalent, Technical Parameters and Applications
16 October 2023
Ⅱ. BD139 symbol, footprint and pin configuration
Ⅲ. Technical parameters of BD139
Ⅴ. Working principle of BD139 transistor
Ⅵ. Circuit of BD139 transistor power amplifier
Ⅶ. What are the applications of BD139 transistor?
Ⅷ. Common faults of BD139 transistor
The BD139 is a bipolar medium power NPN transistor housed in a SOT-32 plastic package. Because of its relatively low manufacturing cost and high collector current, this transistor is widely used in various electronic circuits. Its excellent driving capability can easily drive load components up to 1.5A, such as motors, high-power LEDs, and relays.
The collector-emitter(VCE ) and collector-base(VCB) voltages of the BD139 transistor are also very high, so it can be easily used in electronic circuits. In addition, the transistor's collector dissipation current is as high as 12.5W, which makes it very suitable for the design of audio amplifier circuits.
Complementary BD139 transistor:
• BD140
Equivalent BD139 transistor:
• BD169
• BD139G
• BD230
• BD349
• BD791
• MJE242
• 2SC5171
The BD139 transistor has three pins, namely emitter, base and collector. The emitter and collector are at opposite ends of the package, and the base is between the emitter and collector.
Pin 1 (Emitter): Current drains out through emitter, normally connected to ground
Pin 2 (Collector): Current flows in through collector, normally connected to load
Pin 3 (Base): Controls the biasing of transistor, used to turn ON or OFF the transistor.
• Collector-emitter and collector-base voltages are high and can be easily used in electronic circuits.
• With high collector current, it can drive loads up to 1.5A, such as motors, high-power LEDs, relays, etc.
• High linearity: It has very little distortion on the input signal and can provide good audio reproduction.
• Low saturation voltage: The BD139 has a low voltage drop in the on-state, making it ideal for driving high-power load applications.
• Low noise: BD139 has low noise characteristics to ensure the clarity and quality of audio signals.
• Suitable for audio amplifiers: BD139 is specially designed for audio amplifiers and drivers, so it has special properties related to audio amplification. First of all, its frequency response characteristics are specially optimized for the needs of audio amplifiers, which can ensure the accuracy of the original sound signal, thereby producing stunning sound quality effects. Secondly, the distortion performance of BD139 is also excellent. It can maintain low distortion at high amplification to ensure the purity of the audio signal.
The BD139 transistor is an NPN type, featuring a p-type doped layer nestled between two n-type doped layers. With the base pin grounded, the collector and emitter are active; however, applying a signal to the base pin deactivates the collector and emitter. As an NPN transistor, the primary charge carriers are electrons.
When enough current is applied to the base pin, it will be forward biased and conduct. In this case, the maximum current consumption of the emitter and collector is 1.5A. If the current supplied to the entire transistor reaches 1.5A, then it will enter saturation, where the current must be greater than the collector current. The maximum voltage that can be tolerated between the emitter and collector is 80V. When there is no current input to the base of the transistor, it turns off. This state is called the cut-off state.
The picture above shows a Class AB audio power amplifier with an output power of 2W. The BD139 transistor power amplifier circuit can drive an 8Ωspeaker. Among them, the speaker output power is about 5W. The circuit requires a supply voltage ranging from 12V to 18V and is implemented by a two-stage transistor including 2N3904 and BD139.
After configuring the standard emitter, the input signal can pass through the input capacitor and be amplified to enough strength to drive the next-stage transistor Q2. Q2 amplifies again and outputs the amplified signal, which completes the entire amplification process.
• Audio signal processor: It can be used in conjunction with some audio signal processors or effects, such as noise gates, compressors, equalizers, exciters, etc., to improve the quality and effect of audio signals.
• Audio preamplifiers: The BD139 can be used along with other components to build audio preamplifiers to enhance the amplitude and clarity of audio signals.
• Driving speakers: The BD139 can be used as an integral part of an audio amplifier to drive an 8Ω speaker. Its output power is about 5W, which can make the sound of the speaker clear, bright and with low distortion.
• Complementary output stage: It can also be used in combination with other components of the complementary circuit (such as PNP transistors or other NPN transistors) to form a complete audio amplifier output stage. This improves the efficiency of the amplifier and reduces noise and distortion.
1. Transistor leakage is serious.
First, we need to check the equipment to ensure that it is installed tightly and is not loose. If any loose screws are found, tighten them immediately to prevent the equipment from falling off or shaking during operation. At the same time, we also need to carefully inspect the circuit board and connecting lines to see if there is any damage or short circuit. If any abnormalities are found, they should be repaired or replaced in time to avoid causing the equipment to fail to operate normally or causing safety problems.
2. The transistor cannot amplify the signal properly.
This may be due to improper setting of its static operating point, or abnormal operation of the microvariant equivalent circuit. If we find that the static working point is improperly set, we need to adjust it in time. In addition, we need to check whether the micro-change equivalent circuit is working properly. The microvariable equivalent circuit is an important part of the transistor amplifier. If it fails, it will directly affect the effect of amplifying the signal. If there is a problem with the micro-change equivalent circuit, we need to adjust or replace it in time.
3. Transistor heats up seriously.
In order to ensure the normal operation of the equipment, we need to check whether its operating voltage and current are within the rated range. If it is out of range, we should make adjustments to bring it back to normal. At the same time, we also need to check whether the heat sink is sufficient. If the heat sink is not enough, we can consider increasing the heat sink area or replacing the heat sink with better thermal conductivity.
Frequently Asked Questions
1. How many watts is a BD139 transistor?
Its saturation voltage is 0.5 V and collector terminals dissipation current is 12.5 W with high collector-emitter and collector-base voltage. BD139 has a current limit of 1.5 A.
2. What is the maximum base voltage of BD139?
To run this BD139 transistor in your circuit very safely, this transistor should not be operated above 80V, do not drive load above 1500mA/1.5A & utilize an appropriate heat sink through the transistor. The required base current can be provided by using an appropriate base resistor.
3. What kind of transistor is a BD139?
BD139 is a Bipolar NPN transistor, mounted in the SOT-32 plastic package and is designed for audio amplifier and driver utilizing complementary circuits.
4. What is the replacement and equivalent of BD139?
You can replace the BD139 with the BD139G, BD169, BD179, BD230, BD237, BD237G, BD379, BD789, BD791, MJE242, MJE244 or MJE722.
5. What is BD139 used for?
The BD139 is designed to especially used in audio applications. The gain value of BD139 is a maximum 250, and this number defines the transistor's amplification capacity. Because the maximum current that may flow through the collector pin is 1.5A, we cannot connect loads that use more than 1.5A to this transistor.
