BD140 Description
The BD140 is a silicon-based medium power PNP transistor widely used in audio amplifiers, power drivers, and quasi-complementary or complementary circuit designs. Packaged in a compact TO-126 form factor, it is capable of handling collector currents up to 1.5A, making it suitable for driving relays, motors, speakers, power LEDs, and other medium-power loads. With collector-emitter and collector-base voltage ratings up to 80V, the BD140 delivers stable and reliable performance in both analog and power management applications.
The transistor features a low saturation voltage of approximately -0.5V and a power dissipation capability of around 12.5W, which enhances its efficiency in amplifier and switching circuits. Its DC current gain (Beta) ranges from 40 to 160, providing flexible amplification characteristics for different circuit requirements. In many audio and embedded applications, the BD140 is commonly paired with the BD139 NPN transistor to form complementary output stages, enabling smooth handling of positive and negative signal cycles.
BD140 Operation Principle
The operation of the BD140 PNP transistor mainly relies on the current control relationship between the base, emitter, and collector. When the emitter maintains a higher potential than the base, the transistor enters the conduction state, allowing current to flow from the emitter to the collector. However, when a positive voltage is applied to the base so that the base-emitter junction no longer satisfies the conduction condition, the current flow between the collector and emitter stops, causing the transistor to enter the cut-off state.
In conduction mode, the BD140 can drive currents of up to approximately 1.5A through the emitter-collector path, making it suitable for controlling medium-power loads such as relays, motors, LEDs, and audio power stages. When operating near saturation, the transistor provides a relatively low voltage drop, helping improve circuit efficiency. Once the base current is removed, the BD140 switches into cut-off mode and blocks further current flow.
BD140 Key Specifications
Parameter | Value |
Part Number | BD140 |
Description | TRANS PNP 80V 1.5A SOT-32 |
Lead Free Status / RoHS Status | Lead free / RoHS Compliant |
Vce Saturation (Max) @ Ib, Ic | 500mV @ 50mA, 500mA |
DC Current Gain (hFE) (Min) @ Ic, Vce | 40 @ 150mA, 2V |
Mounting Type | Through Hole |
Moisture Sensitivity Level (MSL) | 1 (Unlimited) |
Current - Collector (Ic) (Max) | 1.5A |
Current - Collector Cutoff (Max) | 100nA (ICBO) |
Voltage - Collector Emitter Breakdown (Max) | 80V |
Power - Max | 1.25W |
Operating Temperature | 150°C (TJ) |
Transistor Type | PNP |
Package | TO-126 |
Base Product Number | BD140 |
BD140 Pinout
1. B (Base): Controls the transistor biasing and is used to switch the transistor ON or OFF during operation.
2. C (Collector): The main current flows through this terminal, which is typically connected to the load.
3. E (Emitter): The current drains out through this terminal and it is commonly connected to the power supply or ground reference depending on the circuit configuration.
BD140 Features and Benefits
l Medium Power Capability: Handles a continuous collector current (IC) of up to 1.5A, making it ideal for driving medium loads like relays, motors, and high-power LEDs.
l High Voltage Rating: Features a collector-emitter voltage (VCEO) of 80V, providing excellent reliability and safety margin for power regulation and high-voltage driver circuits.
l Efficient Thermal Design: Housed in a TO-126 plastic package, which is compact yet easy to mount onto heat sinks for effective power dissipation of up to 12.5W.
l Complementary Pairing: Designed as the perfect PNP complement to the BD139 NPN transistor, allowing for the design of balanced push-pull audio power amplifiers.
l Wide Frequency Response: With a transition frequency of 190MHz, it ensures low signal distortion and high-fidelity performance across the entire audio spectrum.
l Low Saturation Voltage: Offers a low collector-emitter saturation voltage (typically -0.5V), reducing power loss and improving overall circuit efficiency during switching operations.
BD140 Applications
1. Audio Power Amplifier Circuit
One of the most common applications of the BD140 is serving as a driver-stage or output-stage transistor in audio power amplifiers. In practical circuits, the BD140 is often paired with NPN transistors such as the BD139 to form a complementary push-pull output configuration, handling both the positive and negative half-cycles of audio signals.
2. Motor and Relay Drive Circuit
With a maximum collector current of approximately 1.5 A, the BD140 is suitable for driving low and medium-power loads. In embedded control systems, it acts as a current amplification and switching device, using a small base current to control a larger load current to realize functions such as motor start-stop and relay switching.
3. Voltage Regulation and Power Management System
The BD140 is also widely used in linear regulators, power regulation and voltage control circuits. In analog power supply designs, it can function as a series pass transistor. By adjusting base bias, it controls output voltage and current to achieve voltage stabilization.
4. Switching Control and Logic Drive Circuit
In digital and analog circuits, the BD140 is commonly used as an electronic switch for LED control, power switching, and buzzer driving. It supports logic-level control and is compatible with embedded systems such as MCUs and DSPs.
5. Teaching Experiments and Basic Electronic Design
Featuring a simple structure, low cost and versatile applicability, the BD140 is a widely used component in electronic teaching and experimental projects. It is adopted as a demonstration device in basic transistor experiments, motor control tests, and analog amplification experiments.
BD140 Equivalents
Common equivalents of BD140 include TIP42C, 2N2907, BC327, BC557, SS8550, and S8550. These devices are all PNP transistors and can, under certain conditions, be used as functional substitutes for BD140 in medium- and small-power switching, current amplification, and audio driving applications.
Sound-Controlled DC Motor Circuit with CA3140 and BD140
This circuit diagram illustrates a classic sound-controlled DC motor driver using the CA3140 operational amplifier as a voltage comparator. The front-end stage uses an electret microphone (MIC) to capture sound vibrations and convert them into weak electrical signals. This signal is fed into the inverting input of the CA3140, while the non-inverting input is connected to a voltage divider formed by a 10K potentiometer.
By adjusting the potentiometer, a trigger threshold (sensitivity level) can be set. When the voltage generated by the sound signal exceeds this preset value, the output of the op-amp (Pin 6) switches state, triggering the subsequent driver stage.
The output stage adopts a multi-level current amplification structure to drive a DC motor with higher power requirements. Since the CA3140 has limited output driving capability, 2N3906 and BD140 transistors are introduced in the circuit.
When the CA3140 produces a valid output signal, it first switches the 2N3906 transistor, which then drives the high-power BD140 PNP transistor into conduction, allowing current to flow through the DC motor. This design effectively replaces a physical switch with a sound-based control signal.
BD139 vs BD140
The BD139 and BD140 are among the most famous "complementary pairs" in the world of electronics. They are identical in most specifications but differ in their polarity: one is NPN and the other is PNP.
Feature | BD139 | BD140 |
Transistor Type | NPN | PNP |
Package | TO-126 | TO-126 |
Polarity | Positive type | Negative type |
Continuous Collector Current (IC) | 1.5 A | 1.5 A |
Collector-Emitter Voltage (VCEO) | 80V | 80V |
Collector Power Dissipation (PC) | 12.5W | 12.5W |
Transition Frequency (fT) | 190 MHz | 190 MHz |
Complementary pair | Pairs with BD140 | Pairs with BD139 |
Typical use | High side switching | Low side switching |
BD140 Package Outline
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