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The BD140 is a PNP Epitaxial Planar Transistor that is mounted in the SOT-32 plastic package. They are designed for audio amplifiers and drivers utilizing complementary or quasi-complementary circuits. The NPN complement is BD139 and this transistor comes with a VCE of -80V and a continuous collector current of -1.5A. It can be used as a small signal switching transistor. Moreover, it has a low base voltage of -5V.
The BD140 transistor is a very versatile transistor that can be used in many different applications. This is a PNP transistor hence its collector and emitter will be left open when a positive voltage is applied to the base of the transistor, and it will close when no voltage is present on the base.
The Beta value of this transistor can be anywhere between 40 to 160, this parameter determines the amplification factor of the device, the max rated current for this transistor is 1.5A. So we can connect a load up to 1.5A but we do need to consider the power rating and the temperature. This transistor has a maxim base-emitter voltage of 5V that means it can be suitably used for logic level application in embedded system.
When this transistor is in a biased condition, it can allow a maximum of 1.5A through its emitter-collector junction, this state of the device is called the saturation state, flowing more current than 1.5A can damage the device. When the base current is removed the transistor becomes fully off, this stage is called the Cut-off Region so no current flows through the device. The BD140 was originally manufactured by Phillips rated at 160MHz for specific audio applications, later they were cloned by other manufacturers like Samsung, ST, ON Semi, etc.
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