What is 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.due to its high collector current and low cost it is an ideal transistor to be used in educational electronic projects and also in commercial electronics.

Gain Value of BD139 ranges from 40 to 160. (Gain Value of any transistor helps in determining its amplification capacity)

The maximum value of current, which can pass through collector pin, is 1.5A, so if you are working on this transistor then make sure that your load must be less than 1.5A. This is a good feature due to which you can drive many high current components such as high power LEDs, high current relays, motors etc.

In order to operate this transistor in forward biased state, we have to apply current at its base and this base current must be greater than 1/10th of its collector current. Moreover, make sure to apply 5V at its base-emitter pin.

Once it's operating in forward biased state, we can draw a maximum of 1.5A current between its collector & emitter. If maximum current i.e. 1.5A is flowing through a transistor then we can say it's in Saturation Region.

Normally, we can apply a maximum of 80V across collector & emitter. When we remove base current transistor becomes fully off, this situation is called the cut-off region.

One best point about it is that it comes in a plastic package, which is that most medium power transistor available only in the metal package. This reduces its cost and since this package is not conductive it will not be affected by other circuits. Due to this feature, it is mostly used in amplifier applications.

So if you are searching for medium power NPN transistor in a plastic package than this will be the best choice for you.

BD139 was originally manufactured by Phillips rated at 160 MHZ for specific audio applications, with a passage of time it was cloned by other manufacturers like Samsung, ST, etc. 

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STMicroelectronics BD139 technical specifications, attributes, parameters and parts with similar specifications to STMicroelectronics BD139.

● RF Amplifiers

● Switching circuits

● Amplification circuits

● Audio amplifiers

● Load driver circuits

● Switching Loads under 1.5A

● Battery Chargers

● Power Supplies

● Motor Driver

● Darlington Pair

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Download datasheets and manufacturer documentation for STMicroelectronics BD139.