![]() ![]() Using the much less capable 2n3906 in such a task would cause it to pretty much turn into a blob of melted plastic and metal. Current limits: The TIP120 will tolerate 5 Amperes of continuous current, which means a load that passes an Ampere or two at most, such as the little fan shown in the Instructable, will not cause the TIP120 any stress. ![]() To do something similar with a PNP device, one would wire it up as a "high side switch" (inverted connection), and when the base is pulled low the device would conduct (inverted logic) ![]() When the base is pulled low, the TIP120 stops conducting, the motor or fan stops operating. PNP v/s NPN: The TIP120 NPN device is used here as a "low side switch", in other words, when the base of the device is pulled high, the path between collector and emitter acts as a switch that conducts, thus allowing current to flow from the positive supply, via the motor or fan, through the TIP120, into ground.Let us break this down into the key differences: That is not to say that the 2n3906 can never be used in applications somewhat similar to the one described in the Instructable: It will need a change in the schematic, and will also be limited to a far lower current than the TIP120 would be. The 2n3906 is a PNP transistor (not Darlington) rated for 200 mA continuous current, and with a DC gain of 100 to 300.įor ease of understanding: They are different in multiple ways, and are designed for entirely different purposes. The TIP120 is an NPN Darlington pair rated for 5 Amperes of continuous current, and with a DC current gain of 1000 minimum. ![]()
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