![]() ![]() ![]() 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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