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Can a PNP be used to drive a led?
By the way, both a PNP and NPN can be used to drive a LED from the high side, but again, none of that matters with the LED hooked up backwards. You now say the cathode is tied to ground, which makes more sense if you want to light the LED normally.
Can a PNP transistor be used in a NPN circuit?
Generally, the PNP transistor can replace NPN transistors in most electronic circuits, the only difference is the polarities of the voltages, and the directions of the current flow.
What is the terminal resistance of a PNP transistor?
Terminal Resistance Values for PNP and NPN Transistors. Then we can define a PNP Transistor as being normally “OFF” but a small output current and negative voltage at its Base ( B ) relative to its Emitter ( E ) will turn it “ON” allowing a much large Emitter-Collector current to flow.
How are the diodes reversed in a PNP transistor?
Basically, in this type of transistor construction the two diodes are reversed with respect to the NPN type giving a P ositive- N egative- P ositive type of configuration, with the arrow which also defines the Emitter terminal this time pointing inwards in the transistor symbol.
Can a sensor have both PNP and NPN?
The sinking / sourcing logic is the same as for the Black wire. That is, if the sensor is PNP for the Black wire, it is also PNP for the White wire. I have never seen a sensor with mixed PNP and NPN outputs, but perhaps some specialty types exist on the market. An NPN input is looking for the input to be connected to GND to respond.
Why does a NPN trigger a PNP signal?
Depending on the sensor’s internal wiring, there might be some current flow from the NPN input to the sensor, for example there may be reverse current that “leaks” through a protection diode or an LED in the sensor. This current flow might be high enough to falsely trigger the NPN input.
Do you need a NPN for a 3.3V signal?
For a 3.3V signal you don’t need this: a simple emitter-follower NPN circuit, in which the resistor + LED are the load, should do. 3.3V volts minus the 0.7 VBE is still a large enough voltage to drive the LED. The NPN’s collector supplies the current and that is that.