I’v replaced many transistors, but have never sized and source one for a project.
The project i am working on is to modify an inductive sensor connected to a PLC system i am working on. The problem is that the inductive oil sensor i have takes 15-30VDC and outputs 5VDC wich is not enough to drive my 24V PLC I/O card.
I was thinking about using a BJT transistor to relay the needed voltage to pull in this input, I’m just lost in picking out the right transistor to use other than that i will probably need an NPN since my base current will be (+).
The supplied Voltage to the base will be around 1 volt- cut out and 5 Volts cut-in. This will be used to switch 24V to my PLC card
Any help on a common trans to use, sizing of the transistors needed, and any insight on how to preform this math on my own would be greatly appreciated.
Howdy. So if I understand you correctly, you need:
An NPN transistor which, when it has 5V available at the base, turns on a 24V rail through its collector-emitter. You say “1 volt cut out” but it’s important that during “off” it has 0V and no current.
Do you have any size constraints? How much current, and therefore power in Watts, will be going through the transistor? That will determine package size and need of a heatsink.
Digikey has a list of all BJT transistors here:
https://www.digikey.com/product-search/ … =npn%20bjt
You can see the options available are package size, max power, max voltage, and so forth. By using ctrl and shift to select ranges of values in each category you can narrow it down and choose one.
The most important piece of info I need to help you though is current that you expect to have on the base, and through the collector-emitter.