High voltage to Logic level shifting

[Mahen K]

will this circuit work? All NPN transistor switching circuits I have seen switch higher voltages from lower voltages (at base). Here, I need to switch 3.3V with 12V. i.e When no voltage at base Vout should be high (3.3V) and when 12V at base Vout should be Low (0V).

Thanks
mahenk

 

[crutschow]

That circuit should work fine. Since the normal rule-of-thumb is to use a base current of at least 1/10 of the collector current to saturate the transistor, any base resistor (R75) of 330k or less will work.