Electrical – How to connect a CD40109BE Voltage Level Shifter

Check out Sparkfun's Logic Level converter. It includes a schematic, you should be able to do almost exactly the same thing by hand, but you'll probably need to use different resistor values to get the correct voltages. It includes two circuits, one for connecting a low voltage transmitter to a high voltage receiver, and one for connecting a high voltage transmitter to a low voltage receiver. It sounds like the former is what you're asking for.

The single-BJT level shifter in the question would work: If the input impedance of the device on the 5 Volt side is significantly higher than the 6.8 k shown in the question, the expected ~0.3 to ~5 Volt signal would be received (taking a 2n2222 as an example).

However, for lower impedance inputs, the input would act as a voltage divider with the 6.8 k resistor, attenuating the high part of the signal significantly.

For instance, if the input impedance of the load on the 5 Volt side were, say, 100 k, the signal would top out at around 4.6-4.7 Volts. Still not too bad.

Any lower, and the level becomes problematic. This is when one needs an alternative, such as a two-transistor set-up mentioned in the question, to drive the output rail harder.