Level shifter circuit with 50 V output
There is a simple circuit design technique that you can use for a 5V to high voltage level shifter that eliminates a need to provide a separate drive to the upper transistor in the driver. This also uses NPN transistors for both the upper and lower level driver. This works as long as you are OK with the output not pulling fully to GND. 



The way this works is that when the lower NPN turns on current from the load passes through the diode. This puts a forward bias on the diode which in turn reverse biases the BE junction of the upper transistor thus snapping it off whenever there is either load current or residual through current in the upper transistor.