Using this calculator https://learn.adafruit.com/diy-boost-calc/the-calculator I made a small 80Khz boost converter circuit to boost from 12v to 48v.

For Vin Min/Max = 12v and Vout Min/Max = 48v the duty is 75%
The switching divice is using

PULSE(0 5 0 15n 15n 9.375u 25u)

Whats causing it to stop at only 37v?

The diode stack makes the sim go much faster.

 

hi 48,
Please post your asc file so that I can run it.
E

 

hi p48,
The LTS asc extension file is often uploaded to this site.
Please retry.
example upload.
Eric

EDIT:
Downloaded from your link, it is only the boost.log file.?

 

hi,
Got it.
The switcher is running at 41kHz.
Is that Inductor value really 56.25 Henry.?
E

 

hi,
Have a look at this option, its not an ideal design, but it may give you a start.
Note the Inductor and Freq changes.

E

 

hi,
They are UF's.diodes
E

 

75= x / (1/80e3) ; x = 937.5u

You forgot the decimal point in front of the 75.
The sim runs ok with a single Schottky diode instead of the bunch of diodes.

 

hi,
Search the web for a uc3843 LTSpice model and configure a circuit simulation.

E

 

hi,
Check the switching times the current thru the switch and diode.
E