  We present an improved background model for the Large Area X-ray Proportional
Counter (LAXPC) detectors on-board AstroSat. Because of the large collecting
area and high pressure, the LAXPC instrument has a large background count rate,
which varies during the orbit. Apart from the variation with latitude and
longitude during the orbit there is a prominent quasi-diurnal variation which
has not been modelled earlier. Using over 5 years of background observations,
we determined the period of the quasi-diurnal variation to be 84495 s and using
this period, it is possible to account for the variation and also identify time
intervals where the fit is not good. These lead to a significant improvement in
the background model. The quasi-diurnal variation can be ascribed to the
changes in charged particle flux in the near Earth orbit.
