  We present the physical model for the entropy source of a quantum random
number generator chip based on the quantum fluctuations of the photon number
emitted by light-emitting diodes. This model, combined with a characterization
of the chip, estimates a quantum min-entropy of over 0.98 per bit without
post-processing. Finally, we show with our model that the performances in terms
of security are robust against fluctuations over time.
