Patent ID: 7301347

Claim:
A current sensing circuit for sensing the current through a main switch, said circuit comprising: a mirror switch, said mirror switch being substantially similar to said main switch but of different dimensions, a difference amplifier having a first leg and a second leg connected respectively to the output electrodes of said main switch and said mirror switch, said difference amplifier ensuring that the voltage across said first leg and across said second leg are substantially equal and thereby to derive from said mirror switch a sensing current substantially equal to a current flowing in said main switch divided by a sensing ratio, a current source for producing a quiescent current in said difference amplifier, and a compensatory device for compensating for said quiescent current by causing a voltage drop in said first leg between said output electrode of said main switch and said difference amplifier, such that said current sensing circuit senses currents in the main switch which are smaller than the quiescent current multiplied by the sensing ratio.