Patent ID: 7525821

Claim:
A switched mode power supply comprising: input terminals for receiving electric power and output terminals for delivering an output power having an output voltage and an output current; wherein the input terminals are separated from the output terminals by an insulation barrier adapted to electrically insulate the input terminals from the output terminals so that the input terminals are provided on a primary side of the insulation barrier and the output terminals are provided on a secondary side of the insulation barrier; the insulation barrier being provided by a transformer having a primary winding and a secondary winding; the switched mode power supply further comprising: a converter stage coupled between the input terminals and the output terminals, the converter stage having at least one controllable first switching element for generating a converter stage duty cycle so as to cause the converter stage to generate the output signal, the at least one first switching element being located on the primary side of tile insulation barrier; and a programmable digital circuit for controlling the at least one first switching element; wherein: the programmable digital circuit has a memory and means for receiving a signal representing the input current of the converter stage; the switched mode power supply being characterized in that the programmable digital circuit is located on the primary side of the insulation barrier; the programmable digital circuit is adapted to derive the output current from the signal representing the input current of the converter stage by means of executable commands stored in the memory; and the programmable digital circuit is further adapted to use the derived value of the output current in the control of the first switching element; wherein the executable commands are operable to generate the derived value of the output current as a value corresponding to the numerical value of: I out est = ( I int - I int off ) ⁢ N p DN s ⁢ E when the value representing the duty cycle is higher than a first threshold value; wherein: I int is the input current of the converter stage, I int off is an offset current; D is the value representing the duty cycle; N p is the number of turns of the primary winding; N s is the number of turns of the secondary winding; and E is a value representing the efficiency of the switched mode power supply.