Overload protection of switch mode converters

In a switch mode power converter circuit having an input stage, including a voltage source and a switching transistor, and an output stage having an inductor for providing an output current to a load, said inductor having a first terminal and a second terminal, said inductor having an internal resistance, said switch mode power convertor having an output current sensing circuit wherein said output current sensing circuit comprises:

• a filter circuit connected to said inductor for obtaining the DC voltage component of the voltage between said first terminal and said second terminal generated across the internal resistance of said inductor, said filter circuit having a resistance coupled to a capacitance, said resistance and said capacitance forming a common terminal, wherein said common terminal provides said DC voltage proportional, to said output current and internal temperature of said power convertor, and wherein other terminal of said resistance coupled to a capacitance is connected to said inductor to sense said voltage generated between said first terminal and said second terminal across the internal resistance;
• an error amplifier responsive to said DC voltage proportional to said output current, said error amplifier further responsive to a reference voltage, the output of said error amplifier providing an error signal for controlling the switching of said switching transistor.

A method for providing overload protection in a switch mode power convertor comprising the steps of:

• providing an input voltage source to an input stage of said switch mode power convertor;
• providing a switching circuit for coupling said input voltage source to an output stage;
• providing filtered output current to a load circuit by an inductor, said inductor having a first terminal and a second terminal, said inductor having an inherent resistance, said output current thereby providing a voltage between the first terminal of said inductor including a DC voltage component proportional to said inherent resistance and to said output current;
• providing a filter circuit having a pole and having a filter input and a filter output said filter input coupled to said inductor to sense said voltage between the first terminal and the second terminal, said filter circuit generating said DC voltage component at said filter output, said DC voltage component thereby proportional to internal temperature of said power convertor;
• providing an error signal proportional to the difference between said DC voltage component and a reference voltage, said error signal modulating the frequency of operation of said switching circuit.

A method for providing output current sensing in a switch mode power converter circuit having an input stage, including a voltage source and a switching transistor, and an output stage having an inductor for providing an output current to a load, said inductor having a first terminal and a second terminal, said inductor having an inherent resistance, said output current thereby providing a voltage between the first terminal and the second terminal of said inductor including a DC voltage component proportional to said inherent resistance and to said output current, said method comprising the steps of:

• providing a filter circuit connected to said inductor for obtaining said DC voltage component of the voltage generated between the first terminal and the second terminal across the inherent resistance of said inductor, said filter circuit having a resistance coupled to a capacitance, said resistance and said capacitance forming a common terminal, wherein said common terminal exhibits said DC voltage component, said DC voltage component thereby proportional to internal temperature of said power converter, and wherein other terminal of said resistance coupled to a capacitance is connected to said inductor to sense said voltage generated between said first terminal and said second terminal across the internal resistance;
• adjusting said DC voltage component proportional to said output current, according to a reference voltage by controlling the switching of said switching transistor.