Current sensing circuit for power supply with series control transistor

In a voltage converter responsive to an input voltage at first and second input terminals for producing an output voltage at first and second output terminals across which a load impedance is to be connected and including switching transistor means having one and other sides of a primary conduction path therethrough with the one side thereof electrically connected to the first input terminal, and first means electrically connecting the other side of the transistor means to the second input and second output terminals which are common, the first means being responsive to the primary conduction current for producing the output voltage and a load current on an output line thereof that is electrically connected to the first output terminal, apparatus for producing an indication of load current outputted from the first output terminal comprising:

• passive resistive bridge circuit means having a first pair of nodes electrically connected between the first input and first output terminals, said resistive bridge circuit means comprising:
• a first current sensing resistor in series in one of the arms of said bridge circuit means that is adjacent the first output terminal, said first resistor being a load current sensing resistor in series in the electrical connection of the output line of the first means to the first output terminal, said first resistor passing the load current therethrough and to the first output terminal;
• first resistive voltage divider means having one end electrically connected to the first output terminal and one side of said first resistor, having an other end, and having a first tap point;
• second resistive voltage divider means having one end electrically connected to the other side of said first resistor that is electrically connected to the output line of the first means, having an other end, and having a second tap point;
• a second current sensing resistor in series in the electrical connection of the first input terminal to the one side of the transistor means for sensing input current to the latter, said second resistor having one side electrically connected to the first input terminal and the other end of said first voltage divider means and having its other side electrically connected to the one side of the transistor means and the other end of said second voltage divider means, and
• second means responsive to a difference voltage developed between the tap points of said voltage divider means that is an indication of the sum of the input and load currents passed by the voltage converter for selectively controlling conduction of the transistor means;
• the resistance in at least one arm of said bridge circuit means being variable for adjusting the difference voltage between said first and second tap points to be a prescribed value for a prescribed load current in said first resistor.

In a voltage converter responsive to an input voltage at first and second input terminals for producing an output voltage at first and second output terminals across which a load impedance is to be connected and including switching transistor means having one and other sides of a primary conduction path therethrough with the one side thereof electrically connected to the first input terminal, and first means electrically connecting the other side of the transistor means to the second input and second output terminals which are common, the first means being responsive to the primary conduction current for producing the output voltage and a load current on an output line thereof that is electrically connected to the first output terminal, apparatus for producing an indication of load current outputted from the first output terminal comprising:

• passive resistive bridge circuit means having a first pair of nodes electrically connected between the first input and first output terminals, said resistive bridge circuit means comprising:
• a first current sensing resistor in series in one of the arms of said bridge circuit means that is adjacent the first output terminal, said first resistor being a load current sensing resistor in series in the electrical connection of the output line of the first means to the first output terminal, said first resistor passing the load current therethrough and to the first output terminal;
• first resistive voltage divider means having one end electrically connected to the first output terminal and one side of said first resistor, having an other end, and having a first tap point;
• second resistive voltage divider means having one end electrically connected to the other side of said first resistor that is electrically connected to the output line of the first means, having an other end, and having a second tap point;
• a second current sensing resistor in series in the electrical connection of the first input terminal to the one side of the transistor means for sensing input current to the latter, said second resistor having one side electrically connected to the first input terminal and the other end of said second voltage divider means and having its other side electrically connected to the one side of the transistor means and the other end of said first voltage divider means, and
• second means responsive to a difference voltage developed between the tap points of said voltage divider means that is an indication of the difference of the input and load currents passed by the voltage converter for selectively controlling conduction of the transistor means;
• the resistance in at least one arm of said bridge circuit means being variable for adjusting the difference voltage between said first and second tap points to be a prescribed value for a prescribed load current in said first resistor.