Switching power supply device and a semiconductor integrated circuit

Abstract

A capacitor is disposed between the output side and the ground potential of an inductor which creates an output voltage. A first switch element supplies a current from an input voltage to an input side of the inductor, and a second switch element which is turned on when the first switch element is off sets the input side of the inductor to a prescribed potential. A control circuit detects the arrival of the voltage on the input side of the inductor at a high voltage corresponding to the input voltage when the load circuit is in a light load state and the second switch element is off, and turns on the first switch element. It invalidates the detection output of the voltage detecting circuit when the load circuit is in a heavy load state and, after the second switch element is turned off, turns on the first switch element.

1 . A switching power supply device, comprising:
 an inductor,   a capacitor coupled between an output side of said inductor and a ground potential,   a first switch element for supplying a current from an input voltage to an input side of said inductor,   a second switch element which comes on when said first switch element is off to set the input side of said inductor to a predetermined potential, and   a control circuit which generates a first control signal to be supplied to said first switch element and a second control signal to be supplied to said second switch element so as to set the output voltage obtained from the output side of said inductor to a desired voltage,   wherein said control circuit:   includes a voltage detecting circuit which generates a detection signal by which a reach of the voltage on said input side of said inductor to a first voltage is detected,   controls said first switching element to turn on with the detection signal of said voltage detecting circuit when a load circuit supplied with said output voltage is in a first load state after said second switch element is turned off, and   controls said first switching element to turn on without the detection signal of said voltage detecting circuit when said load circuit is in a second load state after said second switch element is turned off.   
     
     
         2 . The switching power supply device according to  claim 1 , wherein said control circuit comprises a permissible time setting circuit and, in case the detection signal of said voltage detecting circuit is not generated within a set period of said permissible time setting circuit, controls to turn on said first switch element. 
     
     
         3 . The switching power supply device according to  claim 2 , wherein the first load state of said load circuit corresponds to a state when an operating mode of said load circuit is a standby or sleep mode. 
     
     
         4 . The switching power supply device according to  claim 3 ,
 wherein said control circuit comprises a voltage dividing circuit for generating a divided voltage as said first voltage, and   wherein said voltage detecting circuit performs said detecting operation with said divided voltage as a reference voltage.   
     
     
         5 . The switching power supply device according to  claim 4 ,
 wherein said first switch element and said second switch element are N-channel MOSFETs, and wherein the switching power supply device further comprises:   a booster circuit including a boot strap capacitance having one end which is connected to the source of the N-channel MOSFET constituting said first switch element, and   a level shift circuit for generating a drive signal using a boosted voltage generated by said booster circuit, and the drive signal is coupled to a gate of the N-channel MOSFET constituting said first switch element.   
     
     
         6 . The switching power supply device according to  claim 5 ,
 wherein the control circuit including said voltage detecting circuit and voltage dividing circuit is formed on a single semiconductor integrated circuit, and   wherein said first and second switch elements, inductor, capacitor and boot strap capacitance constituting the booster circuit are composed of externally attached components.   
     
     
         7 . The switching power supply device according to  claim 6 , further comprising a PWM signal generating circuit for generating a PWM signal which causes said output voltage correspond to a predetermined reference voltage,
 wherein said PWM signal is inputted to said control circuit to set an on-period of said first switch element.   
     
     
         8 . A switching power supply device comprising:
 an inductor,   a capacitor coupled between an output side of said inductor and a ground potential,   a first switch element for supplying a current from an input voltage to an input side of said inductor,   a second switch element which comes on when said first switch element is off to set the input side of said inductor to a predetermined potential, and   a control circuit which controls said first and second switch elements so as to set an output voltage obtained from the output side of said inductor to a predetermined voltage,   said switching power supply comprising:   a first state having a period in which a current flows from a load circuit to which said output voltage is supplied to a second switch element in at least one PWM cycle,   a second state in which a current continuously flows from said switching power supply device to said load circuit,   wherein said control circuit:   includes a voltage detecting circuit which generates a detection signal by which a reach of the voltage on said input side of said inductor to a first voltage is detected,   controls to turn on said first switch element in said first state with the detection signal of said voltage detecting circuit when said second switch element is turned off,   controls turn on said first switch element in said second state after said second switch element is turned off.   
     
     
         9 . The switching power supply device according to  claim 8 , wherein said control circuit comprises a permissible time setting circuit for use in said first state and generates a second control signal which, in case the detection signal of said voltage detecting circuit is not generated within a set period of said permissible time setting circuit, turns on said first switch element after the set period. 
     
     
         10 . The switching power supply device according to  claim 9 , wherein the first state corresponds to a state when an operating mode of said load circuit is a standby or sleep mode. 
     
     
         11 . The switching power supply device according to  claim 10 ,
 wherein said control circuit comprises a voltage dividing circuit for generating a divided voltage as said first voltage which is lower than said input voltage, and   wherein said voltage detecting circuit performs said detecting operation with said first voltage as a reference voltage.   
     
     
         12 . The switching power supply device according to  claim 11 ,
 wherein said first switch element and second switch element are N-channel MOSFETs, the switching power supply device further comprises:   a booster circuit including a boot strap capacitance of which one end is connected to the source of the N-channel MOSFET constituting said first switch element, and   a level shift circuit for generating a drive signal using a boosted voltage generated by said booster circuit, the drive signal being coupled to a gate of the N-channel MOSFET constituting said first switch element.   
     
     
         13 . A semiconductor integrated circuit comprising:
 a first switch element which supplies a current from an input voltage to a external load circuit via an external inductor,   a second switch element which comes on when said first switch element is off and supplies a current to said load circuit via said inductor, and   a control circuit which generates a control signal to be supplied to said first and second switch elements so as to set the voltage obtained to be supplied to said load circuit to a desired level,   wherein said control circuit:   includes a voltage detecting circuit which generates a detection signal by which the reach of the voltage on the input side of an inductor at a first voltage is detected,   validates the operation of said voltage detecting circuit when said load circuit is in a first state, and generates the control signal which turns on the first switch element using the detection signal of said voltage detecting circuit, and   invalidates the detection signal of said voltage detecting circuit when said load circuit is in a second state and, turns on said first switch element.   
     
     
         14 . The semiconductor integrated circuit according to  claim 13 , wherein the first load state of said load circuit corresponds to a state when an operating mode of said load circuit is a standby or sleep mode. 
     
     
         15 . The semiconductor integrated circuit according to  claim 13 ,
 wherein said control circuit comprises a voltage dividing circuit for generating a divided voltage lower than said input voltage, and   wherein said voltage detecting circuit generates the detection signal with said divided voltage as a reference voltage.   
     
     
         16 . The semiconductor integrated circuit according to  claim 13 ,
 wherein said first switch element and second switch element are N-channel MOSFETS, the switching power supply device further comprises:   a booster circuit generates a boosted voltage with a external boot strap capacitance of which one end is connected to the source of the N-channel MOSFET constituting said first switch element, and   a level shift circuit for generating a drive signal using the boosted voltage generated by said booster circuit, the level shift circuit being coupled to a gate of the N-channel MOSFET constituting said first switch element.   
     
     
         17 . The semiconductor integrated circuit according to  claim 13 ,
 wherein said first switch element is formed over a first semiconductor substrate,   wherein said second switch element is formed over a second semiconductor substrate,   wherein said control circuit is formed over a third semiconductor substrate, and   wherein said first, second and third semiconductor substrates are molded in a single package.