Switching regulator control circuit

Abstract

In the related art, there is a problem that the condition of a load is monitored in an indirect manner so that an efficiency enhancing effect is not obtained. A switching regulator control circuit includes an oscillator for generating a carrier signal and a transistor drive circuit for driving a switching transistor and a synchronous rectification transistor based on a PWM signal generated based on the carrier signal. The oscillator switches the frequency of the carrier signal based on the direction of a source-drain voltage of the synchronous rectification transistor.

What is claimed is: 
     
         1 . A switching regulator control circuit comprising:
 an oscillator for generating a carrier signal;   a first PWM (Pulse Width Modulation) comparator for generating a first PWM signal based on the carrier signal;   a first transistor drive circuit including a first input configured to receive the first PWM signal, the first transistor drive circuit being configured to drive a first switching transistor; and   a second transistor drive circuit including a second input configured to receive the first PWM signal, the second transistor drive circuit being configured to drive a first synchronous rectification transistor,   wherein the second transistor drive circuit includes a first output terminal and a second output terminal, outputs a control signal for driving the first synchronous rectification transistor to the first synchronous rectification transistor from the first output terminal, and outputs a frequency selection signal based on a direction of a source-drain voltage of the first synchronous rectification transistor from the second output terminal, and   wherein the oscillator receives the frequency selection signal outputted from the second output terminal of the second transistor driver circuit, and switches a frequency of the carrier signal based on the frequency selection signal outputted from the second output terminal of the second transistor drive circuit.   
     
     
         2 . The switching regulator control circuit according to  claim 1 ,
 wherein when the direction of the source-drain voltage of the first synchronous rectification transistor becomes a direction in which a reverse current flows through the first synchronous rectification transistor in a duration when the first switching transistor is off and the first synchronous rectification transistor is on, the oscillator switches the frequency of the carrier signal from a high frequency to a low frequency, and   wherein when the direction of the source-drain voltage of the first synchronous rectification transistor has never become the direction in which the reverse current flows through the first synchronous rectification transistor in the duration when the first switching transistor is off and the first synchronous rectification transistor is on, the oscillator switches the frequency of the carrier signal from the low frequency to the high frequency.   
     
     
         3 . The switching regulator control circuit according to  claim 1 , wherein when the direction of the source-drain voltage of the first synchronous rectification transistor becomes a direction in which a reverse current flows through the first synchronous rectification transistor in a duration when the first switching transistor is off and the first synchronous rectification transistor is on, the second transistor drive circuit turns off the first synchronous rectification transistor. 
     
     
         4 . The switching regulator control circuit according to  claim 1 , further comprising:
 a second PWM comparator for generating a second PWM signal based on the carrier signal;   a third transistor drive circuit including a third input configured to receive the second PWM signal, the third transistor drive circuit being configured to drive a second switching transistor; and   a fourth transistor drive circuit including a fourth input configured to receive the second PWM signal, the fourth transistor drive circuit being configured to drive a second synchronous rectification transistor.   
     
     
         5 . The switching regulator control circuit according to  claim 2 ,
 wherein a source of the first switching transistor is coupled to a power supply potential,   wherein a drain of the first switching transistor is coupled to a drain of the first synchronous rectification transistor and one terminal of an inductor,   wherein a source of the first synchronous rectification transistor is coupled to a ground potential,   wherein the other terminal of the inductor is coupled to a load and coupled through a smoothing capacitor to the ground potential, and   wherein when the direction of the source-drain voltage of the first synchronous rectification transistor becomes the direction in which the reverse current flows through the first synchronous rectification transistor, a potential at the drain of the first synchronous rectification transistor becomes higher than a potential at the source.   
     
     
         6 . A switching regulator control method comprising:
 generating, by a PWM (Pulse Width Modulation) comparator, a first PWM signal based on a carrier signal;   receiving, by a transistor drive circuit including a first input terminal, a second input terminal, a first output terminal and a second output terminal, the first PWM signal at the first input terminal of the transistor driver circuit and driving, by the transistor drive circuit, a first switching transistor based on the first PWM signal;   receiving, by the transistor drive circuit, the first PWM signal at the second input terminal of the transistor drive circuit;   outputting, by the transistor drive circuit, to a first synchronous rectification transistor, a control signal for driving the first synchronous rectification transistor based on the first PWM signal at the first output terminal of the transistor drive circuit;   outputting, by the transistor drive circuit, a frequency selection signal based on a direction of a source-drain voltage of the first synchronous rectification transistor at the second output terminal of the transistor drive circuit; and   receiving, by an oscillator, the frequency selection signal outputted at the second output terminal of the transistor drive circuit, and switching, by the oscillator, a frequency of the carrier signal based on the frequency selection signal outputted at the second output terminal of the transistor drive circuit.   
     
     
         7 . The switching regulator control method according to  claim 6 , wherein switching the frequency of the carrier signal comprises:
 switching the frequency of the carrier signal from a high frequency to a low frequency when the direction of the source-drain voltage of the first synchronous rectification transistor becomes a direction in which a reverse current flows through the first synchronous rectification transistor in a duration when the first switching transistor is off and the first synchronous rectification transistor is on; and   switching the frequency of the carrier signal from the low frequency to the high frequency when the direction of the source-drain voltage of the first synchronous rectification transistor has never become the direction in which the reverse current flows through the first synchronous rectification transistor in the duration when the first switching transistor is off and the first synchronous rectification transistor is on.   
     
     
         8 . The switching regulator control method according to  claim 6 , further comprising:
 turning off the first synchronous rectification transistor when the direction of the source-drain voltage of the first synchronous rectification transistor becomes a direction in which a reverse current flows through the first synchronous rectification transistor in a duration when the first switching transistor is off and the first synchronous rectification transistor is on.   
     
     
         9 . The switching regulator control method according to  claim 8 , further comprising:
 generating a second PWM signal based on the carrier signal; and   driving a second switching transistor and a second synchronous rectification transistor based on the second PWM signal.   
     
     
         10 . A switching regulator control method comprising:
 generating, by a PWM (Pulse Width Modulation) comparator, a first PWM signal based on a carrier signal;   receiving, by a transistor drive circuit, the first PWM signal at a first input of the transistor driver circuit and driving, by the transistor drive circuit, a first switching transistor based on the first PWM signal;   receiving, by the transistor drive circuit, the first PWM signal at a second input of the transistor drive circuit, and driving, by the transistor drive circuit, a first synchronous rectification transistor based on the first PWM signal;   outputting, by the transistor drive circuit, a frequency selection signal based on a direction of a source-drain voltage of the first synchronous rectification transistor; and   switching, by an oscillator, a frequency of the carrier signal based on the frequency selection signal outputted from the transistor drive circuit,   wherein the switching the frequency of the carrier signal comprises:   switching the frequency of the carrier signal from a high frequency to a low frequency when the direction of the source-drain voltage of the first synchronous rectification transistor becomes a direction in which a reverse current flows through the first synchronous rectification transistor in a duration when the first switching transistor is off and the first synchronous rectification transistor is on; and   switching the frequency of the carrier signal from the low frequency to the high frequency when the direction of the source-drain voltage of the first synchronous rectification transistor has never become the direction in which the reverse current flows through the first synchronous rectification transistor in the duration when the first switching transistor is off and the first synchronous rectification transistor is on,   wherein the switching regulator control method further comprises:   generating a second PWM signal based on the carrier signal; and   driving a second switching transistor and a second synchronous rectification transistor based on the second PWM signal,   wherein the switching the frequency of the carrier signal comprises:   changing a first frequency selection signal from a first level to a second level when the direction of the source-drain voltage of the first synchronous rectification transistor becomes a direction in which a reverse current flows through the first synchronous rectification transistor in a duration when the first switching transistor is off and the first synchronous rectification transistor is on;   changing the first frequency selection signal from the second level to the first level when the direction of the source-drain voltage of the first synchronous rectification transistor has never become the direction in which the reverse current flows through the first synchronous rectification transistor in the duration when the first switching transistor is off and the first synchronous rectification transistor is on;   changing a second frequency selection signal from a third level to a fourth level when the direction of the source-drain voltage of the second synchronous rectification transistor becomes a direction in which a reverse current flows through the second synchronous rectification transistor in a duration when the second switching transistor is off and the second synchronous rectification transistor is on; and   changing the second frequency selection signal from the fourth level to the third level when the direction of the source-drain voltage of the second synchronous rectification transistor has never become the direction in which the reverse current flows through the second synchronous rectification transistor in the duration when the second switching transistor is off and the second synchronous rectification transistor is on,   wherein when the first frequency selection signal is at the second level and the second frequency selection signal is at the fourth level, the frequency of the carrier signal is a low frequency, and   wherein except when the first frequency selection signal is at the second level and the second frequency selection signal is at the fourth level, the frequency of the carrier signal is a high frequency.