DC/DC converter and game machine using it

1. A DC/DC converter comprising:

an input line to which a DC input voltage is supplied;

a smoothing circuit that includes an output line and at least one output capacitor connected to the output line;

N switching circuits that each include a switching transistor and a synchronous rectifier transistor provided in series between the input line and a ground line, and each generate a switching voltage at a switching node that is a connecting node of the switching transistor and the synchronous rectifier transistor according to an input pulse signal, wherein N is an integer at least 2;

N inductors that are each provided for a respective one of the switching circuits and are each provided between the switching node of the switching circuit that corresponds and the output line;

a phase controller that dynamically switches the number K of drive phases according to a state of the DC/DC converter at the time, wherein K is an integer up to N;

a pulse modulator that generates the pulse signal having a duty ratio that is adjusted such that a feedback voltage depending on an output voltage of the output line corresponds with a predetermined reference voltage, and having a frequency that changes according to the number K of drive phases; and

a distributor that selects K switching circuits among the N switching circuits and distributes the pulse signal to each of the selected K switching circuits with a phase difference of 360/K degrees.

2. The DC/DC converter according to claim 1 , wherein if the smoothing circuit has a certain resonant frequency fr, for at least one number K 1 of drive phases, frequency f 1 of the pulse signal is so set as to be equal to fr/K 1 .

3. The DC/DC converter according to claim 2 , wherein if the smoothing circuit has the certain resonant frequency fr, for at least two numbers K 1 and K 2 of drive phases, frequencies fx 1 and fx 2 of the pulse signal are so set as to be equal to fr/K 1 and fr/K 2 , respectively.

4. The DC/DC converter according to claim 2 , wherein if the smoothing circuit has resonant frequencies fr 1 and fr 2 , for at least two numbers K 1 and K 2 of drive phases, frequencies fx 1 and fx 2 of the pulse signal are so set as to be equal to fr 1 /K 1 and fr 2 /K 2 , respectively.

5. The DC/DC converter according to claim 1 , wherein the frequency of the pulse signal is set based on a resonant frequency of impedance of the smoothing circuit for all of the numbers of drive phases.

6. The DC/DC converter according to claim 1 , wherein the state of the DC/DC converter is a load current.

7. The DC/DC converter according to claim 1 , wherein the phase controller selects the number of drive phases giving highest efficiency in the state of the DC/DC converter at the time.

8. A DC/DC converter comprising:

an input line to which a DC input voltage is supplied;

a smoothing circuit that includes an output line and at least one output capacitor connected to the output line;

N switching circuits that each include a switching transistor and a synchronous rectifier transistor provided in series between the input line and a ground line, and each generate a switching voltage at a switching node that is a connecting node of the switching transistor and the synchronous rectifier transistor according to an input pulse signal, wherein N is an integer at least 2;

N inductors that are each provided for a respective one of the switching circuits and are each provided between the switching node of the switching circuit that corresponds and the output line;

a pulse modulator that generates the pulse signal having a duty ratio that is adjusted such that a feedback voltage depending on an output voltage of the output line corresponds with a predetermined reference voltage;

a phase controller that decides the number K of drive phases; and

a distributor that selects K switching circuits among the N switching circuits and distributes the pulse signal to each of the selected K switching circuits with a phase difference of 360/K degrees,

wherein a frequency of the pulse signal for each of the numbers of drive phases is set such that a ripple of the output voltage becomes smaller compared with a case in which the frequency of the pulse signal is set constant irrespective of the number of drive phases.

9. The DC/DC converter according to claim 8 , wherein: the pulse modulator controls frequency of the pulse signal in such a manner that a product of the number K of drive phases and the frequency of the pulse signal becomes a predetermined value set according to a resonant frequency of the smoothing circuit.

10. A game machine comprising

a DC/DC converter including:

an input line to which a DC input voltage is supplied;

a smoothing circuit that includes an output line and at least one output capacitor connected to the output line;

N switching circuits that each include a switching transistor and a synchronous rectifier transistor provided in series between the input line and a ground line, and each generate a switching voltage at a switching node that is a connecting node of the switching transistor and the synchronous rectifier transistor according to an input pulse signal, wherein N is an integer at least 2;

N inductors that are each provided for a respective one of the switching circuits and are each provided between the switching node of the switching circuit that corresponds and the output line;

a phase controller that dynamically switches the number K of drive phases according to a state of the DC/DC converter at the time, wherein K is an integer up to N;

a pulse modulator that generates the pulse signal having a duty ratio that is adjusted such that a feedback voltage depending on an output voltage of the output line corresponds with a predetermined reference voltage and, having a frequency that changes according to the number K of drive phases; and

a distributor that selects K switching circuits among the N switching circuits and distributes the pulse signal to each of the selected K switching circuits with a phase difference of 360/K degrees.