DC/DC converter, switching power supply device, and electronic apparatus

1. A DC/DC converter for a switching power supply device including a plurality of DC/DC converters which include a master DC/DC converter and a plurality of slave DC/DC converters and have output terminals connected in parallel to each other, comprising:

first and second terminals that are used to cascade the plurality of DC/DC converters in a line;

a control circuit that determines that a host DC/DC converter is the master DC/DC converter when a predetermined voltage is detected at the second terminal and determines that the host DC/DC converter is the slave DC/DC converter when the predetermined voltage is not detected, and

controls a current output from the second terminal based on whether the host DC/DC converter is the master DC/DC converter or the slave DC/DC converter.

wherein the first terminal of the slave DC/DC converter which is far from the master DC/DC converter is grounded,

(1) when the host DC/DC converter is determined to be the slave DC/DC converter, the control circuit detects a current value of a current which flows from the first terminal; and

adds a predetermined addition current value to the detected current value and outputs a current with the sum of the current values through the second terminal if the host DC/DC converter is operating, or outputs the current with the detected current value through the second terminal if the host DC/DC converter does not operate, and

(2) when the host DC/DC converter is determined to be the master DC/DC converter, the control circuit divides the detected current value by the addition current value, detects the number of converters which are operating based on the divided value, and transmits information indicating the detected number of operating converters to the slave DC/DC converter.

2. A DC/DC converter for a switching power supply device including a plurality of DC/DC converters which include a master DC/DC converter and a plurality of slave DC/DC converters and have output terminals connected in parallel to each other, comprising:

first and second terminals that are used to cascade the plurality of DC/DC converters in a line;

a control circuit that determines that a host DC/DC converter is the master DC/DC converter when a predetermined voltage is detected at the second terminal and determines that the host DC/DC converter is the slave DC/DC converter when the predetermined voltage is not detected, and

controls a current output from the second terminal based on whether the host DC/DC converter is the master DC/DC converter or the slave DC/DC converter,

wherein a predetermined initial current value is supplied to the first terminal of the slave DC/DC converter which is far from the master DC/DC,

(1) when the host DC/DC converter is determined to be the slave DC/DC converter, the control circuit detects a current value of a current which flows from the first terminal; and

subtracts the initial current value from the detected current value, adds a predetermined addition current value to the subtraction result, and outputs a current with the sum of the current values through the second terminal if the host DC/DC converter is operating, or outputs the current with the detected current value through the second terminal if the host DC/DC converter does not operate, and

(2) when the host DC/DC converter is determined to be the master DC/DC converter, the control circuit divides the detected current value by the addition current value, detects the number of converters which are operating based on the divided value, and transmits information indicating the detected number of operating converters to the slave DC/DC converter.

3. A DC/DC converter for a switching power supply device including a plurality of DC/DC converters which include a master DC/DC converter and a plurality of slave DC/DC converters and have output terminals connected in parallel to each other, comprising:

first and second terminals that are used to cascade the plurality of DC/DC converters in a line;

a control circuit that determines that a host DC/DC converter is the master DC/DC converter when a predetermined voltage is detected at the second terminal and determines that the host DC/DC converter is the slave DC/DC converter when the predetermined voltage is not detected, and

that controls a current output from the second terminal based on whether the host DC/DC converter is the master DC/DC converter or the slave DC/DC converter;

wherein the first terminal of the slave DC/DC converter which is far from the master DC/DC converter is grounded,

the DC/DC converters are configured so as to sequentially operate from the slave DC/DC converter which is far from the master DC/DC converter,

(1) when the host DC/DC converter is determined to be the slave DC/DC converter, the control circuit detects a current value of a current which flows from the first terminal; and

adds a first predetermined addition current value to the detected current value and outputs a current with the sum of the current values through the second terminal if the host DC/DC converter does not operate, or adds a second predetermined addition current value greater than the first addition current value to the detected current value and outputs a current with the sum of the current values through the second terminal if the host DC/DC converter is operating, and

(2) when the host DC/DC converter is determined to be the master DC/DC converter, the control circuit detects the number of converters which are operating based on the detected current value and transmits information indicating the detected number of operating converters to the slave DC/DC converter;

the first and second current addition values of each of the DC/DC converters are set such that the first current addition value of the slave DC/DC converter in a predetermined stage is equal to the second current addition value of the slave DC/DC converter in the next stage, from the slave DC/DC converter which is far from the master DC/DC converter to the slave DC/DC converter which is near the master DC/DC converter; and a current which is detected from a terminal Isink of the master DC/DC converter is set so as to vary depending on the number of operating converters.

4. The DC/DC converter according to claim 1 ,

wherein the control circuit performs PWM modulation on a switching synchronizing clock on the basis of the information indicating the detected number of operating converters and transmits the switching synchronizing clock to the slave DC/DC converter.

5. A switching power supply device comprising:

a plurality of the DC/DC converters according to claim 1 that are connected in parallel to each other.

6. An electronic apparatus comprising:

the switching power supply device according to claim 5 .