Switching power supply unit

A switching power supply unit comprising:

• a first switch whose on-off state is controlled by an on-off control signal, which outputs a DC input voltage according to the on-off state;
• a coil having a first terminal to which the DC input voltage is applied, a second terminal from which a first output voltage is outputted, and an intermediate tap from which a second output voltage is outputted;
• a rectifier element, which is connected between said first terminal and a common potential point such that it has polarity to block said DC input voltage, for rectifying the DC input voltage;
• a smoothing circuit, which is connected to said second terminal, for smoothing said first output voltage to output a first DC output voltage obtained by decreasing said DC input voltage;
• a rectifying-smoothing circuit, which is connected to said intermediate tap, for rectifying and smoothing said second output voltage to output a second DC output voltage obtained by decreasing said DC input voltage;
• and
• control means for outputting said on-off control signal in order to control at least one of said first and second DC output voltages to be a constant voltage.

A switching power supply unit comprising:

• a first switch whose on-off state is controlled by an on-off control signal, which outputs a DC input voltage according to the on-off state;
• a coil having a first terminal to which the DC input voltage is applied, a second terminal from which a first output voltage is outputted, and an intermediate tap from which a second output voltage is outputted;
• a rectifier element, which is connected between said first terminal and a common potential point such that it has polarity to block said DC input voltage, for rectifying the DC input voltage;
• a smoothing circuit, which is connected to said second terminal, for smoothing said first output voltage to output a first DC output voltage obtained by decreasing said DC input voltage;
• a smoothing circuit, which is connected to said intermediate tap through a second switch that is tuned off or on substantially oppositely to the turning on or off of said first switch, for smoothing said second output voltage to output a second DC output voltage obtained by decreasing said DC input voltage;
• and
• control means for outputting said on-off control signal in order to control at least one of said first and second DC output voltages to be a constant voltage.

A switching power supply unit comprising:

• a first switch whose on-off state is controlled by an on-off control signal, which outputs a DC input voltage according to the on-off state;
• a coil having a first terminal to which the DC input voltage is applied, a second terminal from which a first output voltage is outputted, and an intermediate tap connected to a common potential point;
• a first rectifying-smoothing circuit, which is connected to said second terminal, for rectifying and smoothing said first output voltage to output a DC output voltage obtained by converting said DC input voltage;
• and
• control means for outputting said on-off control signal in order to control said DC output voltage to be a constant voltage.

A switching power supply unit comprising:

• a first switch whose on-off state is controlled by an on-off control signal, which outputs a DC input voltage according to the on-off state;
• a coil having a first terminal to which the DC input voltage is applied, a second terminal connected to a common potential point, and an intermediate tap from which a first output voltage is outputted;
• a first rectifying-smoothing circuit, which is connected to said intermediate tap, for rectifying and smoothing said first output voltage to output a first DC output voltage of polarity different from the polarity of said DC input voltage;
• a second rectifying-smoothing circuit, which is connected to said first terminal, for rectifying and smoothing said second output voltage to output a second DC output voltage of polarity different from the polarity of said DC input voltage;
• and
• control means for outputting said on-off control signal in order to control at least one of said first and second DC output voltages to be a constant voltage.

A switching power supply unit comprising:

• a first switch whose on-off state is controlled by an on-off control signal, which outputs a DC input voltage according to the on-off state;
• a coil having a first terminal to which the DC input voltage is applied, a second terminal from which a first output voltage is outputted, and an intermediate tap from which a second output voltage is outputted;
• a rectifier element, which is connected between said first terminal and a common potential point such that it has polarity to block said DC input voltage, for rectifying the DC input voltage;
• a smoothing circuit, which is connected to said intermediate tap, for smoothing said second output voltage to output a first DC output voltage obtained by decreasing said DC input voltage;
• a rectifying-smoothing circuit, which is connected to said second terminal, for rectifying and smoothing said first output voltage to output a second DC output voltage higher than said first DC output voltage outputted from said smoothing circuit;
• and
• control means for outputting said on-off control signal in order to control said first DC output voltage outputted from said smoothing circuit to be a constant voltage.