Power supply unit and portable apparatus using the same

A power supply unit, comprising:

• a series regulator that is enabled by a first enable signal to convert an input voltage into a predetermined output voltage in a continuously controlled manner and outputting said output voltage from the output end thereof;
• a switching DC-DC converter that is enabled by a second enable signal to convert said input voltage into a predetermined output voltage through switching of said input voltage, said DC-DC converter connected at the output end thereof in parallel with the output end of said series regulator;
• and
• a switching circuit for selectively switching said first and second enable signals based on a mode instruction signal and for outputting the selected enable signal such that, when switching said first enable signal to said second enable signal, said first and second enable signals overlap each other for a first predetermined period of time, and when switching said second enable signal to a first enable signal, overlap each other for a second predetermined period, wherein
• said switching DC-DC converter includes an error amplification circuit for controlling said output voltage in accordance with the difference between a reference voltage and a voltage representing said output voltage, said error amplification circuit having an AC and a DC feedback circuits that are switchable from said AC feedback circuit to said DC feedback circuit during said overlapping period.

A power supply unit, comprising:

• a series regulator that is enabled by a first enable signal to convert an input voltage into a predetermined output voltage in a continuously controlled manner and outputting said output voltage from the output end thereof;
• a switching DC-DC converter that is enabled by a second enable signal to convert said input voltage into a predetermined output voltage through switching of said input voltage, said DC-DC converter connected at the output end thereof in parallel with the output end of said series regulator;
• and
• a switching circuit for selectively switching said first and second enable signals based on a mode instruction signal and for outputting the selected enable signal such that, when switching said first enable signal to said second enable signal, said first and second enable signals overlap each other for a first predetermined period of time, and when switching said second enable signal to a first enable signal, overlap each other for a second predetermined period, wherein
• said first enable signal is formed by a first logic circuit that receives said mode instruction signal and a first counter output issued from a first counter counting clock pulses of a clock supplied from said switching DC-DC converter;
• and
• said second enable signal is formed by a second logic circuit that receives said mode instruction signal and a second counter output issued from a second counter counting clock pulses of said clock.

A power supply unit comprising:

• a series regulator that is enabled by a first enable signal to convert an input voltage into a predetermined output voltage in a continuously controlled manner and outputting said output voltage from the output end thereof;
• a switching DC-DC converter that is enabled by a second enable signal to convert said input voltage into a predetermined output voltage through switching of said input voltage, said DC-DC converter connected at the output end thereof in parallel with the output end of said series regulator;
• and
• a switching circuit for selectively switching said first and second enable signal based on a mode instruction signal, wherein
• said switching DC-DC converter includes:
• a first and a second switches connected between power sources, said first and second switches adapted to turn on alternately but turn off simultaneously for a dead time;
• a smoothing coil and a smoothing capacitor for smoothing the switching voltage appearing at the node of said first and second switches to generate said output voltage;
• and
• a pulse width control circuit for generating, and providing said first and second switches with, a switching control signal based on a PWM signal that is modulated so as to enable generation of said predetermined output voltage, and wherein
• said pulse width control circuit is adapted to shorten the width of said PWM signal based on said mode instruction signal to make longer said dead time by a third or a fourth predetermined period when switching DC-DC converter is enabled from its disabled state or disabled from its enabled state, wherein
• said first enable signal is formed by a first logic circuit that receives said mode instruction signal and a first counter output issued from a first counter counting clock pulses of a clock supplied from said switching DC-DC converter;
• and
• said second enable signal is formed by a second logic circuit that receives said mode instruction signal and a second counter output issued from a second counter counting clock pulses of said clock.

A power supply unit, comprising:

• a series regulator that is enabled by a first enable signal to convert an input voltage into a predetermined output voltage in a continuously controlled manner and outputting said output voltage from the output end thereof;
• a switching DC-DC converter that is enabled by a second enable signal to convert said input voltage into a predetermined output voltage through switching of said input voltage, said DC-DC converter connected at the output end thereof in parallel with the output end of said series regulator;
• and
• a switching circuit for selectively switching said first and second enable signals in response to a mode instruction signal;
• wherein
• said switching DC-DC converter includes:
• a first and a second switches connected between power sources, said first and second switches adapted to turn on alternately but turn off simultaneously for a dead time;
• a smoothing coil and a smoothing capacitor for smoothing the voltage appearing at the node of said first and second switches to generate said output voltage;
• and
• a pulse width control circuit for generating, and providing said first and second switches with, a switching control signal based on a PWM signal that is modulated so as to enable generation of said predetermined output voltage;
• and wherein
• said pulse width control circuit is adapted to shorten said dead time in multiple stages from a predetermined long time to a predetermined short time by regulating the width of said PWM signal when said switching DC-DC converter is enabled from its disabled state, and/or adapted to extend said dead time in multiple stages from a predetermined short time to a predetermined long time by regulating the width of said PWM signal when said switching DC-DC converter is disabled from its enabled state, wherein
• said first enable signal is formed by a first logic circuit that receives said mode instruction signal and a first counter output issued from a first counter counting clock pulses of a clock supplied from said switching DC-DC converter;
• and
• said second enable signal is formed by a second logic circuit that receives said mode instruction signal and a second counter output issued from a second counter counting clock pulses of said clock.