Electronic apparatus having DC voltage conversion function, and DC voltage converter

A voltage conversion circuit is provided for efficiently converting the voltage of a DC power source into a lower voltage in accordance with load currents of voltage converters. An electronic apparatus includes: a DC power source for supplying a first DC supply voltage; a first DC voltage converter for converting the first DC supply voltage into a second DC supply voltage which is lower than the first DC supply voltage; a second DC voltage converter for converting either the first DC supply voltage or the second DC supply voltage at an input voltage terminal thereof into a third DC supply voltage which is lower than the second DC supply voltage; a switch for selecting and supplying one of the first DC supply voltage of the DC power source and the second DC supply voltage of the first DC voltage converter to the input voltage terminal of the second DC voltage converter, in accordance with a control signal; a switching controller for providing the control signal to the switch; and a plurality of components, ones of the components receiving the second DC supply voltage, ones of the components receiving the third DC supply voltage.

FIELD OF THE INVENTION

The present invention generally relates to an electronic apparatus having a DC voltage converter function, and in particular to an electronic apparatus including a DC voltage converter circuit for converting a DC source voltage into a plurality of DC supply voltages.

BACKGROUND OF THE INVENTION

In mobile notebook personal computers (PCs), there are needs for an improvement in the power supply efficiency for longer battery run time, and for reduction in the component mounting areas to reduce the sizes of printed circuit boards for reduction in size, weight and thickness of the PCs. However, the employed ICs of the PC, such as a CPU, a set of chips and a graphic chip, tend to use lower operation voltages to reduce their electric power consumptions, and require their respective different supply voltages. Hence the number of desired different supply voltages in the PC tends to increase.

Matsumura discloses in Japanese Patent Application Publication No. JP H 11-41825-A published on Feb. 12, 1999 describes a power supply switching device for switching power supplies depending on the load power consumption. This power supply switching device includes a battery to be incorporated into a portable device, and at least one or more constant voltage means. The power supply switching device further includes DC voltage converting means for generating a DC voltage lower than the battery voltage, switching means for switching between the battery voltage and the DC voltage generated by the DC voltage converting means to thereby supply the electric power to an input of the constant voltage means, and control means for controlling the switching means so that the power source should be switched to the DC voltage generated by the DC voltage converting means in a main driving state in which the power consumption is large, while the power source should be switched to the battery voltage in a standby state in which the power consumption is small.

A DC voltage conversion circuit which includes a plurality of DC-DC converters, each having a switching element, a diode, a capacitor and an inductor, is well known. DC-DC converters are disclosed by Maxim Integrated Products, Inc. in a document entitled “DC-DC Converter Tutorial”, Oct. 19, 2000 on a Web page at http://pdfserv.maxim-ic.com/en/an/AN710.pdf, and by ON Semiconductor in a document entitled “Understanding the Output Current Capability of DC-DC Buck Converters”, April, 2003-Rev.0 on a Web page at http://www. onsemi.com/pub/Collateral/AND8117-D.PDF, which are incorporated herein by reference.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, an electronic apparatus includes: a DC power source for supplying a first DC supply voltage; a first DC voltage converter for converting the first DC supply voltage into a second DC supply voltage which is lower than the first DC supply voltage; a second DC voltage converter for converting either the first DC supply voltage or the second DC supply voltage at an input voltage terminal thereof into a third DC supply voltage which is lower than the second DC supply voltage; a switch for selecting and supplying one of the first DC supply voltage of the DC power source and the second DC supply voltage of the first DC voltage converter to the input voltage terminal of the second DC voltage converter, in accordance with a control signal; a switching controller for providing the control signal to the switch; and a plurality of components, ones of the components receiving the second DC supply voltage, ones of the components receiving the third DC supply voltage.

The invention also relates to a voltage converter for use in the electronic apparatus described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

When DC-DC converters (DDCs) in the number of supply voltages required in a PC are coupled in parallel to a DC source voltage, the total voltage conversion efficiency becomes low in general. In contrast, when DC-DC converters (DDCs) in the number of supply voltages required in a PC are coupled in series to a DC power supply voltage, the entire voltage conversion efficiency becomes high in general. In this case, however, the first stage DC-DC converter coupled in series for converting the DC source voltage requires a larger allowable current, so that the size of the first stage DC-DC converter increases. This is undesirable for reducing the size of a PC.

An object of the present invention is to provide a voltage conversion circuit for efficiently converting the voltage of a DC power source into a lower voltage in accordance with load currents of voltage converters.

Another object of the invention is to provide a voltage conversion circuit for efficiently converting a voltage of a DC power source into a lower voltage in accordance with actual or estimated load currents of voltage converters.

According to the invention, without an increase in the size of a voltage converter, a voltage conversion circuit is provided for efficiently converting the voltage of a DC power source into a lower voltage in accordance with the actual or estimated load currents of the voltage converters.

The invention will be described in connection with non-limiting embodiments with reference to the accompanying drawings. Throughout the drawings, similar symbols and numerals indicate similar items and functions.

FIGS. 1A and 1Bshow the arrangements of prior art DC voltage conversion circuits100and102, respectively, in each of which two DC-DC voltage converters (DDCs) employed in an electronic apparatus such as a notebook personal computer (PC) are coupled in fixed parallel connection or in fixed series connection. The prior art DC voltage conversion circuits100and102are provided with DC-DC voltage converters in the number of desired supply voltages. However, for simplicity of description, only two supply voltages of 3.3 V and 1.5 V are shown in these figures. InFIG. 1A, the DC-DC voltage converters2and3in parallel connection are coupled to a DC battery power source10of the electronic apparatus. In contrast, inFIG. 1B, the DC-DC voltage converters21and31in series connection are coupled to a DC battery power source10of the electronic apparatus. The voltage conversion efficiency of each of the DC-DC voltage converters2and21for converting the output voltage of the battery power source10ofFIGS. 1A and 1Bis denoted by Eddc2. Further, the voltage conversion efficiency of the DC-DC voltage converter3for converting the output voltage of the battery power source10ofFIG. 1Ais denoted by Eddc11, while the voltage conversion efficiency of the DC-DC voltage converter31for converting the output voltage of the DC-DC voltage converter21ofFIG. 1Bis denoted by Eddc12. Then, the voltage conversion efficiency of the DC voltage conversion circuit102is Eddc2×Eddc12for the load current through the terminal for the supply voltage of 1.5 V of the DC-DC voltage converter31ofFIG. 1B.

In the DC voltage conversion circuit100ofFIG. 1A, the voltage difference is large between the high DC voltage of the battery power source10and the nominal voltage (e.g., 1.5 V or 2.5 V) of IC chips or devices in the electronic apparatus, and hence a large power loss arises in the voltage conversion. The voltage of the battery power source10varies, for example, in a voltage range of 9 to 12 V. In the DC voltage conversion circuit102ofFIG. 1B, the DC-DC voltage converter21is required to admit an extra current flow therethrough corresponding to the load current of the DC-DC voltage converter31, and hence is required to have a large allowable current. Thus, the size of the DC-DC voltage converter21is increased.

FIG. 2shows the changes of the voltage conversion efficiencies as functions of the load currents for conversion of the DC power supply voltage from the battery power source10into a desired low supply voltage by the DC-DC voltage converter3, and for conversion of the intermediate supply voltage from the DC-DC voltage converter21coupled to the battery power source10into the desired low supply voltage by the other DC-DC voltage converter31, respectively. In this case, the input voltage Vin of the DC-DC voltage converter3has, for example, the lower voltage limit of 9 V and the upper voltage limit of 12 V of the battery power source10, while the input voltage Vin of the DC-DC voltage converter31is the output supply voltage of 3.3 V of the DC-DC voltage converter21. The desired low supply voltage Vout of the DC-DC voltage converter3or31is 1.5 V. As can be seen fromFIG. 2, the way of converting the high battery power source voltage of 9 V or 12 V into the low supply voltage of 1.5 V by the single DC-DC voltage converter3ofFIG. 1Aexhibits a lower voltage conversion efficiency than the way of converting the intermediate supply voltage of 3.3 V of the DC-DC voltage converter21into the low supply voltage of 1.5 V by the DC-DC voltage converter31ofFIG. 1B. In general, a larger difference between the voltage to be converted and the resultant converted voltage results in lower voltage conversion efficiency. However, the DC-DC voltage converter21ofFIG. 1Bhas the allowable current which is increased by the amount of a current supplied to the DC-DC voltage converter31, and has components, such as a coil, which have larger sizes or larger heights than those of the DC-DC voltage converter2ofFIG. 1A. Accordingly, the DC-DC voltage converter21ofFIG. 1Bis not applicable to electronic apparatuses having thin bodies, such as notebook PCs.

The inventors have recognized that the conversion efficiency of the voltage of the DC battery power source10into the nominal voltages of respective components is required to be enhanced without increasing the heights or the sizes of the components incorporated into the electronic apparatus. Further, the inventors have recognized fromFIG. 2that the size of the DC-DC voltage converter21can be reduced, by generating the voltage of 1.5 V from the voltage of 3.3 V for the small load current, and by generating the voltage of 1.5 V from the battery power source voltage of 9 to 12 V for the large load current.

FIG. 3shows the configuration of an electronic apparatus, such as a notebook PC, including a DC voltage conversion circuit110or112, in accordance with an embodiment of the invention. The electronic apparatus ofFIG. 3includes a DC battery power source10, an AC power supply adapter11for supplying a DC voltage, a PMU/ASIC16, and a DC voltage conversion circuit110or112. The electronic apparatus also includes other components, for example, a CPU61, a memory control unit62, an I/O control unit63, an audio device64, a USB port65, a memory66, a graphic control unit67, a wired LAN card68, a wireless LAN card69, a PC card control unit70, an LCD71, an HDD72, a LAN connection unit (CN)73and a card slot74. The PMU/ASIC16has a power supply microcomputer function. In this case, the DC voltage conversion circuit110or112includes DC-DC voltage converters (DDCs)20,22,30and32for outputting respective supply voltages Vout's of 5 V, 3.3 V, 2.5 V and 1.5 V. Each of the DC-DC voltage converters20,22,30and32has a well known configuration, and includes a switching element, a smoothing capacitor and an inductor. The PMU/ASIC16has the function of managing the charging, discharging and the like of the battery and the function of keyboard control (the keyboard connection is not shown).

The embodiments of the invention are described herein in connection with the battery power source10employed as the DC power source. However, the invention is also applicable to a DC voltage conversion circuit with the AC power source adapter11employed as the DC power source.

InFIG. 3, the DC-DC voltage converter20provides the supply voltage of 5 V to the PC card control unit70and the HDD72. The DC-DC voltage converter22provides the supply voltage of 3.3 V to the PMU/ASIC16, the I/O control unit63, the audio device64, the wired LAN card68, the wireless LAN card69, the PC card control unit70, the LCD71, the HDD72and the card slot74. The DC-DC voltage converter30provides the supply voltage of 2.5 V to the memory control unit62, the memory66and the graphic control unit67. The DC-DC voltage converter32provides the supply voltage of 1.5 V to the CPU61, the memory control unit62and the I/O control unit63.

FIG. 4shows the configuration of a DC voltage conversion circuit110and a switching controller12, in accordance with an embodiment of the invention.

InFIG. 4, the DC voltage conversion circuit110includes a DC-DC voltage converter22connected to the output terminal of the battery power source10for providing a supply voltage Vout of 3.3 V, and a DC-DC voltage converter32selectively connected to the output terminals of the battery power source10and the DC-DC voltage converter22via a switch (SW)40for providing a supply voltage Vout of 1.5 V. The operating condition of the switching controller12is set up manually by a user through a hardware circuit switch or an application. The switching controller12receives a setting signal from the hardware circuit switch, the application or the like, to thereby provide a control signal CTRL to the switch40. The switching controller12may be the function of the PMU/ASIC16ofFIG. 3.

The output terminal of the DC supply voltage 9 to 12 V of the battery power source10and the output terminal of the DC supply voltage 3.3 V of the DC-DC voltage converter22are connected to the respective input terminals of the switch40via the respective conductors122and124. The DC voltage conversion circuit110and the switching controller12are mounted typically on a single printed circuit board PCB. The conductors122and124may be formed by foil conductors of the printed circuit board. Alternatively, at least one of the conductors122and124may be formed by a separate electrically conductive wire which is different from the conductor of the printed circuit board. This facilitates the design of the arrangement of circuits on the printed circuit board, even if a high density of the circuit elements on the printed circuit board and the limited number of layers of the printed circuit board (e.g., a six-layered board) inhibit the formation of a low impedance conductor foil pattern having sufficient area and width for the power supply on the printed circuit board.

In response to a control signal CTRL from the switching controller12, the switch40selects either the power supply voltage terminal (e.g., 12 V) of the battery power source10or the supply voltage terminal (e.g., 3.3 V) of the DC-DC voltage converter22to connect to the input voltage terminal of the DC-DC voltage converter32. The DC-DC voltage converter32controls its switching operation in accordance with the input voltage to regulate the input voltage to provide the predetermined supply voltage of 1.5 V as the output. The operating condition of the switching controller12is set up manually through the hardware switch (not shown) or the application (the function of the CPU61that operates in accordance with the application stored in the memory66) such that, when the operational states of the components of the electronic apparatus correspond to a state that the load current of the supply voltage terminal of the DC-DC voltage converter32is estimated not to exceed a predetermined threshold current (e.g., 0.5 A), the input voltage terminal of the DC-DC voltage converter32should be switched and connected to the output voltage terminal (3.3 V) of the DC-DC voltage converter22, while, when the operational states of the components of the electronic apparatus correspond to a state that the load current of the supply voltage terminal of the DC-DC voltage converter32is estimated to exceed the predetermined threshold current (e.g., 0.5 A), the input voltage terminal of the DC-DC voltage converter32should be switched and connected to the power supply voltage terminal (9 V or 12 V) of the battery power source10.

In a simple way, for example, an operation monitoring application that is implemented on the CPU61or the like may monitor the operational states of the components of the electronic apparatus, and then provide to the switching controller12a conditional signal corresponding to the operational state, so that, in response to the conditional signal, the switching controller12provides the control signal CTRL to the switch40. In this case, for example, if the electronic apparatus is in an inactive state, or a predetermined low-loading application of the electronic apparatus is in an active state or in a predetermined operation state (e.g., not using the PC card), in which the electronic apparatus is in such a state that the load current level at the supply voltage terminal of the DC-DC voltage converter32is estimated not to exceed a predetermined threshold current (e.g., 0.5 A), then the switching controller12may receive a conditional signal indicating the estimated low loading state of the DC-DC voltage converter32from the operation monitoring application, and then provide to the switch40a control signal CTRL for switching and connecting the input voltage terminal of the DC-DC voltage converter32to the output voltage terminal of the DC-DC voltage converter22. On the other hand, if a predetermined high-loading application is in an active state or in other predetermined operation states (e.g., using a PC card), in which the electronic apparatus is in such a state that the load current level at the supply voltage terminal of the DC-DC voltage converter32is estimated to exceed the predetermined threshold current, then the switching controller12may receive another conditional signal indicating the estimated high loading state of the DC-DC voltage converter32from the operation monitoring application, and then provide to the switch40a control signal CTRL for switching and connecting the input voltage terminal of the DC-DC voltage converter32to the power supply voltage terminal of the battery power source10.

As a further example, the operational states of the components of the electronic apparatus are monitored similarly. If the electronic apparatus is in an inactive state and applications of the electronic apparatus except for the operation monitoring application are in inactive states, in which the load current level of the DC-DC voltage converter32is low as described above, the switching controller12may receive a conditional signal indicating these states from the operation monitoring application, and then provide to the switch40a control signal CTRL for switching and connecting the input voltage terminal of the DC-DC voltage converter32to the output voltage terminal of the DC-DC voltage converter22. On the other hand, if any of the applications is in an active state as activated by the user, in which the load current level of the DC-DC voltage converter32is high as described above, then the switching controller12may receive a conditional signal indicating this state from the operation monitoring application, and then provide to the switch40a control signal CTRL for switching and connecting the input voltage terminal of the DC-DC voltage converter32to the power supply voltage terminal of the battery power source10. In this case, for detecting the activation of the application, a conditional signal indicating the activation may be provided to the switching controller12in response to operation of a key or a hardware switch or alternatively a software switch or an icon on a display screen by a user who activates the application. Alternatively, a hardware switch may be provided in the housing of the electronic apparatus so that, for activating the application, the user is allowed to operate the switch, to thereby provide a conditional signal indicating the activation to the switching controller12.

FIG. 5shows the change of the voltage conversion efficiency of the DC voltage conversion circuit110as a function of the load current through the supply voltage terminal (1.5 V) of the DC-DC voltage converter32, in which the switch40operates in response to the switching control signal CTRL from the switching controller12. When the load current of the DC-DC voltage converter32is at 0.5 A or lower, the DC-DC voltage converter32converts the supply voltage of 3.3 V of the DC-DC voltage converter22into 1.5 V, where the voltage conversion efficiency Eddc2is approximated as 90% which is near the maximum efficiency inFIG. 2. Thus, the voltage conversion efficiency Eddc2×Eddc12is about 75% to 85%. On the other hand, when the load current of the DC-DC voltage converter32is higher than 0.5 A, the DC-DC voltage converter32converts the output voltage 12 V of the battery power source10into 1.5 V. Thus, the voltage conversion efficiency Eddc11is about 80% to 90%. The load current described here is an estimated value. Thus, in order to prevent an excessive current from actually flowing through the DC-DC voltage converter32, the predetermined threshold current should be set somewhat lower, for example, by the amount corresponding to 3% of the efficiency, than the point at the intersection between the curves of the voltage conversion efficiencies Eddc2×Eddc12and Eddc11. Thus, the DC-DC voltage converter22is not involved in the voltage conversion for a load current higher than the predetermined threshold current of 0.5 A, and hence does not require an increase in size.

FIG. 6shows a modification of the configuration ofFIG. 4, and shows the configuration of a DC voltage conversion circuit110and a switching controller14in accordance with another embodiment of the invention. In this case, the switching controller14receives signals indicating the respective operational states of the components of the system of the electronic apparatus ofFIG. 3, and then processes the signals to provide a control signal CTRL to the switch40.

FIG. 7is a flow chart for determining the control signal CTRL provided to the switch40, which is performed by the switching controller14.

Tables that approximate the graph or curves ofFIG. 2and are used by the switching controller14are prestored, for example, in a flash memory of the PMU16. These tables include a table (not shown) representing the approximated voltage conversion efficiencies of the DC-DC voltage converter22for a plurality of load current values for the output voltage of 9 to 12 V (e.g., 10 V) of the battery power source10as the input voltage, and a table (not shown) representing the approximated voltage conversion efficiencies of the DC-DC voltage converter32for a plurality of selected load current values for the output voltage of 9 to 12 V (e.g., 10 V) of the battery power source10and the supply voltage of 3.3 V of the DC-DC voltage converter22as the input voltages. Further, a further table is also prestored, for example, in the flash memory of the PMU16. This table represents the relation of the consumed electric current values with the operational states, i.e., an inactive state, an idle state, an active state, and a maximum current state or the sleep ratio of the components such as the CPU61, the I/O devices (e.g., the PC card control unit70, the wired LAN card68, and the wireless LAN card69) and the audio device64. In accordance with these tables, the switching controller14determines the value of the estimated consumed electric current of each component corresponding to the operational state of that component.

FIGS. 8A and 8Bshow examples of Tables 1 and 2 of the relation between the estimated consumed electric currents and the operational states of respective components receiving the nominal voltages of 3.3 V and 1.5 V. Table 1 represents the consumed electric currents in respective operational states of the wired LAN card68, the wireless LAN card69, the PC card control unit70and the audio device64, which receive the nominal voltage of 3.3 V. Table 2 represents the consumed electric currents in respective operational states of the CPU61receiving the nominal voltage of 1.5 V.

With reference toFIG. 7, at Step702, the switching controller14polls the CPU61periodically, and detects the presence or absence of a change in the system operational state, such as the CPU operational state and the I/O device connection state (e.g., of the PC card control unit70). At Step704, the switching controller14determines whether there has been a change in the system operational state. If it is determined that there is no change, the procedure returns to Step702.

If it is determined that there has been such a change, the switching controller14at Step706interrupts the CPU61, and acquires information indicating the operational states of the components of the system of the electronic apparatus. More specifically, the switching controller14collects the information on the operational states of the CPU61, the I/O devices (e.g., the PC card control unit70and the LAN cards68and69), the audio device64, and the like, by inquiring the devices and the PMU/ASIC16as a power supply microcomputer. The operational state is any one of an inactive state, an idle state, an active state and a maximum current state of each device, or is the ratio of sleep duration of the CPU.

At Step708, in accordance with the acquired operational states of the components, the switching controller14estimates the supply current of the DC-DC voltage converters22and32in accordance with the tables of the consumed electric currents in the respective operational states of components as shown inFIGS. 8A and 8B. In this estimation, for example, the value of the difference between the electric current value in the idle state and the electric current value in the current operational state for a particular component may be acquired, and then be added to or subtracted from the electric current value in the idle state. In this way, the current or present electric currents of all related devices are estimated.

For example, in Table 1 ofFIG. 8A, the consumed electric current in the idle state of the wired LAN card68that receives the supply voltage of 3.3 V of the DC-DC voltage converter22is estimated to be 30 mA, and the consumed electric current of the PC card74in the idle state is estimated to be 30 mA. It is assumed that the estimated value of the sum of the hypothetical consumed electric currents in the idle states of all the components that receive the supply voltage of 3.3 V of the DC-DC voltage converter22is, for example, 1 A. On the other hand, it is assumed that the current operational state of the wired LAN card68is an active state of receiving an estimated current of 560 mA, the current operational state of the PC card74is a maximum current state of receiving a current of 1.03 A, and the current operational states of the other components that receive the supply voltage of 3.3 V are an idle state. In this case, with reference to Table 1 ofFIG. 8A, the estimated value of the sum of the consumed electric currents in the current states of all the components that receive the supply voltage of 3.3 V is 1 A (in idle states of all the components)+0.5 A (the difference of the current of the wired LAN card)+1 A (the difference of the current of the PC card)=2.5 A.

For example, in Table 2 ofFIG. 8B, in the idle state of the CPU61that receives the supply voltage of 1.5 V of the DC-DC voltage converter32, the ratio of sleep duration is larger than 98%, and hence the estimated consumed electric current is 100 mA. In the sleep duration of the CPU61, the CPU clock stops, and the CPU also stops its operation. When the ratio of sleep duration in the CPU61is greater than 90% and not greater than 98%, the estimated consumed electric current is 300 mA. When the ratio of sleep duration is greater than 70% and not greater than 90%, the estimated consumed electric current is 600 mA. When the ratio of sleep duration is greater than 50% and not greater than 70%, the estimated consumed electric current is 1 A. When the ratio of sleep duration is greater than 0% and not greater than 50%, the estimated consumed electric current is 2 A.

When the CPU61is the only component that receives the supply voltage of 1.5 V of the DC-DC voltage converter32and the current operational state of the CPU61is the state of 80% of sleep duration, the estimated consumed electric current of the CPU61is determined to be 600 mA in accordance with Table 2 ofFIG. 8B.

At Step710, in accordance with the tables that approximate the graph ofFIG. 2and the like and with the estimated consumed electric current of the component, the switching controller14estimates the voltage conversion efficiencies Eddc11and the like of the DC-DC voltage converters22and32in a single stage configuration for the voltage (e.g., 10 V) of the battery power source10.

As a first example, it is assumed that the total consumed electric current in the idle state of all the components that receive the supply voltage of 3.3 V of the DC-DC voltage converter22is 1 A, and that the voltage conversion efficiency Eddc2of the DC-DC voltage converter22for the total consumed electric current is about 90% in accordance with a table (not shown) representing voltage conversion efficiencies for the load currents. If the total consumed electric current in the idle state of all the components that receive the supply voltage of 1.5 V of the DC-DC voltage converter32is 100 mA, then the voltage conversion efficiency Eddc11of the DC-DC voltage converter32for the total consumed electric current is approximated as 50% in accordance with the table (not shown) that approximates the graph ofFIG. 2.

As a second example, it is assumed that the total consumed electric current in the operational states of all the components that receive the supply voltage of 3.3 V of the DC-DC voltage converter22is 2.5 A, and that the voltage conversion efficiency of the DC-DC voltage converter22for the total consumed electric current is about 91% in accordance with the table (not shown) representing a voltage conversion efficiency for load currents. If the total consumed electric current in the operational states of all the components that receive the supply voltage of 1.5 V of the DC-DC voltage converter32is 600 mA, then the voltage conversion efficiency Eddc11of the DC-DC voltage converter32at the consumed electric current is approximated as 85% in accordance with the table (not shown) that approximates the graph ofFIG. 2.

At Step712, in accordance with the two total estimated consumed electric currents of the respective groups of components that receive the respective supply voltages of 3.3 V and of 1.5 V, the switching controller14estimates the voltage conversion efficiency Eddc12of the DC-DC voltage converter32in the two-stage configuration that receives as the input voltage the supply voltage of 3.3 V of the DC-DC voltage converter22. It may be assumed that the voltage conversion efficiency Eddc2of the DC-DC voltage converter22in the two-stage configuration is approximately equal to the efficiency in the single stage configuration.

In the first example described above, with reference to the graph ofFIG. 2, for the supply voltage of 3.3 V of the DC-DC voltage converter22used as the input, the voltage conversion efficiency Eddc12of the DC-DC voltage converter32is about 78% for the load current of 0.1 A in the idle states of all the components that receive the supply voltage of 1.5 V of the DC-DC voltage converter32. Thus, the product of the voltage conversion efficiencies of the DC-DC voltage converters22and32in the two-stage configuration is Eddc2×Eddc12=about 90%×about 78%=about 70% for the load current of 0.1 A.

In the second example described above, with reference to the graph ofFIG. 2, for the supply voltage of 3.3 V of the DC-DC voltage converter22used as the input, the voltage conversion efficiency Eddc12of the DC-DC voltage converter32is about 92% for the load current of 600 mA in the operational states of all the components that receive the supply voltage of 1.5 V of the DC-DC voltage converter32. Thus, the product of the voltage conversion efficiencies of the DC-DC voltage converters22and32in the two-stage configuration is Eddc2×Eddc12=about 91%×about 92%=about 83.7% for the load current of 600 mA.

At Step714, the switching controller14compares the product Eddc2×Eddc12of the voltage conversion efficiencies of the DC-DC voltage converters22and32with the conversion efficiency Eddc11of the DC-DC voltage converter32alone, to thereby determine that the configuration for connection having the higher voltage conversion efficiency should be selected. If it is determined that the product Eddc2×Eddc12of the conversion efficiencies is higher than the single conversion efficiency Eddc11, the two-stage configuration should be selected to provide the supply voltage of the DC-DC voltage converter22to the input of the DC-DC voltage converter32. In contrast, if it is determined that the product Eddc2×Eddc12of the conversion efficiencies is not higher than the single conversion efficiency Eddc11, the single stage configuration should be selected to provide the supply voltage of the battery power source10to the input of the DC-DC voltage converter32.

In the first example described above, the product Eddc2×Eddc12of the voltage conversion efficiencies of the DC-DC voltage converters22and32in the two-stage configuration is about 70%, while the single conversion efficiency Eddc11of the DC-DC voltage converter32in the single stage configuration is about 50%. Thus, in this case, the two-stage configuration is advantageous in the voltage conversion efficiency.

In contrast, in the second example described above, the product Eddc2×Eddc12of the voltage conversion efficiencies of the DC-DC voltage converters22and32in the two-stage configuration is about 83.7%, while the single conversion efficiency Eddc11of the DC-DC voltage converter32in the single stage configuration is about 85%. Thus, in this case, the single stage configuration is advantageous in the voltage conversion efficiency.

At Step716, the switching controller14compares the current position of the switch40with the position of the switch40to be selected for achieving the above-mentioned configuration for the higher efficiency, to determine whether the switch40should operate to change its position. If it is determined that the operation for changing its position is required, the switching controller14at Step718switches the switch40to change the current position to the desired position. If it is determined that the operation for changing its position is not required, the procedure returns to Step702. The load current in this case is an estimated value, and hence, in order to prevent an excessive current from actually flowing through the DC-DC voltage converter32, it may be arranged so that the two-stage configuration is selected only if the product Eddc2×Eddc12of the voltage conversion efficiencies of the DC-DC voltage converters22and32in the two-stage configuration is higher, for example, by 3% or more, than the single conversion efficiency Eddc11of the DC-DC voltage converter32in the single stage configuration, while otherwise the single stage configuration is selected.

FIG. 9shows the configuration of a DC voltage conversion circuit110and a switching controller16in place of the switching controller12or14ofFIG. 4or6, in accordance with a further embodiment of the invention.

InFIG. 9, a current detector52is provided for detecting a component load current through the terminal of the supply voltage of 3.3 V of the DC-DC voltage converter22, and another current detector53is provided for detecting a component load current through the terminal of the supply voltage of 1.5 V of the DC-DC voltage converter32. The current detection values of the current detectors52and53are provided to the inputs of the switching controller16. In this case, in contrast to the switching controller12ofFIG. 4which operates in accordance with the estimated load current, the switching controller16generates a switching control signal CTRL in accordance with the detected load current of the DC-DC voltage converter32and in accordance with the table (not shown) that approximates the graph ofFIG. 2or5representing the voltage conversion efficiencies for the load current values. Alternatively, in contrast to the switching controller14ofFIG. 6which operates in accordance with the estimated load current of the components obtained from the tables ofFIGS. 8A and 8B, the switching controller16may determine the respective voltage conversion efficiencies for the comparison, as described above, in accordance with the load current values of the DC-DC voltage converters22and32detected by the current detectors52and53, and in accordance with the tables (not shown) representing voltage conversion efficiencies for the detected load current values, to thereby generate a control signal CTRL.

According to the embodiments described above, the voltage of the DC battery power source10can be converted efficiently into the supply voltages of 3.3 V and 1.5 V in accordance with the estimated or detected load currents of the DC-DC voltage converters22and32, without an increase in the size of the voltage converter.

The embodiments have been described only for the DC-DC voltage converters22and32in a single stage configuration or in a two-stage configuration. However, it should be understood that the invention is applicable also to the switching control of a switch for selection for connection in a three- or more-stage configuration including the DC-DC voltage converters20and30and other converters as shown inFIG. 3. This increases the number of combinations of the voltage converters and the number of the voltage conversion efficiencies of the voltage converters and the combinations to be compared.

The above-described embodiments are only typical examples, and their combination, modifications and variations are apparent to those skilled in the art. It should be noted that those skilled in the art can make various modifications to the above-described embodiments without departing from the principle of the invention and the accompanying claims.