Embodiments of the present invention will be described below with reference to
The multi-output power supply apparatus includes a first power supply circuit 10A and a second power supply circuit 20. A first output voltage Vo1 of the first power supply circuit 10A is, for example, 5 V. A second output voltage Vo2 of the second power supply circuit 20 which uses the first output voltage Vo1 as an input power supply is, for example, 12 V.
In
Incidentally, when using the first power supply circuit 10A and the second power supply circuit 20 described above to configure a multi-output power supply apparatus for electronic equipment on which an external power supply apparatus such as an AC adaptor is mounted as an input power supply and whose input voltage Vi is 4.5 to 5.5 V, it is possible to operate the second power supply circuit 20 while deactivating the first power supply circuit 10A by short-circuiting an input and output of the first power supply circuit 10A by an external connection 50 and grounding the third external connection terminal P3 as shown in
Reference numeral 1 denotes the lithium-ion battery which supplies the input voltage Vi, where Vi=2.5 to 4 V in the case of a single-cell lithium-ion battery. Reference numeral 10A denotes the first power supply circuit—specifically, a boost converter—which includes an inductor 11 and main switch 12 connected in series with each other and in parallel to the input power supply 1, a diode 13 connected to a junction point of the main switch 12 and inductor 11, an output capacitor 14 which, being connected to an output of the diode 13, outputs the first output voltage Vo1 (e.g., 5 V), a resistor 15 and resistor 16 which produce a fraction of the first output voltage Vo1 as a feedback voltage Vf1, and a first control circuit 17 which turns on and off the main switch 12. The first control circuit 17 has a control terminal 17a, feedback terminal 17b, and pulse output terminal 17c. It starts operation when a High signal is applied to the control terminal 17a. The first control circuit 17 outputs, from the pulse output terminal 17c, a pulse signal Vg1 whose on-off time ratio has been adjusted so that the feedback voltage Vf1 inputted in the feedback terminal 17b will be equal to a predetermined reference voltage Vr.
Reference numeral 3 denotes a power-on signal generating circuit that includes a comparison circuit 31 which outputs a High signal when the first output voltage Vo1 is equal to or larger than a predetermined output voltage value (e.g., 90% of a target voltage), a comparison circuit 33 serving as a second comparison circuit which outputs a High signal when the feedback voltage Vf1 of the first power supply circuit 10A is equal to or higher than a predetermined lower limit (e.g., 0.2 V), an AND circuit 34 which outputs a first signal V1 which is a logical product of a comparison circuit's (33) output and the first control signal Vc1, an inverter 35 which inverts the output of the comparison circuit 33, an OR circuit 36 which outputs a logical sum of an inverter's (35) output and the first control signal Vc1, and an AND circuit 37 which outputs a power-on signal which is a logical product of an output of the comparison circuit 31 and output of the OR circuit 36. Reference character Vs1 denotes a detection signal which indicates that the first output voltage is equal to or larger than the predetermined output voltage value and reference character Vs2 denotes a detection signal which indicates that the feedback voltage Vf1 is equal to or lower than a prescribed potential (0.2 V). The first signal V1 outputted from the AND circuit 34 is inputted in the control terminal 17a of the first control circuit 17.
Reference numeral 20 denotes the second power supply circuit—specifically, a boost converter—which includes a sixth external connection terminal P6 connected with an output of the first power supply circuit 10A, a seventh external connection terminal P7 which produces the second output voltage Vo2, an eighth external connection terminal P8 in which the power-on signal Von is inputted from the first power supply circuit 10A, and a ninth external connection terminal P9 in which a second control signal Vc2 is inputted instructing the second power supply circuit 20 to start operation.
More specifically, the second power supply circuit 20 includes an inductor 21 and main switch 22 connected in series with each other and in parallel to the output capacitor 14 of the first power supply circuit 10A, a diode 23 connected to a junction point of the main switch 22 and inductor 21, an output capacitor 24 which, being connected to an output of the diode 23, outputs a second output voltage Vo2 (e.g., 12 V), a resistor 25 and resistor 26 which produce a fraction of the second output voltage Vo2 as a feedback voltage Vf2, and a second control circuit 27 which turns on and off the main switch 22. The second control circuit 27 has a control terminal 27a, feedback terminal 27b, and pulse output terminal 27c. It starts operation when a High signal is applied to the control terminal 27a. The second control circuit 27 outputs, from the pulse output terminal 27c, a pulse signal Vg2 whose on-off time ratio has been adjusted so that the feedback voltage Vf2 inputted in the feedback terminal 27b will be equal to the predetermined reference voltage Vr. Reference numeral 28 denotes an AND circuit which outputs a logical product of the power-on signal Von and second control signal Vc2 to the control terminal 27a.
Operation of the first power supply circuit 10A of the multi-output power supply apparatus in
If the input voltage Vi (2.5 to 4 V) is being applied, the first output voltage Vo1 is generated and a voltage fraction produced by the resistor 15 and resistor 16 is equal to or higher than a predetermined lower limit.
Thus, the output of the comparison circuit 33 is High. When the first control signal Vc1 goes High, the first signal V1 outputted by the AND circuit 34 goes High as well, causing the first control circuit 17 to start operating and output the pulse signal Vg1 from the pulse output terminal 17c. When the main switch 12 is turned on by the pulse signal Vg1, the inductor 11 to which the input voltage Vi is applied is energized, passing an increasing current. Next, when the main switch 12 is turned off, a decreasing current flows through the output capacitor 14 via the diode 13, causing the inductor 11 to release energy. Through repetition of the on/off operation, power is supplied from the input power supply 1 to the output capacitor 14 and the first output voltage Vo1 is outputted. The first output voltage Vo1 is controlled by an on-off time ratio of the main switch 12. Under ideal conditions in which forward voltage drops and the like of the diode 13 are ignored, if a proportion (referred to as a duty factor) of a conduction period in one switching cycle of the main switch 12 is δ1, the first output voltage Vo1 is given by:
Vo1=Vi/(1−δ1) (1)
As the first control circuit 17 adjusts the duty factor of the pulse signal Vg1 so that the feedback voltage Vf1 will be equal to the predetermined reference voltage Vr, the first output voltage Vo1 is stabilized at a target value. If resistance values of the resistors 15 and 16 are R15 and R16, respectively, the stabilized first output voltage Vo1 is given by:
Vo1=Vr·(1+R15/R16) (2)
Next, when the first output voltage Vo1 exceeds a predetermined voltage value, the comparison circuit 31 of the power-on signal generating circuit 3 outputs a High. On the other hand, the OR circuit 36, in which the first control signal Vc1 in a High state has been inputted, also outputs a High. The power-on signal Von—which is the logical product of the output of the OR circuit 36 and output of the comparison circuit 31—outputted from the AND circuit 37 is also High. Thus, when the second control signal Vc2 goes High, the second signal V2, which is the logical product of the second control signal Vc2 and power-on signal Von, also goes High. In the second power supply circuit 20, the second control circuit 27 starts operation when the second signal V2 in a High state is inputted in the control terminal 27a, and turns on and off the main switch 22 based on the pulse signal Vg2 from the pulse output terminal 27c. Subsequent operation of the second power supply circuit 20 is the same as the first power supply circuit 10A. Specifically, by turning on and off the main switch 22, the second power supply circuit 20 boosts the first output voltage Vo1 to the second output voltage Vo2 and stabilizes the second output voltage Vo2 at a target value.
As an input power supply, instead of using the single-cell lithium-ion battery 1 described above, some electronic equipment uses, for example, an AC adaptor which outputs 4.5 to 5.5 VDC or a step-down power supply apparatus which draws power from a two-cell lithium-ion battery and outputs 5 V. The multi-output power supply apparatus according to the present invention can be used as well for such electronic equipment and this will be described with reference to
Configuration in
Operation of the multi-output power supply apparatus in
Since the input to the comparison circuit 33, is grounded, the output from the comparison circuit 33 is Low. Consequently, the output of the AND circuit 34 goes Low as well and the first control circuit 17 stops operation with a Low inputted in the control terminal 17a. On the other hand, since the inverter 35 outputs a High, the OR circuit 36 outputs a High regardless of the first control signal Vc1 which no longer makes any sense. Also, the first output voltage V61 is high enough because of power supply from the external power supply apparatus 2, and consequently the output of the comparison circuit 31 is High as well. The power-on signal Von—which is the logical product of the output of the comparison circuit 31 and output of the OR circuit 36—outputted from the AND circuit 37 is also High. Thus, when the second control signal Vc2 goes High, the second signal V2, which is the logical product of the second control signal Vc2 and power-on signal Von, also goes High. In the second power supply circuit 20, the second control circuit 27 starts operation when the second signal V2 in a High state is inputted in the control terminal 27a.
Thus, whereas when operating the first power supply circuit 10A using a lithium-ion battery 1 as an input power supply, a fraction of the first output voltage Vo1 is applied to the feedback terminal 17b via the resistors 15 and 16; when an external power supply apparatus 2 such as an AC adaptor is used as an input power supply and output voltage of the external power supply apparatus 2 is applied directly to the feedback terminal 17b as the first output voltage Vo1, it is possible to operate the second power supply circuit 20 while deactivating the first power supply circuit 10A by grounding the feedback terminal 17b.
Although the first control circuit 17 and power-on signal generating circuit 3 are treated as separate blocks for convenience of illustration, if at least these two circuits are formed in the same semiconductor integrated circuit, configurations in
Out of the inductor 11, main switch 12, diode 13, and output capacitor 14 of the switching unit interposed between the first external connection terminal P1 and second external connection terminal P2, the inductor 11, for example, is installed outside the semiconductor circuit apparatus.
Although boost converters are used for both first power supply circuit 10A and second power supply circuit 20 described above, the present invention is not limited to such configuration. Since the present invention deactivates the first power supply circuit by grounding the feedback terminal of the first power supply circuit, if the first output voltage becomes zero on start-up such as when a step-down converter is used, it is recommended to provide a dead time for the comparison circuit 33 during start-up so that the voltage of the feedback terminal will be equal to or higher than a predetermined lower limit during the dead time i.e., the comparison circuit 33 will output a High. This makes it possible to use a voltage transformation circuit other than a boost converter.
In the first embodiment, the resistors 15 and 16 used to generate the feedback voltage Vf1 are installed separately at the input to the comparison circuit 33. This makes it necessary to install a separate detection resistor for the first output voltage Vo1 because the feedback terminal 17b is grounded when an external power supply apparatus is used as an input power supply.
Thus, in the second embodiment shown in
The comparison circuit 31 compares the feedback voltage Vf1 with 90% of the reference voltage Vr, and outputs a High if Vf1>0.9 Vr.
The comparison circuit 33 compares the feedback voltage Vf1 with a voltage value of 0.2 V, and outputs a High if Vf1>0.2 V.
With this configuration, when a battery is mounted supplying a low-voltage input, a voltage applied to the feedback terminal 18a and a voltage applied to the input terminal 18b of the comparison circuit 31 can be shared with a voltage at a junction point of the resistors 15 and 16. Also, when an external power supply apparatus is mounted, the feedback terminal 18a can be grounded and the voltage at the junction point of the resistors 15 and 16 can be applied to the terminal 18b. That is, there is no need to install a detection resistor separately in order to compare the first output voltage Vo1 with a predetermined output voltage value.
Incidentally, although not mentioned in the description of the first and second embodiments, it is assumed that the first control circuit 17 and second control circuit 27 operate on the input voltage Vi or first output voltage Vo1.
The present invention is useful for a multi-output power supply apparatus which supplies DC voltages to various types of electronic equipment.
Number | Date | Country | Kind |
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2006-266151 | Sep 2006 | JP | national |