Power supply unit and control method therefor

Abstract

To provide a power supply unit that can suppress lowering of efficiency.SOLUTION: A power supply unit comprises: a first power supply that sets a first output voltage for a first wiring to a first voltage when a first output current flowing in the first wiring is zero and reduces the first output voltage in accordance with an increase of the first output current; and a second power supply that sets a second output voltage for a second wiring connected to the first wiring to a second voltage lower than the first voltage when a second output current flowing in the second wiring is zero, and supplies the second output current when the first output voltage has decreased to the second voltage.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a power supply unit and a control method thereof. [Background technology]

[0002] 2. Description of the Related Art A power supply system having a plurality of power supply modules connected in parallel is known (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-040426 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the voltages output by multiple power supplies connected in parallel to a common load are set to the same voltage value, the load current burden is the same for each power supply, and therefore, when the total load on the multiple power supplies is low, the efficiency of each power supply may decrease.

[0005] The present disclosure provides a power supply unit and a control method thereof that can suppress a decrease in efficiency. [Means for solving the problem]

[0006] The present disclosure relates to a first power supply that sets a first output voltage to a first wiring to a first voltage when a first output current flowing through the first wiring is zero, and reduces the first output voltage in response to an increase in the first output current; A power supply unit is provided, comprising: a second power supply that sets a second output voltage to the second wiring to a second voltage lower than the first voltage when a second output current flowing in a second wiring connected to the first wiring is zero, and supplies the second output current when the first output voltage drops to the second voltage.

[0007] The present disclosure also provides A method for controlling a power supply unit including a first power supply that supplies a first output current to a first wiring and a second power supply that supplies a second output current to a second wiring connected to the first wiring, comprising: When the first output current is zero, a first output voltage from the first power supply to the first wiring is set to a first voltage, and the first output voltage is reduced in response to an increase in the first output current; A method for controlling a power supply unit is provided, which sets a second output voltage from the second power supply to the second wiring to a second voltage lower than the first voltage when the second output current is zero, and causes the second power supply to supply the second output current to the second wiring when the first output voltage drops to the second voltage. Effect of the Invention

[0008] According to the present disclosure, it is possible to suppress a decrease in the efficiency of a power supply unit. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of an electronic device including a power supply unit according to an embodiment. [Diagram 2] FIG. 2 is a characteristic diagram showing an example of an efficiency curve of a power supply. [Diagram 3] FIG. 4 is a diagram showing two droop characteristics used when setting the output characteristics of each power source in a first setting example. [Figure 4] FIG. 11 is a diagram showing the relationship between the device load factor, the output current, and the output voltage when the output characteristics of each power supply are set in the first setting example. [Diagram 5] FIG. 11 is a diagram showing the loss reduction effect when the output characteristics of each power source are set in the first setting example. [Figure 6] FIG. 13 is a diagram showing two droop characteristics used when setting the output characteristics of each power source in a second setting example. [Figure 7] FIG. 13 is a diagram showing the relationship between the device load factor, the output current, and the output voltage when the output characteristics of each power supply are set in the second setting example. [Figure 8]FIG. 13 is a diagram showing the loss reduction effect when the output characteristics of each power source are set in the second setting example. [Figure 9] FIG. 13 is a diagram showing two droop characteristics used when setting the output characteristics of each power source in a third setting example. [Figure 10] FIG. 13 is a diagram showing the relationship between the device load factor, the output current, and the output voltage when the output characteristics of each power supply are set in the third setting example. [Figure 11] FIG. 13 is a diagram showing the loss reduction effect when the output characteristics of each power source are set in the third setting example. [Figure 12] FIG. 2 is a block diagram showing a configuration example of a power supply. [Figure 13] FIG. 13 illustrates an example of a droop slope and offset adjustment circuit. [Figure 14] 10 is a flowchart showing an example of the operation of a device control unit. [Figure 15] 10 is a flowchart illustrating an example of the operation of a power supply. [Figure 16] FIG. 2 is a hardware configuration diagram of a control device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An embodiment will be described below.

[0011] Fig. 1 is a diagram showing an example of the configuration of an electronic device including a power supply unit according to an embodiment. The electronic device 200 shown in Fig. 1 includes a power supply unit 100 that generates a DC output voltage Vo, a load 22 that operates on DC power supplied from the power supply unit 100, and a device control unit 21 that is connected to the power supply unit 100 so as to be capable of transmitting signals.

[0012] Examples of the electronic device 200 include, but are not limited to, a server, a supercomputer, a personal computer, a mobile computer, a smart phone, a tablet, a mobile phone, and the like.

[0013] The power supply unit 100 is a power supply device that generates a DC output voltage Vo that is output to a load 22. The power supply unit 100 includes a first power supply 11 and a second power supply 12.

[0014] The first power supply 11 generates and outputs a first output voltage V1 to a first wiring 31. The second power supply 12 generates and outputs a second output voltage V2 to a second wiring 32. The second wiring 32 is connected to the first wiring 31 at a connection point 33. A first output current I1 flowing from the first power supply 11 to the first wiring 31 and a second output current I2 flowing from the second power supply 12 to the second wiring 32 join at the connection point 33. The power supply unit 100 supplies an output current IL, which is the sum of the first output current I1 and the second output current I2, to the load 22 connected to the connection point 33. The output current IL is also referred to as a load current IL.

[0015] The first power supply 11 is a power supply circuit that generates and outputs DC power of a first output voltage V1 from AC or DC input power supplied from an external power supply (not shown). The second power supply 12 is a power supply circuit that generates and outputs DC power of a second output voltage V2 from AC or DC input power supplied from an external power supply (not shown). The external power supply (not shown) may be a power supply provided in common to the first power supply 11 and the second power supply 12, or may be a power supply provided separately for the first power supply 11 and the second power supply 12.

[0016] The load 22 operates using the DC output voltage Vout generated by the power supply unit 100 as a power supply voltage. The load 22 may be a single load or a combination of multiple loads. Specific examples of the load 22 include a processor such as a CPU (Central Processing Unit), a hard disk, a memory, a fan, and the like, but the load 22 is not limited to these.

[0017] The device control unit 21 transmits a signal S for setting whether each of the first power source 11 and the second power source 12 is to operate as a main power source or a standby power source to the first power source 11 or the second power source 12. By transmitting the signal S, the device control unit 21 sets each of the first power source 11 and the second power source 12 as whether it is to operate as a main power source or a standby power source.

[0018] The device control unit 21 may be communicatively connected to the first power source 11 and the second power source 12, and may transmit and receive a signal S between the first power source 11 or the second power source 12 in accordance with a communication protocol such as PMBus (Power Management Bus). In the case of PMBus, the signal S includes a data signal SDA and a clock signal SCL.

[0019] The signal S for setting whether each of the first power source 11 and the second power source 12 operates as a main power source or a standby power source is not limited to being transmitted and received according to a communication protocol such as PMBus. The signal S may be a setting signal generated by hardware such as a pull-down resistor or a pull-up resistor.

[0020] FIG. 2 is a characteristic diagram showing an example of a power supply efficiency curve. Both the first power supply 11 and the second power supply 12 have a characteristic that their efficiency drops sharply in a region where the load factor is low, as shown in FIG. 2. The load factor represents the ratio of actual output power to rated output. The efficiency represents the ratio of output power to input power. By operating each of the first power supply 11 and the second power supply 12 at a highly efficient load factor R (for example, 20% to 80% in the case of FIG. 2), the efficiency of the entire power supply unit 100 is improved, and power saving of the power supply unit 100 and the electronic device 200 can be achieved.

[0021] However, when the first output voltage V1 of the first power supply 11 and the second output voltage V2 of the second power supply 12 are set to the same voltage value, the first power supply 11 and the second power supply 12 each share half of the load current IL generated by the load 22. For this reason, when the total load on the first power supply 11 and the second power supply 12 by the load 22 is low (when the load current IL is low), the first power supply 11 and the second power supply 12 may each operate at a load factor with low efficiency (for example, in the area to the left of the area of ​​the load factor R in FIG. 2). In this case, the efficiency of each of the first power supply 11 and the second power supply 12 decreases, and the efficiency of the entire power supply unit 100 decreases.

[0022] For example, the power supply unit 100 is designed to be capable of handling the maximum load that can be generated by the load 22. Therefore, if the time during which the load 22 operates at or near the maximum load is very short relative to the overall operating time, the first power supply 11 and the second power supply 12 each operate at a low-efficiency load factor for a relatively long time.

[0023] In this embodiment, the output characteristics of the first power source 11 and the second power source 12 are set to droop characteristics adjusted so that the first power source 11 and the second power source 12 each operate at a highly efficient load factor R (for example, 20% to 80% in the case of FIG. 2). This improves the efficiency of the entire power source unit 100, and enables power saving of the power source unit 100 and the electronic device 200.

[0024] Next, we will explain several setting examples when setting droop characteristics for the output characteristics of the first power source 11 and the second power source 12. The droop characteristics are output characteristics in which the amount of drop in the output voltage from a power source increases as the output current from the power source increases.

[0025] 1, the output characteristic of the first power supply 11 is set to a droop characteristic in which a first output current I1 flowing through the first wiring 31 is detected, and the larger the detected first output current I1, the lower the first output voltage V1 to the first wiring 31. Similarly, the output characteristic of the second power supply 12 is set to a droop characteristic in which a second output current I2 flowing through the second wiring 32 is detected, and the larger the detected second output current I2, the lower the second output voltage V2 to the second wiring 32.

[0026] 3 is a diagram showing two droop characteristics used when setting the output characteristics of each power supply in the first setting example. The output current Iout on the horizontal axis represents the first output current I1 from the first power supply 11 to the first wiring 31 or the second output current I2 from the second power supply 12 to the second wiring 32. The output voltage Vout on the vertical axis represents the first output voltage V1 from the first power supply 11 to the first wiring 31 or the second output voltage V2 from the second power supply 12 to the second wiring 32.

[0027] When the first power supply 11 is set to operate as the main power supply based on the signal S, the output characteristic of the first output voltage V1 with respect to the first output current I1 is set to a first droop characteristic D1 during normal operation. The first droop characteristic D1 is as follows: Vout = Va - Iout × (ΔV1 / Im) It is expressed as:

[0028] Va represents the first output voltage V1 when the first output current I1 is zero (e.g., 12.5 [V]). Im represents the first output current I1 at maximum load or maximum rating (e.g., 210 [A]). ΔV1 represents the amount of voltage drop in the first output voltage V1 when the first output current I1 is the maximum current Im (e.g., 0.5 [V]). (ΔV1 / Im) represents the droop slope of the first droop characteristic D1.

[0029] When the first output current I1 flowing through the first wiring 31 is zero, the first power supply 11 sets the first output voltage V1 to the first wiring 31 to a first voltage Va in accordance with the first droop characteristic D1. Then, the first power supply 11 reduces the first output voltage V1 from the first voltage Va as the first output current I1 increases from zero in accordance with the first droop characteristic D1.

[0030] On the other hand, when the second power supply 12 is set to operate as a standby power supply based on the signal S, the output characteristic of the second output voltage V2 with respect to the second output current I2 is set to a second droop characteristic D2 during standby operation. The second droop characteristic D2 is Vout = Vb - Iout × (ΔV2 / Im) It is expressed as:

[0031] Vb represents the second output voltage V2 when the second output current I2 is zero (e.g., 12.25 [V]). Im represents the second output current I2 at maximum load or maximum rating (e.g., 210 [A]). ΔV2 represents the amount of voltage drop in the second output voltage V2 when the second output current I2 is the maximum current Im (e.g., 0.5 [V]). (ΔV2 / Im) represents the droop slope of the second droop characteristic D2.

[0032] The second droop characteristic D2 has the same droop slope as the first droop characteristic D1, and is offset from the first droop characteristic D1 by a voltage offset (Va-Vb).

[0033] The second power supply 12 sets the second output voltage V2 to the second wiring 32 to the second voltage Vb in accordance with the second droop characteristic D2 when the second output current I2 flowing through the second wiring 32 is zero. The second voltage Vb has a value lower than the first voltage Va. Then, the second power supply 12 reduces the second output voltage V2 from the second voltage Vb as the second output current I2 increases from zero in accordance with the second droop characteristic D2.

[0034] 1, in a configuration in which the output part of the first power supply 11 and the output part of the second power supply 12 are commonly connected to a connection point 33, if the first output voltage V1 and the second output voltage V2 are different, when the load current (output current IL) increases, the power supply with the higher output voltage bears most of the load current. However, in the output characteristics illustrated in FIG. 3, when the first output current I1 is zero, the first output voltage V1 is set to the first voltage Va, and when the second output current I2 is zero, the second output voltage V2 is set to the second voltage Vb.

[0035] Since the second voltage Vb is lower than the first voltage Va, when the load current IL increases from zero, the first power supply 11, which has a higher output voltage, bears most of the load current IL. In other words, as the load current IL increases from zero, the first power supply 11 starts to output the first output current I1, but the second power supply 12 does not output the second output current I2. In a low current region where the load current IL is equal to or greater than zero and less than the current value Ib, the first output voltage V1 is higher than the second voltage Vb. Therefore, in a low current region where the load current IL is equal to or greater than zero and less than the current value Ib, the first power supply 11 outputs the first output current I1 in accordance with the first droop characteristic D1, and the second power supply 12 does not output the second output current I2 (output current IL=first output current I1).

[0036] The second power supply 12 has a second droop characteristic D2 whose droop slope is the same as the first droop characteristic D1, as shown in Fig. 3. As a result, when the first output voltage V1 decreases to the second voltage Vb, the second power supply 12 decreases the second output voltage V2 in response to an increase in the second output current I2 with the same slope as the slope at which the first output voltage V1 decreases in response to an increase in the first output current I1.

[0037] Fig. 4 is a diagram showing the relationship between the device load factor, output current, and output voltage when the output characteristics of each power source are set in the first setting example using the two droop characteristics of Fig. 3. The device load factor on the horizontal axis represents the ratio of the total output power, which is the combination of the actual output power of the first power source 11 and the actual output power of the second power source 12, to the total rated output, which is the combination of the rated output of the first power source 11 and the rated output of the second power source 12.

[0038] When the load current IL is zero, the second output voltage V2 is set to a second voltage Vb lower than the first voltage Va set to the first output voltage V1. Therefore, as the load current IL increases from zero, the first output current I1 increases, but the second output current I2 remains at zero and does not increase. As the first output current I1 increases due to the increase in the load current IL, the first output voltage V1 gradually decreases from the first voltage Va in accordance with the first droop characteristic D1. When the first output voltage V1 decreases to the second voltage Vb, the first output voltage V1 becomes equal to the second output voltage V2 set to the second voltage Vb.

[0039] When the first output current I1 begins to exceed the current value Ib due to a further increase in the load current IL, the second power supply 12 begins to supply the second output current I2. As the output current IL increases from the current value Ib, the first power supply 11 further increases the first output current I1 from the current value Ib, and the second power supply 12 increases the second output current I2 from zero.

[0040] That is, the first power supply 11 reduces the first output voltage V1 from the second voltage Vb as the first output current I1 increases from the current value Ib in accordance with the first droop characteristic D1. Meanwhile, the second power supply 12 reduces the second output voltage V2 from the second voltage Vb as the second output current I2 increases from zero in accordance with the second droop characteristic D2. At this time, the second power supply 12 reduces the second output voltage V2 in accordance with the increase in the second output current I2 so that the second output voltage V2 is equal to the first output voltage V1.

[0041] However, in a low current region after the second output current I2 starts to flow, the second power supply 12 operates at a low-efficiency load factor (see FIG. 2). Therefore, when the detected second output current I2 rises above a predetermined threshold current Ith, the second power supply 12 switches the output characteristic of the first output voltage V1 with respect to the first output current I1 from the second droop characteristic D2 during standby operation to the first droop characteristic D1 during normal operation (see FIG. 3). As a result, the second power supply 12 operates according to the same first droop characteristic D1 as the first power supply 11, so that the output current IL is shared equally between the first power supply 11 and the second power supply 12. Therefore, as shown in FIG. 4, the first output current I1 decreases from a current value Ic to a current value Id, the second output current I2 increases from the threshold current Ith to a current value Id, and the first output voltage V1 and the second output voltage V2 increase from a third voltage Vc to a fourth voltage Vd. Therefore, when the second output current I2 rises above a predetermined threshold current Ith, the second output current I2 and the second output voltage V2 increase rapidly, causing the second power supply 12 to operate at a highly efficient load factor.

[0042] In a high current region where the second output current I2 is equal to or greater than the threshold current Ith, the first power supply 11 reduces the first output voltage V1 from the fourth voltage Vd as the first output current I1 increases from the current value Id in accordance with the first droop characteristic D1. Meanwhile, the second power supply 12 also reduces the second output voltage V2 from the fourth voltage Vd as the second output current I2 increases from the current value Id in accordance with the first droop characteristic D1.

[0043] Therefore, when the second output current I2 is higher than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in response to an increase in the second output current I2 so that the second output voltage V2 is equal to the first output voltage V1 and the second output current I2 is equal to the first output current I1. On the other hand, when the second output current I2 is higher than zero and lower than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in response to an increase in the second output current I2 so that the second output voltage V2 is equal to the first output voltage V1.

[0044] In this way, when the first output current I1 flowing through the first wiring 31 is zero, the first power supply 11 sets the first output voltage V1 to the first wiring 31 to the first voltage Va, and reduces the first output voltage V1 according to an increase in the first output current I1. When the second output current I2 flowing through the second wiring 32 connected to the first wiring 31 is zero, the second power supply 12 sets the second output voltage V2 to the second wiring 32 to the second voltage Vb lower than the first voltage Va, and supplies the second output current I2 when the first output voltage V1 drops to the second voltage Vb. Since the power supply unit 100 of this embodiment has such a configuration, in a low load state where the load current IL is low, the second output voltage V2 is maintained lower than the first output voltage V1. For this reason, the first power supply 11 bears most of the load current IL, so the first power supply 11 can be used at a highly efficient load factor, while the output of the second power supply 12 is stopped, so that the use of the second power supply 12 at a low load factor can be suppressed. Therefore, under low load conditions, a decrease in the efficiency of the entire power supply unit 100 can be suppressed.

[0045] Fig. 5 is a diagram showing the loss reduction effect when the output characteristics of each power source are set in the first setting example using the two droop characteristics of Fig. 3. The device load factor on the horizontal axis represents the ratio of the total output power, which is the combination of the actual output power of the first power source 11 and the actual output power of the second power source 12, to the total rated output, which is the combination of the rated output of the first power source 11 and the rated output of the second power source 12. The loss on the vertical axis represents the loss of the power source unit 100 (=input power of the power source unit 100-output power of the power source unit 100).

[0046] The "comparative example" represents a case where the output characteristics of the first power source 11 and the second power source 12 are both fixed to the first droop characteristic D1. The "first setting example" represents a case where the output characteristics of the first power source 11 are fixed to the first droop characteristic D1, and the output characteristics of the second power source 12 are switched from the second droop characteristic D2 to the first droop characteristic D1 as shown in FIG. 4.

[0047] In the "Comparative Example", the first power source 11 and the second power source 12 equally share the load current IL. Therefore, in a low load state, the first power source 11 and the second power source 12 operate at a low load factor. This increases the loss of the entire power source unit 100, and reduces the overall efficiency. On the other hand, in the "First Setting Example", in a low load state, the first power source 11 bears most of the load current IL. Therefore, the first power source 11 operates at a high load factor, while the second power source 12 does not operate at a low load factor. This prevents an increase in the loss of the entire power source unit 100, and prevents a decrease in the overall efficiency.

[0048] In the case of the "first setting example," the loss at a device load factor of about 30% temporarily increases. However, when the second output current I2 increases above the threshold current Ith, the output characteristic of the second power source 12 switches from the second droop characteristic D2 to the first droop characteristic D1, so that the second power source 12 can be prevented from continuing to operate at a low-efficiency load factor. Therefore, the decrease in efficiency of the entire power source unit 100 can be suppressed.

[0049] 6 is a diagram showing two droop characteristics used when setting the output characteristics of each power source in the second setting example. In the second setting example, the same explanation as in the first setting example will be omitted by citing the above explanation.

[0050] When the first power supply 11 is set to operate as a main power supply based on the signal S, the output characteristic of the first output voltage V1 relative to the first output current I1 is set to a first droop characteristic D1 during normal operation. On the other hand, when the second power supply 12 is set to operate as a standby power supply based on the signal S, the output characteristic of the second output voltage V2 relative to the second output current I2 is set to a third droop characteristic D3 during standby operation. The third droop characteristic D3 is Vout = Vb - Iout × (ΔV2 / Im) It is expressed as:

[0051] The second output voltage V2 when the second output current I2 is zero is offset by a voltage offset (Va-Vb) with respect to the first output voltage V1 when the first output current I1 is zero.

[0052] The second power supply 12 has a third droop characteristic D3 whose droop slope is gentler than the first droop characteristic D1, as shown in Fig. 6. As a result, when the first output voltage V1 decreases to the second voltage Vb, the second power supply 12 decreases the second output voltage V2 in response to an increase in the second output current I2 at a slope gentler than the slope at which the first output voltage V1 decreases in response to an increase in the first output current I1.

[0053] When the detected second output current I2 rises above a predetermined threshold current Ith, the second power supply 12 switches the output characteristic of the first output voltage V1 with respect to the first output current I1 from the third droop characteristic D3 during standby operation to the first droop characteristic D1 during normal operation. That is, when the second output current I2 is lower than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in response to an increase in the second output current I2 at a slope (third droop characteristic D3) that is gentler than the slope at which the first output voltage V1 decreases with respect to an increase in the first output current I1. On the other hand, when the second output current I2 is higher than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in response to an increase in the second output current I2 at the same slope (first droop characteristic D1) as the slope at which the first output voltage V1 decreases with respect to an increase in the first output current I1.

[0054] FIG. 7 is a diagram showing the relationship between the device load factor, the output current, and the output voltage when the output characteristics of each power supply are set in the second setting example using the two droop characteristics of FIG. 6. As in the first setting example, when the second output current I2 is higher than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in response to an increase in the second output current I2 so that the second output voltage V2 is aligned with the first output voltage V1 and the second output current I2 is aligned with the first output current I1. On the other hand, when the second output current I2 is higher than zero and lower than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in response to an increase in the second output current I2 so that the second output voltage V2 is aligned with the first output voltage V1. In the second setting example, as in the first setting example, the decrease in the efficiency of the entire power supply unit 100 can be suppressed under a low load condition.

[0055] FIG. 8 is a diagram showing the loss reduction effect when the output characteristics of each power source are set in the second setting example using the two droop characteristics of FIG. 6. The "comparison example" represents a case where the output characteristics of the first power source 11 and the second power source 12 are both fixed to the first droop characteristic D1. The "second setting example" represents a case where the output characteristics of the first power source 11 are fixed to the first droop characteristic D1, and the output characteristics of the second power source 12 are switched from the third droop characteristic D3 to the first droop characteristic D1 as shown in FIG. 7. In the second setting example, as in the first setting example, an increase in loss in the entire power source unit 100 is suppressed, and a decrease in the overall efficiency is suppressed.

[0056] 9 is a diagram showing two droop characteristics used when setting the output characteristics of each power source in setting example 3. Regarding setting example 3, the same explanation as in setting example 1 will be omitted by citing the above explanation.

[0057] When the first power supply 11 is set to operate as a main power supply based on the signal S, the output characteristic of the first output voltage V1 relative to the first output current I1 is set to a first droop characteristic D1 during normal operation. On the other hand, when the second power supply 12 is set to operate as a standby power supply based on the signal S, the output characteristic of the second output voltage V2 relative to the second output current I2 is set to a fourth droop characteristic D4 during standby operation. The fourth droop characteristic D4 is Vout = Vb (0≦Iout <Ib) Vout=Va-Iout×(ΔV1 / Im) (Ib≦Iout≦Im) It is expressed as:

[0058] The fourth droop characteristic D4 has a droop slope that is gentler than the first droop characteristic D1 in the current range from zero to less than the current value Ib, and has the same droop slope as the first droop characteristic D1 in the high current range above the current value Ib (more specifically, a characteristic that overlaps with the first droop characteristic D1).

[0059] In a high current region equal to or greater than the current value Ib, the second power supply 12 has a fourth droop characteristic D4 whose droop slope is the same as the first droop characteristic D1. As a result, when the first output voltage V1 decreases to the second voltage Vb, the second power supply 12 decreases the second output voltage V2 in response to an increase in the second output current I2 with the same slope as the slope at which the first output voltage V1 decreases in response to an increase in the first output current I1.

[0060] When the detected second output current I2 rises above a predetermined threshold current Ith, the second power supply 12 switches the output characteristic of the first output voltage V1 with respect to the first output current I1 from the fourth droop characteristic D4 during standby operation to the first droop characteristic D1 during normal operation. That is, when the second output current I2 is lower than the threshold current Ith, the second power supply 12 sets the output characteristic of the second output voltage V2 with respect to the second output current I2 to a slope that is gentler than the slope at which the first output voltage V1 decreases with respect to an increase in the first output current I1. The gentle slope in this example is the fourth droop characteristic D4 where the slope is zero. On the other hand, when the second output current I2 is higher than the threshold current Ith, the second power supply 12 decreases the second output voltage V2 in response to an increase in the second output current I2 with the same slope (first droop characteristic D1) as the slope at which the first output voltage V1 decreases with respect to an increase in the first output current I1.

[0061] FIG. 10 is a diagram showing the relationship between the device load factor, the output current, and the output voltage when the output characteristics of each power supply are set in the third setting example using the two droop characteristics of FIG. 9. As in the first setting example, when the second output current I2 is higher than the threshold current Ith, the second power supply 12 reduces the second output voltage V2 in accordance with an increase in the second output current I2 so that the second output voltage V2 is aligned with the first output voltage V1 and the second output current I2 is aligned with the first output current I1. When the second output current I2 is higher than zero and lower than the threshold current Ith, the second power supply 12 fixes the second output voltage V2 to the second voltage Vb while maintaining the second output current I2 at zero. In the second setting example, as in the first setting example, the decrease in the efficiency of the entire power supply unit 100 can be suppressed under a low load condition.

[0062] FIG. 11 is a diagram showing the loss reduction effect when the output characteristics of each power source are set in the third setting example using the two droop characteristics of FIG. 9. "Comparative Example" shows a case where the output characteristics of the first power source 11 and the second power source 12 are both fixed to the first droop characteristic D1. "Third Setting Example" shows a case where the output characteristics of the first power source 11 are fixed to the first droop characteristic D1, and the output characteristics of the second power source 12 are switched from the fourth droop characteristic D4 to the first droop characteristic D1 as shown in FIG. 10. In the third setting example, as in the first setting example, an increase in loss in the entire power source unit 100 is suppressed, and a decrease in the overall efficiency is suppressed.

[0063] Fig. 12 is a block diagram showing an example of the configuration of the power supplies. The first power supply 11 and the second power supply 12 may each have a configuration as shown in Fig. 12. The first power supply 11 and the second power supply 12 each have a power conversion circuit 41, a current sensor 42, a variable resistor 43, regulators 45 and 46, an amplifier 44, a PWM (Pulse Width Modulation) control unit 49, a register 47, and an output control unit 48.

[0064] The power conversion circuit 41 converts input power supplied from an external power supply into output power in accordance with a PWM signal generated by the PWM control unit 49. The power conversion circuit 41 has an AC / DC conversion circuit that converts alternating current (AC) supplied from the external power supply into direct current (DC) and outputs the DC, and a DC / DC conversion circuit that converts the direct current (DC) output from the AC / DC conversion circuit into direct current (DC) and outputs the DC.

[0065] In the first power supply 11, the current sensor 42 detects the first output current I1 and outputs a current sense signal proportional to the magnitude of the first output current I1. The current sense signal is input to a first input section of a regulator 46 such as an adder via a variable resistor 43. A constant reference voltage VREF is input to a second input section of the regulator 46 via a regulator 45 such as an adder. The sum of the current sense signal and the reference voltage VREF is input to a non-inverting input section of an amplifier 44. A voltage detection signal proportional to the magnitude of the first output voltage V1 detected by remote sensing is input to an inverting input section of the amplifier 44. The PWM control section 49 controls the duty ratio of a PWM signal that controls the switching of the power conversion circuit 41 according to the output signal of the amplifier 44. This makes it possible to realize a droop characteristic in which the first output voltage V1 is reduced according to an increase in the first output current I1. The second power supply 12 also has a similar configuration, making it possible to realize a droop characteristic in which the second output voltage V2 is reduced according to an increase in the second output current I2.

[0066] A first power supply 11 and a second power supply 12 are connected in parallel as a PSU (Power Supply Unit) capable of adjusting the droop slope and output voltage via PMBus. Before powering on each PSU, a device control unit 21 sets the droop slope and output voltage via PMBus. A PSU set as a standby power supply switches the droop characteristics based on the detection value of the output current it is supplying.

[0067] The device control unit 21 transmits, for example, a signal S for setting whether to operate as a standby power supply via the PMBus. The first power supply 11 and the second power supply 12 each have a register 47 for setting whether to operate as a main power supply or a standby power supply. When the device control unit 21 operates the second power supply 12 as a standby power supply, it sets a flag for operating as a standby power supply in the register 47 within the second power supply 12. When the device control unit 21 operates the first power supply 11 as a main power supply, it sets a flag for operating as a main power supply in the register 47 within the first power supply 11, or does not set a flag for operating as a standby power supply in the register 47 within the first power supply 11.

[0068] The output control unit 48 sets whether the power supply it controls operates as a main power supply or a standby power supply according to the flag set in the register 47. The output control unit 48 adjusts the resistance value of the variable resistor 43 and the voltage value to be added to the reference voltage VREF by the regulator 45 according to the setting of the flag for whether the power supply it controls operates as a main power supply or a standby power supply. The output control unit 48 can adjust the droop slope by adjusting the resistance value of the variable resistor 43, and can adjust the voltage offset of the droop characteristic by adjusting the voltage value to be added to the reference voltage VREF. In this way, when the output control unit 48 operates the power supply it controls as a main power supply, it can adjust the output characteristic to a desired droop characteristic such as the droop characteristic D1 described above. On the other hand, when the output control unit 48 operates the power supply it controls as a standby power supply, it can adjust the output characteristic to a desired droop characteristic such as the droop characteristics D2, D3, and D4 described above.

[0069] 13 is a diagram illustrating an adjustment circuit for the droop slope and offset. The above-mentioned adjusters 45, 46 have, for example, amplifiers 45a, 46a. The output control unit 48 adjusts the reference voltage VREF by adjusting the offset voltage input to the amplifier 45a, thereby adjusting the voltage offset of the droop characteristic. The output control unit 48 adjusts the voltage of the current sense signal input to the amplifier 46a by adjusting the resistance value of the variable resistor 43, thereby adjusting the droop slope.

[0070] 14 is a flowchart showing an example of the operation of the device control unit. In step S11, device control unit 21 sets the output characteristics of each of first power source 11 and second power source 12. Device control unit 21 sets a flag by, for example, PMBus, indicating whether each power source is to operate as a main power source or a standby power source. In step S13, device control unit 21 turns on the power of each power source.

[0071] 15 is a flow chart showing an example of the operation of the power supplies. The first power supply 11 and the second power supply 12 are started by a power-on signal from the device control unit 21. In step S21, the output control unit 48 of each of the first power supply 11 and the second power supply 12 refers to a flag stored in its own register 47, and determines whether or not a standby flag for operating in standby mode is set. If the standby flag is not set, the output control unit 48 sets the output characteristics of its own power supply to droop characteristics during normal operation in order to operate the power supply as a main power supply (step S23).

[0072] When the standby flag is set, the output control unit 48 operates its own power supply as a standby power supply. In this case, the output control unit 48 judges whether the output current of its own power supply is less than the threshold current Ith (step S25). When the output current is equal to or less than the threshold current Ith, the output control unit 48 sets the output characteristics of its own power supply to the droop characteristics during standby operation (step S27). When the output current is greater than the threshold current Ith, the output control unit 48 sets the output characteristics of its own power supply to the droop characteristics during normal operation (step S29). Steps S25, S27, and S29 enable switching of the droop characteristics.

[0073] 16 is a hardware configuration diagram of the control unit. The device control unit 21 or the control units in each power supply (such as the output control unit 48 and the PWM control unit 49) may be realized by a configuration like that of a control device 500. The control device 500 has a drive device 508, an auxiliary storage device 502, a memory device 503, a CPU (Central Processing Unit) 504, an interface device 505, and the like, which are mutually connected by a bus 506.

[0074] A program for realizing the processing in the control device 500 is provided by a recording medium 507. When the recording medium 507 on which the program is recorded is set in the drive device 508, the program is installed from the recording medium 507 via the drive device 508 into the auxiliary storage device 502. However, the program does not necessarily have to be installed from the recording medium 507, but may be downloaded from another computer via a network. The auxiliary storage device 502 stores the installed program as well as necessary files, data, etc.

[0075] When an instruction to start a program is received, the memory device 503 reads out the program from the auxiliary storage device 502 and stores it. The CPU 504 is a processor that executes functions related to the control device 500 in accordance with the program stored in the memory device 503. The interface device 505 is used as an interface for connecting to the outside.

[0076] An example of the recording medium 507 is a portable recording medium such as a CD-ROM, a DVD disk, or a USB memory. An example of the auxiliary storage device 502 is a hard disk drive (HDD) or a flash memory. Both the recording medium 507 and the auxiliary storage device 502 correspond to computer-readable recording media.

[0077] A program for causing the control device 500 to execute each of the processes described above may be stored in the auxiliary storage device 502. The DB 501 may be stored in the auxiliary storage device 502 or the memory device 503.

[0078] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0079] The following supplementary notes are further disclosed regarding the above embodiment. (Appendix 1) a first power supply that sets a first output voltage to a first wiring to a first voltage when a first output current flowing through the first wiring is zero, and reduces the first output voltage in response to an increase in the first output current; a second power supply that sets a second output voltage to the second wiring to a second voltage lower than the first voltage when a second output current flowing in a second wiring connected to the first wiring is zero, and supplies the second output current when the first output voltage drops to the second voltage. (Appendix 2) 2. The power supply unit of claim 1, wherein the second power supply reduces the second output voltage in response to an increase in the second output current when the first output voltage reduces to the second voltage. (Appendix 3) 3. The power supply unit according to claim 1, wherein when the first output voltage drops to the second voltage, the second power supply reduces the second output voltage in response to an increase in the second output current so that the second output voltage becomes equal to the first output voltage. (Appendix 4) 4. The power supply unit according to claim 1, wherein when the first output voltage drops to the second voltage, the second power supply reduces the second output voltage in response to an increase in the second output current so that the second output voltage becomes equal to the first output voltage and the second output current becomes equal to the first output current. (Appendix 5) 5. The power supply unit according to claim 1, wherein, when the second output current is higher than a threshold current, the second power supply reduces the second output voltage in response to an increase in the second output current so that the second output voltage is aligned with the first output voltage and the second output current is aligned with the first output current. (Appendix 6) 6. The power supply unit of claim 5, wherein the second power supply reduces the second output voltage in response to an increase in the second output current when the second output current is lower than the threshold current, so that the second output voltage is aligned with the first output voltage. (Appendix 7) 3. The power supply unit of claim 2, wherein when the first output voltage drops to the second voltage, the second power supply reduces the second output voltage in response to an increase in the second output current with the same slope as a slope at which the first output voltage drops in response to an increase in the first output current. (Appendix 8) 3. The power supply unit of claim 2, wherein when the first output voltage drops to the second voltage, the second power supply reduces the second output voltage in response to an increase in the second output current at a slope that is gentler than a slope at which the first output voltage drops in response to an increase in the first output current. (Appendix 9) The second power source is When the second output current is lower than a threshold current, the second output voltage is reduced in response to an increase in the second output current at a slope that is gentler than a slope at which the first output voltage is reduced in response to an increase in the first output current; 3. The power supply unit of claim 2, wherein, when the second output current is higher than the threshold current, the second output voltage is reduced in response to an increase in the second output current with the same slope as a slope at which the first output voltage is reduced in response to an increase in the first output current. (Appendix 10) A method for controlling a power supply unit including a first power supply that supplies a first output current to a first wiring and a second power supply that supplies a second output current to a second wiring connected to the first wiring, comprising: When the first output current is zero, a first output voltage from the first power supply to the first wiring is set to a first voltage, and the first output voltage is reduced in response to an increase in the first output current; A method for controlling a power supply unit, comprising: setting a second output voltage from the second power supply to the second wiring to a second voltage lower than the first voltage when the second output current is zero; and supplying the second output current from the second power supply to the second wiring when the first output voltage drops to the second voltage. (Appendix 11) 11. The method of controlling a power supply unit according to claim 10, further comprising: when the first output voltage decreases to the second voltage, decreasing the second output voltage in response to an increase in the second output current. (Appendix 12) 12. The method for controlling a power supply unit according to claim 10 or 11, wherein when the first output voltage drops to the second voltage, the second output voltage is lowered in accordance with an increase in the second output current so that the second output voltage becomes equal to the first output voltage. (Appendix 13) 13. The method for controlling a power supply unit according to any one of Addenda 10 to 12, wherein when the first output voltage drops to the second voltage, the second output voltage is lowered in accordance with an increase in the second output current so that the second output voltage becomes equal to the first output voltage and the second output current becomes equal to the first output current. (Appendix 14) 14. The method of controlling a power supply unit according to any one of claims 10 to 13, wherein, when the second output current is higher than a threshold current, the second output voltage is reduced in accordance with an increase in the second output current so that the second output voltage is aligned with the first output voltage and the second output current is aligned with the first output current. (Appendix 15) 15. The method of controlling a power supply unit of claim 14, wherein when the second output current is lower than the threshold current, the second output voltage is reduced in response to an increase in the second output current so that the second output voltage is aligned with the first output voltage. (Appendix 16) 12. The method for controlling a power supply unit according to claim 11, wherein, when the first output voltage drops to the second voltage, the second output voltage is lowered in response to an increase in the second output current with the same slope as a slope at which the first output voltage drops in response to an increase in the first output current. (Appendix 17) 12. The method for controlling a power supply unit according to claim 11, wherein, when the first output voltage drops to the second voltage, the second output voltage is lowered in response to an increase in the second output current at a slope that is gentler than a slope at which the first output voltage drops in response to an increase in the first output current. (Appendix 18) When the second output current is lower than a threshold current, the second output voltage is reduced in response to an increase in the second output current at a slope that is gentler than a slope at which the first output voltage is reduced in response to an increase in the first output current; 12. The method for controlling a power supply unit according to claim 11, wherein, when the second output current is higher than the threshold current, the second output voltage is reduced in response to an increase in the second output current with the same slope as a slope at which the first output voltage is reduced in response to an increase in the first output current. [Explanation of symbols]

[0080] 11 1st power supply 12 2nd power supply 21 Device control section 22 Load 31 1st wiring 32 2nd wiring 33 Connection points 41 Power Conversion Circuit 100 Power Supply Units 200 Electronic equipment 500 Control device

Claims

1. a first power supply that sets a first output voltage to a first wiring to a first voltage when a first output current flowing through the first wiring is zero, and reduces the first output voltage in response to an increase in the first output current; a second power supply that sets a second output voltage to the second wiring to a second voltage lower than the first voltage when a second output current flowing in a second wiring connected to the first wiring is zero, and supplies the second output current when the first output voltage drops to the second voltage.

2. 2 . The power supply unit according to claim 1 , wherein the second power supply reduces the second output voltage in response to an increase in the second output current when the first output voltage reduces to the second voltage.

3. 3. The power supply unit of claim 2, wherein the second power supply reduces the second output voltage in response to an increase in the second output current so that the second output voltage becomes equal to the first output voltage when the first output voltage decreases to the second voltage.

4. 4. The power supply unit of claim 3, wherein the second power supply reduces the second output voltage in response to an increase in the second output current such that, when the first output voltage reduces to the second voltage, the second output voltage becomes equal to the first output voltage and the second output current becomes equal to the first output current.

5. 5. The power supply unit of claim 4, wherein the second power supply reduces the second output voltage in response to an increase in the second output current when the second output current is higher than a threshold current, so that the second output voltage matches the first output voltage and the second output current matches the first output current.

6. 6. The power supply unit of claim 5, wherein the second power supply reduces the second output voltage in response to an increase in the second output current when the second output current is lower than the threshold current, so that the second output voltage is aligned with the first output voltage.

7. 3. The power supply unit according to claim 2, wherein when the first output voltage drops to the second voltage, the second power supply reduces the second output voltage in response to an increase in the second output current with a slope equal to a slope at which the first output voltage drops in response to an increase in the first output current.

8. 3. The power supply unit according to claim 2, wherein when the first output voltage drops to the second voltage, the second power supply reduces the second output voltage in response to an increase in the second output current at a slope that is gentler than a slope at which the first output voltage drops in response to an increase in the first output current.

9. The second power source is When the second output current is lower than a threshold current, the second output voltage is reduced in response to an increase in the second output current at a slope that is gentler than a slope at which the first output voltage is reduced in response to an increase in the first output current; 3. The power supply unit according to claim 2, wherein when the second output current is higher than the threshold current, the second output voltage is reduced in response to an increase in the second output current with the same slope as a slope at which the first output voltage is reduced in response to an increase in the first output current.

10. 1. A method for controlling a power supply unit including a first power supply that supplies a first output current to a first wiring and a second power supply that supplies a second output current to a second wiring connected to the first wiring, comprising: When the first output current is zero, a first output voltage from the first power supply to the first wiring is set to a first voltage, and the first output voltage is reduced in response to an increase in the first output current; A method for controlling a power supply unit, comprising: setting a second output voltage from the second power supply to the second wiring to a second voltage lower than the first voltage when the second output current is zero; and supplying the second output current from the second power supply to the second wiring when the first output voltage drops to the second voltage.

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