JP2009171670A - Power circuit and power system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power circuit and a power system which can control their start up properties. <P>SOLUTION: The power circuit includes: a voltage output part 11; a voltage controller 12 which compares a feedback voltage Vfb geared to the output voltage Vout with a reference voltage Vref and feeds it back to the voltage output part 11 thereby controlling it; a first selecting circuit 13 that selects a first feedback voltage Vref1 equal to the output voltage Vout or a second feedback voltage Vref being obtained by dividing the output voltage Vout, as the feedback voltage Vfb; a second selecting circuit 14 that selects the first reference voltage Vref1 or the second reference voltage Vref2, as the feedback voltage Vfre; a comparator circuit 15 that compares the second feedback voltage Vfb2 with the second reference voltage Vref2; and a voltage selection means 16 which selects the first feedback voltage Vfb1 and the first reference voltage Vref1 when the second feedback voltage Vfb2 is equal to or lower than the second reference voltage Vref2 and which selects the second feedback voltage Vfb2 and the second reference voltage Vref2 when the second feedback voltage Vfb2 is equal to or higher than the second reference voltage Vref2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a power supply circuit and a power supply system.

  In an electronic device using an integrated circuit, a plurality of power supply voltages are generated and used from a commercial power supply using a linear regulator, a switching regulator, or the like.

  Conventionally, when a plurality of power supply voltages are simultaneously applied to an integrated circuit that operates with a plurality of power supply voltages using an operation start signal, the rising characteristics of the power supply voltages vary due to manufacturing variations of the power supply circuit elements and changes over time. There was a problem. For this reason, there is a risk of hindering the operation of the integrated circuit.

  On the other hand, a multi-output power supply circuit that matches rising / falling characteristics of a plurality of reference power supplies is known (see, for example, Patent Document 1).

The power supply circuit disclosed in Patent Document 1 is a multiple output power supply circuit that generates a plurality of reference voltages from an original reference voltage, and based on the rising and falling characteristics of the original reference voltage, A control circuit that matches the rising and falling characteristics of each of the plurality of reference voltages is provided in series with the plurality of reference voltages.
The control circuit includes switching means connected in series to the plurality of reference voltages, and a control terminal of the switching means is connected to a bias circuit. The bias circuit is connected to one end of the plurality of reference voltages from the original reference voltage via a Zener diode, a resistor element, a capacitor element, a control terminal, and a variable resistor element.

However, since the power supply circuit disclosed in Patent Document 1 delays the first output voltage to match the rising and falling characteristics of the second and third output voltages, the rising and falling characteristics of all output voltages. There is a problem that cannot be matched.
In addition, since the control circuits that match the rising and falling characteristics are connected in series, there is a problem that voltage loss occurs in the control circuit and wasteful power is consumed.
JP-A-8-317553

  The present invention provides a power supply circuit and a power supply system whose rise characteristics can be controlled.

  A power supply circuit of one embodiment of the present invention is connected between a power supply voltage and a reference potential, and compares a voltage output unit that outputs an output voltage obtained by transforming the power supply voltage with a feedback voltage corresponding to the output voltage and a reference voltage. And a voltage control unit that performs feedback control to the voltage output unit so that the feedback voltage is equal to the reference voltage, and the feedback voltage is obtained by dividing the first feedback voltage or the output voltage that is equal to the output voltage. A first selection circuit that selects the second feedback voltage; and a first reference voltage that serves as a reference for the first feedback voltage or a second reference voltage that serves as a reference for the second feedback voltage as the reference voltage. And a comparison circuit that compares the second feedback voltage with the second reference voltage, and when the second feedback voltage is equal to or lower than the second reference voltage, the first feedback voltage and the second feedback voltage Select the first reference voltage, before When the second feedback voltage is more than the second reference voltage, it is characterized by comprising a voltage selecting means for selecting the second feedback voltage and the second reference voltage.

  A power supply system according to an aspect of the present invention compares a voltage output unit connected between a power supply voltage and a reference potential and outputs an output voltage obtained by transforming the power supply voltage, and a feedback voltage corresponding to the output voltage and a reference voltage And a voltage control unit that performs feedback control to the voltage output unit so that the feedback voltage is equal to the reference voltage, and the feedback voltage is obtained by dividing the first feedback voltage or the output voltage that is equal to the output voltage. A first selection circuit that selects the second feedback voltage; and a first reference voltage that serves as a reference for the first feedback voltage or a second reference voltage that serves as a reference for the second feedback voltage as the reference voltage. And a comparison circuit that compares the second feedback voltage with the second reference voltage, and when the second feedback voltage is equal to or lower than the second reference voltage, the first feedback voltage and the second feedback voltage Select the first reference voltage A plurality of power supply circuits comprising: a voltage selection means for selecting the second feedback voltage and the second reference voltage when the second feedback voltage is equal to or higher than the second reference voltage; The power supply circuit having the highest setting voltage equal to the second reference voltage is set as a master, and the power supply circuit excluding the master is set as a slave, and the master previously stores the second feedback voltage and the second reference voltage. The slave sets the first reference voltage equal to the output voltage of the master, so that the output voltage of the slave tracks the output voltage of the master and rises to the set voltage. And a second control mode in which the output voltage of the slave is maintained at the set voltage.

  According to the present invention, it is possible to obtain a power supply circuit and a power supply system whose rise characteristics can be controlled.

  Embodiments of the present invention will be described below with reference to the drawings.

  A power supply circuit according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a circuit diagram showing a power supply circuit according to the first embodiment, FIG. 2 is a circuit diagram showing a selection circuit of the power supply circuit, and FIG. 3 is a timing chart showing the operation of the power supply circuit.

  As shown in FIG. 1, the power supply circuit 10 of this embodiment is connected between a power supply voltage Vin and a reference potential GND, and outputs a voltage output unit 11 that outputs an output voltage Vout obtained by transforming the power supply voltage Vin. A voltage control unit 12 that compares the corresponding feedback voltage Vfb with the reference voltage Vref and performs feedback control to the power supply unit 11 so that the feedback voltage Vfb becomes equal to the reference voltage Vref is provided.

  Further, the power supply circuit 10 includes a first selection circuit 13 that selects the first feedback voltage Vfb1 equal to the output voltage Vout or the second feedback voltage Vfb2 obtained by dividing the output voltage Vout as the feedback voltage Vfb, and the reference voltage Vref. The second selection circuit 14 selects the first reference voltage Vref1 serving as the reference of the first feedback voltage Vfb1 or the second reference voltage Vref2 serving as the reference of the second feedback voltage Vfb2, and the second feedback voltage Vfb2 and the second reference. A comparison circuit 15 that compares the voltage Vref2 with the second feedback voltage Vfb2, and when the second feedback voltage Vfb2 is equal to or lower than the second reference voltage Vref2, the first feedback voltage Vfb1 and the first reference voltage Vref1 are selected and the second feedback voltage Vfb2 Voltage selecting means for selecting the second feedback voltage Vfb2 and the second reference voltage Vref2 when the voltage is equal to or higher than the second reference voltage Vref2 It is equipped with 6, a.

  The voltage output unit 11 includes an output circuit 17 having a first transistor M1 and a second transistor M2 connected in series, a comparator 18 that compares, for example, a triangular wave repetition signal Vosc and a control signal Ver, and a comparison result of the comparator 18 And a drive circuit 19 for driving the output circuit 17 according to the above.

  In the output circuit 17, the first transistor M1 is, for example, a p-channel insulated gate field effect transistor (hereinafter referred to as a p-MOS transistor), and the second transistor M2 is, for example, an n-channel insulated gate field effect transistor (hereinafter, n-type). -Referred to as a MOS transistor) and connected to a so-called toten pole type.

  The source of the first transistor M1 is connected to the power supply voltage Vin, the drain of the first transistor M1 is connected to the drain of the second transistor M2, and the source of the second transistor M2 is connected to the reference potential GND. The gates of the first and second transistors M1 and M2 are connected to the control circuit 19, respectively.

  A connection node N1 between the drain of the first transistor M1 and the drain of the second transistor M2 is connected to a smoothing circuit of an inductor L and a capacitor C that smoothes the PWM-controlled DC voltage of the output circuit 17, for example, a power supply voltage A smoothed output voltage Vout of about 1.2 to 3.3 V with respect to Vin of 3 to 5 V is supplied to a load (not shown).

  The voltage control unit 12 has a negative input terminal connected to the common terminal z of the first selection circuit 13, a positive input terminal connected to the common terminal z of the second selection circuit 14, and an output terminal connected to the positive input terminal of the comparator 18. A connected differential amplifier 20 is provided.

The first selection circuit 13 and the second selection circuit 14 are double throw switches having, for example, MOS transistors (hereinafter, the selection circuit is also referred to as a double throw switch).
The double throw switch has a first terminal x, a second terminal y, and a common terminal z. The first terminal x is a normally-on contact, and the second terminal y is a normally-off contact.

The first selection circuit 13 has resistors R1, R2 whose first terminal x is connected to a first feedback voltage Vfb1 equal to the output voltage Vout, and whose second terminal y divides the output voltage Vout to generate a second feedback voltage Vfb2. Connected to the connection node N2.
Here, it is desirable that the first terminal x is connected to the reference potential GND via the resistor R3 so that the differential amplifier 20 operates stably.

  The double throw switch 14 has a first terminal x connected to the first reference voltage Vref1 supplied from the outside, and a second terminal y connected to the internal second reference voltage Vref2.

  The comparison circuit 15 is, for example, a comparator, a positive input terminal is connected to the node N2, a negative input terminal is connected to the second reference voltage Vref2, and an output terminal is connected to the control terminals of the first selection circuit 13 and the second selection circuit 14. It is connected.

  The comparison circuit 15 outputs a selection signal Vslt of “L” level when the second feedback voltage Vfb2 is equal to or lower than the second reference voltage Vref2, and when the second feedback voltage Vfb2 is equal to or higher than the second reference voltage Vref2, The level selection signal Vslt is output.

FIG. 2 is a circuit diagram showing a double throw switch 13 using two MOS transistors and configured to operate complementarily to each other.
As shown in FIG. 2, there are provided n-MOS transistors 30 and 31 whose sources are commonly connected, and an inverter 32 that connects the gate of the n-MOS transistor 30 and the gate of the n-MOS transistor 31.

  The double throw switch 13 is configured such that when the selection signal Vslt is at “L” level, the n-MOS transistor 30 is turned on, the n-MOS transistor 31 is turned off, and when the selection signal Vslt is at “H” level, 30 turns off and the n-MOS transistor 31 turns on.

  Accordingly, the commonly connected source of the n-MOS transistors 30 and 31 becomes the common terminal z of the double throw switch 13, and the drain of the n-MOS transistor 30 through the inverter 32 becomes the first terminal x of the double throw switch 13. The drain of the n-MOS transistor 31 becomes the second terminal y of the double throw switch 13. The same applies to the double throw switch 14, and the description thereof is omitted.

  When the operation start signal EN is input from the outside, the power supply circuit 10 is set so that power is supplied to the power supply circuit 10 and the voltage output unit 11, the voltage control unit 12, and the voltage selection unit 16 start operation. Yes.

  Since the voltage output unit 11 is connected to the output circuit 17 and the smoothing circuit of the inductor L and the capacitor C having a large time constant, the rise of the voltage output unit 11 is slower than that of the voltage control unit 12 and the voltage selection unit 16. That is, the rise times of the voltage control unit 12 and the voltage selection means 16 are substantially negligible compared to the rise time of the output voltage Vout.

  FIG. 3 is a timing chart showing the operation of the power supply circuit 10 and shows a case where the operation start signal EN is input from the outside and the first reference signal Vref1 rising in a ramp shape is input from the outside.

  As shown in FIG. 3, when the operation start signal EN is input to the power supply circuit 10 when the time t is t0, the voltage control unit 12 and the voltage selection unit 16 start operation instantaneously, and the second feedback voltage Since Vref2 is equal to or lower than the second reference voltage Vref2, the selection signal Vslt becomes “L” level.

As a result, the first feedback voltage Vfb1 is selected as the feedback voltage Vfb, and the first reference signal Vref1 is selected as the reference signal.
The output voltage Vout is feedback-controlled so that the first feedback voltage Vfb1 is equal to the first reference signal Vref1 that rises in a ramp shape, and thus rises by tracking the first reference signal Vref1.

  Next, when the output voltage Vout reaches the set voltage Vset at which the second feedback voltage Vfb2 is equal to the second reference voltage Vref2 when the time t is t1, the second feedback voltage Vfb2 is equal to or higher than the second reference voltage Vref2. The selection signal Vslt becomes “H” level.

As a result, the second feedback voltage Vfb2 is selected as the feedback voltage Vfb, and the second reference signal Vref2 is selected as the reference signal.
The output voltage Vout is feedback-controlled so that the second feedback voltage Vfb2 is equal to the constant second reference signal Vref2, and thus is maintained at the set voltage Vset.

Here, after the output voltage Vout reaches the set voltage Vset and the selection signal Vslt becomes “H” level, the selection signal Vslt needs to be held at “H” level.
Specifically, an RS flip-flop that is reset every time the operation start signal EN is input is connected to the output terminal of the comparison circuit 15, and when the comparison circuit 15 outputs “H” level, the RS flip-flop compares The output of the circuit 15 may be latched so as to keep the “H” level.

  The time t is from t0 to t1 is the first control mode in which the output voltage Vout rises by tracking the first reference voltage Vref1, and when the time t is after t1, the output voltage Vout is maintained at the set voltage Vset. The second control mode.

  Therefore, it is possible to raise the output voltage Vout to the set voltage Vset by tracking the first reference voltage Vref1.

  As described above, the power supply circuit 10 of this embodiment selects the first feedback voltage Vfb1 and the first reference voltage Vref1 when the second feedback voltage Vfb2 is equal to or lower than the second reference voltage Vref2, and the second feedback voltage. Voltage selection means 16 is provided for selecting the second feedback voltage Vfb2 and the second reference voltage Vref2 when Vfb2 is equal to or higher than the second reference voltage Vref2.

  As a result, the first reference voltage Vref1 can be tracked and the output voltage Vout can be raised to the set voltage Vset. Therefore, the power supply circuit 10 whose rise characteristics can be controlled is obtained.

  Although the case where the first reference voltage Vref1 rises in a ramp shape has been described here, it may be a voltage that rises in a staircase shape, an exponential function shape, or an S shape. The starting characteristic of the power supply circuit 10 can be set flexibly according to the rising characteristic of the first reference voltage Vref1.

  Although the case where the first and second selection circuits 13 and 14 are double throw switches using two n-MOS transistors has been described, double throw using a transmission gate having a p-MOS transistor and an n-MOS transistor. It does not matter as a switch.

Although the case where the first and second transistors M1 and M2 of the output circuit 17 are MOS transistors has been described, the output circuit 17 may be formed of a bipolar transistor or an insulated gate bipolar transistor (IGBT).
In the case of using a bipolar transistor or IGBT, unlike a MOS transistor, it does not have a parasitic diode. Therefore, it is necessary to externally attach a diode for releasing a regenerative current.

Although the case where the voltage output unit 10 is a step-down DC-DC converter has been described, another voltage output unit may be used.
For example, a step-up DC-DC converter shown in FIG. Moreover, the linear regulator shown in FIG.4 (b) may be sufficient.

  Although the case where the repetitive signal Vosc is a triangular wave has been described, another repetitive signal such as a trapezoidal wave may be used.

  A power supply system according to Embodiment 2 of the present invention will be described with reference to FIGS. 5 is a block diagram showing the configuration of the power supply system, FIG. 6 is a timing chart showing the operation of the power supply system in comparison with the comparative example, FIG. 6A is a timing chart showing the present embodiment, and FIG. ) Is a timing chart showing a comparative example.

In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, description thereof will be omitted, and only different portions will be described.
This embodiment is different from the first embodiment in that a master power supply and a slave power supply are provided so that the slave power supply starts up by tracking the master power supply.

That is, as shown in FIG. 5, the power supply system 50 of this embodiment is a system that supplies the same three power supply circuits 51, 52, and 53 as the power supply circuit 10, and the operation start signal EN to the power supply circuits 51, 52, and 53 Contra 54 is provided.
The power supply system 50 rises in response to the operation start signal EN and supplies the output voltages Vout1, Vout2, and Vout3 to the system LSI 55 that is a load.

  The set voltage Vset1 of the power supply circuit 51 is set higher than the set voltages Vset2 and Vset3 of the power supply circuits 52 and 53. The set voltage Vset3 of the power supply circuit 53 is set higher than the set voltage Vset2 of the power supply circuit 52. That is, there is a relationship of Vset2 <Vset3 <Vset1.

In the power supply circuit 51, the first and second selection circuits 13 and 14 are fixed so that the second feedback voltage Vfb2 and the second reference voltage Vref2 are selected in advance.
As the first reference voltage Vref1 of the power supply circuits 52 and 53, the output voltage Vout1 of the power supply circuit 51 is supplied.
Thus, in the power supply system 50, the power supply circuit 51 having the highest setting voltage Vset operates as a master, and the power supply circuits 52 and 53 operate as slaves. The output voltages Vout2 and Vout3 of the slaves 52 and 53 track the output voltage Vout1 of the master 51 and rise to the set voltages Vest2 and Vset3.

6 is a timing chart showing the operation of the power supply system 50 in comparison with the comparative example. FIG. 6A is a timing chart showing the present embodiment, and FIG. 6B is a timing chart showing the comparative example.
Here, in the comparative example, the first and second selection circuits 13 and 14 are fixed so that the second feedback voltage Vfb2 and the second reference voltage Vref2 are selected in advance in the power supply circuits 51, 52, and 53. Means power system. First, a comparative example will be described.

  As shown in FIG. 6B, in the comparative example, the output voltages Vout1, Vout2, and Vout3 of the power supply circuits 51, 52, and 53 rise independently by the operation start signal EN. The rise characteristics of the output voltages Vout1, Vout2, and Vout3 are deviated due to manufacturing variations and changes with time of the elements used. For example, the rising slope is not constant, and the rising characteristics vary.

  On the other hand, in this embodiment, the output voltage Vout1 of the power supply circuit 51 rises to the set voltage Vset1 independently by the operation start signal EN, and the output voltages Vout2 and Vout3 of the power supply circuits 52 and 53 become the output voltage Vout1 of the power supply circuit 51. To rise to the set voltages Vset2 and Vset3.

  Thereafter, the output voltages Vout1, Vout2, and Vout3 of the power supply circuits 51, 52, and 53 are independently maintained at the set voltages Vset1, Vset2, and Vset3.

Specifically, at time t1, the output voltage Vout2 of the power supply circuit 52 reaches the set voltage Vset2, and the output voltage Vout2 is maintained at the set voltage Vset2.
At time t2, the output voltage Vout3 of the power supply circuit 53 reaches the set voltage Vset3, and the output voltage Vout3 is maintained at the set voltage Vset3.
At time t3, the output voltage Vout1 of the power supply circuit 51 reaches the set voltage Vset1, and the output voltage Vout1 is maintained at the set voltage Vset1.
Therefore, the power supply circuit 51 is in the first control mode until time t3, and the second control mode thereafter. The power supply circuit 52 is in the first control mode until time t1, and the second control mode is thereafter. The power supply circuit 53 is in the first control mode until time t2, and the second control mode is thereafter.

  As a result, the output voltages Vout1, Vout2, and Vout3 of the power supply system 50 can be raised together without being affected by variations in device manufacturing and changes over time.

As described above, the power supply system 50 of this embodiment operates with the power supply circuit 51 having the highest setting voltage Vset as a master and the power supply circuits 52 and 53 as slaves.
As a result, the output voltages Vout2 and Vout3 of the power supply circuits 52 and 53 can track the output voltage Vout1 of the power supply circuit 51 and rise to the set voltages Vset2 and Vset3. Therefore, the power supply system 50 whose rise characteristics can be controlled is obtained.

  Although the case where there are two power supply circuits serving as slaves has been described here, the number of power supply circuits serving as slaves is not particularly limited.

Although the case where the output voltages of the power supply circuits 51, 52, and 53 have a relationship of Vset2 <Vset3 <Vset1 has been described, a relationship of Vset2 = Vset3 <Vset1 may be used.
Furthermore, a relationship of Vset2 = Vset3 = Vset1 is possible. In that case, any power supply circuit may be used as a master.

A power supply system according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 7 is a block diagram showing the configuration of the power supply system. In the present embodiment, the same components as those in the second embodiment are denoted by the same reference numerals, description thereof is omitted, and only different portions will be described.
This embodiment is different from the second embodiment in that the first reference voltage is supplied from an external power source.

  That is, as shown in FIG. 7, the power supply circuit 60 is supplied with the first reference voltage Vref <b> 1 of the power supply circuits 51, 52, 53 from the external power supply 61.

As a result, the output voltages Vout1, Vout2, and Vout3 of the power supply circuits 51, 52, and 53 are tracked to the voltages supplied from the external power supply 61 and rise to the set voltages Vset1, Vset2, and Vset3.
Thereafter, the output voltages Vout1, Vout2, and Vout3 of the power supply circuits 51, 52, and 53 are independently maintained at the set voltages Vset1, Vset2, and Vset3.

  The external power supply 61 has an output voltage higher than the set voltages Vset1, Vset2, and Vset3 of the power supply circuits 51, 52, and 53, and has a rising characteristic that is slower than the rising characteristics of the output voltages of the power supply circuits 51, 52, and 53. It is necessary to have.

As described above, the power supply system 61 of this embodiment supplies the first reference voltage of the power supply circuits 51, 52, 53 from the external power supply 16.
As a result, there is an advantage that the startup characteristic of the power supply system 61 can be set flexibly according to the rising characteristic of the voltage supplied from the external power supply 16.

1 is a circuit diagram showing a configuration of a power supply circuit according to Embodiment 1 of the present invention. 1 is a circuit diagram showing a selection circuit of a power supply circuit according to Embodiment 1 of the present invention. 3 is a timing chart showing the operation of the power supply circuit according to the first embodiment of the present invention. The circuit diagram which shows another voltage output part of the power supply circuit which concerns on Example 1 of this invention. The block diagram which shows the structure of the power supply system which concerns on Example 2 of this invention. FIG. 6A is a timing chart showing the operation of the power supply system according to the second embodiment of the present invention in comparison with the comparative example, FIG. 6A is a timing chart showing the present embodiment, and FIG. 6B is a timing chart showing the comparative example. . The block diagram which shows the structure of the power supply system which concerns on Example 3 of this invention.

Explanation of symbols

10, 51, 52, 53 Power supply circuit 11 Voltage output unit 12 Voltage control unit 13 First selection circuit 14 Second selection circuit 15 Comparison circuit 16 Voltage selection means 17 Output circuit 18 Comparator 19 Drive circuit 20 Differential amplifier M1 First transistor M2 Second transistor L Inductor C Capacitors R1, R2, R3 Resistor Vin Power supply voltage Vout Output voltage Vfb Feedback voltage Vfb1 First feedback voltage Vfb2 Second feedback voltage Vref Reference voltage Vref1 First reference voltage Vref2 Second reference voltage 30, 31 n -MOS transistor 32 Inverter 50, 60 Power supply system 54 System controller 55 System LSI
61 External power supply

Claims (5)

A voltage output unit connected between a power supply voltage and a reference potential and outputting an output voltage obtained by transforming the power supply voltage;
A voltage control unit that compares a feedback voltage according to the output voltage with a reference voltage, and feedback-controls the voltage output unit so that the feedback voltage is equal to the reference voltage;
A first selection circuit that selects a first feedback voltage equal to the output voltage or a second feedback voltage obtained by dividing the output voltage as the feedback voltage;
A second selection circuit that selects a first reference voltage serving as a reference for the first feedback voltage or a second reference voltage serving as a reference for the second feedback voltage as the reference voltage;
A comparison circuit for comparing the second feedback voltage and the second reference voltage;
Selecting the first feedback voltage and the first reference voltage when the second feedback voltage is less than or equal to the second reference voltage;
Voltage selection means for selecting the second feedback voltage and the second reference voltage when the second feedback voltage is equal to or higher than the second reference voltage;
A power supply circuit comprising:   A first control mode in which the output voltage tracks the first reference voltage and the second feedback voltage rises to a set voltage equal to the second reference voltage; and a second control mode in which the output voltage is maintained at the set voltage. The power supply circuit according to claim 1, further comprising a control mode. A voltage output unit that is connected between a power supply voltage and a reference potential and outputs an output voltage obtained by transforming the power supply voltage is compared with a feedback voltage corresponding to the output voltage and a reference voltage, and the feedback voltage becomes the reference voltage. A voltage control unit that performs feedback control to the voltage output unit to be equal, and a first feedback voltage that is equal to the output voltage or a second feedback voltage obtained by dividing the output voltage as the feedback voltage. A selection circuit; a second selection circuit that selects a first reference voltage serving as a reference for the first feedback voltage or a second reference voltage serving as a reference for the second feedback voltage as the reference voltage; and the second feedback voltage. And a comparison circuit for comparing the second reference voltage, and when the second feedback voltage is less than or equal to the second reference voltage, the first feedback voltage and the first reference voltage are selected, and the first feedback voltage is selected. 2 feedback voltage is the second reference When on the pressure or comprises a plurality of power supply circuits and a voltage selecting means for selecting the second feedback voltage and the second reference voltage,
The power supply circuit having the highest setting voltage at which the second feedback voltage becomes equal to the second reference voltage is set as a master, and the power supply circuit excluding the master is set as a slave. A second reference voltage, and the slave sets the first reference voltage equal to the output voltage of the master,
A first control mode in which the output voltage of the slave tracks the output voltage of the master and rises to the set voltage; and a second control mode in which the output voltage of the slave is maintained at the set voltage. A power supply system characterized by that.   The first reference voltage of the plurality of power supply circuits is supplied from an external power supply different from the master, and the output voltage of the plurality of power supply circuits tracks the first reference voltage supplied from the external power supply. The power supply system according to claim 3, further comprising: a first control mode that rises to the set voltage; and a second control mode in which the output voltages of the plurality of power supply circuits are maintained at the set voltage. .   5. The power supply according to claim 4, wherein the external power supply includes an output voltage higher than the set voltage of the plurality of power supply circuits and a rise later than a rise of the output voltage of the plurality of power supply circuits. system.

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