JPH0654532A - Multi-output switching power supply apparatus - Google Patents

Abstract

PURPOSE:To supply a stable power from a multi-output switching power supply apparatus which supplies respective rectified outputs from a plurality of windings provided on the secondary side of an output transformer even if a load fluctuates and, further, suppress a loss caused by a dummy resistor. CONSTITUTION:The primary side of an output transformer 2 is driven to switch by a switching device 3 and AC voltages induced in respective secondary windings S1 and S2 are rectified by diodes 4 and 5 respectively and smoothed by smoothing capacitors 6 and 7 and smoothing coils 11 and 12 and outputted. The respective coils 11 and 12 have a common core 13. Further, resistors 18 and 19 are inserted between the coils 11 and 12 and the diodes 4 and 5 so as to be in series with the coils 11 and 12 and the capacitors 6 and 7 respectively and a power is regenerated on a heavy load side through elements while the switching device is in an OFF state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an output transformer having a plurality of secondary windings, and the primary side of the transformer is switching-driven to obtain a multi-output DC (direct current) power supply. It relates to a power supply device.

[0002]

2. Description of the Related Art Conventionally, when a switching power supply such as a printer is used to obtain multiple outputs, an on / off system (flyback system) circuit as shown in FIG. 10 is used to provide multiple outputs. In the figure, 1 is a DC power supply, 2 is an output transformer in which the DC power supply 1 is connected to the primary winding F1, and has a plurality of (here, two) secondary windings S1 and S2. . 3 is an F for switching the primary side of the output transformer 2
Switching elements such as ET, 4 and 5 are secondary windings S
1, a rectifying diode for rectifying the AC voltage generated in S2, 6 and 7 for smoothing capacitors for smoothing the rectified voltage, 8 for at least one of the smoothed DC outputs in accordance with the DC output A control circuit such as a regulator IC that controls the driving (on-duty) of the switching element 3 feeds back the output voltage of the secondary winding S1 here.

The circuits after the secondary windings S1 and S2 of the output transformer 2 are similar to each other. Further, in the figure, Vin is an input voltage, and E1 is 1 of the output transformer 2.
Secondary winding voltage, E2, E3 are secondary winding voltage, Vf
1, Vf2 is the voltage across the rectifying diodes 4, 5, Vo
1, Vo2 is the output voltage of each secondary winding S1, S2, Io
Reference numeral 1 denotes the output current of the secondary winding S1.

In the flyback type circuit configured as described above, the flyback voltage of each of the secondary windings S1 and S2 generated when the switching element 3 is turned off is generated in proportion to the number of each winding. Each rectifying diode 4,
Since the smoothing capacitors 6 and 7 are charged via the switch 5, the output of one of the plurality of outputs (the output most desired to be stabilized) is fed back to the control circuit 8 to switch the switching element 3 By controlling the switching timing of, it is possible to obtain a relatively stable output as each output.

However, when the load connected to each output changes, as in the equivalent circuit shown in FIG.
The leakage inductance elements 9 and 10 are inserted in series between the output side of the transformer 2 and the rectifier circuit. The leakage rectification component that is in series with this rectification circuit is charged as magnetic energy every time the switching element 3 switches because a normal rectification current flows, and affects the rectification operation. In the case of a two-system output power supply, for example, this operation causes the output voltage on the lighter load side to be output as a value larger than the flyback voltage given by the number of turns.

Therefore, in order to prevent the above-mentioned voltage from greatly increasing above the target voltage due to the load, the minimum necessary load current (point b) is consumed as a dummy current by the resistor as shown in FIG. The output voltage is prevented from rising during this time.

FIG. 12 shows a forward (on / off) system circuit as a system other than the flyback system. A feature of this method is that it is often used when relatively high output power is desired with high efficiency, and FIG. 2 shows the main operation waveforms (voltage waveform, current waveform) in this forward method.

In FIG. 12, the same reference numerals as those in FIG. 10 indicate the same components, and 11 and 12 are smoothing coils for smoothing the rectified voltage from the secondary windings S1 and S2 of the output transformer 2, respectively. , Are commonly magnetically coupled to each other by the shared magnetic core 13. 14 and 15 are each coil, 1
Reference numerals 1 and 12 are regenerative diodes, and 16 and 17 are resistors connected to each output terminal.

In the circuit configured as described above, the input voltage Vin is switched by the switching element 3 to supply a voltage pulse to the primary winding F1 of the transformer 2. As a result, the secondary windings S1 and S2 of the transformer 2 are
A voltage waveform corresponding to the turn ratio is induced in the. The induced voltage pulse charges the smoothing capacitors 6 and 7 via the rectifying diodes 4 and 5. The charged current flows from the capacitors 6 and 7 to the coils 11 and 12 (I1),
Exciting the coils 11 and 12, the secondary winding S of the transformer 2
It flows as a return current to one end of S1 and S2.

The operation waveforms due to the above operation are as shown in FIG. 13, and at the point a in FIG. 3, each of the secondary windings S1 and S2.
The load of the output from is a rated load region, that is, each load current (Io) is a region where the following continuous condition Io ≧ ΔIo / 2 = ((Vo + Vf) / L ^* Ton) / 2 is satisfied. Where ΔIo is the ripple current, Vo is the output voltage, Vf is the voltage of the diodes 4 and 5, and
L is the inductance of the coils 11 and 12, and Ton is the switching on time.

Therefore, assuming that the winding voltage of the transformer 2 is E and the switching cycle is T, each output voltage Vo is Vo = E × (Ton / T).

Here, the ripple voltage ΔV of the output voltage Vo
o is ΔVo = ∫ ^{Ton / 2} ₀ (E2- (Vo + Vf)) / L1 ^* t) dt + ∫ ^{Toff / 2} ₀ (Vo + Vf) / L1 ^* t) dt, so L1 ^* C = ( E2 ^* Ton ² -2 ^* (Vo + Vf) ^* T ^* Ton + (Vo + Vf) ^* T ² ) / (8 ^* ΔVo). Further, the ripple current ΔIo can be expressed as ΔIo = (Vo + Vf) / L2 ^* Ton. Since this ripple current ΔIo is a current flowing through the coils 11 and 12 of the inductances L1 and L2,
As shown in FIG. 2, it has a triangular waveform.

Therefore, when the load is zero, that is, when there is no load, the capacitors 6 and 7 are sequentially charged, and finally the winding voltages E2 and E appearing in the secondary windings S1 and S2.
3 will be charged as it is. This voltage E
2, E3 can be expressed as E2 (E3) = Vo / switching duty. Therefore, if 5 V is output from the circuit operating with the switching duty of 20%, the winding voltage E2, E
Since 3 is a pulse voltage having a peak value of 25V, the output voltage when there is no load is 25V. Therefore, in order to set the output voltage to a value obtained by multiplying E2 and E3 by the switching duty (continuous condition of the filter), the average value of the ripple current ΔIo / 2 is attached to each voltage output side with a dummy resistor. The voltage is made to flow so that the proportional relationship can be maintained even if the voltages of the plurality of outputs each have a load change.

[0014]

However, in the conventional multi-output switching power supply device as described above,
In order to reduce the dummy current and improve the efficiency, a coil with a large inductance is required, which makes the device larger and
There was a problem that it became expensive.

That is, as described above, when a plurality of outputs are obtained by rectifying with a rectifying element from a transformer having a plurality of secondary windings using one switching element, the output voltage is unbalanced due to each load variation. In order to prevent the occurrence of (in order to maintain the continuous condition of the circuit), it is necessary to wastefully lose the output voltage by the dummy resistor. The power loss in the dummy resistor is, for example, about 5 to 1 in a 2-output 50 W power supply in order to maintain the continuous condition.
It reaches 0W. For this reason, as a natural effect, the dummy electric power causes adverse effects such as an increase in device temperature and a decrease in efficiency.

Further, as shown in the above-mentioned conventional example, the dummy current Id is expressed as Id = ΔIo / 2 = ((Vo + Vf) / L ^* Ton) / 2. As can be seen from this equation, in order to reduce the dummy current and make an efficient power supply, the inductance L must be increased, but in this case, the size of the coil itself becomes large, and the size of the power supply and There was a problem of raising the cost.

As another means, a method of increasing the switching frequency of the switching element is conceivable. In this method, when a load above a certain level is applied, switching loss of the switching element and recovery of the diode. Loss will increase. Further, for the transformers and coils, the skin effect causes a reduction in the effective cross-sectional area, which increases copper loss, resulting in a reduction in the efficiency of the entire power supply and an adverse effect such as an increase in temperature.

The present invention has been made by paying attention to the above problems, and it is possible to supply a stable power supply against a wide load variation of each output without flowing a dummy current. The purpose is to obtain a switching power supply.

Another object of the present invention is to obtain a highly efficient multi-output switching power supply device which can minimize unnecessary power loss due to dummy resistors.

[0020]

The multi-output switching power supply device of the present invention is configured as follows.

(1) An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to a DC power source, and each secondary winding of the output transformer. A rectifying element for rectifying the AC voltage generated in the, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. And a control circuit for controlling the above. The smoothing coil shares a magnetic core with each other, and a resistor is connected in series with the smoothing coil and the smoothing capacitor between the smoothing coil and the rectifying element.

(2) An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to the DC power supply, and each secondary winding of the output transformer. A rectifying element for rectifying the AC voltage generated in the, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. And a control circuit for controlling the above, the smoothing coil shares a magnetic core with each other, and a switching element is connected in series with the smoothing coil and the smoothing capacitor between the smoothing coil and the rectifying element.

(3) An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to the DC power supply, and each secondary winding of the output transformer. A rectifying element for rectifying the AC voltage generated in the, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. A control circuit for controlling the output current and a current detection circuit for detecting the output current, a dummy resistor is connected to the output side of each secondary winding, and a current flowing through the dummy resistor according to the detected value of the output current. To control.

(4) An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer, which is connected to a DC power supply, and each secondary winding of the output transformer. A rectifying element for rectifying the AC voltage generated in the, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. And a dummy resistor is connected to the output side of each secondary winding, and the current flowing through the dummy resistor is controlled according to the sequence control signal of the load.

(5) An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer, which is connected to a DC power supply, and each secondary winding of the output transformer. A rectifying element for rectifying the AC voltage generated in the, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. And a current detection circuit for detecting the output current, and the drive frequency of the switching element is controlled according to the detected value of the output current.

[0026]

In the multi-output switching power supply device of the present invention, the resistor or switching element connected between the rectifying element and the smoothing coil becomes conductive when the main switching element of the output transformer is turned off, so that the light load side When the output voltage is about to rise, electric power is regenerated to the heavy load side through the coil having the shared magnetic core.

Further, the current flowing in the dummy resistor connected to each output side is changed according to the detected value of the output current or the sequence control signal of the load, and the drive frequency of the main switching element of the output transformer is the output current. Can be changed according to.

[0028]

1 is a circuit diagram showing a structure of a multi-output switching power supply device according to a first embodiment of the present invention, and the same reference numerals as those in FIG. 12 indicate the same constituent parts. In the figure, 1
Is a DC power supply, 2 is an output transformer having a plurality of secondary windings S1 and S2, and the DC power supply 1 is connected to the primary winding F1. 3 is a switching element for switching the primary side of the output transformer 2, 4 and 5 are each 2 of the output transformer 2.
Rectifying diodes (rectifying elements) that rectify the AC voltage generated in the secondary windings S1 and S2, 6 and 7 are smoothing capacitors that smooth the rectified voltages, and 8 is a plurality of smoothed DC outputs. A control circuit for controlling the driving of the switching element 3 in accordance with at least one DC output (here, Vo1), 11 and 12 are smoothing coils for smoothing the rectified voltage together with the capacitors 6 and 7, and have a magnetic core 1
Share 3

Reference numerals 14 and 15 denote the coils 11 and 12 of the respective coils.
Regenerative diode, 18 and 19 are smoothing coils 11,
12 and a rectifying diode 4, 5 between the smoothing coil 1
The resistors 1 and 12 and the smoothing capacitors 6 and 7 are connected in series. The secondary winding S1 of the output transformer 2
The circuits after S2 and S2 are similar to each other as in FIG. Further, FIG. 2 shows operation waveforms of the forward type circuit.

In the circuit configured as described above, the input voltage vin from the DC power supply 1 is switched by the switching element 3 to supply a voltage pulse to the primary winding F1 of the transformer 2. As a result, a voltage waveform corresponding to the turn ratio is induced in the secondary windings S1 and S2 of the transformer 2. This voltage pulse charges the smoothing capacitors 6 and 7 via the rectifying diodes 4 and 5. The charged current flows from the capacitors 6 and 7 to the coils 11 and 12, excites the coils 11 and 12, and flows as a return current to one end of the secondary windings S1 and S2 of the transformer 2.

Here, in the operation waveform diagram of FIG. 2, the load of each output is in the rated load region, that is, each load current is a continuous condition: Io ≧ ΔIo / 2 = ((Vo + Vf) / L ^* Ton) / 2 is the area that is satisfied.

Therefore, each output voltage Vo corresponds to point a in FIG. 3 in that Vo = E × (Ton / T), where T is the switching period and Ton is the switching on time. FIG. 3 shows the load characteristics in the circuit of FIG. 1, and shows the state of each output voltage when Vo1 is the rated load and Vo2 is varied. In addition,
The characteristic shown by the broken line is the regeneration resistor 1 in the circuit of FIG.
This is the characteristic when there is no 8 or 19.

Next, Vo1 is tentatively loaded in the rated current region, and Vo2 is below the continuous current region, that is, in the region of Io <ΔIo / 2 = ((Vo + Vf) / L2 ^* Ton) / 2. The case will be described. In order to clarify the gist of the present invention, the operation without the regenerative resistors 18 and 19 will be described first.

In FIG. 3, the load of Vo2 is from point a to point b.
When changing from a point, that is, from heavy load to light load, coil 1
The magnetic energy stored in the switching elements 1 and 12 when the switching element 3 is turned on charges the smoothing capacitors 6 and 7 on the output side by the circuit composed of the regenerative diodes 14 and 15 when the switching element 3 is turned off. Since the output Vo1 is constantly monitored and fed back as the switching timing by the control circuit 8, the switching timing (duty) is (Ton / T) ≈Vo / E. On the other hand, the output Vo2 becomes a discontinuous condition as the load power, and only the charging operation is performed as shown in FIG. 4, and as a result, the winding voltage E rises, and the output characteristics shown by the broken line in FIG. Will adversely affect the load.

Therefore, in the present embodiment, the regenerative resistors 18 and 19 as shown in FIG. 1 are attached to solve the above problem.

FIG. 5 shows an operation waveform when the regenerative resistor 19 is attached. Compared with the operation waveform of FIG. 4 in which the regenerative resistor 19 is not attached, the current of the capacitor 7 on the Vo2 side, that is, the light load side is shown. The waveform has a discharge waveform as well as a charge waveform. It goes without saying that, of course, a dummy resistor is attached to the output side to allow a dummy current to flow, and the same waveform (continuous condition is satisfied) can be obtained even with power loss, but the loss power PL at that time is PL = (Vo (Vo + Vf) / 2 × L) × Ton (W), and in general power supply design, dummy power of about 10% of the rated load is generally taken. It is economically disadvantageous and unrealistic to increase the inductance of the coil in order to further reduce the dummy current.

Next, when the smoothing capacitors 6 and 7 are charged and exceed a specified voltage (winding voltage × on-duty), the smoothing capacitor 7 charges the coil 12 when the switching element 3 is on. A current in a direction opposite to that of the above-mentioned current flows through the regenerative resistor 19 when turned off. As a result, in the coil 11 on the Vo1 side that is magnetically coupled, the current synthesized from the regenerative current on the Vo1 side according to the ampere-turn rule of the winding ratio flows from the capacitor 6, and this coil 11, the regeneration coil is used. The current flowing in the path of the diode 14 is Vo
It is supplied to the load as a load current on the first side.

By the above operation, when the output voltage on the light load side is about to rise, it becomes possible to load the regenerative electric power on the other magnetically coupled regenerative circuit. Therefore, it is possible to realize a circuit that is not affected by the load fluctuation as shown by the solid line in FIG. 3 without unnecessary power loss. Therefore, it is possible to supply a stable power supply against a wide load variation of each output without flowing a dummy current.

FIG. 6 is a circuit diagram showing the configuration of the second embodiment of the present invention. The same components as those in FIG. 1 are designated by the same reference numerals. In this embodiment, switching elements 20, 21 such as FETs are attached instead of the resistors 18, 19 in the circuit of FIG. That is, the smoothing coils 11 and 12 are provided between the smoothing coils 11 and 12 and the rectifying diodes 4 and 5.
The switching elements 20 and 21 are connected in series with the smoothing capacitors 6 and 7.

As described above, even if the switching elements 20 and 21 are used in the regenerative circuit, it is possible to obtain the same effects as those of the above-described embodiment. That is, when the switching element 3 is turned off, the flyback voltage of the coils 11 and 12 is monitored from the winding voltage, and the switching elements 20 and 21 connected in parallel with the regenerative diodes 14 and 15 are conducted to make the voltage output on the light load side. Since the circuit is regenerated, it is possible to cope with a wide range of load fluctuations without flowing a dummy current.

FIG. 7 is a circuit diagram showing the configuration of the third embodiment of the present invention. In the figure, 16 and 17 are secondary windings S1 and S, respectively.
2 is a resistor (dummy resistor) connected to the output side, 22 is a current detection circuit for detecting the output current, 23 is a transistor connected in series with the resistor 17, and is controlled by the output of the current detection circuit 22 The current flowing through the resistor 17 is controlled according to the detection value of the detection circuit 22.

The current detection circuit 22 is composed of a comparator and a resistor. For example, when the output current Io2 becomes more than half (Id) of the ripple current, an "L" signal is sent to the transistor 23 and the dummy resistor 17 receives a current. Will not flow. On the contrary, when Io <Id, the transistor 2
"H" signal is sent to 3, current is passed through dummy resistor 17,
Make sure that the continuous condition of the circuit is satisfied. By having this function, it is possible to prevent a considerable power loss as a whole, and it is possible to minimize a wasteful power loss due to the dummy resistor 17.

FIG. 8 is a circuit diagram showing the configuration of the fourth embodiment of the present invention. In the figure, 24 and 25 are fans and motors that are loads, 26 is a sequence controller that controls the fans 24 and motor 25, and 27 is a sequence control signal (FON, M
It is a NOR circuit that receives (ON) and controls the transistor 23 connected in series with the dummy resistor 17.

In this embodiment, the current flowing through the dummy resistor 17 is controlled according to the sequence control signal from the controller 26. Further, the current consumption during driving of each load is larger than half (Id) of the ripple current on the Vo2 side.

When the controller 26 drives the fan 24 and the motor 25, the FON signal and M
Turn ON signal to "H". And the MON signal is "L"
When the FON signal is "L", the transistor 23 is turned on and a current flows through the dummy resistor 17 to establish the continuous condition of the circuit. Further, when the MON signal is "L" and the FON signal is "H", when the MON signal is "H" and the FON signal is "L", the MON signal is "H" and the FON signal is " In the case of H ″, the transistor 23 is turned off and no current flows through the dummy resistor 17, and as a result, it is possible to suppress heat generation and unnecessary power consumption by the resistor, and to obtain the same effect as the above embodiment. Obtainable.

FIG. 9 is a circuit diagram showing the configuration of the fifth embodiment of the present invention. In the figure, 28 is a multiplication circuit interposed between the switching element 3 and the control circuit 8, and is a current detection circuit 22.
When the control signal (detection signal) from is “H”, the control circuit 8
The pulse wave from is tripled in frequency. Reference numeral 29 denotes a dummy resistor, which has a resistance value three times that of the dummy resistor 17 of the previous embodiment and is a circuit in which a dummy current of 1/3 flows.

In the above circuit, the drive frequency of the switching element 3 is controlled according to the detection value of the current detection circuit 22, and the equation of the ripple current at that time is expressed by ΔIo = Vo / L ^* Ton. The shorter Ton, the smaller the ripple current. That is, if the frequency is tripled, the ripple current becomes 1/3.

Therefore, when Io becomes half or less (Id) of the ripple current, the current detection circuit 22 sends an "H" signal to the multiplication circuit 28 to triple the switching frequency.
Conversely, when Io> Id, the "L" signal is sent to the multiplication circuit 28 and the switching frequency is not changed. Further, when Io takes a load equal to or less than half (Id) of the ripple current, the switching loss of the switching element 3 and the recovery loss of the diode hardly increase. Further, for transformers and coils, copper loss due to the skin effect is not so large as to cause a problem. Therefore, the power loss of the dummy resistor 29 becomes 1/3 in the entire power source, which leads to the improvement of efficiency.

[0049]

As described above, according to the present invention, the magnetic cores of the smoothing coils are shared, and the resistor or the switching element is connected between the rectifying element and the smoothing coil. There is an effect that a stable power supply can be supplied even when a wide load variation of each output is caused without flowing the current.

Further, the current flowing through the dummy resistor connected to each output side is controlled according to the detected value of the output current or the sequence control signal of the load, or the primary side of the output transformer is detected according to the detected value of the output current. Since the switching frequency is changed, useless power loss due to the dummy resistor can be suppressed to the minimum, and a highly efficient device can be obtained.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is an operation waveform diagram of a forward type circuit.

FIG. 3 is a load characteristic diagram of the circuit of FIG.

FIG. 4 is an explanatory diagram showing an operation when there is no regenerative resistor in the circuit of FIG.

5 is an explanatory diagram showing the operation of the circuit of FIG. 1 with a regenerative resistor attached.

FIG. 6 is a circuit diagram showing a configuration of a second embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 9 is a circuit diagram showing the configuration of a fifth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a configuration of a conventional example.

FIG. 11 is an equivalent circuit diagram when the load changes in FIG.

FIG. 12 is a circuit diagram showing the configuration of another conventional example.

[Explanation of symbols]

 1 DC power supply 2 Output transformer 3 Switching element 4,5 Rectifying diode (rectifying element) 6,7 Smoothing capacitor 8 Control circuit 11,12 Smoothing coil 13 Magnetic core 16,17 Resistance (dummy resistance) 18,19 Resistance 20, 21 switching element 22 current detection circuit 24 fan (load) 25 motor (load) 26 sequence controller 29 dummy resistor

Claims (5)

[Claims] 1. An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to a DC power source, and each secondary winding of the output transformer. A rectifying element for rectifying the generated AC voltage, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. A smoothing coil and a smoothing capacitor are connected in series between the smoothing coil and the rectifying element, and the smoothing coil shares a magnetic core with each other. Multi-output switching power supply device. 2. An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to a DC power supply, and each secondary winding of the output transformer. A rectifying element for rectifying the generated AC voltage, a smoothing coil and a smoothing capacitor for smoothing the rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. A control circuit for controlling the smoothing coil shares a magnetic core with each other, and a switching element is connected in series with the smoothing coil and the smoothing capacitor between the smoothing coil and the rectifying element. And a multi-output switching power supply device. 3. An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to a DC power source, and each secondary winding of the output transformer. A rectifying element for rectifying the generated AC voltage, a smoothing coil and a smoothing capacitor for smoothing each rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. A control circuit for controlling and a current detection circuit for detecting an output current are provided, a dummy resistor is connected to the output side of each secondary side winding, and a current flowing through the dummy resistor is detected according to the detected value of the output current. A multi-output switching power supply device that is controlled. 4. An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to a DC power source, and each secondary winding of the output transformer. A rectifying element for rectifying the generated AC voltage, a smoothing coil and a smoothing capacitor for smoothing each rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. A multi-output switching power supply characterized by comprising a control circuit for controlling, connecting a dummy resistor to the output side of each secondary winding, and controlling the current flowing through the dummy resistor according to the sequence control signal of the load. apparatus. 5. An output transformer having a plurality of secondary windings, a switching element for switching the primary side of the output transformer connected to a DC power source, and each secondary winding of the output transformer. A rectifying element for rectifying the generated AC voltage, a smoothing coil and a smoothing capacitor for smoothing each rectified voltage, and the switching element according to at least one DC output of the plurality of smoothed DC outputs. A multi-output switching power supply device comprising a control circuit for controlling and a current detection circuit for detecting an output current, and controlling a drive frequency of the switching element according to a detected value of the output current.