JP3410578B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device for supplying a predetermined DC voltage using a magnetic amplifier.

[0002]

2. Description of the Related Art Conventionally, a magnetic amplifier using amorphous metal as a core material is used on the secondary side of a transformer, and a switching element connected to the primary side of the transformer is switched at a constant cycle (constant on-duty). In addition, various switching power supply devices have been proposed in which the output can be varied by variably controlling the magnitude of the reset current of the magnetic amplifier (for example, Japanese Patent Publication No. 6-6718).
No. 7 and Japanese Utility Model Publication No. 6-2472).

FIG. 6 is described in Japanese Patent Publication No. 6-67187.
It is a circuit diagram which shows the switched switching power supply device. this
In the switching power supply, both ends of the unstable DC power supply E
Primary winding of transformer T via main switching element QM
Line n₁And the main switching by the self-excited oscillation circuit 10.
Switching the element QM at a predetermined frequency
Thus, an AC output is obtained on the secondary side of the transformer T. To
Secondary winding n of lance T ₂Magnetic amplifier ML, rectifying die
Aether D_Five, The choke coil LF is connected in series,
In addition, the secondary winding n₂Smoothing capacitor CF and commutation between
Diode D₆Are connected in parallel. This commutation
Diode D₆Is the energy stored in the choke coil LF
To regenerate the smoothing capacitor CF.

Here, the magnetic amplifier ML is a main switching device.
Secondary winding n of the transformer T during the ON period of the element QM₂Induced in
Output voltage V₀Is constant
Is controlled so that The above control is output
Voltage V₀Of the detection signal Vs of
Input to the control circuit 11 composed of a path, etc.
Reset voltage from the sensor CF via the switching element QR.
It is done by supplying a flow. Es is the control circuit 11
If it is an auxiliary power supply that supplies electric power and is dedicated
Output voltage V₀May be supplied by. Also,
Indexer C₇, Capacitor C₈And resistance R₂, Resistance R₃Is
A snubber circuit is composed of a rectifier diode D_FiveYatari
Current diode D ₆Provided to suppress the surge voltage of
is there. Here, the control circuit 11 compares the detected signal Vs with the detected signal Vs.
The reference voltage (target value) to be compared is changed by an external command.
Magnetic field increases the magnetic field through the switching element QR.
Change the magnitude of the reset current supplied to the width device ML.
Output voltage V₀Can be adjusted to the target value
Growling.

[0005]

By the way, in the above-mentioned conventional configuration, when the adjustment range of the output voltage V ₀ is large, the output voltage V ₀ is adjusted by using the switching power supply device as a power source of the DC motor, for example. When the speed of the DC motor is controlled by the output voltage V ₀ within that range
The value of the magnetic flux of the magnetic amplifier ML required to adjust the magnetic field becomes large.

[0006] That is, the difference Δφ between the maximum value and the minimum value of the magnetic flux of the magnetic amplifier ML that is required when adjusting the output voltage V ₀ from a maximum value V _0max to a minimum value V _0min is self-excited oscillation circuit If the frequency of 10 is f, its on-duty is D, and the secondary side voltage design value of the transformer T is E ₂ , it is expressed by the following equation.

[0007]

[Formula 1]

However, E ₂ = V _0max × α, α is a constant determined by design conditions. As apparent from the above equation, as the difference between the maximum value V _0max and the minimum value V _0min output voltage V ₀ becomes larger, the magnetic flux required for the magnetic amplifier ML value Δφ
Also grows. Further, FIG. 7 is a graph showing a magnetic hysteresis curve of the core of the magnetic amplifier ML, and a portion surrounded by points A, B and C in the figure represents a control region as the magnetic amplifier ML. When the magnetization state of the core of the magnetic amplifier ML is between the points A and B in the figure and is in a state where the inductance value is small, the magnetic amplifier ML is in the so-called ON state, and a reset current is passed from this state to the magnetic amplifier ML. The core magnetization from point B to C
It is possible to control the output voltage V ₀ to be reduced to the minimum value V _0min by shifting to the point and increasing the inductance value of the core of the magnetic amplifier ML to suppress the current flowing through the magnetic amplifier ML.

However, when the above Δφ of the magnetic amplifier ML is insufficient, the output voltage V ₀ cannot be reduced to the minimum value V _0min even when the magnetized state of the core is at the point C in FIG. Once the core reaches the point D in the saturation region, the magnetized state of the core does not change no matter how much the reset current flows. As in the conventional arrangement, since the control reset current in accordance with the output voltage V _0, despite the core magnetic amplifier ML is saturated, attempts to lower the output voltage V ₀ to a minimum value V _0min The reset current is supplied to the magnetic amplifier ML, and as a result, many times as many reset currents as usual flow into the magnetic amplifier ML and damage the magnetic amplifier ML, and of course, the output voltage V ₀ is the minimum value V _0min.
I couldn't control it. Therefore,
Adjustment range of the output voltage V ₀ (maximum value V _0max and the minimum value V _0min
However, it is necessary to increase the size of the saturable core that constitutes the magnetic amplifier ML and to greatly increase the number of turns of the coil, which makes the entire switching power supply device large and expensive. There was a problem.

An object of the present invention is to solve the above problems, and an object of the present invention is to provide a switching power supply device which has a wide output voltage adjustment range, is small in size, and is inexpensive.

[0011]

In order to achieve the above object, the invention of claim 1 has a transformer and a switching element, and a DC voltage supplied to the primary side of the transformer is intermittently connected by the switching element. A power source section for outputting an AC voltage to the secondary side of the transformer, a magnetic amplifier connected to the secondary side of the transformer, and a converter section for converting the AC output voltage of the power source section supplied via the magnetic amplifier into a DC voltage. A reset current varying unit for varying the reset current supplied to the magnetic amplifier, a detecting unit for detecting the DC output voltage of the converter unit, and a DC output voltage of the converter unit having a predetermined target value based on the output of the detecting unit. In the switching power supply device including a control unit for controlling the reset current variable unit so as to adjust the reset current so as to be within the adjustment range of the DC output voltage of the converter unit. Turn on the switching element so as to reduce the on-duty of the switching elements of the power supply unit in accordance with lowering the predetermined target value, characterized by comprising a switching control unit for turning off control.

According to a second aspect of the present invention, in the first aspect of the invention, the switching control section includes a reference voltage generating circuit for outputting a reference voltage according to a predetermined target value, an oscillator, and an output of the oscillator as a reference voltage. And a comparator which outputs a pulse signal having an on-duty corresponding to the level of the reference voltage as compared with the reference voltage of the generating circuit.

In order to achieve the above object, a third aspect of the present invention has a transformer and a switching element, and a DC voltage supplied to the primary side of the transformer is interrupted by the switching element so that an AC voltage is applied to the secondary side of the transformer. A power supply section for outputting a voltage, a magnetic amplifier connected to the secondary side of the transformer, a converter section for converting the AC output voltage of the power supply section supplied via the magnetic amplifier into a DC voltage, and a magnetic amplifier. Reset current variable unit that changes the reset current, a detection unit that detects the DC output voltage of the converter unit, and a reset current variable that adjusts the DC output voltage of the converter unit to a predetermined target value based on the output of the detection unit. Of a reset power supply device having a control unit for controlling a reset unit and adjusting a reset current by detecting a reset current flowing through a magnetic amplifier If the reset current detected by the reset current detection unit is equal to or greater than a predetermined value, the switching control unit that turns on and off the switching element so as to change the on-duty of the switching element of the power supply unit according to the change of the reset current. Is provided.

According to a fourth aspect of the present invention, in the third aspect of the invention, the switching control section generates a reference voltage generating circuit for outputting a reference voltage according to the reset current value, an oscillator, and an output of the oscillator for generating a reference voltage. And a comparator for outputting a pulse signal having an on-duty corresponding to the level of the reference voltage as compared with the reference voltage of the circuit.

[0015]

According to the structure of the present invention, the switching element is turned on and off so that the on-duty of the switching element of the power supply unit is reduced as the predetermined target value is lowered within the adjustment range of the DC output voltage of the converter unit. Since the switching control section for controlling is provided, even when the adjustment range of the DC output voltage of the converter section is increased, the magnetic flux required for the magnetic amplifier is reduced as the target value approaches the lower limit value of the adjustment range, and the magnetic amplifier is reduced. It is possible to reduce the capacity of the saturable core and the number of turns of the coil wound around the saturable core.

According to another aspect of the present invention, the switching control section outputs the reference voltage according to the predetermined target value, the oscillator, and the oscillator, and the output of the oscillator is the reference voltage of the reference voltage generator. Since it has a comparator that outputs a pulse signal having an on-duty corresponding to the level of the reference voltage, the target value is the lower limit of the adjustment range even when the adjustment range of the DC output voltage of the converter is increased. The magnetic flux required for the magnetic amplifier can be reduced as the value approaches the value, and the capacity of the saturable core and the number of turns of the coil wound around the saturable core that form the magnetic amplifier can be reduced.

According to the third aspect of the present invention, a reset current detector for detecting the reset current flowing through the magnetic amplifier,
If the reset current detected by the reset current detection unit is a predetermined value or more, the switching control unit controls ON / OFF of the switching element so that the ON duty of the switching element of the power supply unit is changed according to the change of the reset current. Therefore, even when the adjustment range of the DC output voltage of the converter is increased, a change in the reset current that increases beyond a predetermined value as the target value approaches the lower limit value of the adjustment range is detected, and the change in the reset current is detected. By changing the on-duty of the switching element to suppress it, the magnetic flux required for the magnetic amplifier is reduced, and the capacity of the saturable core and the number of turns of the coil wound around the saturable core that configure the magnetic amplifier are reduced. be able to.

According to another aspect of the present invention, the switching control unit outputs the reference voltage according to the reset current value, the oscillator, and the output of the oscillator as the reference voltage of the reference voltage generator. Since it is equipped with a comparator that outputs a pulse signal having an on-duty corresponding to the level of the reference voltage for comparison, the target value is the lower limit value of the adjustment range even when the adjustment range of the DC output voltage of the converter is increased. As the change in the reset current that increases beyond a predetermined value as is approached is detected, and the on-duty of the switching element is changed so as to suppress the change in the reset current, the magnetic flux required for the magnetic amplifier is reduced, It is possible to reduce the capacity of the saturable core that constitutes the magnetic amplifier and the number of turns of the coil wound around the saturable core.

[0019]

【Example】

(Embodiment 1) FIG. 1 is a circuit block diagram showing a first embodiment of the present invention. The switching power supply device of the present embodiment is
A power supply unit 1 for converting a DC voltage into a pulsed AC voltage;
A magnetic amplifier ML connected to the secondary side of the transformer T, a converter unit 2 for converting an AC output voltage of the power supply unit 1 supplied via the magnetic amplifier ML into a DC output voltage V ₀ ,
A reset current varying unit 3 that varies the reset current supplied to the magnetic amplifier ML, a detecting unit 4 that detects the DC output voltage V ₀ of the converter unit 2, and a DC output of the converter unit 2 based on the output of the detecting unit 4. The control unit 5 controls the reset current variable unit 3 so that the voltage V ₀ becomes a predetermined target value and adjusts the reset current.

The power supply unit 1 includes a transformer T and a transformer T 1.
And a switching element Q ₁ to the next side are connected in series, the induced electromotive force on the secondary side of the transformer T by intermittent DC voltage V _in input to the primary side of the transformer T by the switching element Q ₁ to generate, and convert the DC voltage V _in the pulsed AC voltage. The magnetic amplifier ML has a characteristic that the inductance value changes according to the magnitude of the reset current, and is connected in series to the secondary side of the transformer T and is supplied in a pulse form from the power supply unit 1 to the converter unit 2. The AC voltage is controlled to adjust the output voltage V ₀ to a predetermined target value.

The converter unit 2 includes a rectifier diode D ₁ connected in series to the magnetic amplifier ML, a smoothing capacitor C _1, is connected in parallel with the smoothing capacitor C ₁ to the connection point of the rectifier diode D ₁ and a smoothing capacitor C ₁ comprising a commutation diode D ₂ has, to obtain an output voltage V ₀ which direct a pulsed AC voltage supplied from the power supply unit 1 through the magnetic amplifier ML rectifying and smoothing it.

The reset current variable unit 3 is a magnetic amplifier ML.
And a diode D ₃ whose cathode is connected to the connection point between the converter circuit 2, a switching element Q ₂ to which the emitter is connected to the positive electrode side of the smoothing capacitor C ₁ with collector connected to the anode of the diode D ₃ And a variable control section 3a for turning on and off the switching element Q ₂ and supplying a predetermined reset current to the magnetic amplifier ML.
When the switching element Q ₂ is turned on by the variable controller 3a, the current induced on the secondary side of the transformer T is supplied to the magnetic amplifier ML as a reset current.

Further, the detecting section 4 outputs the output voltage of the converter section 2.
Pressure V₀Of the output voltage V₀Indicates the level of
Signal v₀Is output. On the other hand, the control unit 5
Output voltage V₀The target value of
A signal m that determines and indicates the target value₀Output
The target value determination unit 5a and the reset supplied to the magnetic amplifier ML.
The reset current determined with the
Signal m to the reset current variable unit 3 in order to flow₁Output
Reset current determining unit 5b and switching of power supply unit 1
Element Q₁And an on / off control unit 5c for turning on and off.
A signal indicating the target value output from the target value determination unit 5a
m₀Is a reset current determination unit 5b and an on / off control unit 5
It is input to each c. In the on / off control unit 5c,
Signal m indicating the input target value₀Based on the output voltage
V₀Is the duty of the power supply unit 1 at the on-duty corresponding to the target value.
Itching element Q ₁Is turned on and off, and input to the power supply unit 1.
DC voltage Vin is converted to pulsed AC voltage and output
It is supposed to do.

Further, the reset current determination unit 5b of the control unit 5
, As shown in the flow chart of FIG. 2, the signal m ₀ indicating a target value from the target value determination unit 5a is inputted (S1), the signal v ₀ indicating the detection unit 4 the level of the output voltage V ₀ is input And (S2), both m ₀ and v ₀ are compared, and the difference Δ
V = (v ₀ −m ₀ ) is obtained (S3), and the output voltage V ₀ is adjusted so that this ΔV is made substantially zero, that is, the error of the actual output voltage V ₀ with respect to the target value is eliminated. A reset current value Ir (= ΔV × β, β is a predetermined constant) necessary for the above is determined (S4), and the signal m ₁ is given to the variable control unit 3a of the reset current variable unit 3 to obtain the predetermined reset current. Are supplied to the magnetic amplifier ML.

Then, the variable controller 3a, to which the signal m ₁ is input, turns on / off the switching element Q ₂ so that the value of the reset current becomes the determined value Ir, whereby the output voltage V ₀ is changed. It is adjusted to the target value. Here, in the present embodiment, as the target value determined by the target value determination unit 5a of the control unit 5 approaches the minimum value V _0min of the adjustment range in the switching power supply device, the switching element Q ₁ of the power supply unit ₁ is turned on. The ON / OFF control unit 5c of the control unit 5 controls the switching element Q ₁ so as to reduce the duty.
Is turned on / off. As a result, the maximum value of the magnetic flux φ required to control the output voltage V ₀ within the adjustment range can be made small from the relationship of Expression 1 described in the conventional configuration.

In the configuration of this embodiment, when the output voltage V ₀ of the switching power supply unit is set to a predetermined target value within the adjustment range, the on / off control unit 5c of the control unit 5 controls the power supply as the target value decreases. Since the on-duty of the switching element Q ₁ of the section 1 is made small, even if the adjustment range of the switching power supply device is wide, the saturable core of the magnetic amplifier ML is made large in order to obtain the magnetic flux φ required for the adjustment. Or the number of turns of the coil wound around the saturable core does not have to be increased. In other words, for the same adjustment range, the saturable core can be made smaller or the number of turns of the coil can be made smaller than before, and switching can be performed. The size and cost of the power supply device can be reduced.

(Embodiment 2) FIG. 3 is a circuit block diagram showing a second embodiment of the present invention. As shown in FIG. 3, the basic configuration of the present embodiment is almost the same as that of the first embodiment, the common portions are denoted by the same reference numerals, and the description thereof will be omitted. Only the characteristic features of the present embodiment will be described. explain.

The present embodiment is characterized in that the switching element Q ₁ of the power supply unit 1 is turned on / off at a predetermined on-duty, and the level of the triangular wave, sawtooth wave or sine wave changes periodically. The oscillator 6 that outputs a signal, the reference voltage output unit 7 that outputs a reference voltage signal of a predetermined level, and the output of the oscillator 6 and the reference voltage of the reference voltage output unit 7 are compared, and according to the level of the reference voltage. The power supply unit 1 includes a comparator 8 that outputs a square wave signal having an on-duty,
The switching element Q ₁ with turning on / off the output of the comparator 8 is supplied to the base of the switching element Q _1,
A reference voltage changing unit 5d that controls the reference voltage output unit 7 to change the level of the reference voltage is provided in the control unit 5 instead of the on / off control unit 5c.

The comparator 8 outputs a signal of H level when the output of the oscillator 6 is larger than the reference voltage of the reference voltage output section 7, and the level of the reference voltage output from the reference voltage output section 7 is changed. By changing it, the output of the comparator 8, that is, the on-duty of the switching element Q ₁ can be changed. Note that the relationship between the output of the comparator 8, the output of the oscillator 6, and the reference voltage may be reversed.

Next, the operation of the characteristic part of the present embodiment will be described. The signal m ₀ indicating the target value is input from the target value determining unit 5a to the reference voltage varying unit 5d, and the smaller the target value, The reference voltage output from the reference voltage output unit 7 is increased to reduce the on-duty of the switching element Q ₁ . Thereby, the first embodiment
As in the above, the maximum value of the magnetic flux φ required to control the output voltage V ₀ within the adjustment range can be small. The other operations are the same as those in the first embodiment, and the description thereof will be omitted.

(Embodiment 3) FIG. 4 is a circuit block diagram showing a third embodiment of the present invention. As shown in FIG. 4, even in the case of this embodiment, the basic configuration is common to that of the first embodiment, the common parts are denoted by the same reference numerals, and the description thereof is omitted, which is a feature of this embodiment. Only the part will be described.

This embodiment includes a reset current detector 9 for detecting the level of the reset current flowing through the magnetic amplifier ML, and switches the power supply 1 according to the level of the reset current detected by the reset current detector 9. having features the on-duty of the element Q ₁ in that the switching control unit 5e for turning on / off the switching element Q ₁ so that the variable is provided to the control unit 5.

The reset current detection unit 9 includes a current transformer CT provided between the reset current variable unit 3 and the magnetic amplifier ML, and a level detection unit 9a for detecting the level of the reset current by the output of the current transformer CT. A signal indicating the level of the reset current that is provided and detected is input from the level detection unit 9a to the switching control unit 5e of the control unit 5.

The switching controller 5e receives the above signal.
The reset current level is, for example,
The value is several times the level of the reset current determined in 5b.
If the reset current cannot be controlled due to
The pulsed AC from the power supply 1 until it becomes controllable.
Switching element Q to lower the voltage₁On Dew
Reduce the tee. This gives the formula described in the conventional configuration.
From the relationship of 1, the output voltage V ₀To control within the adjustment range
It means that the required maximum value of the magnetic flux φ is small. Na
The other configurations and operations are the same as those in the first embodiment.
The description is omitted.

In the configuration of this embodiment, when the output voltage V ₀ of the switching power supply unit is set to a predetermined target value within the adjustment range, the magnetic flux φ of the magnetic amplifier ML is not sufficient, so that the magnetic amplifier ML is actually used. When the level of the reset current that flows is several times the level determined by the reset current determination unit 5b, the switching control unit 5e is configured to reduce the on-duty of the switching element Q ₁ of the power supply unit 1, so that the switching power supply Even if the adjustment range of the device is wide, without increasing the saturable core of the magnetic amplifier ML or increasing the number of turns of the coil wound around the saturable core in order to obtain the magnetic flux φ required for adjustment. In other words, for the same adjustment range, the saturable core can be made smaller or the number of coil turns can be made smaller than in the conventional case, and the switching power supply can be made small. And cost reduction can be achieved.

(Embodiment 4) FIG. 5 shows a circuit block diagram of a fourth embodiment of the present invention. As shown in FIG. 5, the basic configuration of the present embodiment is common to those of the first to third embodiments, common portions are denoted by the same reference numerals, and description thereof will be omitted. Only explained. In the present embodiment, the control unit controls the reference voltage changing unit 5f that changes the level of the reference voltage of the reference voltage output unit 7 provided in the power supply unit 1 according to the signal indicating the reset current supplied from the reset current detecting unit 9. 5 is characterized in that it is provided in FIG.

In the reference voltage varying section 5f, the level of the reset current indicated by the signal is, for example, the reset current determining section 5b.
If the reset current cannot be controlled due to a value that is several times the level of the reset current determined in step 1, the pulsed AC voltage from the power supply unit 1 is lowered until it becomes controllable. The reference voltage level of the voltage output unit 7 is increased to reduce the on-duty of the pulse output from the comparison unit 8, that is, the on-duty of the switching element Q ₁ . As a result, the maximum value of the magnetic flux φ required to control the output voltage V ₀ within the adjustment range can be made small from the relationship of Expression 1 described in the conventional configuration. Note that the other configurations and operations are the same as those of the first to third embodiments, and thus the description thereof will be omitted.

[0038]

According to the first aspect of the present invention, a power supply unit having a transformer and a switching element, which interrupts the DC voltage supplied to the primary side of the transformer with the switching element and outputs an AC voltage to the secondary side of the transformer. A magnetic amplifier connected to the secondary side of the transformer; a converter section for converting the AC output voltage of the power supply section supplied via the magnetic amplifier into a DC voltage; and a reset current supplied to the magnetic amplifier. A reset current variable unit, a detection unit that detects the DC output voltage of the converter unit, and the reset current variable unit is controlled and reset so that the DC output voltage of the converter unit reaches a predetermined target value based on the output of the detection unit. In a switching power supply device including a control unit that adjusts a current, as the predetermined target value is lowered within the adjustment range of the DC output voltage of the converter unit, the power supply unit switches. Since a switching control unit that controls the switching elements to be turned on and off is provided so as to reduce the on-duty of the switching elements, the target value becomes the lower limit value of the adjustment range even when the adjustment range of the DC output voltage of the converter unit is increased. As it approaches, the capacity of the saturable core and the number of turns of the coil wound around the saturable core that configure the magnetic amplifier can be reduced, and as a result, the size and cost of the switching power supply device can be reduced. There is.

According to a second aspect of the present invention, the switching control unit compares the reference voltage generating circuit for outputting the reference voltage according to the predetermined target value, the oscillator, and the output of the oscillator with the reference voltage of the reference voltage generating circuit. Since it is equipped with a comparator that outputs a pulse signal having an on-duty according to the level of the reference voltage, the target value becomes the lower limit value of the adjustment range even when the adjustment range of the DC output voltage of the converter unit is increased. As it approaches, the capacity of the saturable core and the number of turns of the coil wound around the saturable core that configure the magnetic amplifier can be reduced, and as a result, the size and cost of the switching power supply device can be reduced. There is.

According to a third aspect of the present invention, a power supply unit having a transformer and a switching element, which interrupts the DC voltage supplied to the primary side of the transformer with the switching element and outputs an AC voltage to the secondary side of the transformer, A magnetic amplifier connected to the secondary side of the transformer, a converter unit for converting the AC output voltage of the power supply unit supplied via the magnetic amplifier into a DC voltage, and a reset current for varying the reset current supplied to the magnetic amplifier. A variable section, a detection section for detecting the DC output voltage of the converter section, and a reset current control section that controls the reset current variable section so that the DC output voltage of the converter section reaches a predetermined target value based on the output of the detection section. In a switching power supply device including a control unit for adjusting, a reset current detection unit for detecting a reset current flowing in a magnetic amplifier and a reset current detection unit are provided. If the output reset current is a predetermined value or more, the converter unit is equipped with a switching control unit that controls the ON / OFF of the switching element so that the ON duty of the switching element of the power supply unit is changed according to the change of the reset current. Even when the DC output voltage adjustment range is increased, a switching element that detects a change in the reset current that increases beyond a specified value as the target value approaches the lower limit value of the adjustment range and suppresses the change in the reset current is detected. By changing the on-duty of, the magnetic flux required for the magnetic amplifier can be reduced, and the capacity of the saturable core that constitutes the magnetic amplifier and the number of turns of the coil wound around the saturable core can be reduced. As a result, it is possible to reduce the size and cost of the switching power supply device.

According to a fourth aspect of the present invention, the switching control section compares the reference voltage generating circuit for outputting the reference voltage corresponding to the reset current value, the oscillator, and the output of the oscillator with the reference voltage of the reference voltage generating circuit. And a comparator that outputs a pulse signal having an on-duty according to the level of the reference voltage, the target value approaches the lower limit value of the adjustment range even when the adjustment range of the DC output voltage of the converter unit is increased. As the change in the reset current that increases beyond a predetermined value is detected, the on-duty of the switching element is changed so as to suppress the change in the reset current.
The magnetic flux required for the magnetic amplifier can be reduced, the capacity of the saturable core and the number of turns of the coil wound around the saturable core that constitute the magnetic amplifier can be reduced, and as a result, downsizing of the switching power supply device can be achieved. There is an effect that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a first embodiment.

FIG. 2 is a flowchart for explaining the operation of the above.

FIG. 3 is a circuit block diagram showing a second embodiment.

FIG. 4 is a circuit block diagram showing a third embodiment.

FIG. 5 is a circuit block diagram showing a fourth embodiment.

FIG. 6 is a circuit block diagram showing a conventional example.

FIG. 7 is a diagram for explaining the operation of the above.

[Explanation of symbols]

1 Power Supply Section 2 Converter Section 3 Reset Current Variable Section 4 Detecting Section 5 Control Section 5a Target Value Determining Section 5b Reset Current Determining Section 5c ON / OFF Control Section Q ₁ Switching Element

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichi Morii 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Kouji Soshin, 1048, Kadoma, Kadoma City Osaka Prefecture 56) References Japanese Patent Laid-Open No. 7-75333 (JP, A) Japanese Patent Laid-Open No. 6-319258 (JP, A) Actual Flat 6-17388 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/28 G05F 1/32 H03K 17/20

Claims (4)

(57) [Claims] 1. A power supply unit having a transformer and a switching element, which interrupts a DC voltage supplied to the primary side of the transformer by a switching element to output an AC voltage to the secondary side of the transformer, and a secondary side of the transformer. And a magnetic amplifier connected to the magnetic amplifier, a converter unit for converting an AC output voltage of a power supply unit supplied via the magnetic amplifier into a DC voltage, a reset current variable unit for varying a reset current supplied to the magnetic amplifier, and a converter. Detection unit for detecting the DC output voltage of the unit,
In the switching power supply device including a control unit that controls the reset current variable unit so that the DC output voltage of the converter unit becomes a predetermined target value based on the output of the detection unit, A switching power supply device comprising a switching control unit for controlling ON / OFF of the switching element so that the ON duty of the switching element of the power supply unit is reduced as the predetermined target value is lowered within the adjustment range of the output voltage. . 2. The switching control unit includes a reference voltage generating circuit that outputs a reference voltage according to a predetermined target value, an oscillator, and an output of the oscillator compared with a reference voltage of the reference voltage generating circuit to generate a reference voltage. The switching power supply device according to claim 1, further comprising a comparator that outputs a pulse signal having an on-duty according to a level. 3. A power source unit having a transformer and a switching element, which interrupts a DC voltage supplied to the primary side of the transformer with the switching element to output an AC voltage to the secondary side of the transformer, and a secondary side of the transformer. And a magnetic amplifier connected to the magnetic amplifier, a converter unit for converting an AC output voltage of a power supply unit supplied via the magnetic amplifier into a DC voltage, a reset current variable unit for varying a reset current supplied to the magnetic amplifier, and a converter. Detection unit for detecting the DC output voltage of the unit,
In the switching power supply device, which includes a control unit that controls the reset current variable unit so that the DC output voltage of the converter unit has a predetermined target value based on the output of the detection unit and adjusts the reset current, the current flows to the magnetic amplifier. A reset current detection unit that detects the reset current, and a switching element that changes the on-duty of the switching element of the power supply unit according to the change of the reset current if the reset current detected by the reset current detection unit is a predetermined value or more. Turn on the
A switching power supply device comprising a switching control unit for performing off control. 4. A switching control section, a reference voltage generating circuit for outputting a reference voltage according to a reset current value, an oscillator, and an output of this oscillator is compared with a reference voltage of the reference voltage generating circuit to compare the level of the reference voltage. 4. The switching power supply device according to claim 3, further comprising a comparator that outputs a pulse signal having an on-duty corresponding to the above.