JP2003111404A - Dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter capable of attaining high efficiency at low cost and significant noise reduction. SOLUTION: This DC-DC converter includes a switching device Q1 connected with a DC power Ein through a primary winding P1 of a transformer T1, a control unit 11 which performs ON-OFF control of the switching device, rectifier circuits D2, D3, L2, C0 which take out DC output by rectifying the voltage induced in a secondary winding S1 of the transformer, and a series circuit which is connected in parallel with a primary winding of the transformer or the switching device and in which a diode D0, a register R0, and a capacitor C1 are connected in series. During the off-period of the switching device, after forward current is flowed through the diode and energy engaged in the transformer is stored in the capacitor, voltage dummy resonance can be developed by recovery current flowing through the diode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage quasi-resonant DC-DC converter.

[0002]

2. Description of the Related Art In a DC-DC converter, a switching element composed of a MOSFET or the like that is on / off controlled by a control unit is used. In this switching element, a value having both voltage and current at the same time is set. If held, power loss, that is, switching loss occurs. In order to prevent this switching loss, it is sufficient to prevent the current from rising until the voltage becomes zero.

Conventionally, a voltage quasi-resonant type D is used to reduce the switching loss and the switching noise.
C-DC converters are known. This voltage quasi-resonance type DC-DC converter resonates between a reactor and a capacitor and utilizes the oscillation period of the resonance voltage to turn off (change from an on state to an off state) or turn on (resonance) until the resonance voltage becomes zero. It does not change from the off state to the on state), that is, the zero volt switch (ZVS) is performed to reduce the switching loss.

FIG. 12 shows a circuit configuration diagram of a conventional DC-DC converter of this type. In the DC-DC converter shown in FIG. 12, a switching element Q1 composed of a MOSFET is connected to a DC power source Ein via a primary winding P1 of a transformer T1, and both ends of the primary winding P1 of the transformer T1 are connected in series. The connected diode D1 and the capacitor C1 for voltage resonance are connected, and the switching element Q2 and the resistor R1 connected in series are connected. The diode D1 and the switching element Q2 are connected in parallel, and the capacitor C1 and the resistor R1 are connected in parallel. A capacitor C2 for voltage resonance is connected between the drain and source of the switching element Q1. The switching elements Q1 and Q2 have a period (dead time) in which both are off, and are alternately turned on / off by the PWM control of the control unit 51.

Further, a saturable reactor L1 is connected in series to the secondary winding S1 of the transformer T1, and a rectifying circuit composed of a diode D2, a diode D3, an inductor L2 and a capacitor C0 is connected to the saturable reactor L1. ing. This rectifying circuit rectifies the voltage (on-off controlled pulse voltage) induced in the secondary winding of the transformer T1 and outputs a DC output to the load resistor RL1. The operational amplifier OP1 has an output voltage of the load resistor RL1 and a reference voltage E.
Compared with S1, when the output voltage of the load resistance RL1 becomes equal to or higher than the reference voltage ES1, the photodiode in the photocoupler PC1 connected to the output side of the operational amplifier OP1 is caused to emit light.

The phototransistor in the photocoupler PC1 receives light from the photodiode and is turned on,
The control unit 51 controls so that the ON width of the pulse applied to the switching element Q1 is narrowed and the ON width of the pulse applied to the switching element Q2 is widened by the current flowing through the phototransistor. That is, when the output voltage of the load resistor RL1 becomes equal to or higher than the reference voltage ES1, the ON width of the pulse of the switching element Q1 is narrowed to control the output voltage to a constant voltage.

Next, the operation of the DC-DC converter configured as described above, particularly the voltage quasi-resonant operation, will be described with reference to the timing chart shown in FIG. Note that FIG. 13 shows the drain-source voltage Vds of the switching elements Q1 and Q2, the drain current Id, and the current IF of the diode D1 at low voltage under heavy load, high voltage under heavy load, and low voltage under light load. ing.

First, before time t ₀ , the switching element Q1 is turned on, and the drain current Id flows from the DC power source Ein to the switching element Q1 through the primary winding P1 of the transformer T1.

Next, from time t ₀ to time t ₁ , the switching element Q1 changes from the ON state to the OFF state. The switching element Q2 will change from the off state to the on state. From time t ₀ to time t ₁ , the inductance L of the primary winding P1 of the transformer T1
A voltage quasi-resonance is formed by the capacitor C2 and the capacitor C2, and the resonance frequency f ₁ is expressed by the equation (1).

F ₁ = 1 / {2π * (L * C2) ^1/2 } (1) The resonance waveform at that time is a waveform W1 which is a part of a sine wave as shown in FIG. Becomes

Next, from time t ₁ to time t ₂ ,
The diode D1 is turned on after the switching element Q1 is turned off and the current IF flows through the diode D1, and the excitation energy induced in the primary winding P1 of the transformer T1 is stored in the capacitor C1 via the diode D1. Therefore, a voltage pseudo-resonance is formed by the inductance L of the primary winding P1 of the transformer T1, the capacitor C1, and the capacitor C2, and the resonance frequency f ₂ is expressed by the equation (2).

F ₂ = 1 / {2π * {L * (C1 + C2)} ^1/2 } (2) The resonance waveform at that time is a part of a sine wave as shown in FIG. It becomes a waveform W2. The resonance frequency f
₂ becomes lower than the resonance frequency f ₁ , and therefore the waveform W2
Becomes a sine wave that is gentler than the waveform W1.

Next, the switching element Q2 is turned on while the diode D1 is on. When the current time t ₂ to the diode D1 becomes zero, the energy stored in the capacitor C1, flows as the drain current Id through the switching element Q2. That is, the time t ₂ later be continued, the voltage quasi-resonant generated by the inductance L and the capacitors C1 and C2 of the primary winding P1 of the transformer T1, the resonance frequency f ₂ is represented by the formula (2) It The resonance waveform at that time is, as shown in FIG.
The waveform W3 is a part of the sine wave.

Next, from time t ₃ to time t ₅ , the switching element Q1 changes from the off state to the on state, and the switching element Q2 changes from the on state to the off state. Therefore, a voltage quasi-resonance is formed by the inductance L of the primary winding P1 of the transformer T1 and the capacitor C2,
The resonance frequency f ₁ is represented by the equation (1). The resonance waveform at that time is a waveform W4 which is a part of a sine wave, as shown in FIG.

During the voltage quasi-resonant period, the saturable reactor L1 is connected in series with the output rectifier circuit in order to prevent rectification by the output rectifier circuit.

As a result, when voltage quasi-resonance occurs and the switching element Q1 is turned on when the voltage of the switching element Q1 is near zero volt, a zero volt switch can be realized and switching loss is reduced.

Since a zero volt switch can be realized, a relatively large capacitor C2 can be inserted between the drain and source of the switching element Q1. By this capacitor C2, the slope of the voltage, that is, the temporal change (dv / dt) of the voltage becomes gentle, and switching noise (hereinafter abbreviated as noise).
Can be reduced.

[0018]

However, in the conventional DC-DC converter of this type, the switching element Q2 is required to generate the voltage quasi-resonance. In addition, the switching element Q whose potential is greatly different
There is a drawback that a special drive circuit for driving 2 is required, and the cost of the product is high.

It is an object of the present invention to provide a DC-DC converter which is inexpensive, improves efficiency, and can significantly reduce noise.

[0020]

The present invention has the following constitution in order to solve the above problems. According to the invention of claim 1, a switching element connected to a DC power supply via a primary winding of a transformer, a control means for controlling ON / OFF of the switching element, and a voltage induced in a secondary winding of the transformer. A rectifying circuit for rectifying the DC output to obtain a DC output, and a series circuit connected in parallel with the primary winding of the transformer or the switching element and including a diode, a resistor, and a first capacitor connected in series. Generating a voltage quasi-resonance by a recovery current flowing in the diode after a forward current is passed through the diode to store energy excited in the transformer in the first capacitor during an off period of the switching element. Is the gist.

A second aspect of the present invention is summarized as having a second capacitor connected in parallel with the primary winding of the transformer or the switching element.

According to a third aspect of the present invention, an inductance element connected to the secondary winding of the transformer and connected in series to the rectifier circuit, and a comparator section for comparing the DC output of the rectifier circuit with a reference voltage, The gist of the present invention is to have a reset element that causes a reset current to flow through the inductance element when the DC output of the rectifier circuit becomes equal to or higher than a reference voltage.

A fourth aspect of the present invention is characterized in that the inductance element is a saturable reactor or an inductor.

According to a fifth aspect of the present invention, a comparing section for comparing the DC output of the rectifying circuit with a reference voltage, a switch element connected to the secondary winding of the transformer through the rectifying circuit, and the comparing section. And an on / off control means for on / off controlling the switch element based on the comparison output from

According to a sixth aspect of the present invention, there is provided detection means for detecting a voltage quasi-resonant waveform generated in the primary winding of the transformer, and the control means applies the voltage quasi-resonant waveform detected by the detection means. Based on this, the gist is to turn on the switching element when the resonance voltage reaches zero volts.

According to a seventh aspect of the present invention, there is provided detection means for detecting a voltage quasi-resonant waveform generated in the primary winding of the transformer, and the control means has the voltage quasi-resonant waveform detected by the detection means. Based on this, the gist is to turn on the switching element when a predetermined delay time elapses from when the resonance voltage reaches zero volts.

The invention of claim 8 is characterized in that the control means varies the ON width of the switching element in accordance with the voltage of the DC power supply.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a DC-DC converter of the present invention will be described in detail below with reference to the drawings.

(First Embodiment) The DC-DC converter according to the first embodiment uses a recovery current of a diode to generate voltage quasi-resonance, thereby
It is characterized by being composed of two switching elements. Further, in the conventional DC-DC converter shown in FIG. 12, the control unit performs PWM control, but the DC-DC of the first embodiment
The converter is characterized in that resetting of the magnetic flux of the transformer is observed by the winding voltage, and a voltage quasi-resonance for turning on the switching element Q1 is set.

FIG. 1 shows a DC-DC according to the first embodiment.
It is a circuit block diagram which shows a converter. DC- shown in FIG.
In the DC converter, the transformer T is connected to the DC power source Ein.
A switching element Q1 composed of a MOSFET is connected via the primary winding P1 of the transformer 1 and the primary winding P of the transformer T1.
A diode D0, a resistor R0, and a capacitor C1 for voltage resonance connected in series are connected to both ends of 1.

The resistor R0 is a resistor for preventing vibration.
The diode D0 is a diode having a sufficient recovery time (reverse recovery time), and is a switching element Q1.
When the forward current finishes flowing during the OFF period of, the recovery current (reverse current) flows, causing voltage quasi-resonance in the switching element Q1.

A resistor R1 is connected in parallel with the capacitor C1. A capacitor C2 for voltage resonance is connected between the drain and source of the switching element Q1.

The primary winding P2 of the transformer T1 is electromagnetically coupled to the primary winding P1 to detect the voltage quasi-resonant waveform generated in the primary winding P1 of the transformer T1. The control unit 11 turns on the switching element when a predetermined delay time elapses from when the resonance voltage reaches zero volts based on the voltage pseudo resonance waveform detected by the primary winding P2 of the transformer T1. The switching element Q1 has a period in which it is turned off (dead time), and is turned on / off by the control unit 11.

Further, a saturable reactor L1 is connected in series to the secondary winding S1 of the transformer T1, and a rectifying circuit composed of a diode D2, a diode D3, an inductor L2 and a capacitor C0 is connected to the saturable reactor L1. ing. The rectifier circuit rectifies the voltage (on-off controlled pulse voltage) induced in the secondary winding S1 of the transformer T1 and outputs a DC output to the load resistor RL1.
The operational amplifier OP1 compares the output voltage of the load resistor RL1 with the reference voltage ES1, and when the output voltage of the load resistor RL1 becomes equal to or higher than the reference voltage ES1, a reset current is supplied to the saturable reactor L1 via the diode D4. It is designed to flow and control the DC output at a constant level. The constant output control by the saturable reactor L1 will be described later in detail.

Next, the operation of the DC-DC converter constructed as described above, particularly the voltage quasi-resonant operation, will be described with reference to the timing chart shown in FIG.
In addition, in FIG. 2, the switching element Q1 for low voltage under light load, low voltage under heavy load, and high voltage under heavy load, respectively.
Drain-source voltage Vds, drain current Id,
The current Ir of the diode D0 is shown.

First, before time t ₀ , the switching element Q1 is turned on, and the drain current Id flows from the DC power source Ein to the switching element Q1 via the primary winding P1 of the transformer T1.

Next, from time t ₀ to time t ₁ , the switching element Q1 changes from the ON state to the OFF state. From time t ₀ to time t ₁ , the inductance L of the primary winding P1 of the transformer T1 and the capacitor C
A voltage quasi-resonance is formed by 2 and the resonance frequency f
₁ is represented by the above-mentioned formula (1). The resonance waveform at that time is, as shown in FIG. 2, a waveform W that is a part of a sine wave.
It becomes 1.

Next, from time t ₁ to time t ₂ ,
The diode D0 is turned on after the switching element Q1 is turned off, a forward current flows through the diode D0, and the excitation energy induced in the primary winding P1 of the transformer T1 is
It is stored in the capacitor C1 via the diode D0.
Therefore, a voltage pseudo resonance is formed by the inductance L of the primary winding P1 of the transformer T1, the capacitor C1, and the capacitor C2, and the resonance frequency f ₂ is represented by the above-mentioned formula (2). The resonance waveform at that time becomes a waveform W2 which is a part of a sine wave, as shown in FIG.

Next, when the time t ₂ the forward current of the diode D0 is zero, flow recovery current Ir is a reverse current from the cathode to the anode in the diode D0. That is, continuously from time t ₂ to time t ₃ ,
A voltage quasi-resonance occurs due to the inductance L of the primary winding P1 of the transformer T1, the capacitor C1 and the capacitor C2, and the resonance frequency f ₂ is represented by the equation (2). The resonance waveform at that time is, as shown in FIG. 2, a waveform W3 which is a part of the sine wave.

An ideal voltage quasi-resonance can be generated by selecting a recovery time at which the recovery current flows is about half of the off time of the switching frequency. The recovery time of the diode D0 can be changed by adjusting the capacitance of the capacitor C1 or the value of the resistor R0 to adjust the forward current.

Next, from time t ₃ to time t ₅ , the switching element Q1 changes from the off state to the on state. Therefore, the inductance L of the primary winding P1 of the transformer T1
A voltage quasi-resonance is formed by the capacitor C2 and the capacitor C2, and the resonance frequency f ₁ is expressed by the equation (1). The resonance waveform at that time becomes a waveform W4 which is a part of a sine wave, as shown in FIG.

The primary winding P1 of the transformer T1 has
As shown in FIG. 3, the drain of the switching element Q1
The same voltage as the source-to-source voltage Vds is generated, and the transformer T1
As shown in FIG. 3, the voltage generated in the primary winding P1 of
It is detected as a voltage quasi-resonant waveform by the primary winding P2. Then, the control unit 11 controls the primary winding P of the transformer T1.
When the resonance voltage based on a voltage quasi-resonant waveform detected in 2 reaches zero volts (zero point P ₀₎ on the switching element Q1 from (time t ₄ in this _example) at time t ₅ the lapse of a predetermined delay time Let

That is, as shown in FIG. 2, since the drain current is made to flow after the resonance voltage becomes zero volts, the switching loss can be greatly reduced. Further, since a relatively large capacitor C2 is inserted between the drain and the source of the switching element Q1, the slope of the voltage, that is, the temporal change (dv / dt) of the voltage is moderated by the capacitor C2, and noise is generated. Can be reduced.

As described above, the DC- according to the first embodiment
According to the DC converter, one switching element Q1
In order to generate a voltage quasi-resonance by the recovery current flowing through the diode D0 after the forward current is passed through the diode D0 and the energy excited by the transformer T1 is accumulated in the capacitor C1 during the OFF period of the switching element Q1. did. That is, without using an expensive switching element, without using an expensive drive circuit having a different potential,
The ideal diode quasi-resonance was made possible by an inexpensive diode. Therefore, the zero volt switch (ZVS) can be realized at low cost, so that efficiency can be improved and noise can be significantly reduced.

Next, the constant output control by the saturable reactor L1 will be described in detail. First, the operational amplifier OP
1 causes a reset current to flow through the saturable reactor L1 via the diode D4 when the output voltage of the load resistor RL1 becomes equal to or higher than the reference voltage ES1. Saturable reactor L1
Has a high impedance before saturation and shows a state close to a short circuit after saturation, and is used as a switch. A current flows through the saturable reactor L1 and, once saturated, has a high residual magnetic flux density Br even after the current is cut off.

Therefore, as shown in the B-H curve characteristic of FIG. 4A, when a current is passed again in the same direction, the magnetic flux density is saturated with a slight change. In addition, B- in FIG.
As shown in the H-curve characteristic, when a current flows in the opposite direction after saturation, the residual magnetic flux density decreases, and as shown in the B-H curve characteristic of FIG. The magnetic flux density finally decreases to -Br.

The reduction of the residual magnetic flux density means that the range of change in the magnetic flux density until saturation becomes wide,
The width of change in magnetic flux density until saturation is wide
That is, it takes a long time from applying a voltage to the saturable reactor L1 to turning on the saturable reactor L1 (saturating the saturable reactor L1).

Therefore, the secondary winding S1 of the transformer T1 is
When a pulse as shown in FIG.
In the state where almost no reset current flows in the saturable reactor L1, the positive pulse width hardly changes (corresponding to FIG. 4A), as shown in FIG. 5B.

Further, when a small amount of reset current flows in the saturable reactor L1, the positive pulse width becomes slightly narrower (corresponding to FIG. 4B), as shown in FIG. 5C. Further, in a state where the reset current is sufficiently flown in the saturable reactor L1 and the saturable reactor L1 is completely reset,
As shown in (d), the positive pulse width becomes extremely narrow (corresponding to FIG. 4C). That is, by setting the reset current to an appropriate value, the pulse width passing through the saturable reactor L1 can be controlled, and thus the DC output can be controlled to be constant.

DC-DC according to the first embodiment
Although the saturable reactor L1 is used as the inductance element in the converter, an inductor may be used instead of the saturable reactor L1.

(Second Embodiment) Next, a DC-DC converter according to a second embodiment will be described. FIG. 6 is the second
It is a circuit block diagram which shows the DC-DC converter which concerns on embodiment of this. DC- according to the first embodiment shown in FIG.
In the DC converter, the resistor R1 is connected in parallel with the capacitor C1.
The DC according to the second embodiment shown in FIG.
-In a DC converter, a capacitor C connected in series
The resistor R1 is connected in parallel with the resistor R1 and the resistor R0. It should be noted that the other configuration shown in FIG.
The same configuration as that of the DC-DC converter according to the first embodiment shown in FIG.
Detailed description thereof will be omitted.

Even with the configuration shown in FIG. 6, the same effect as that of the DC-DC converter according to the first embodiment can be obtained.

(Third Embodiment) Next, a DC-DC converter according to a third embodiment will be described. FIG. 7 is the third
It is a circuit block diagram which shows the DC-DC converter which concerns on embodiment of this. DC-according to the second embodiment shown in FIG.
In the DC converter, the capacitor C2 is connected in parallel with the switching element Q1, but in the DC-DC converter according to the third embodiment shown in FIG.
A feature is that a capacitor C2 is connected in parallel to the next winding P1. The other configuration shown in FIG. 7 is the same as the configuration of the DC-DC converter according to the second embodiment shown in FIG. 6, and the same reference numerals are given to the same portions, and the detailed description thereof will be omitted. Omit it.

As shown in FIG. 7, even if the capacitor C2 is connected in parallel with the primary winding P1 of the transformer T1, in terms of AC, the capacitor C2 is connected in parallel with the switching element Q1. . Therefore, even with the configuration shown in FIG. 7, the DC-DC according to the second embodiment shown in FIG.
The same effect as that of the converter can be obtained.

(Fourth Embodiment) Next, a DC-DC converter according to a fourth embodiment will be described. FIG. 8 is the fourth
It is a circuit block diagram which shows the DC-DC converter which concerns on embodiment of this. DC-according to the second embodiment shown in FIG.
Although the saturable reactor L1 is used in the DC converter, in the DC-DC converter according to the fourth embodiment shown in FIG. 8, instead of the saturable reactor L1, a rectifier circuit is provided in the secondary winding S1 of the transformer T1. A switching element Q3 and a control unit 12 that controls the switching element Q3 are used. Note that FIG.
Other configurations shown in are the same as the configurations of the DC-DC converter according to the second embodiment shown in FIG. 6, and the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

As described above, the DC- according to the fourth embodiment
According to the DC converter, the control unit 12 controls the operational amplifier O
Based on the output from P1 and the voltage induced in the secondary winding P2 of the transformer T1, the switching element Q by the control unit 11
The switching element Q3 is ON / OFF controlled in synchronization with the ON / OFF control period of 1. The switch element Q3 is
The control section 12 performs PWM control to turn on / off. Therefore, the DC output can be controlled to be constant.

(Fifth Embodiment) Next, a DC-DC converter according to a fifth embodiment will be described. FIG. 9 is the fifth
It is a circuit block diagram which shows the DC-DC converter which concerns on embodiment of this. DC- according to the first embodiment shown in FIG.
In the DC converter, the one-winding type saturable reactor L1
However, the DC- according to the fifth embodiment shown in FIG.
In the DC converter, the two-winding type saturable reactor L5
Is used. This saturable reactor L5
The number of turns of the primary winding is N1, the number of turns of the secondary winding is N2, and the primary winding of the saturable reactor L5 is the transformer T1.
The secondary winding of the saturable reactor L5 is connected to the other end of the secondary winding of the transformer T1 and the diode D4 as a reset element. The other configuration shown in FIG. 9 is the same as the configuration of the DC-DC converter according to the first embodiment shown in FIG. 1, and the same portions are denoted by the same reference numerals, and detailed description thereof will be omitted. Omit it.

As described above, the DC- according to the fifth embodiment
According to the DC converter, the operational amplifier OP1 compares the output voltage of the load resistor RL1 with the reference voltage ES1 and saturates via the diode D4 when the output voltage of the load resistor RL1 becomes equal to or higher than the reference voltage ES1. A reset current is passed through the secondary winding of the reactor L1. Then, a current corresponding to the reset current flowing through the secondary winding of the saturable reactor L1 also flows as a reset current in the primary winding of the saturable reactor L1. Therefore, the DC output can be controlled to be constant.

(Sixth Embodiment) Next, a DC-DC converter according to a sixth embodiment will be described. FIG. 10 is a circuit configuration diagram showing a DC-DC converter according to the sixth embodiment. DC according to the third embodiment shown in FIG.
In the DC converter, the control unit 11 controls the switching element Q1 to be turned on / off regardless of the voltage of the DC power source Ein, but the DC according to the sixth embodiment shown in FIG.
In the DC converter, the control unit 13 detects the voltage of the DC power supply Ein, and according to the detected voltage, the switching element Q1
The ON width of the ON / OFF control of is changed.

As described above, the DC- according to the sixth embodiment
According to the DC converter, the control unit 13 controls the DC power source Ein.
The ON width of the switching element Q1 is changed in accordance with the detected voltage of. For example, if the detected voltage is increased, the ON width is narrowed. Therefore, the output voltage can be controlled to be constant.

(Seventh Embodiment) Next, a DC-DC converter according to a seventh embodiment will be described. FIG. 11 is a circuit configuration diagram showing a DC-DC converter according to the seventh embodiment. DC according to the first embodiment shown in FIG.
In the -DC converter, one output is used, but in the DC-DC converter according to the seventh embodiment shown in Fig. 11, two outputs are used.

That is, in addition to the configuration of the DC-DC converter shown in FIG. 1, a secondary winding S2 electromagnetically coupled to the primary winding P2 of the transformer T1 and a secondary winding S2 connected to the secondary winding S2 in series may be used. The saturation reactor L3 is provided and a rectification circuit including a diode D5, a diode D6, an inductor L4, and a capacitor CP is provided. This rectifier circuit rectifies the voltage (on-off controlled pulse voltage) induced in the secondary winding S2 of the transformer T1 and outputs a DC output to the load resistor RL2. The operational amplifier OP2 compares the output voltage of the load resistor RL2 with the reference voltage ES2, and when the output voltage of the load resistor RL2 becomes equal to or higher than the reference voltage ES2, applies a reset current to the saturable reactor L3 via the diode D7. It is designed to flow and control the DC output at a constant level.

As described above, the DC according to the seventh embodiment
According to the DC converter, the secondary winding S of the transformer T1
By providing the primary winding S2 and the secondary winding S2, two DC outputs can be obtained.

The present invention is not limited to the DC-DC converters according to the first to seventh embodiments described above. In the DC-DC converters of the first to seventh embodiments, the control unit 11 is
Based on the voltage quasi-resonant waveform detected by the primary winding P2 of the transformer T1, the switching element Q1 is turned on when a predetermined delay time elapses from when the resonance voltage reaches zero volts. Therefore, the switching element Q1 may be turned on when the resonance voltage reaches zero volts.

[0065]

According to the invention of claim 1, one switching element is used, and during the OFF period of the switching element,
Since the forward current is passed through the diode and the energy excited by the transformer is accumulated in the first capacitor, the voltage quasi-resonance is generated by the recovery current flowing through the diode. Therefore, the cost is low, the efficiency is improved, and the noise is reduced. It can be significantly reduced.

According to the second aspect of the invention, since the second capacitor is connected in parallel with the primary winding of the transformer or the switching element, the gradient of the voltage across the switching element becomes gentle and the noise is greatly reduced. can do.

According to the invention of claim 3 and the invention of claim 4, the comparator compares the DC output of the rectifier circuit with a reference voltage,
When the DC output of the rectifier circuit becomes equal to or higher than the reference voltage, the reset element causes a reset current to flow through the inductance element formed of the saturable reactor or the inductor, so that the DC output can be controlled to be constant.

According to the fifth aspect of the present invention, the comparison section compares the DC output of the rectifier circuit with the reference voltage, and the on / off control means controls the switching element on / off based on the comparison output from the comparison section. The output can be controlled to be constant.

According to the sixth aspect of the invention, the control means turns on the switching element when the resonance voltage reaches zero volt based on the voltage quasi-resonance waveform detected by the detection means, so that before the voltage becomes zero. Since the current does not rise, the switching loss is reduced.

According to the invention of claim 7, the control means turns on the switching element when a predetermined delay time elapses from when the resonance voltage reaches zero volt based on the voltage quasi-resonance waveform detected by the detection means. Therefore, since the current does not rise before the voltage becomes zero, the switching loss is reduced.

According to the eighth aspect of the invention, the control means varies the ON width of the switching element in accordance with the voltage of the DC power supply, so that the voltage can be controlled to be constant.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a DC-DC converter according to a first embodiment.

FIG. 2 is a timing chart of signals in each unit of the DC-DC converter according to the first embodiment.

FIG. 3 is a diagram illustrating detection of a zero point at which a resonance voltage becomes zero based on a voltage quasi-resonance waveform.

FIG. 4 is a diagram showing a BH curve characteristic of a saturable reactor.

FIG. 5 is a timing chart showing pulse width control by a saturable reactor.

FIG. 6 is a circuit configuration diagram showing a DC-DC converter according to a second embodiment.

FIG. 7 is a circuit configuration diagram showing a DC-DC converter according to a third embodiment.

FIG. 8 is a circuit configuration diagram showing a DC-DC converter according to a fourth embodiment.

FIG. 9 is a circuit configuration diagram showing a DC-DC converter according to a fifth embodiment.

FIG. 10 is a circuit configuration diagram showing a DC-DC converter according to a sixth embodiment.

FIG. 11 is a circuit configuration diagram showing a DC-DC converter according to a seventh embodiment.

FIG. 12 is a circuit configuration diagram showing a conventional DC-DC converter.

FIG. 13 is a timing chart of signals in each unit of a conventional DC-DC converter.

[Explanation of symbols]

Ein DC power supply 11-13 Control unit Q1-Q3 switching elements R0, R1 resistance RL1 load resistance C0, C1, C2 capacitors T1 transformer L1, L3 saturable reactor L2, L4 inductor D0 to D7 diode OP1, OP2 operational amplifier ES1, ES2 reference voltage PC1 photo coupler

Claims (8)

[Claims] 1. A switching element connected to a DC power supply through a primary winding of a transformer, a control means for controlling ON / OFF of the switching element, and a voltage induced in a secondary winding of the transformer. A series circuit connected in parallel with the primary winding of the transformer or the switching element and in which a diode, a resistor, and a first capacitor are connected in series, During the OFF period of the switching element, a forward current is passed through the diode to store energy excited by the transformer in the first capacitor, and then a recovery current flowing through the diode causes voltage quasi-resonance. And a DC-DC converter. 2. The DC-DC converter according to claim 1, further comprising a second capacitor connected in parallel with the primary winding of the transformer or the switching element. 3. An inductance element connected to a secondary winding of the transformer and connected in series to the rectifier circuit, a comparison unit comparing a DC output of the rectifier circuit with a reference voltage, and a DC of the rectifier circuit. 3. The DC-DC converter according to claim 1, further comprising a reset element that causes a reset current to flow through the inductance element when the output becomes equal to or higher than a reference voltage. 4. The inductance element is a saturable reactor or an inductor.
The described DC-DC converter. 5. A comparison unit for comparing the DC output of the rectification circuit with a reference voltage, a switch element connected to the secondary winding of the transformer via the rectification circuit, and a comparison output from the comparison unit. 3. The DC-DC converter according to claim 1 or 2, further comprising: an on / off control unit that controls on / off of the switch element based on the switch element. 6. A detection means for detecting a voltage quasi-resonant waveform generated in the primary winding of the transformer, wherein the control means has a resonance voltage of zero volt based on the voltage quasi-resonant waveform detected by the detection means. The DC-DC converter according to any one of claims 1 to 5, wherein the switching element is turned on when the temperature reaches a certain level. 7. A detection means for detecting a voltage quasi-resonant waveform generated in the primary winding of the transformer, wherein the control means has a resonance voltage of zero volts based on the voltage quasi-resonant waveform detected by the detection means. The DC-DC converter according to any one of claims 1 to 5, wherein the switching element is turned on when a predetermined delay time elapses from the time when the voltage reaches the threshold. 8. The DC-DC device according to claim 1, wherein the control unit varies the ON width of the switching element in accordance with the voltage of the DC power supply. converter.