JPH11299236A - Transformer-insulated dc-to-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the switching loss and noise of a DC-to-DC converter and improve the efficiency. SOLUTION: This converter is provided with a diode 11, whose one end is connected to a connecting point between a primary winding 2a of a transformer 2 and a transistor 3, a resonance capacitor 12 connected between the other end of the diode 11 and the cathode terminal of a DC power supply 1, a primary winding 13a of an auxiliary transformer 13 and a diode 14 which are serially-connected between the resonance capacitor 12 and the primary winding 2a of the transformers 2, and a secondary winding 13b of the auxiliary transformer 13 and a diode 15 serially-connected to both ends of the DC power supply 1. At the transistor 3 turned on, voltage generated at the secondary winding 13b of the auxiliary transformer 13 is regenerated at the DC power supply 1 by resonance capacitor 12 and the auxiliary transformer 13 via the diode 15 for resonance current which flows through a closed-circuit of the primary winding 13a - diode 14 - transistor 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer-isolated DC-DC converter capable of reducing switching loss and noise and improving efficiency.

[0002]

2. Description of the Related Art A DC power supply, a primary winding of a transformer, and a switching element are connected in series, and the switching element is turned on and off, so that a DC power supply is supplied from a secondary winding of the transformer via a rectifying and smoothing circuit. Transformer-isolated type D that supplies a DC output of a constant voltage different from the voltage of
2. Description of the Related Art C-DC converters have been widely used in power supply circuits of electronic devices and the like. For example, a conventional transformer-isolated DC-DC converter shown in FIG. 7 includes a DC power supply 1 such as a battery or a capacitor input type rectifier circuit and a primary winding 2a.
A transformer 2 having a secondary winding 2b, a primary winding 2a of the transformer 2 connected in series to both ends of the DC power supply 1, and a transistor 3 as a switching element;
A rectifier smoothing circuit consisting of rectifier diodes 4 and a smoothing capacitor 5 is connected to the secondary winding 2b, a load 6 connected in parallel to the smoothing capacitor 5, a control pulse signal V _B to the base terminal of the transistor 3 Granting Transistor 3
And a control circuit 7 for turning on and off the. Although not specifically shown, the control circuit 7 includes an oscillation circuit section for generating a triangular wave voltage having a constant period, an error amplification circuit section for arithmetically amplifying an error voltage of the terminal voltage of the load 6 with respect to the reference voltage, and an error amplification circuit section. a comparing circuit for comparing the error output voltage and the triangular wave voltage of the oscillator circuit portion of the circuit, and generates a control pulse signal V _B proportional to the time width of the output voltage of the comparator circuit is applied to the base terminal of the transistor 3 And a control pulse generation circuit section. This transformer-insulated DC-
In the DC converter, the control circuit 7 controls the transistor 3
The pulse width of the control pulse signal V _B for the grant to the base terminal is changed according to the terminal voltage of the load 6, the transistor 3
By controlling the ON / OFF period of the DC power supply 1, a DC output V _O having a constant voltage different from the voltage E of the DC power supply 1 is supplied to the load 6.

[0003]

By the way, in the transformer-insulated DC-DC converter shown in FIG. 7, when the transistor 3 is turned on and turned off, the collector-emitter voltage waveform V _CE of the transistor 3 is changed as shown in FIG. large switching losses based on overlapping portion W of the collector current waveform I _C of the transistor 3 is a drawback to occur. Further, since the rise of the collector-emitter voltage waveform V _CE and the collector current waveform I _C of the transistor 3 is steep, spike-shaped surge voltages V _sr and surge current I _sr are generated, and noise based on these is generated. There were drawbacks. Therefore, power loss inside the converter increases due to the occurrence of switching loss, noise, and the like, and the efficiency of the converter decreases.

Accordingly, the present invention provides a transformer-isolated DC that can reduce switching loss and noise and improve efficiency.
-To provide a DC converter.

[0005]

According to a first aspect of the present invention, there is provided a transformer-insulated DC-DC converter in which a DC power supply, a primary winding of a transformer, and a switching element are connected in series. By performing the on / off operation, a DC output of a constant voltage different from the voltage of the DC power supply is supplied from the secondary winding of the transformer via the rectifying and smoothing circuit to the load. In the transformer-insulated DC-DC converter, a first rectifier element having one end connected to a connection point between the primary winding of the transformer and the switching element;
A resonance capacitor connected between the other end of the first rectifier element and the other end of the DC power supply; a connection point between the resonance capacitor and the first rectifier element; and a primary winding of the transformer. And a primary winding of an auxiliary transformer and a second rectifier element connected in series between a connection point of the first rectifier element and
A secondary winding of the auxiliary transformer and a third rectifying element connected in series between one end and the other end of the DC power supply, wherein when the switching element changes from an off state to an on state, the resonance occurs. Current flows through a closed circuit formed by the capacitor for use and the primary winding of the auxiliary transformer and the second rectifying element and the switching element, whereby a voltage generated in the secondary winding of the auxiliary transformer is reduced. The DC power is regenerated through the third rectifier.

When the switching element is turned off with the switching element turned on, the current flowing from the primary winding of the transformer to the switching element is switched to a current flowing to the resonance capacitor via the first rectifier. The resonance capacitor is charged in a sinusoidal manner.
As a result, the voltage at both ends of the switching element rises in a sinusoidal manner from 0 V, so that when the switching element is turned off, zero voltage switching (ZVS) is performed.
Switching loss is reduced. When the switching element is turned on from the off state, the resonance capacitor charged to the voltage of the DC power supply during the off period starts discharging, and the resonance capacitor, the primary winding of the auxiliary transformer, and the second rectifier. A resonance current flows in a closed circuit formed by the element and the switching element. As a result, the current of the switching element increases in a sine wave form from 0, so that when the switching element is turned on, zero current switching (ZCS) is performed, and the switching loss is reduced. As described above, the switching loss at the time of the ON / OFF operation of the switching element can be reduced. At the same time, the spike-like surge voltage and current generated when the switching element is turned off and turned on are absorbed by the resonance action of the leakage inductance of the resonance capacitor and the transformer, and the falling and rising of the voltage and current waveforms of the switching element are gradual. Therefore, noise based on the surge voltage and the current can be reduced. Further, when the switching element is turned on, a voltage generated in the secondary winding of the auxiliary transformer is regenerated to the DC power supply through the third rectifying element due to the resonance current flowing in the closed circuit. Most of the discharge energy is regenerated to the DC power supply, thereby reducing power loss inside the converter and improving efficiency.

Further, in the transformer-isolated DC-DC converter according to the second aspect of the present invention, a current limiting reactor is connected between the primary winding of the transformer and the switching element. In this transformer-insulated DC-DC converter, when the switching element is turned on, the surge current flowing from the primary winding of the transformer to the transistor is absorbed by the self-inducing action of the current limiting reactor, and the current flowing through the switching element gradually decreases from zero. As a result, even when the transformer is an ideal transformer having no leakage inductance, zero current switching is ensured, so that switching loss and noise at the time of turning on the switching element can be reduced as compared with the invention according to claim 1. Can be reduced.

According to a third aspect of the present invention, there is provided a transformer-insulated DC-DC converter, wherein one end is connected to a connection point between the primary winding of the transformer and the switching element.
Rectifying element, a resonance capacitor connected between the other end of the first rectifying element and the other end of the DC power supply, a connection point between the resonance capacitor and the first rectifying element, and the transformer And an auxiliary winding of the transformer connected in series between a primary winding of the transformer and a connection point of the first rectifier.
When the switching element changes from the off state to the on state, when the resonance capacitor and the auxiliary winding of the transformer and the second rectifying element and the switching element form a closed circuit. A resonance current flows, whereby a voltage generated in the auxiliary winding of the transformer is supplied to the load via the secondary winding of the transformer and the rectifying and smoothing circuit.

When the switching element is turned off with the switching element turned on, the current flowing from the primary winding of the transformer to the switching element is switched to the current flowing to the resonance capacitor via the first rectifying element. The resonance capacitor is charged in a sinusoidal manner.
As a result, the voltage at both ends of the switching element rises in a sine wave form from 0 V, so that zero-voltage switching is performed when the switching element is turned off, and the switching loss is reduced. When the switching element is turned on from the off state, the resonance capacitor charged to the voltage of the DC power supply during the off period starts discharging, and the resonance capacitor and the auxiliary winding of the transformer, the second rectifying element, A resonance current flows in a closed circuit formed by the switching elements. Thereby, the current of the switching element becomes 0
, A zero current switching is performed when the switching element is turned on, and the switching loss is reduced. As described above, the switching loss at the time of the ON / OFF operation of the switching element can be reduced. At the same time, a spike-like surge voltage and current generated when the switching element is turned off and on are absorbed by the resonance action of the resonance capacitor and the leakage inductance of the transformer, so that noise based on the surge voltage and current can be reduced. . Further, when the switching element is turned on, the voltage generated in the auxiliary winding of the transformer by the resonance current flowing in the closed circuit is supplied to the load via the secondary winding of the transformer and the rectifying and smoothing circuit. Most of the discharge energy of the storage capacitor is supplied to the load, thereby reducing the power loss inside the converter and improving the efficiency. In particular, the transformer-insulated DC-DC converter according to the third aspect of the invention has an advantage that the circuit configuration is simpler than the invention according to the first aspect.

Further, in the transformer-insulated DC-DC converter according to the present invention, a current limiting reactor is connected between the primary winding of the transformer and the switching element. In this transformer-insulated DC-DC converter, when the switching element is turned on, the surge current flowing from the primary winding of the transformer to the transistor is absorbed by the self-inducing action of the current limiting reactor, and the current flowing through the switching element gradually decreases from zero. As a result, even when the transformer is an ideal transformer having no leakage inductance, zero current switching is ensured, and switching loss and noise at the time of turning on the switching element are more reduced than in the invention according to claim 3. Can be reduced.

According to a fifth aspect of the present invention, there is provided a transformer-isolated DC-DC converter, comprising: an auxiliary winding of the transformer connected between a primary winding of the transformer and the switching element; A first rectifier element having one end connected to a connection point between the auxiliary winding and the switching element;
A resonance capacitor connected between the other end of the first rectifier element and the other end of the DC power supply; a connection point between the resonance capacitor and the first rectifier element; and a primary winding of the transformer. And a second rectifier element connected between the auxiliary winding and a connection point, wherein when the switching element is turned on from an off state, the resonance capacitor and the second rectifier element and A resonance current flows in a closed circuit formed by the auxiliary winding of the transformer and the switching element, whereby a voltage generated in the auxiliary winding of the transformer is transmitted through the secondary winding of the transformer and the rectifying and smoothing circuit. Supplied to the load.

When the switching element is switched to the off state while the switching element is on, the current flowing from the primary winding of the transformer to the switching element via the auxiliary winding is used for resonance via the first rectifying element. The current is switched to the current flowing through the capacitor, and the resonance capacitor is charged in a sine wave shape. As a result, the voltage at both ends of the switching element rises in a sine wave form from 0 V, so that zero-voltage switching is performed when the switching element is turned off, and the switching loss is reduced. Also, when the switching element is turned on from the off state, the resonance capacitor charged to the voltage of the DC power supply during the off period starts discharging, and the resonance capacitor, the second rectifier, the auxiliary winding of the transformer, and the like. A resonance current flows in a closed circuit formed by the switching elements. As a result, the current of the switching element increases in a sine wave form from 0, so that zero current switching is performed when the switching element is turned on, and the switching loss is reduced. As described above, the switching loss at the time of the ON / OFF operation of the switching element can be reduced. At the same time, the spike-like surge voltage and current generated when the switching element is turned off and turned on are absorbed by the resonance action of the leakage inductance of the resonance capacitor and the transformer, and the falling and rising of the voltage and current waveforms of the switching element are gradual. Therefore, noise based on the surge voltage and the current can be reduced. Further, when the switching element is turned on, the voltage generated in the auxiliary winding of the transformer by the resonance current flowing in the closed circuit is supplied to the load via the secondary winding of the transformer and the rectifying and smoothing circuit. Most of the discharge energy of the storage capacitor is supplied to the load, thereby reducing the power loss inside the converter and improving the efficiency. Furthermore, when the switching element is turned on, a surge current flowing from the primary winding of the transformer to the switching element via the auxiliary winding is absorbed by the self-induction action of the auxiliary winding of the transformer, and the current flowing to the switching element is reduced from zero. Since the increase is gradual, the current limiting reactor required when the transformer is an ideal transformer having no leakage inductance becomes unnecessary. Therefore, zero current switching at the time of turning on the switching element can be more reliably performed with a small number of parts, and switching loss and noise can be further reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a transformer-insulated DC-DC converter according to the present invention will be described below with reference to FIGS. However, in FIG. 1, substantially the same parts as those shown in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 1, the transformer-isolated DC-DC converter according to the present embodiment includes a primary winding 2a of a transformer 2.
And a diode 11 as a first rectifying element having an anode terminal (one end) connected to a connection point of the transistor 3;
A resonance capacitor 12 connected between the cathode terminal (the other end) of the diode 11 and the cathode terminal (the other end) of the DC power supply 1, and a connection point between the resonance capacitor 12 and the cathode terminal of the diode 11 and the transformer 2 A primary winding 13a of the auxiliary transformer 13 and a diode 14 as a second rectifier connected in series between the primary winding 2a and a connection point of the anode terminal of the diode 11, and an anode terminal of the DC power supply 1 A secondary winding 13b of the auxiliary transformer 13 and a diode 15 as a third rectifier are connected in series between the (one end) and the cathode terminal. The transformer 2
For both the auxiliary transformer 13 and the auxiliary transformer 13, a leakage transformer having a leakage inductance is used. Other configurations are
This is substantially the same as the transformer-insulated DC-DC converter of FIG.

Next, a transformer-insulated DC-D shown in FIG.
The operation of the C converter will be described. As shown in FIG. 2A, when the transistor 3 is turned on before t ₁ , a current I ₀ flows through the primary winding 2a of the transformer 2 and the transistor 3. At this time, a voltage having the same polarity as the voltage of the primary winding 2a is induced in the secondary winding 2b of the transformer 2,
Since the rectifier diode 4 is in the conductive state, the smoothing capacitor 5 is charged from the secondary winding 2b of the transformer 2 via the rectifier diode 4, and DC power is supplied to the load 6. On the other hand, before t ₁ , the resonance capacitor 12 is not charged, and the voltage at both ends is 0V.

As shown in FIG. 2A, at t ₁ , the control pulse signal voltage V _B applied from the control circuit 7 to the base terminal of the transistor 3 goes from a high level to a low level,
When the transistor 3 changes from the on state to the off state, the current I _{0 of the} primary winding 2 a of the transformer 2 flowing through the transistor 3 is transmitted through the diode 11 to the resonance capacitor 12.
The current is switched to Therefore, the current I _TR flowing through the transistor 3 becomes 0 as shown in FIG.
At this time, the current flowing in the resonance capacitor 12 increases sinusoidally, and the resonance capacitor 12 is charged with the polarity shown in FIG. 1, and the voltage of the resonance capacitor 12 rises sinusoidally from 0V. Thus, as shown in FIG. 2B, the voltage V _TR across the transistor 3 rises in a sine wave form from 0V. For this reason, when the transistor 3 is turned off, zero voltage switching is performed with little overlap between the voltage waveform and the current waveform. At t ₂ , when the resonance capacitor 11 is charged to the voltage E of the DC power supply 1 and the voltage V _TR across the transistor 3 becomes equal to the voltage E of the DC power supply 1 as shown in FIG. Secondary winding 2b
Becomes 0 V, the rectifier diode 4 is reverse-biased and becomes non-conductive, and the charge charged in the smoothing capacitor 5 during the ON period of the transistor 3 is discharged to the load 6.

As shown in FIG. 2A, at t ₃ , the control pulse signal voltage V _B applied from the control circuit 7 to the base terminal of the transistor 3 changes from a low level to a high level,
When the transistor 3 changes from the off state to the on state, FIG.
As shown in (B), the voltage V _TR across the transistor 3 quickly drops to 0V. At the same time, the resonance capacitor 12 starts discharging, and the resonance capacitor 12 and the leakage inductance of the transformer 2 and the auxiliary transformer 13 resonate, and the resonance capacitor 12 and the auxiliary transformer 13
A resonance current flows in a closed circuit formed by the next winding 13a, the diode 14, and the transistor 3. At this time, a voltage is generated in the secondary winding 13b of the auxiliary transformer 13, and the voltage generated in the secondary winding 13b is regenerated to the DC power supply 1 via the diode 15. As a result, most of the discharge energy of the resonance capacitor 12 when the transistor 3 is turned on is regenerated to the DC power supply 1 via the auxiliary transformer 13 and the diode 15. Transistor 3
The current I _TR flowing from the primary winding 2a of the transformer 2 to the transistor 3 during turn-on of gradually linearly increases from 0 as shown in FIG. 2 (C), a current I _TR of the transistor 3 is at t ₄ Current I _{0 of} primary winding 2a of transformer 2
After that, it increases in a sinusoidal manner thereafter. Therefore, when the transistor 3 is turned on, zero current switching with little overlap between the voltage waveform and the current waveform is achieved. In t _5, the resonant current component becomes zero current I _TR of the transistor 3, trans as shown in FIG. 2 (C) 2
The primary winding when 2a becomes equal to the current I ₀ of the, thereafter current I ₀ flows in the primary winding 2a and the transistor 3 of the transformer 2 from the DC power source 1. Thereby, 2 of the transformer 2
A voltage having the same polarity as that of the voltage of the primary winding 2a is induced in the secondary winding 2b, and the rectifier diode 4 is turned on. The smoothing capacitor 5 is charged from the secondary winding 2b of the transformer 2 via the rectifier diode 4. At the same time, DC power is supplied to the load 6.

As described above, in this embodiment, zero voltage switching and zero current switching are performed when the transistor 3 is turned off and turned on, so that switching loss can be reduced. Further, a spike-shaped surge voltage and a surge current generated when the transistor 3 is turned off and turned on are absorbed by the resonance action of the resonance capacitor 11 and the leakage inductance of the transformer 2 and the auxiliary transformer 21, and the voltage and current waveforms of the transistor 3 Rises and falls slowly, so that the surge voltage when the transistor 3 is turned on and off,
Noise based on the surge current can be reduced. Further, when the transistor 3 is turned on, most of the discharge energy of the resonance capacitor 12 is supplied to the auxiliary transformer 13.
In addition, since the power is regenerated to the DC power supply 1 through the diode 15, the power loss inside the converter can be reduced and the efficiency can be improved.

The transformer-insulated DC of the embodiment shown in FIG.
-The DC converter can be changed. For example, the transformer-isolated DC-DC converter according to the embodiment shown in FIG. 3 is different from the transformer-isolated DC-DC converter shown in FIG. Are connected. In this case, an ideally manufactured transformer having no leakage inductance may be used as the transformer 2. Other configurations are substantially the same as those of the transformer-insulated DC-DC converter shown in FIG. Therefore, in the transformer-insulated DC-DC converter of the embodiment shown in FIG. 3, substantially the same operation and effect as in FIG. 1 can be obtained. In the transformer-insulated DC-DC converter shown in FIG. 3, when the transistor 3 is turned on, the primary winding 2a of the transformer 2 is turned on.
, The surge current flowing through the transistor 3 is absorbed by the self-inducing action of the current limiting reactor 16, and the current I _TR flowing through the transistor 3 gradually increases from zero. Therefore, even when the transformer 2 is an ideal transformer having no leakage inductance, no surge current is generated.
Therefore, the zero current switching at the time of turning on the transistor 3 becomes more reliable, and the transistor 3
, Switching loss and noise at the time of turn-on can be further reduced.

The transformer-isolated DC-DC converter of the embodiment shown in FIG.
The primary winding 13a of the auxiliary transformer 13 shown in FIG.
And the secondary winding 13b and the diode 15 of the auxiliary transformer 13 shown in FIG. 1 are omitted.
However, the number of turns of the auxiliary winding 2c is set to be extremely smaller than the number of turns of the primary winding 2a. Other configurations are substantially the same as those of the transformer-insulated DC-DC converter shown in FIG. FIG.
In the transformer-isolated DC-DC converter shown in FIG. 2, when the transistor 3 is turned on, the resonance current flowing in a closed circuit formed by the resonance capacitor 12, the auxiliary winding 2 c of the transformer 2, the diode 14, and the transistor 3 is used. A voltage is generated in the auxiliary winding 2c, and this voltage is supplied to the load 6 via the secondary winding 2b of the transformer 2, the rectifier diode 4 and the smoothing capacitor 5. Thus, most of the discharge energy of the resonance capacitor 12 when the transistor 3 is turned on is supplied from the auxiliary winding 2c of the transformer 2 to the load 6 via the secondary winding 2b, the rectifier diode 4, and the smoothing capacitor 5. . The other operations when the transistor 3 is turned off or turned on are substantially the same as those in the embodiment shown in FIG. Therefore, in the embodiment shown in FIG. 4, substantially the same effects as in the embodiment shown in FIG. 1 can be obtained. Further, in the transformer-isolated DC-DC converter shown in FIG. 4, the secondary circuit of the auxiliary transformer 13 in the case of FIG. 1, that is, the secondary winding 13b and the diode 15 of the auxiliary transformer 13 can be omitted. It has the advantage of being simpler.
Further, the transformer-isolated DC-DC converter shown in FIG. 4 can be changed in the same manner as shown in FIG. 3 as shown in FIG. Therefore, in the transformer-insulated DC-DC converter of the embodiment shown in FIG. 5, substantially the same operation and effect as in the case of FIG. 3 can be obtained.

In the transformer-isolated DC-DC converter of the embodiment shown in FIG. 6, the connection position of the auxiliary winding 2c of the transformer 2 shown in FIG. 4 is changed between the primary winding 2a and the transistor 3. Things. Other configurations are substantially the same as those of the transformer-insulated DC-DC converter shown in FIG. Therefore, the embodiment shown in FIG. 6 can obtain substantially the same operation and effect as the embodiment shown in FIG. Further, in the transformer-isolated DC-DC converter shown in FIG. 6, when the transistor 3 is turned on, a surge current flowing from the primary winding 2a of the transformer 2 to the transistor 3 via the auxiliary winding 2c causes an auxiliary winding of the transformer 2 to be turned on. The current flowing through the transistor 3 is absorbed by the self-inducing action of 2c and gradually increases from 0. For this reason, for example, as shown in FIG. 5, the current limiting reactor 16 required when the transformer 2 is an ideal transformer having no leakage inductance is unnecessary, and even in that case, no surge current is generated. Therefore, the transformer isolation type DC-
In the DC converter, even when the transformer 2 is an ideal transformer having no leakage inductance, the zero current switching at the time of turning on the transistor 3 is more reliably performed with a small number of parts, and the switching loss and noise at the time of turning on the transistor 3 are reduced. It can be further reduced.

The embodiments of the present invention are not limited to the above embodiments, and various modifications are possible. For example, FIG.
In each of the embodiments shown in FIG.
3A and 5A, the primary current limiting reactor 16 is connected between the connection point of the diode 14 and the connection point of the transistor 3 and the diode 11 as shown in FIG. 3 and FIG. Similar effects can be obtained by connecting the current limiting reactor 16 in series with the line 2a. Also,
In each of the above embodiments, the embodiment in which the present invention is applied to the forward type DC-DC converter is shown.
For each embodiment shown in FIG.
It is also applicable to a C converter. Further, in each of the above embodiments, a mode in which a bipolar transistor is used as a switching element has been described, but a MOS-FET (M
Other switching elements such as OS field effect transistors), J-FETs (junction field effect transistors), IGBTs (insulated gate transistors) or thyristors can also be used.

[0022]

According to the present invention, the switching loss and noise can be reduced and the power loss inside the converter can be reduced, so that the conversion efficiency of the transformer-isolated DC-DC converter can be greatly improved.

[Brief description of the drawings]

FIG. 1 shows a transformer insulation type D showing an embodiment of the present invention.
Electric circuit diagram of C-DC converter

FIG. 2 is a waveform chart showing voltages and currents of respective parts of the circuit of FIG.

FIG. 3 is an electric circuit diagram showing a modified embodiment of the circuit of FIG. 1;

FIG. 4 is an electric circuit diagram of a transformer-insulated DC-DC converter showing another embodiment of the present invention.

FIG. 5 is an electrical diagram showing a modified embodiment of the circuit of FIG.

FIG. 6 is an electrical diagram showing another modified embodiment of the circuit of FIG.

FIG. 7 is an electric circuit diagram showing a conventional transformer-insulated DC-DC converter.

FIG. 8 is a waveform chart showing an overlapping portion of a switching voltage waveform and a switching current waveform of the circuit of FIG. 7;

[Explanation of symbols]

1. . . DC power supply, 2. . . Transformer, 2a. . . Primary winding, 2b. . . Secondary winding, 2c. . . Auxiliary winding,
3. . . 3. transistors (switching elements); . .
Rectifier diode, 5. . . 5. smoothing capacitor; . . Load, 7. . . Control circuit, 11. . . 11. diode (first rectifying element), . . 12. resonance capacitor; . .
Auxiliary transformer, 13a. . . Primary winding, 13b. . . Secondary winding, 14. . . Diode (second rectifier), 1
5. . . 15. diode (third rectifier); . . Current limiting reactor

 ──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Seiya Fukumoto 3-6-3 Kitano, Niiza-shi, Saitama Sanken Electric Co., Ltd.

Claims (5)

[Claims] 1. A DC power supply, a primary winding of a transformer, and a switching element are connected in series, and the switching element is turned on and off so that a secondary winding of the transformer is connected via a rectifying and smoothing circuit. In a transformer-insulated DC-DC converter for supplying a DC output of a constant voltage different from the voltage of a DC power supply to a load, a first rectifier having one end connected to a connection point between a primary winding of the transformer and the switching element. An element, a resonance capacitor connected between the other end of the first rectifying element and the other end of the DC power supply, the resonance capacitor and the first capacitor.
A primary winding and a second rectifier element of an auxiliary transformer connected in series between a connection point of the rectifier element and a primary winding of the transformer and a connection point of the first rectifier element; A secondary winding of the auxiliary transformer and a third rectifying element connected in series between one end and the other end of the power supply, wherein when the switching element changes from an off state to an on state, the resonance capacitor And a resonance current flows through a closed circuit formed by the primary winding of the auxiliary transformer, the second rectifier element, and the switching element, whereby the voltage generated in the secondary winding of the auxiliary transformer becomes 3. A transformer-isolated DC-DC converter, wherein the DC power is regenerated by the DC power supply via the rectifier element. 2. The transformer-isolated DC-DC converter according to claim 1, wherein a current limiting reactor is connected between a primary winding of the transformer and the switching element. 3. A DC power supply, a primary winding of a transformer, and a switching element are connected in series, and the switching element is turned on and off so that the secondary winding of the transformer is connected via a rectifying and smoothing circuit. In a transformer-insulated DC-DC converter for supplying a DC output of a constant voltage different from the voltage of a DC power supply to a load, a first rectifier having one end connected to a connection point between a primary winding of the transformer and the switching element. An element, a resonance capacitor connected between the other end of the first rectifying element and the other end of the DC power supply, the resonance capacitor and the first capacitor.
An auxiliary winding and a second rectifier element of the transformer connected in series between a connection point of the rectifier element and a primary winding of the transformer and a connection point of the first rectifier element, When the switching element changes from the off state to the on state, a resonance current flows in a closed circuit formed by the resonance capacitor and the auxiliary winding of the transformer and the second rectifying element and the switching element. A transformer-isolated DC-DC converter, wherein a voltage generated in an auxiliary winding of the transformer is supplied to the load via a secondary winding of the transformer and the rectifying / smoothing circuit. 4. The transformer-isolated DC-DC converter according to claim 3, wherein a current limiting reactor is connected between a primary winding of the transformer and the switching element. 5. A DC power supply, a primary winding of a transformer, and a switching element are connected in series, and the switching element is turned on / off to perform a rectifying / smoothing circuit from a secondary winding of the transformer. A transformer-insulated DC-DC converter for supplying a constant-voltage DC output different from the voltage of a DC power supply to a load, wherein an auxiliary winding of the transformer is connected between a primary winding of the transformer and the switching element. A first rectifier element having one end connected to a connection point between the auxiliary winding of the transformer and the switching element; and a first rectifier element connected between the other end of the first rectifier element and the other end of the DC power supply. And a second rectifier element connected between a connection point between the resonance capacitor and the first rectification element and a connection point between the primary winding and the auxiliary winding of the transformer. When the switching element changes from an off state to an on state, a resonance current flows in a closed circuit formed by the resonance capacitor, the second rectifying element, the auxiliary winding of the transformer, and the switching element. A transformer-isolated DC-DC converter, wherein a voltage generated in an auxiliary winding of the transformer is supplied to the load via a secondary winding of the transformer and the rectifying / smoothing circuit.