JP2000152621A - Transformer-insulated dc-to-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce switching loss and noise of a transformer-insulated DC-DC converter, and prevent the breakage of a switching element due to the magnetic saturation of the transformer in case of a forward system. SOLUTION: A transformer-insulated DC-DC converter is equipped with a diode 10, whose anode terminal is connected to the junction between a primary winding 2a of a transformer 2 and a transistor 3, a capacitor 11 for resonance, which is connected between the cathode terminal of the diode 10 and the emitter terminal of the transistor 3, and a reactor 13 for resonance and a diode 14, which are connected in series between the junction between the diode 10 and the capacitor 11 for resonance and the junction between the primary winding 2a and the transistor 3, and the capacitor 11 for resonance is charged to a voltage higher than a voltage E of a DC power source 1 from 0 V by the current flowing through the primary winding 2a and the diode 10 from the DC power source 1 at the turn-off of the transistor 3 and the exciting current of the transformer 2, and the primary winding 2a of the transformer 2 is excited in reverse.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transformer-insulated DC.
More particularly, the present invention relates to a transformer-isolated DC-DC converter that reduces switching loss and noise and prevents damage to a switching element due to magnetic saturation of a transformer in a forward system.

[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 DC-D that takes out a DC output of a constant voltage different from the
Conventionally, C 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. 5 includes a DC power supply 1 such as a battery or a capacitor input type rectifier circuit, and a primary winding connected in series with an anode terminal of the DC power supply 1. A transformer 2 having a secondary winding 2a and a secondary winding 2b; a collector terminal (first main terminal) connected in series with the primary winding 2a of the transformer 2;
A rectifying / smoothing circuit including a transistor 3 as a switching element having an emitter terminal (second main terminal) connected to a cathode terminal of the rectifying diode 4, and a rectifying diode 4 and a smoothing capacitor 5 connected to a secondary winding 2b of a transformer 2. When, a smoothing capacitor 5 and the load 6 connected in parallel, on the transistor 3 by applying a control pulse signal V _B to the base terminal of the transistor 3 (the control terminal) in accordance with the terminal voltage of the load 6
A control circuit 7 for turning off and a primary winding 2 of the transformer 2
a of the first resonance capacitor 8 having one end connected between the first resonance capacitor a and the collector terminal of the transistor 3, and a discharge connected between the other end of the first resonance capacitor 8 and the anode terminal of the DC power supply 1. Diode 9 and first resonance capacitor 8
A charging diode 10 having an anode terminal (one end) connected between one end of the transistor 3 and the collector terminal of the transistor 3; a cathode terminal (the other end) of the charging diode 10; The second resonance capacitor 11 connected between the terminal and the emitter terminal of the transistor 3, the connection point between the first resonance capacitor 8 and the discharge diode 9, the charging diode 10 and the second resonance capacitor It comprises a resonance reactor 13 and a backflow preventing diode 14 as a backflow rectifying element connected in series with the connection point 11. That is, the transformer-isolated DC-DC converter of FIG. 5 stores energy in the transformer 2 during the ON period of the transistor 3 and the rectifying diode 4 on the secondary side is in a non-conductive state, and the transistor 3 is turned off from the on state. In this state, energy is released from the transformer 2 and the rectifier diode 4 on the secondary side becomes conductive when the state is established.

[0004] Although not shown in the figure due to well-known technology,
An oscillation circuit for generating a triangular wave voltage having a constant period, an error amplifier for calculating and amplifying an error voltage of a terminal voltage of the load 6 with respect to a reference voltage, and an error output voltage of the error amplifier are included in the control circuit 7. and a comparing circuit for comparing the triangular wave voltage of the oscillation circuit, and a control pulse generating circuit portion for imparting to generate a control pulse signal V _B proportional to the time width of the output voltage of the comparator circuit to the base terminal of the transistor 3 Is provided.

[0005] In the above transformer isolated DC-DC converter, the control circuit 7, the pulse width of the control pulse signal V _B to be applied to the base terminal of the transistor 3 is changed according to the terminal voltage of the load 6, the transistor 3 By controlling the ON / OFF period, a constant DC output voltage V _O different from the voltage E of the DC power supply 1 is supplied to the load 6. Further, the voltage between the collector and the emitter terminal (between both main terminals) of the transistor 3 is reduced to 0 V by the resonance action of the first and second resonance capacitors 8 and 11 and the resonance reactor 13.
, A zero voltage switching (ZVS) when the transistor 3 is turned off, and the switching loss is reduced. Further, a spike-shaped surge voltage and surge current generated at the time of turning off and turning on the transistor 3 are absorbed by the resonance action between the first and second resonance capacitors 8 and 11 and the resonance reactor 13, and the transistor 3 is turned on. -Surge voltage, surge current and noise during off operation are reduced.

[0006]

In the transformer-isolated DC-DC converter shown in FIG. 5, when the transistor 3 is on, an exciting current flows from the DC power supply 1 to the transformer 2 to accumulate energy, and The magnetic flux density of the second core increases. Next, when the transistor 3 changes from the on state to the off state, the magnetic flux density of the core of the transformer 2 decreases by the rise during the on period of the transistor 3 while releasing the energy stored in the transformer 2 and the transformer 2 is reset. Is done. However, when the transformer isolation type DC-DC converter shown in FIG. 5 has a forward-type circuit configuration, when the transistor 3 is turned off from the on-state, the energy stored during the on-time remains as it is. Each time the transistor 3 is turned on, energy is accumulated, and the magnetic flux density of the core of the transformer 2 increases. If the magnetic flux density exceeds the maximum magnetic flux density, the transformer 2 is magnetically saturated and the inductance is reduced, so that a large exciting current flows through the transformer 2 and the transistor 3 may be damaged. Therefore, FIG.
When the transformer-isolated DC-DC converter is applied to the forward method, the transformer 2 cannot be reset during the off-period of the transistor 3, so that the transistor 3 is destroyed by magnetic saturation of the transformer 2.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a transformer-insulated DC-DC converter that can reduce switching loss and noise and prevent the switching element from being destroyed due to magnetic saturation of the transformer in the case of the forward system.

[0008]

A transformer-isolated DC-DC converter according to the present invention comprises a DC power supply and a transformer.
A secondary winding and a switching element are connected in series, and the switching element is turned on and off, so that a DC voltage of a constant voltage different from the voltage of the DC power supply from a secondary winding of the transformer via a rectifying and smoothing circuit. Get the output. The transformer-isolated DC-DC converter includes a resonance circuit connected between both main terminals of the switching element, and a bypass circuit connected between the resonance circuit and a primary winding of the transformer. The resonance circuit includes a charging rectifier element having one end connected between the primary winding and a first main terminal of the switching element; a charging rectifier element having the other end connected to the DC power supply and the switching element. And a resonance capacitor connected between the second main terminal of the element and the bypass circuit, wherein a connection point between the charging rectifying element and the resonance capacitor and the primary winding and the switching element are connected to each other. A resonance reactor and a backflow prevention rectifier are connected in series between the first main terminal and the connection point.
When the switching element changes from the on state to the off state, a current flowing from the DC power supply through the primary winding to the resonance circuit and an exciting current of the transformer cause a resonance capacitor in the resonance circuit to be substantially 0V. To a voltage higher than the voltage of the DC power supply, and reversely excites the primary winding via the bypass circuit by the charged voltage of the resonance capacitor.

When the switching element is turned off with the switching element turned on, the current flowing through the switching element is switched to the current to the resonance circuit side, and the resonance capacitor is changed into a sine wave via the charging rectifying element. Charged. Thereby, the first of the switching elements
Since the voltage between the main terminal and the second main terminal rises in a sine wave form from 0 V, zero voltage switching is performed when the switching element is turned off, and the switching loss of the switching element can be reduced.

At this time, the current flowing from the DC power supply through the primary winding of the transformer to the resonance circuit and the excitation current of the transformer cause the resonance capacitor in the resonance circuit to have a voltage of approximately 0V.
To a voltage higher than the voltage of the DC power supply, a voltage in the opposite direction is applied to the primary winding of the transformer via the bypass circuit by the charging voltage of the resonance capacitor, and the primary winding of the transformer is reversely excited. You. Thus, the transformer is reset by reducing the magnetic flux density of the core of the transformer during the ON period of the switching element, so that the magnetic saturation of the transformer can be prevented and the transistor can be prevented from being destroyed.

As described above, the switching loss during the operation of the switching element can be reduced, and the destruction of the switching element due to the magnetic saturation of the transformer can be prevented in the case of the forward system. Further, spike-shaped surge voltage, surge current and noise generated at the time of turning off and turning on the switching element are absorbed by the resonance action of the resonance capacitor in the resonance circuit and the resonance reactor in the bypass circuit, and the voltage and the voltage of the switching element are absorbed. Since the falling and rising of the current waveform become gentle, the surge voltage, surge current and noise during the operation of the switching element can be reduced.

A tertiary winding coupled to the transformer with a polarity opposite to that of the primary winding is provided. When the switching element changes from an on state to an off state, a voltage generated in the tertiary winding causes When a reverse voltage is generated in the primary winding and the primary winding is reversely excited by the reverse voltage and the charging voltage of the resonance capacitor, the charging voltage of the resonance capacitor is changed to DC during the OFF period of the switching element. Since the voltage can be maintained at a constant value equal to or higher than the voltage of the power supply, there is an advantage that the reset of the transformer becomes more reliable, and the breakdown of the transistor due to the magnetic saturation of the transformer can be more reliably prevented.

[0013]

1 and 2 show an embodiment of a transformer-insulated DC-DC converter according to the present invention.
It will be described based on. However, in FIG. 1, portions substantially the same as the portions shown in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 1, the transformer-isolated DC-DC converter of the present embodiment is different from the transformer-isolated DC-DC converter shown in FIG. 5 in that a first resonance capacitor 8 and a discharge diode 9 are used. Omitted, the cathode terminal of the reverse current blocking diode 14 is connected between the primary winding 2a of the transformer 2 and the collector terminal of the transistor 3, and the secondary winding 2b of the transformer 2 has the same polarity as the primary winding 2a. In addition, a commutating diode 16 and a reactor 17 are connected between the rectifying diode 4 and the smoothing capacitor 5 to change to a forward-type circuit configuration.
In the circuit of FIG. 1, the charging diode 10 and the resonance capacitor 11 form a resonance circuit 12, and the resonance reactor 13 and the backflow prevention diode 14 form a bypass circuit 15. Other configurations are substantially the same as those of the transformer-insulated DC-DC converter of FIG.

Next, the 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 on before t ₁ , the transformer 2 is excited by the voltage E of the DC power supply 1, and the current I ₀ flows through the primary winding 2a of the transformer 2 and the transistor 3. Is flowing. At this time, since 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, the rectifying diode 4 is biased in the forward direction and becomes conductive, so that the secondary winding 2b , A current flows through the rectifying diode 4 and the reactor 17 to the smoothing capacitor 5, and the DC output voltage V _O is supplied to the load 6.

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 changes from the high level to the low level, and the transistor 3 changes from the on state. When turned off,
The current I _S flowing through the transistor 3 shown in FIG.
Is immediately switched to the current flowing to the resonance circuit 12 side. At the same time, the rectifying diode 4 is turned off, so that a back electromotive force is generated in the reactor 17 and the reactor 1
7, a current flows through the path of the smoothing capacitor 5 and the commutating diode 16, and the DC output voltage V _O is supplied to the load 6. At this time, the charging diode 10 in the resonance circuit 12
As the current flowing through the resonance capacitor 11 increases, the resonance capacitor 11 is charged with the polarity shown in FIG. 1, and the voltage V _C across the resonance capacitor 11 becomes 0 V as shown in FIG. And rises in a sine wave form. As a result, as shown in FIG. 2D, the voltage V _S between the collector and emitter terminals of the transistor 3 rises in a sine wave form from 0 V, so that when the transistor 3 is turned off, the overlap between the voltage waveform and the current waveform is small. Voltage switching is performed.

At this time, the current flowing through the resonance capacitor 11 is supplied from the DC power source 1 to the primary winding 2 of the transformer 2.
a, and the sum of the current flowing through the charging diode 10 and the exciting current of the transformer 2, the resonance capacitor 11 is charged to a voltage higher than the voltage E of the DC power supply 1 as shown in FIG. to reach a maximum value E ₁ in the t _2. Therefore, a reverse voltage is applied from the resonance capacitor 11 to the primary winding 2a of the transformer 2 via the bypass circuit 15, and the primary winding 2a of the transformer 2 is reversely excited. As a result, the magnetic flux density of the core of the transformer 2 decreases by an amount increased during the ON period of the transistor 3, and the transformer 2 is reset. Then, the resonance capacitor 11
Is a resonance reactor 13 and a backflow prevention diode 14
Is discharged through the bypass circuit 15 and the primary winding 2a of the transformer 2 as shown in FIG.
Voltage V _C of 1 at both ends is equal to the voltage E of the DC power source 1 in the t _3.

As shown in FIG. 2A, at t ₄ , 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, and the transistor 3 changes from the off state. When turned on,
The collector of the transistor 3 as shown in FIG. 2 (D) - voltage V _S between emitter terminal quickly drops to 0V.
At the same time, the voltage V _C across the resonance capacitor 11
As shown in FIG. 2 (B), the voltage drops from the voltage E in a cosine wave, and the resonance capacitor 11 and the resonance reactor 13 resonate, and the resonance capacitor 11 and the resonance reactor 1
3. A resonance current flows through the path of the backflow preventing diode 14 and the transistor 3. Therefore, the resonance reactor 1
Current I _L flowing through the 3 becomes a sinusoidal wave as shown in FIG. 2 (C). Further, since the current I _S flowing through the transistor 3 is the sum of the resonance current flowing through the above-described path and the excitation current of the transformer 2, the resonance current increases sinusoidally as shown in FIG.

As shown in FIG. 2B, when the voltage V _C across the resonance capacitor 11 becomes 0 V at t ₅ ,
Current I _L flowing through the resonant reactor 13 becomes substantially maximum value of the sine wave as shown in FIG. 2 (C), is a circulating current path resonant reactor 13, reverse current blocking diode 14 and charging diode 10 Try to keep flowing. However, this circulating current is gradually attenuated as shown in FIG. 2C by the resistance of the impedance of the charging diode 10, the resonance reactor 13, the backflow preventing diode 14, the wiring, and the like, and finally becomes zero. Becomes At this time, the resonance current component of the current I _S of the transistor 3 becomes 0, and therefore, as shown in FIG.
a is equal to the current I ₀ flowing in the DC power source 1 after t _5.
, A current I ₀ flows through the primary winding 2 a of the transformer 2 and the transistor 3. Thereby, the secondary winding 2 of the transformer 2
b, a voltage having the same polarity as that of the voltage of the primary winding 2a is induced, and the rectifying diode 4 becomes conductive, and a current flows from the secondary winding 2b to the smoothing capacitor 5 via the rectifying diode 4 and the reactor 17. , The DC output voltage V _O is supplied to the load 6.

As described above, in this embodiment, zero voltage switching is performed when the transistor 3 is turned off, so that power loss during operation of the transistor 3, that is, switching loss can be reduced. Also, when the transistor 3 is turned off, the current flowing from the DC power supply 1 through the primary winding 2a of the transformer 2 and the charging diode 10 and the exciting current of the transformer 2 cause the resonance capacitor 11 to change the voltage of the resonance capacitor 11 from 0V to the voltage E of the DC power supply 1. Higher voltage E ₁
Is charged in the reverse voltage primary winding 2a of the applied transformer 2 is inverse excitation in the primary winding 2a of the transformer 2 by the voltage E _1. As a result, the magnetic flux density of the core of the transformer 2 is reduced by the amount increased during the ON period of the transistor 3, and the transformer 2 is reset. Therefore, magnetic saturation of the transformer 2 does not occur, and the breakdown of the transistor 3 can be prevented. . 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 between the resonance capacitor 11 and the resonance reactor 13, and the rising and falling of the voltage and current waveforms of the transistor 3 are performed. , The surge voltage, surge current, and noise during the on / off operation of the transistor 3 can be reduced.

The transformer insulation type D according to the embodiment shown in FIG.
The C-DC converter can be changed. For example, FIG.
In the transformer-insulated DC-DC converter according to the embodiment shown in FIG. 1, in the transformer-insulated DC-DC converter shown in FIG. 1, a tertiary winding 2c coupled to the primary winding 2a with a reverse polarity to the transformer 2 is provided. This tertiary winding 2c is connected to both ends of a smoothing capacitor 5 via a rectifying diode 18. Other configurations are substantially the same as those of the transformer-insulated DC-DC converter shown in FIG. Further, the control pulse signal voltage V _B , the voltage V _C of the resonance capacitor 11 in the transformer-insulated DC-DC converter shown in FIG.
Current I _L flowing through the resonant reactor 12, the collector of the transistor 3 - respectively the waveforms of the voltage V _S and the current flowing through the transistor 3 I _S between the emitter terminals Figure 4 (A)
To (E). In the transformer-insulated DC-DC converter shown in FIG. 3, when the transistor 3 changes from the on state to the off state, a voltage generated in the tertiary winding 2c of the transformer 2 generates a reverse voltage in the primary winding 2a, reverse voltage to the primary winding 2a of the transformer 2 by the charging voltage E ₁ of the reverse voltage and the resonance capacitor 11 is applied,
The primary winding 2a of the transformer 2 is reversely excited. For this reason,
As shown in FIG. 4B, during the off period of the transistor 3 (t _{1 to} t ₃ ), the voltage V _C of the resonance capacitor 11 is obtained.
Since the possible kept constant high voltage E ₁ than the voltage E of the DC power source 1, a reset transformer 2 becomes more reliable, it is possible to more reliably prevent the breakdown of the transistor 3 due to magnetic saturation of the transformer 2.

The embodiments of the present invention are not limited to the above embodiments, and various modifications are possible. For example, the connection order of the resonance reactor 13 and the backflow prevention diode 14 constituting the bypass circuit 15 of each of the above embodiments may be reversed. 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 (MOS field effect transistor), a J-FET (junction field effect transistor), and an IGBT (insulating Other switching elements such as gated transistors) or thyristors can also be used. It is also possible to divide the secondary winding 2b of the transformer 2 into a plurality of windings having different numbers of windings and connect a rectifying / smoothing circuit to each secondary winding to form a multi-output DC-DC converter. is there. Further, in the embodiment shown in FIG. 1, the primary winding 2a and the secondary winding 2b of the transformer 2 are coupled with the same polarity, and the rectifying diode 4 is in a conductive state when the transistor 3 is in the ON period. Although the embodiment applied to the DC-DC converter of the system is shown, the rectifying diode 4 is connected when the primary winding 2a and the secondary winding 2b of the transformer 2 are coupled with opposite polarities and the transistor 3 is in the ON period. The present invention is also applicable to a flyback type DC-DC converter in a non-conductive state.

[0023]

According to the present invention, switching loss and noise during operation of the switching element can be reduced,
In the case of the forward method, it is possible to prevent the switching element from being destroyed due to the magnetic saturation of the transformer, so that it is possible to improve the conversion efficiency and reduce the noise filter and to improve the reliability in both the forward and flyback methods. It becomes possible.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a transformer-insulated DC-DC converter showing one embodiment of the present invention.

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 of a transformer-insulated DC-DC converter showing another embodiment of the present invention.

FIG. 4 is a waveform chart showing the voltage and current of each part of the circuit of FIG.

FIG. 5 is an electric circuit diagram showing a conventional transformer-insulated DC-DC converter.

[Explanation of symbols]

1. DC power supply, 2. Transformer, 2a primary winding, 2b secondary winding, 2c tertiary winding, 3.
-Transistor (switching element), 4-Rectifier diode, 5-Smoothing capacitor, 6-Load,
7. Control circuit, 10. Diode for charging (rectifying element for charging), 11. Capacitor for resonance, 12.
・ Resonant circuit, 13 ・ ・ Resonant reactor, 14.
Backflow prevention diode (backflow prevention rectifier), 15
..Bypass circuits, 16..Diodes for commutation, 1
7. Reactor, 18. Diode for rectification

Continued on the front page F-term (reference)

Claims (2)

[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. Transformer-isolated DC that takes out a DC output of a constant voltage different from the voltage of the DC power supply
-A DC converter, comprising: a resonance circuit connected between both main terminals of the switching element; and a bypass circuit connected between the resonance circuit and a primary winding of the transformer. A charging rectifying element having one end connected between the primary winding and a first main terminal of the switching element; a second end of the charging rectifying element and a second end of the DC power supply and the switching element; A resonance capacitor connected between the main terminal and the main terminal; the bypass circuit includes a connection point between the charging rectifying element and the resonance capacitor, and a first main terminal of the primary winding and the switching element. And a rectifying element for preventing backflow, which is connected in series with the connection point of the following. When the switching element changes from an on state to an off state, the primary winding is supplied from the DC power supply. The resonance capacitor in the resonance circuit is charged from approximately 0 V to a voltage higher than the voltage of the DC power supply by a current flowing through the resonance circuit and an excitation current of the transformer, and the charging voltage of the resonance capacitor is used to charge the capacitor. A transformer-isolated DC, wherein the primary winding is reversely excited via a bypass circuit.
-DC converter. 2. A tertiary winding coupled to the transformer with a polarity opposite to that of the primary winding, wherein a voltage generated in the tertiary winding when the switching element changes from an on state to an off state. 2. The transformer isolated DC-D according to claim 1, wherein a reverse voltage is generated in a primary winding, and the primary winding is reversely excited by the reverse voltage and a charging voltage of the resonance capacitor.
C converter.