JP3138998B2 - Transformer isolated DC-DC converter - Google Patents

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. Transformer-isolated DC-DC that supplies a DC output of a constant voltage different from the voltage of
Converters have been widely used in electronic devices such as power supply circuits. For example, the conventional transformer-insulated DC-DC converter shown in FIG. 5 includes a DC power supply 1 such as a battery or a capacitor input type rectifier circuit, a transformer 2 having a primary winding 2a and a secondary winding 2b, and a DC power supply. A rectifying / smoothing circuit (a rectifying / smoothing circuit) comprising a primary winding 2a of a transformer 2 and a transistor 3 as a switching element connected in series to both ends of the transformer 1 and a rectifying diode 4 and a smoothing capacitor 5 connected to a secondary winding 2b of the transformer 2 4, and 5), and a smoothing capacitor 5 and the load 6 connected in parallel, and a control circuit 7 for imparting to the on-off operation of the transistor 3 and a control pulse signal V _B to the base terminal of the transistor 3 . Although not 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, control pulses for applying to the base terminal of the error output voltage and a comparator circuit for comparing the triangular wave voltage of the oscillator circuit unit, generates a control pulse signal V _B proportional to the time width of the output voltage of the comparator circuit transistor 3 And a generating circuit section. In the transformer isolated DC-DC converter, the control circuit 7 is changed in accordance with the pulse width of the control pulse signal V _B to be applied to the base terminal of the transistor 3 to the terminal voltage of the load 6, the on-off period of the transistor 3 By controlling, 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]

Figure 6 The object of the invention is to solve the above-collector trans-insulated DC-DC converter of the transistor 3 shown in FIG. 5 - a waveform diagram of the collector current waveform I _C emitter voltage waveform V _CE of the transistor 3 Show. As shown in FIG. 6, when the transistor 3 is turned on and turned off, an overlapping portion W of the collector-emitter voltage waveform V _CE of the transistor 3 and the collector current waveform I _C of the transistor 3 is obtained.
However, there is a disadvantage that a large switching loss occurs due to the above. In addition, since the collector-emitter voltage waveform V _CE and the collector current waveform I _C of the transistor 3 rise sharply, the spike-like surge voltage V _sr and the surge current I _sr
And there is a drawback that noise based on these is generated. Therefore, power loss inside the converter increases due to generation of switching loss, noise, and the like, and there is a disadvantage that the efficiency of the converter is reduced.

Accordingly, the present invention provides a transformer-insulated type D which can reduce switching loss and noise and improve efficiency.
It is an object to provide a C-DC converter.

[0005]

A transformer-isolated DC-DC converter according to the present invention comprises one end of a DC power supply (1), a primary winding (2a) of a transformer (2), and a switching element (3). Are connected in series, and the switching element (3) is turned on and off to turn on the voltage of the DC power supply (1) from the secondary winding (2b) of the transformer (2) through the rectifying and smoothing circuits (4, 5). A DC output of a constant voltage different from the above is supplied to the load (6). This transformer-isolated DC-DC converter is a primary winding of a transformer (2).
(2a) and a first rectifier element (11) having one end connected to a connection point of the switching element (3), and a second rectifier element (11) having the other end connected to the other end of the DC power supply (1). A resonance capacitor (12) connected therebetween, a resonance capacitor (12) and a first rectifying element.
(11) and an auxiliary winding (2) of the transformer (2) connected in series between a connection point of the primary winding (2a) of the transformer (2) and a connection point of the first rectifying element (11). 2c) and a second rectifying element (14).

When the switching element (3) is switched from the on state to the off state, a current flowing from the primary winding (2a) of the transformer (2) to the switching element (3) is applied to the first rectifier element (1).
The current is switched to the current flowing through the resonance capacitor (12) via 1), and the resonance capacitor (12) is charged in a sine wave shape.
As a result, the voltage across the switching element (3) becomes 0 V
, A zero voltage switching (ZVS) is performed when the switching element (3) is turned off, and the switching loss is reduced.

When the switching element (3) is turned on from the off state, the resonance capacitor (12) charged to the voltage of the DC power supply (1) starts discharging during the off period,
Resonant capacitor (12) and auxiliary winding (2c) of transformer (2)
In addition, a resonance current flows in a closed circuit formed by the second rectifying element (14) and the switching element (3). As a result, the voltage generated in the auxiliary winding (2c) of the transformer (2) is
Through the secondary winding (2b) and the rectifying and smoothing circuits (4, 5)
(6), the current of the switching element (3) increases in a sine wave form from 0, so that when the switching element (3) is turned on, zero current switching (ZCS) is performed, and the switching loss is reduced.

The spike-like surge voltage and current generated when the switching element (3) is turned off and turned on are absorbed by the resonance action of the leakage inductance of the resonance capacitor (12) and the transformer (2), and the switching element (3) is absorbed. Since the falling and rising of the voltage and current waveforms in ()) become gentle, noise based on surge voltage and current can be reduced. Further, when the switching element (3) is turned on, a voltage generated in the auxiliary winding (2c) of the transformer (2) due to a resonance current flowing in the closed circuit is generated in the transformer (2).
Through the secondary winding (2b) and the rectifying and smoothing circuits (4, 5)
(6), most of the discharge energy of the resonance capacitor (12) is supplied to the load (6), and a simpler circuit configuration reduces power loss inside the converter and improves efficiency. be able to.

In the embodiment of the present invention, when a current limiting reactor (16) is connected between the primary winding (2a) of the transformer (2) and the switching element (3), the switching element (3) is turned on. At times, the surge current flowing from the primary winding (2a) of the transformer (2) to the transistor (3) is absorbed by the self-inducing action of the current limiting reactor (16), and the current flowing to the switching element (3) gradually decreases from zero. So increase the transformer
(2) Even with an ideal transformer without leakage inductance, zero current switching is ensured, and the switching element
(3) Switching loss and noise at the time of turn-on can be further reduced.

A transformer-isolated DC-DC converter according to another embodiment of the present invention comprises a primary winding of a transformer (2).
(2a) and the auxiliary winding (2c) of the transformer (2) connected between the switching element (3) and the connection point of the auxiliary winding (2c) of the transformer (2) and the switching element (3). A first rectifier element (11) having one end connected thereto; and a resonance capacitor (1) connected between the other end of the first rectifier element (11) and the other end of the DC power supply (1).
2), the connection point between the resonance capacitor (12) and the first rectifying element (11), the primary winding (2a) and the auxiliary winding (2c) of the transformer (2).
And a second rectifying element (14) connected between the connection points (1) and (2).

When the switching element (3) is switched from the on state to the off state, a current flowing from the primary winding (2a) of the transformer (2) to the switching element (3) via the auxiliary winding (2c) is reduced. Resonant capacitor (12) via 1 rectifying element (11)
And the resonance capacitor (12) is charged in a sine wave shape. With this, the switching element
Since the voltage at both ends of (3) rises in a sine wave form from 0 V,
Zero-voltage switching is performed when the switching element (3) is turned off, and switching loss is reduced.

When the switching element (3) is turned on from the off state, the resonance capacitor (12) charged to the voltage of the DC power supply (1) during the off period starts discharging,
A resonance current flows in a closed circuit formed by the resonance capacitor (12), the second rectifier (14), the auxiliary winding (2c) of the transformer (2), and the switching element (3). As a result, the voltage generated in the auxiliary winding (2c) of the transformer (2) is transferred to the load (6) via the secondary winding (2b) of the transformer (2) and the rectifying and smoothing circuits (4, 5).
And the current of the switching element (3) increases in a sine wave form from 0, so that zero current switching is performed when the switching element (3) is turned on, and the switching loss is reduced. The spike-like surge voltage and current generated when the switching element (3) is turned off and turned on are absorbed by the resonance action of the leakage inductance of the resonance capacitor (12) and the transformer (2), and the voltage of the switching element (3) is absorbed. Further, since the falling and rising of the current waveform become gentle, noise based on the surge voltage and the current can be reduced. Further, when the switching element (3) is turned on, a voltage generated in the auxiliary winding (2c) of the transformer (2) by a resonance current flowing in the closed circuit is generated by the transformer.
Since it is supplied to the load (6) through the secondary winding (2b) and the rectifying and smoothing circuits (4, 5) of (2), most of the discharge energy of the resonance capacitor (12) is To reduce the power loss inside the converter and improve the efficiency.
Further, when the switching element (3) is turned on, a surge current flowing from the primary winding (2a) of the transformer (2) to the switching element (3) via the auxiliary winding (2c) causes an auxiliary winding of the transformer (2). Absorbed by the self-inducing action of the line (2c), the current flowing through the switching element (3) gradually increases from 0,
The current limiting reactor (16) required when the transformer (2) is an ideal transformer having no leakage inductance becomes unnecessary. Therefore, a switching element with a small number of parts
(3) Zero current switching can be more reliably performed at the time of turn-on, and switching loss and noise can be further reduced.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One 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, 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 according to the present embodiment is a first rectifier element having an anode terminal (one end) connected to a connection point between a primary winding 2 a of a transformer 2 and a transistor 3. And a resonance capacitor 1 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.
2, an auxiliary winding 2c of the transformer 2 connected in series between a connection point between the resonance capacitor 12 and the cathode terminal of the diode 11 and a connection point between the primary winding 2a of the transformer 2 and the anode terminal of the diode 11. And a diode 14 as a second rectifying element. 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.

Next, a transformer-insulated DC-D shown in FIG.
The operation of the C converter will be described. When 2 time as shown in (A) t ₁ before transistor 3 is turned on, a current I ₀ flowing through the primary winding 2a and the transistor 3 of the transformer 2. 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 and the rectifier diode 4 is in a conducting state. Via the smoothing capacitor 5
And supplies DC power to the load 6. On the other hand, the resonant capacitor 12 at time t ₁ previously not charged, the voltage across is 0V.

As shown in FIG. 2A, at time 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 a high level to a low level, and the transistor 3 is turned on. Then, the current I _{0 of the} primary winding 2 a of the transformer 2 flowing to the transistor 3 is switched to the current flowing to the resonance capacitor 12 via the diode 11. Therefore, as shown in FIG. 2C, the current I _TR flowing through the transistor 3 becomes zero. At this time,
The current flowing through the resonance capacitor 12 increases sinusoidally, and the resonance capacitor 12 is charged with the polarity shown in FIG.
The voltage of the resonance capacitor 12 rises in a sine wave form 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 with little overlap between the voltage waveform and the current waveform is achieved.
Becomes a time t _2, the resonant capacitor 11 is a DC power source 1
2B, the voltage V _TR across the transistor 3 becomes equal to the voltage E of the DC power supply 1 as shown in FIG. As a result, the voltage of the secondary winding 2b of the transformer 2 becomes 0 V, so that the rectifier diode 4 is reverse-biased and becomes non-conductive, and the electric charge charged in the smoothing capacitor 5 during the ON period of the transistor 3 is transferred to the load 6 Released to

As shown in FIG. 2A, at time 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, and the transistor 3 is turned off. Fig. 2
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 a resonance current flowing in a closed circuit formed by the resonance capacitor 12 -the auxiliary winding 2c of the transformer 2 -the diode 14 -the transistor 3 causes the auxiliary winding of the transformer 2 to be discharged. A voltage is generated at 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. For this reason, when the transistor 3 is turned on, most of the discharge energy of the resonance capacitor 12 is transferred from the auxiliary winding 2 c of the transformer 2 to 2.
Secondary winding 2b, rectifier diode 4, and smoothing capacitor 5
Is supplied to the load 6 via the. The current flowing at the time of turn-on of the transistor 3 from the primary winding 2a of the transformer 2 to the transistor 3 I _TR increases linearly from 0 as shown in FIG. 2 (C), the current of the transistor 3 to time t ₄ I _TR
Becomes equal to the current I _{0 of the} primary winding 2a of the transformer 2,
Thereafter, it increases in a sinusoidal manner. Therefore, when the transistor 3 is turned on, zero current switching is performed with little overlap between the voltage waveform and the current waveform. At time t _5, the resonant current component becomes zero current I _TR of the transistor 3, becomes equal to the current I ₀ of the primary winding 2a of the transformer 2 as shown in FIG. 2 (C), thereafter the direct current power source 1 , A current I ₀ flows through the primary winding 2 a of the transformer 2 and the transistor 3. As a result, a voltage having the same polarity as that of the voltage of the primary winding 2a is induced in the secondary winding 2b of the transformer 2, and the rectifier diode 4 is turned on.
The smoothing capacitor 5 is charged via the
Is supplied with DC power.

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. The spike-shaped surge voltage and 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 of the transistor 3 are absorbed. Since the rise and fall of the waveform become gentle, it is possible to reduce noise based on surge voltage and surge current when the transistor 3 is turned on and off. Furthermore, when the transistor 3 is turned on, most of the discharge energy of the resonance capacitor 12 is regenerated to the DC power supply 1 via the auxiliary transformer 13 and the diode 15, so that the power loss inside the converter can be reduced with a simpler circuit configuration. Efficiency can be improved.

The transformer-insulated DC of the embodiment shown in FIG.
-The DC converter can be changed. For example, the transformer 2 of the transformer-insulated DC-DC converter shown in FIG.
By connecting the current limiting reactor 16 between the primary winding 2a and the transistor 3, the transformer-insulated DC-DC converter of the embodiment shown in FIG. 3 is obtained. 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, the transformer-insulated DC of the embodiment shown in FIG.
With the -DC converter, substantially the same operation and effect as in the case of FIG. 1 can be obtained. Also, a transformer-insulated DC-DC shown in FIG.
In the converter, when the transistor 3 is turned on, the surge current flowing from the primary winding 2a of the transformer 2 to 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, zero current switching when the transistor 3 is turned on becomes more reliable, and switching loss and noise when the transistor 3 is turned on can be further reduced.

When the connection position of the auxiliary winding 2c of the transformer 2 shown in FIG. 1 is changed between the primary winding 2a and the transistor 3, the transformer-insulated DC-DC of the embodiment shown in FIG.
A converter is obtained. Other configurations are substantially the same as those of the transformer-insulated DC-DC converter shown in FIG. 1, and the embodiment shown in FIG. 4 can obtain substantially the same operation and effect as the embodiment shown in FIG. Further, the transformer insulation type D shown in FIG.
In the C-DC converter, 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 is absorbed by the self-induction action of the auxiliary winding 2c of the transformer 2, and the transistor is turned on. The current flowing through 3 gradually increases from 0. For this reason,
For example, as shown in FIG. 3, the current limiting reactor 16 required for the transformer 2 which is an ideal transformer having no leakage inductance is unnecessary, and no surge current is generated. Therefore, the transformer-insulated DC-DC of the embodiment shown in FIG.
In the converter, even if the transformer 2 is an ideal transformer having no leakage inductance, zero current switching can be more reliably performed at the time of turning on the transistor 3 with a small number of parts, and switching loss and noise at the time of turning on the transistor 3 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 described above, an example in which the current limiting reactor 16 is connected between the connection point between the primary winding 2a and the diode 14 of the transformer 2 and the connection point between the transistor 3 and the diode 11 is shown. As shown in
Similar effects can be obtained even if the current limiting reactor 16 is connected in series with the secondary winding 2a. In each of the above embodiments, a mode using a bipolar transistor as a switching element has been described. However, a MOS-FET (MOS field effect transistor), a J-FET (junction field effect transistor), and an IGBT (insulated gate) are used. Other switching elements such as type transistors) or thyristors can also be used.

[0021]

According to the present invention, the switching loss and the 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 shown in 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 showing another modified embodiment of the circuit of FIG. 1;

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

FIG. 6 is a waveform chart showing an overlapping portion between a switching voltage waveform and a switching current waveform of the circuit of FIG. 5;

[Explanation of symbols]

1. . 1. DC power supply, . Transformer, 2a. . Primary winding, 2b. . Secondary winding, 2c. . 2. auxiliary winding; .
3. transistor (switching element); . Rectifier diode, 5. . 5. smoothing capacitor; . load,
7. . Control circuit, 11. . 11. diode (first rectifying element); . 13. resonance capacitor; . 15. diode (second rectifying element); . Current limiting reactor,

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Seiya Fukumoto 3-6-3 Kitano, Niiza-shi, Saitama Sanken Electric Co., Ltd. (56) References JP-A-58-15469 (JP, A) JP-A-56-31116 (JP, A) JP-A-5-236738 (JP, A) JP-A-58-145086 (JP, U) JP-A-63-51584 (JP, U) (58) Fields investigated (Int) .Cl. ⁷ , DB name) H02M 3/28

Claims (3)

(57) [Claims] 1. A rectifying and smoothing circuit from a secondary winding of the transformer by connecting one end of a DC power supply, a primary winding of a transformer, and a switching element in series, and turning on and off the switching element. A transformer-isolated DC-DC converter for supplying a DC output of a constant voltage different from the voltage of the DC power supply to a load via a transformer, one end of which is connected to a connection point between the primary winding of the transformer and the switching element. A first rectifying element, a resonance capacitor connected between the other end of the first rectification element and the other end of the DC power supply, the resonance capacitor and the first capacitor;
And an auxiliary winding and a second rectifying element of the transformer connected in series between a connection point of the rectifying element and a primary winding of the transformer and a connection point of the first rectifying element. A transformer-isolated DC-DC converter characterized by the above-mentioned. 2. A current limiting reactor is connected between a primary winding of the transformer and the switching element.
3. The transformer-insulated DC-DC converter according to item 1. 3. A rectifying and smoothing circuit from a secondary winding of the transformer by connecting one end of a DC power supply, a primary winding of a transformer, and a switching element in series, and turning on and off the switching element. A transformer-isolated DC-DC converter that supplies a DC output of a constant voltage different from the voltage of the DC power supply to a load via a transformer, wherein the transformer connected between a primary winding of the transformer and the switching element An auxiliary winding, 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 second end of the first rectifier element and the other end of the DC power supply. A resonance capacitor connected therebetween, and a second connection connected between a connection point between the resonance capacitor and the first rectifying element and a connection point between the primary winding and the auxiliary winding of the transformer. Trans-insulated DC-DC converter, characterized in that a flow element.