JP3525427B2 - Transformer isolated DC-DC converter - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a transformer insulation type DC.
It belongs to a DC converter, in particular, a transformer insulation type DC-DC converter that reduces switching loss and noise and prevents damage to a switching element due to magnetic saturation of a transformer.

[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 / off to operate a DC power supply from a secondary winding of the transformer through a rectifying / smoothing circuit. Isolated DC-D with a configuration that extracts a DC output of a constant voltage different from that of the
Conventionally, C converters have been widely used in power supply circuits of electronic devices and the like.

For example, a conventional transformer insulation type DC-DC converter shown in FIG. 3 is a DC power source 1 such as a battery or a capacitor input type rectifier circuit, and primary windings 2a and 2 connected in series to the DC power source 1. A transformer 2 having a secondary winding 2b, and a transistor 3 as a switching element in which both main terminals are connected in series to a primary winding 2a of the transformer 2.
A rectifying diode 4 whose anode terminal is connected to the secondary winding 2b of the transformer 2; a commutation diode 5 connected between the cathode terminal of the rectifying diode 4 and the secondary winding 2b; Reactor 6 having one end connected to the connection point of the diode 4 and the commutation diode 5, a smoothing capacitor 7 connected between the other end of the reactor 6 and the secondary winding 2b, and both ends of the smoothing capacitor 7 A control circuit 9 for applying a control pulse signal V _B to the base terminal of the transistor 3 according to the connected load 8 and the DC output voltage supplied to the load 8 to turn on / off the transistor 3.
And the primary winding 2a of the transformer 2 and the first of the transistor 3
And a diode 11 connected between the other end of the first resonance capacitor 10 and the anode terminal of the DC power supply 1.
And a charging diode 14 whose anode terminal is connected between one end of the first resonance capacitor 10 and the first main terminal of the transistor 3, a cathode terminal of the charging diode 14 and a cathode terminal of the DC power supply 1. The second connected between and
Of the resonance capacitor 15 and the resonance reactor 16 connected in series between the connection point of the diode 11 and the first resonance capacitor 10 and the connection point of the second resonance capacitor 15 and the charging diode 14. A reverse current blocking diode 17 is provided. That is, in the transformer-insulated DC-DC converter of FIG. 3, the rectifying diode 4 on the secondary side is in the conducting state during the ON period of the transistor 3, and the rectifying on the secondary side is when the transistor 3 is switched from the ON state to the OFF state. The circuit configuration is a forward system in which the working diode 4 becomes non-conductive. Although not shown in the figure because it is a well-known technique, the control circuit 9 includes an oscillation circuit unit that generates a triangular wave voltage having a constant cycle and an error amplification unit that arithmetically amplifies the error voltage of the terminal voltage of the load 8 with respect to the reference voltage. The circuit section compares the error output voltage of the error amplification circuit section and the triangular wave voltage of the oscillation circuit section, and generates the control pulse signal V _B having a time width proportional to the output voltage of the comparison circuit section to generate the transistor 3 And a control pulse generating circuit section to be applied to the base terminal of the.

In the above-mentioned transformer insulation type DC-DC converter, the control circuit 9 changes the pulse width of the control pulse signal V _{B applied} to the base terminal of the transistor 3 in accordance with the terminal voltage of the load 8 to change the pulse width of the transistor 3. By controlling the on / off period, a DC output having a constant voltage different from the voltage E of the DC power supply 1 is supplied to the load 8. Further, due to the resonance action of the first and second resonance capacitors 10 and 15 and the resonance reactor 16, the voltage between both main terminals of the transistor 3 and the current flowing through the transistor 3 rise from approximately 0 in a sine wave shape. When the transistor 3 is turned off and on, zero voltage and zero current switching is performed, and switching loss is reduced. Furthermore, the spike-shaped surge voltage and surge current generated when the transistor 3 is turned off and turned on are
And the second resonance capacitors 10 and 15 and the resonance reactor 16 are absorbed by the resonance action, so that the transistor 3
The surge voltage, surge current and noise during operation are reduced.

[0005]

In the transformer-insulated DC-DC converter shown in FIG. 3, when the transistor 3 is turned on and the second resonance capacitor 15 starts discharging, the first and second resonance capacitors 15 are used. Capacitors 10, 1
5 and the resonance reactor 16 resonate, and a resonance current flows through the paths of the second resonance capacitor 15, the resonance reactor 16, the backflow prevention diode 17, the first resonance capacitor 10 and the transistor 3. At this time, the first resonance capacitor 10 is charged in a cosine wave shape, and the DC power supply 1
Voltage E.

However, the first resonance capacitor 1
When the capacitance of 0 is smaller than that of the second resonance capacitor 15, the second resonance capacitor 15 is not sufficiently discharged, and the second resonance capacitor 15 is left with electric charges. When the transistor 3 is switched from the on state to the off state in this state, the second resonance capacitor 1
Since the voltage between both ends of 5 is not 0V, the electric charge accumulated in the second resonance capacitor 15 is not charged from 0V, and the voltage waveform and the current waveform overlap each other when the transistor 3 operates. This causes switching loss instead of zero voltage switching (ZVS).

Therefore, according to the present invention, by fully discharging the electric charge of the resonance capacitor during the ON period of the switching element and setting the voltage at both ends to approximately 0 V, the overlapping of the voltage and current waveforms during the operation of the switching element is achieved. It is an object of the present invention to provide a transformer insulation type DC-DC converter which is reduced in size to reduce switching loss and noise, and prevents magnetic saturation of a transformer to prevent transistor destruction.

[0008]

DISCLOSURE OF THE INVENTION A transformer insulation type DC-DC converter according to the present invention comprises a primary winding (2a) of a transformer (2) and a switching element (3) connected in series to a DC power source (1). And a resonance circuit (12) connected between both main terminals of the switching element (3), and a bypass circuit connected between the resonance circuit (12) and the primary winding (2a) of the transformer (2). (13) and are provided. The resonance circuit (12) includes a charging rectifying element (14) having one end connected to a connection point between the primary winding (2a) and the first main terminal of the switching element (3), and a charging rectifying element (14). ) And the resonance capacitor (15) connected to the connection point of the DC power supply (1) and the second main terminal of the switching element (3). By turning on / off the switching element (3), the rectifying and smoothing circuit (4, 4) can be connected from the secondary winding (2b) of the transformer (2).
Take out a DC output of constant voltage different from the voltage (E) of DC power supply (1) via 5). The bypass circuit (13) is a transformer that connects the charging rectifier (14) and the resonance capacitor (15) to the transformer.
A tertiary winding that is connected between the primary winding (2a) of (2) and the connection point of the DC power supply (1) and is connected to the primary winding (2a) in the opposite polarity.
(2c) and a backflow blocking rectifier (17) connected in series with the tertiary winding (2c). When the switching element (3) changes from the on state to the off state, due to the current flowing from the DC power supply (1) through the primary winding (2a) and the charging rectifying element (14) and the exciting current of the transformer (2). , Resonance capacitor (1
5) is charged to a voltage (2E) higher than that of the DC power supply (1) from approximately 0V, and the transformer (2) is reversely excited by the charge accumulated in the resonance capacitor (15). The tertiary winding (2c) of the transformer (2) when the switching element (3) changes from the off state to the on state.
The voltage of the opposite polarity to the primary winding (2a) is generated in the primary winding (2a)
And the total voltage of the third winding (2c) becomes 0V,
The charge accumulated in the resonance capacitor (15) is used as a resonance current that circulates through the reverse current blocking rectifier element (17), the tertiary winding (2c), the primary winding (2a) and the switching element (3). Discharge fully.

When the switching element (3) is switched from the ON state to the OFF state, the current flowing from the DC power source (1) through the primary winding (2a) and the charging rectifying element (14) and the transformer.
Due to the exciting current of (2), the resonance capacitor (15) is approximately 0V.
Is charged to a voltage (2E) higher than that of the DC power supply (1), and the transformer (2) is reversely excited by the charge accumulated in the resonance capacitor (15), that is, the charging voltage of the resonance capacitor (15). This reduces the magnetic flux density of the core of the transformer (2) by the amount that it increased during the ON period of the switching element (3) and resets the transformer (2), preventing magnetic saturation of the transformer (2). It is possible to prevent the switching element (3) from being damaged.

When the switching element (3) is switched from the off state to the on state, the tertiary winding (2c) of the transformer (2) is set to 1
The voltage of the opposite polarity to the secondary winding (2a) is generated and the primary winding (2a) and 3
The total voltage of the secondary winding (2c) becomes substantially 0V, and at this time, the electric charge accumulated in the resonance capacitor (15) is blocked by the backflow preventing rectifier (17), the tertiary winding (2c), When the switching element (3) is turned on, the resonance current that circulates through the primary winding (2a) and the switching element (3) is fully discharged, and the current of the switching element (3) increases in a sinusoidal wave from approximately 0A. At zero current switching (ZCS), the switching loss when the switching element (3) is turned on can be reduced.

Further, since the total voltage of the primary winding (2a) and the tertiary winding (2c) of the transformer (2) is substantially 0V, the charging voltage of the resonance capacitor (15) is sufficient. To be discharged. After switching, when switching the switching element (3) to the off state, the current flowing in the switching element (3) is switched to the current to the resonance circuit side, and the resonance capacitor (15) is passed through the charging rectifier element (14). ) Is charged sinusoidally from about 0V, the voltage between the first main terminal and the second main terminal of the switching element (3) also rises sinusoidally from about 0V, and the switching element (3) Zero voltage switching (ZVS) occurs at the time of turning off of 3), and the switching loss at the time of turning off of the switching element (3) can be reduced.

From the above, it is possible to reduce the switching loss during the on / off operation of the switching element (3), and
The spike-shaped surge voltage, surge current and noise generated when the switching element (3) is turned off are absorbed by the resonance action of the resonance capacitor (15) and the resonance reactor (16), and the voltage waveform of the switching element (3) rises. Is moderated, and it becomes possible to reduce surge voltage, surge current and noise during the operation of the switching element (3). When the switching element (3) is switched from the ON state to the OFF state, the transformer (2) is reversely excited and reset by the voltage (2E) higher than the DC power source (1) charged in the resonance capacitor (15). Therefore, the magnetic saturation of the transformer (2) can be prevented, and the switching element (3) can be prevented from being destroyed.

In one embodiment of the transformer insulation type DC-DC converter according to the present invention, the bypass circuit (13) includes a connection point of the charging rectifying element (14) and the resonance capacitor (15) and a tertiary winding ( A resonance reactor (16) connected in series with the backflow prevention rectifying element (17) is provided between it and 2c). When the switching element (3) changes from the off state to the on state,
The voltage of opposite polarity to the primary winding (2a) is generated in the tertiary winding (2c) of the transformer (2), and the total voltage of the primary winding (2a) and the tertiary winding (2c) is The electric charge accumulated in the resonance capacitor (15) becomes substantially 0V, and the resonance reactor (16), the reverse current blocking rectifier (17), the tertiary winding (2c), the primary winding (2a) and It fully discharges as a resonance current circulating through the switching element (3).

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a transformer insulation type DC-DC converter according to the present invention will be described below with reference to FIGS.
It will be described based on. However, in FIG. 1, parts that are substantially the same as the parts shown in FIG. 3 are given the same reference numerals, and descriptions thereof are omitted. As shown in FIG. 1, the transformer-insulated DC-DC converter according to the present embodiment is configured so that there is 1 between the cathode terminal of the reverse current blocking diode 17 and the connection point between the DC power supply 1 and the primary winding 2a of the transformer 2. The tertiary winding 2c is connected in the opposite polarity to the secondary winding 2a. In the circuit of FIG.
In the transformer insulation type DC-DC converter shown in
The first resonance capacitor 10 and the diode 11 are omitted, and other configurations are the transformer insulation type DC-D of FIG.
It is almost the same as the C converter.

Next, the transformer insulation type DC-D shown in FIG.
The operation of the C converter will be described. As shown in FIG. 2A, the control pulse signal voltage V _B applied from the control circuit 9 to the base terminal of the transistor 3 changes from the low level to the high level at t ₁ , and the transistor 3 changes from the off state to the on state. Then, as shown in FIG. 2 (E), the voltage V _S between the collector and the emitter, which is the first and second main terminals of the transistor 3, rapidly drops to about 0V. At the same time, a voltage having a polarity opposite to that of the primary winding 2a is generated in the tertiary winding 2c of the transformer 2, and the total voltage of the primary winding 2a and the tertiary winding 2c becomes substantially 0V. At this time,
The charge accumulated in the resonance capacitor 15 is transferred from the bypass circuit 13 to the resonance capacitor 15 and the resonance reactor 1.
6, reverse current blocking diode 17, transformer tertiary winding 2
c is discharged as a resonance current that circulates in the path of the primary winding 2a and the transistor 3, and the voltage V _C across the resonance capacitor 11 drops from the voltage E in a cosine wave shape as shown in FIG. It becomes approximately 0 V at t ₂ .

On the other hand, the current I flowing through the transistor 3
_S is from the bypass circuit 13, the resonance capacitor 15, the resonance reactor 16, the backflow prevention diode 17, the tertiary winding 2c of the transformer, the primary winding 2a, and the transistor 3
Since the resonant current circulating in a path between the sum of the current of the DC power source 1, a substantially 0A at t ₁ as shown in FIG. 2 (D)
Increases sinusoidally. Therefore, when the transistor 3 is turned on, the zero current switching (ZCS) in which the voltage waveform and the current waveform do not overlap each other is small, and the switching loss can be reduced.

A current I flowing through the resonance reactor 16
_When the transistor 3 is turned on, the _L is as shown in FIG.
When the voltage V _C of the resonance capacitor 15 becomes approximately 0 V at t ₂ as shown in FIG. 5, the resonance reactor 16, the reverse current blocking diode 17, the transformer tertiary winding 2 c, the primary winding 2 a, and It is short-circuited in the path of the charging diode 14 and tries to continue flowing as a circulating current. However, this current is attenuated by the resonance reactor 16, the backflow prevention diode 17, the tertiary winding 2c of the transformer, the primary winding 2a, the charging diode 14, and the resistance of the wiring, and eventually becomes 0A. At this time, the transistor 3
2D, since the resonance current component of the current I _S is 0 A.
As shown in, the current I ₀ flows from the DC power supply 1 to the primary winding 2a of the transformer 2 and the transistor 3 after t ₂ .
As a result, the primary winding 2a is attached to the secondary winding 2b of the transformer 2.
The voltage having the same polarity as that of the rectifying diode 4 is induced to bring the rectifying diode 4 into a conductive state, and the rectifying diode 4 moves from the secondary winding 2b.
Also, a current flows through the smoothing capacitor 7 via the reactor 6 and a DC voltage is supplied to the load 8.

Next, as shown in FIG. 2A, the control pulse signal voltage V _B applied from the control circuit 9 to the base terminal of the transistor 3 changes from the high level to the low level at t ₃ , and the transistor 3 turns on. When the on-state is changed to the off-state, the current I _S flowing in the transistor 3 shown in FIG. _2E is immediately switched to the current flowing to the resonance circuit 12 side, and the rectifying diode 4 becomes non-conductive. Therefore, the reactor 6 A counter electromotive force is generated in the current, and a current flows in the path of the reactor 6, the smoothing capacitor 7, and the commutation diode 5. At this time, due to the current flowing from the DC power supply 1 through the primary winding of the transformer 2 and the 2a charging diode 14 and the exciting current due to the energy accumulated in the transformer 2,
The resonance capacitor 15 is charged, and the voltage V _C across the resonance capacitor 15 rises from approximately 0 V in a sine wave shape as shown in FIG. As a result, as shown in FIG. 2E, the voltage V between the collector and the emitter of the transistor 3 is
_S rises from about 0 V in a sinusoidal manner, and when the transistor 3 is turned off, zero voltage switching (ZVS) is achieved in which the voltage waveform and the current waveform do not overlap each other.

As shown in FIG. 2B, the resonance capacitor 15 is charged to a voltage 2E higher than that of the DC power supply 1, and the transformer 2 is reversely excited by this charging voltage. This allows
Since the magnetic flux density of the core of the transformer 1 is reduced by the amount of increase during the ON period of the transistor 3 and the transformer 1 is reset, magnetic saturation of the transformer 1 is prevented and destruction of the transistor 3 can be prevented. When the transformer 2 is reset, the voltage of the transformer 2 becomes 0 V, and the collector-emitter voltage V _S of the transistor 3 becomes equal to the voltage E of the DC power supply 1 at time t ₄ as shown in FIG.

As described above, in this embodiment, the zero current switching and the zero voltage switching are performed when the transistor 3 is turned on / off, so that the power loss during the operation of the transistor 3, that is, the switching loss can be reduced. . The spike-shaped surge voltage and surge current generated when the transistor 3 is turned on / off is absorbed by the resonance action of the resonance capacitor 15 and the resonance reactor 16, and the current and voltage of the transistor 3 gradually fall and rise. Therefore, it is possible to reduce the surge voltage, surge current and noise during the operation of the transistor 3. Also, the resonance capacitor 1
Since the transformer is reverse-excited and reset by the high voltage 2E from the DC power supply 1 charged in 5, the magnetic saturation of the transformer 2 can be prevented and the transistor 3 can be prevented from being destroyed.

The embodiment of the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the embodiment, a mode in which a bipolar type transistor is used as a switching element is shown, but a MOS-FET (MOS
Field effect transistor), J-FET (junction field effect transistor), IGBT (insulated gate transistor), thyristor, or other switching element can be used. It is also possible to divide the secondary winding 2b of the transformer 2 into a plurality of windings each having a different number of turns and connect a rectifying / smoothing circuit to each secondary winding to form a multi-output DC-DC converter. is there.

In the series circuit constituting the bypass circuit 13, the resonance reactor 16, the backflow prevention diode 17, and the tertiary winding 2c of the transformer can be arranged in a different order, and the resonance reactor 16 is omitted. You may.

[0023]

According to the present invention, since switching loss and noise during operation of the switching element can be reduced, noise filters and the like can be eliminated. Further, it is possible to prevent the switching element from being broken due to the magnetic saturation of the transformer.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing the voltage and current of each part of the circuit shown in FIG.

FIG. 3 is an electric circuit diagram showing a conventional transformer insulation type 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 ・ ・ Rectifying diode, 5 ・ ・ Commutation diode, 6 ・ ・ Reactor, 7 ・ ・ Smoothing capacitor, 8 ・ ・ Load, 9
..Control circuit, 12 ... Resonance circuit, 13 ... Bypass circuit, 14 ... Charging diode (charging rectifying element), 15 ... Resonance capacitor, 16 ... Resonance reactor, 17 ... Reverse current blocking Diode (backflow blocking rectifier)

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/335

Claims (2)

(57) [Claims] 1. A primary winding of a transformer and a switching element connected in series to a DC power source, a resonance circuit connected between both main terminals of the switching element, and a primary winding of the resonance circuit and the transformer. A bypass circuit connected to a line, wherein the resonant circuit has a charging rectifying element whose one end is connected to a connection point between the primary winding and the first main terminal of the switching element; The resonance capacitor connected to the connection point of the DC power source and the second main terminal of the switching element is provided with the other end of the charging rectifying element, and the switching element is turned on / off to operate the switching capacitor. In a transformer-insulated DC-DC converter for extracting a DC output of a constant voltage different from the voltage of the DC power supply from a next winding through a rectifying / smoothing circuit, the bypass circuit includes the charging adjustment unit. A third winding connected between the connection point of the current element and the resonance capacitor and the connection point of the primary winding of the transformer and the DC power source and connected to the primary winding in the opposite polarity; A backflow blocking rectifying element connected in series with a secondary winding, and a current flowing from the DC power supply through the primary winding and the charging rectifying element when the switching element is switched from an on state to an off state. And the excitation current of the transformer charges the resonance capacitor from about 0 V to a voltage higher than that of the DC power supply, reversely excites the transformer by the charge accumulated in the resonance capacitor, and the switching element is turned off. When turned on, a voltage having a polarity opposite to that of the primary winding is generated in the tertiary winding of the transformer, and the total voltage of the primary winding and the tertiary winding becomes substantially 0V. , The above The reverse blocking rectifier element charges accumulated in the cotton rose capacitor, tertiary winding, 1
A transformer insulation type DC-DC converter which is sufficiently discharged as a resonance current circulating through a secondary winding and a switching element. 2. The bypass circuit includes a resonance reactor connected in series with the backflow blocking rectification element between a connection point of the charging rectification element and the resonance capacitor and the tertiary winding, When the switching element is switched from the off state to the on state, a voltage having a polarity opposite to that of the primary winding is generated in the tertiary winding of the transformer, and the voltage of the primary winding and the tertiary winding is changed. The sum total becomes substantially 0V, and the charge accumulated in the resonance capacitor is sufficient as a resonance current that circulates through the resonance reactor, the reverse current blocking rectifying element, the tertiary winding, the primary winding, and the switching element. The transformer insulation type DC-DC converter according to claim 1, which discharges into the air.