JPH11191961A - Transconnection dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce switching loss of a transconnection DC-DC converter and power loss due to residual energy on the primary of a transformer. SOLUTION: In a transconnection DC-DC converter, a first resonance capacitor 8 is connected to the joint of the primary winding 2a of a transformer and a transistor 3, a diode 10 is connected to the joint of a first resonance capacitor 8 and the transistor 3, a second resonance capacitor 11 is connected between the diode 10 and the - terminal of a DC power supply 1, an auxiliary transistor 21 being turned off Δt seconds after the charging voltage Vc2 of the capacitor 11 reaches the voltage E of the DC power supply 1 and turned on several seconds after the transistor 3 is turned on is connected between the capacitor 8 and the + terminal of the DC power supply 1, and a resonance reactor 12 and a diode 13 are connected in series between the transistor 21 and the capacitor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a transformer-connected DC.
More particularly, the present invention relates to a transformer-connected DC-DC converter that reduces switching loss and power loss generated by residual energy on the primary side 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 and off, so that a DC power supply is supplied from a secondary winding of the transformer via a rectifying and smoothing circuit. Transformer connection type 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, the conventional transformer-connected DC-DC converter shown in FIG. 4 includes a DC power supply 1 such as a battery or a capacitor input type rectifier circuit and primary windings 2a and 2a.
A transformer 2 having a secondary winding 2b, a primary winding 2a and a transistor 3 as a switching element of the transformer 2 connected in series to both ends of the DC power supply 1, and a rectifier connected to the secondary winding 2b of the transformer 2. A rectifying / smoothing circuit including a diode 4 and a smoothing capacitor 5, a load 6 connected in parallel with the smoothing capacitor 5, and control for applying a control pulse signal V _B1 to a base terminal of the transistor 3 to turn on / off the transistor 3. A circuit 7, a first resonance capacitor 8 having one end connected to a connection point between the primary winding 2a of the transformer 2 and the transistor 3, and a first resonance capacitor 8
And a diode 9 connected between the other end of the DC power supply 1 and one end of the first resonance capacitor 8 and the connection point of the transistor 3.
0 and the second resonance capacitor 1 connected between the other end of the diode 10 and the cathode terminal (the other end) of the DC power supply 1.
1, the connection point between the diode 9 and the first resonance capacitor 8, the second resonance capacitor 11 and the diode 10
Reactor 1 connected in series with the connection point of
2 and a diode 13. Although not shown, the control circuit 7 includes an oscillation circuit for generating a triangular wave voltage having a constant period, and an error amplifier for calculating and amplifying an error voltage of the terminal voltage of the load 6 with respect to the reference voltage. A comparison circuit for comparing the error output voltage of the error amplification circuit with the triangular wave voltage of the oscillation circuit; and generating a control pulse signal V _B1 having a time width proportional to the output voltage of the comparison circuit to generate the base of the transistor 3. And a control pulse generation circuit section provided to the terminal.

In the above-described transformer-connected DC-DC converter, the control circuit 7 changes the pulse width of the control pulse signal V _{B1 applied} to the base terminal of the transistor 3 according to the terminal voltage of the load 6, and By controlling the ON / OFF period, a DC output of a constant voltage different from the voltage E of the DC power supply 1 is supplied to the load 6. In addition, the resonance between the first and second resonance capacitors 8 and 11 and the resonance reactor 12 causes the voltage at both ends of the transistor 3 and the current flowing through the transistor 3 to rise in a sine wave form from zero. Zero voltage and zero current switching are performed at the time of turn-off and turn-on, and switching loss is reduced. Further, a spike-shaped surge voltage and surge current generated when the transistor 3 is turned off and turned on are absorbed by the resonance action between the first and second resonance capacitors 8 and 11 and the resonance reactor 12, and the transistor 3 is turned on. -Surge voltage, surge current and noise during off operation are reduced.

[0004]

In the transformer connection type DC-DC converter shown in FIG. 4, when the transistor 3 is turned off from the on state, the transistor 3 is turned off.
Is switched to a current flowing through the second resonance capacitor 11 via the diode 10, and the second resonance capacitor 11 is charged in a sine wave form from 0V, so that the voltage across the transistor 3 becomes 0V. And rises in a sine wave form. Therefore, transistor 3 is turned off by zero voltage switching (ZVS), and switching loss is reduced. However, when the charging voltage of the second resonance capacitor 11 reaches the voltage E of the DC power supply 1 and energy remains in the primary winding 2a of the transformer 2, the primary winding 2a of the transformer 2, the diode 10 and the resonance A small amount of current continues to flow through the reactor 12-diode 13-diode 9 path. For this reason, there is a drawback that power loss occurs due to the current that continues to flow in the above-described path.

Accordingly, an object of the present invention is to provide a transformer-connected DC-DC converter that can reduce switching loss and power loss generated by residual energy on the primary side of a transformer.

[0006]

A transformer-connected DC-DC converter according to the present invention comprises one of 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. In this transformer connection type DC-DC converter, the first resonance capacitor connected to the connection point between the primary winding of the transformer and the switching element, the first resonance capacitor and one end of the DC power supply are connected to each other. An auxiliary switching element connected therebetween, a first rectifying element connected to a connection point between the first resonance capacitor and the switching element, and the other end of the first rectifying element and the DC power supply. Between the second resonance capacitor connected between the second switching capacitor and the connection point between the auxiliary switching element and the first resonance capacitor and the connection point between the second resonance capacitor and the first rectifying element. A resonance reactor and a second rectifier element connected in series to the auxiliary switching element, the charging voltage of the second resonance capacitor reaching the voltage of the DC power supply. It turned off at the time or later,
When the switching element is turned on, it is turned on at the same time or later.

In another embodiment, in a transformer-connected DC-DC converter, a resonance reactor connected between a primary winding of the transformer and the switching element, a primary winding of the transformer, A first resonance capacitor having one end connected to a connection point of the resonance reactor, an auxiliary switching element connected between the other end of the first resonance capacitor and one end of the DC power supply,
A first rectifier element having one end connected to a connection point between the resonance reactor and the switching element; and a second rectifier element connected between the other end of the first rectifier element and the other end of the DC power supply. A resonance capacitor, and a second rectifier connected between a connection point between the auxiliary switching element and the first resonance capacitor and a connection point between the second resonance capacitor and the first rectifier. The auxiliary switching element is turned off when or after the charging voltage of the second resonance capacitor reaches the voltage of the DC power supply, and simultaneously or after the switching element is turned on. It turns on.

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 flowing through the second resonance capacitor via the first rectifying element, and the second current flows through the second resonance capacitor. The resonance capacitor is charged in a sinusoidal manner. Thus, the voltage at both ends of the switching element rises in a sine wave form from 0 V, so that zero voltage switching (ZVS) at the time of turning off the switching element is achieved, and the switching loss at the time of turning off the switching element can be reduced. Further, when energy remains in the primary winding of the transformer by turning the auxiliary switching element from the on state to the off state when the charging voltage of the second resonance capacitor reaches the voltage of the DC power supply or thereafter. In the above, the current that continues to flow through the path of the primary winding of the transformer, the first rectifying element, the resonance reactor, the second rectifying element, and the auxiliary switching element is cut off, so that the power loss generated by the current is reduced. be able to. Furthermore,
When the switching element is turned on from the off state, the second resonance capacitor is discharged and the first and second resonance capacitors are discharged.
The resonance capacitor and the resonance reactor resonate, and a resonance current flows through the switching element. As a result, the current of the switching element increases sinusoidally from 0,
Zero current switching (ZCS) when the switching element is turned on is achieved, and the switching loss when the switching element is turned on can be reduced. As described above, the switching loss at the time of the ON / OFF operation of the switching element can be reduced, and the transformer 1
Power loss generated by residual energy on the secondary side can be reduced. Further, the spike-shaped surge voltage and current generated when the switching element is turned off and turned on are absorbed by the resonance action of the resonance capacitor and the resonance reactor, and the falling and rising of the voltage and current waveforms of the switching element become gentle. Therefore, it is possible to reduce the surge voltage and the current during the ON / OFF operation of the switching element.

[0009] In another embodiment in which a resonance reactor is connected between the primary winding of the transformer and the switching element, the primary winding of the transformer is connected via the resonance reactor when the switching element is turned on. The surge current flowing through the switching element is absorbed by the self-inducing action of the resonance reactor, and the current flowing through the switching element gradually increases from zero. This eliminates the need for a current limiting reactor, which is required in the past, and reduces the number of components.Moreover, it is possible to more reliably perform zero current switching when the switching element is turned on, thereby further reducing switching loss and noise when the switching element is turned on. it can.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a transformer-connected 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. 4 are denoted by the same reference numerals, and description thereof will be omitted. As shown in FIG. 1, the transformer-connected DC-DC converter of the present embodiment has an auxiliary transistor 21 as an auxiliary switching element connected in place of the diode 9 in the transformer-connected DC-DC converter shown in FIG. is there. The control circuit 7 includes a voltage E of the DC power supply 1 and a voltage V _{C2 of} the second resonance capacitor 10.
The control pulse signal voltage V _B2 applied to the base terminal of the auxiliary transistor 21 after Δt seconds from when the voltage V _{C2 of} the second resonance capacitor 11 reaches the voltage E of the DC power supply 1 (t ₂ ). Switch from high level to low level,
In addition, the control pulse signal voltage V _B2 applied to the base terminal of the auxiliary transistor 21 is switched from the low level to the high level several seconds after the control pulse signal voltage V _B1 applied to the base terminal of the transistor 3 changes from the low level to the high level. An auxiliary transistor control circuit has been added. As a result, the auxiliary transistor 21 is turned off at Δt seconds after the voltage V _C2 across the second resonance capacitor 11 reaches the voltage E of the DC power supply 1, and turned on several seconds after the transistor 3 is turned on. Becomes Other configurations are the same as those of the transformer connection type DC-DC converter of FIG.

Next, a transformer connection type DC-D shown in FIG.
The operation of the C converter will be described. When the transistor 3 is turned on before t ₁ as shown in FIG. 2A, the primary winding 2a of the transformer 2 as shown in FIG.
The current I ₀ flows through the transistor 3. At this time, energy is accumulated in the transformer 2, and the first resonance capacitor 8 is charged to the voltage E of the DC power supply 1 with the polarity shown in FIG. 1 as shown in FIG. FIG. 2 (B)
The auxiliary transistor 21 is also in the ON state as shown in FIG.
On the other hand, since a voltage having a polarity opposite to the voltage of the primary winding 2a is induced in the secondary winding 2b of the transformer 2, the rectifier diode 4b
In the non-conductive state, no current flows and current flows from the smoothing capacitor 5 to the load 6.

[0012] As shown in FIG. 2 (A), becomes the control pulse signal voltage V _B1 applied from the control circuit 7 at t ₁ to the base terminal of the transistor 3 from the high level to the low level,
When the transistor 3 changes from the on state to the off state, the current flowing through the primary winding 2a of the transformer 2 is switched to the current I _C1 flowing through the first resonance capacitor 8 as shown in FIG. At the same time, as shown in FIGS. 2D and 2G, the current I _TR1 flowing through the transistor 3 is immediately switched to the current I _C2 flowing through the diode 10 through the second resonance capacitor 11. At this time, the first resonance capacitor 8 supplies energy to the transformer 2 via the auxiliary transistor 21 in the ON state and discharges the energy. Therefore, the current I _C1 flowing through the first resonance capacitor 8 decreases in a sine wave shape as shown in FIG. 2 (H), and the first resonance capacitor 8 as shown in FIG. both ends of the voltages V _C1 of going to drop in a sine wave from the voltage E of the DC power supply 1. Accordingly, as shown in FIG. 2 (G), the current I _C2 flowing through the second resonance capacitor 11 increases in a cosine waveform, and the second resonance capacitor 11 is charged.
As shown in (E), the voltage V _C2 across the second resonance capacitor 11 rises in a sine wave form from 0V. This allows
As shown in FIG. 2C, the voltage V across the transistor 3
_TR1 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 , the second resonance capacitor 1
As shown in FIG. 2 (E), the voltage V _C2 across
When the voltage V _TR1 across the transistor 3 becomes equal to the voltage E of the DC power supply 1 as shown in FIG. 2C, a back electromotive force is generated in the secondary winding 2b of the transformer 2. The rectifier diode 4 becomes conductive, energy stored in the transformer 2 is released from the secondary winding 2b to the load 6 via the rectifier diode 4, and the smoothing capacitor 5 is charged. At this time, due to the energy remaining in the primary winding 2a of the transformer 2, the primary winding 2a of the transformer 2, the diode 10, the resonance reactor 12, the diode 13,
A minute current continues to flow through the path of the auxiliary transistor 21. Therefore, as shown in FIG. 2B, the control pulse signal voltage V _B2 applied to the base terminal of the auxiliary transistor 21 from the control circuit 7 is changed from a high level to a low level after Δt seconds from t ₂ to turn on the auxiliary transistor 21. By changing the state from the off state to the off state, the current that continues to flow in the above path is cut off, and the power loss caused by the current can be reduced.

As shown in FIG. 2A, at t ₃ , the control pulse signal voltage V _B1 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 (C), the voltage V _TR1 across the transistor 3 quickly drops to 0V. At the same time, the second resonance capacitor 11 starts discharging, the first and second resonance capacitors 8 and 11 and the resonance reactor 12 resonate, and the second resonance capacitor 11 -the resonance reactor 1
A resonance current flows through a path of 2-diode 13-first resonance capacitor 8-transistor 3. The first at this time
The waveforms of the currents I _C1 , I _C2 and I _L flowing through the second resonance capacitors 8 and 11 and the second resonance capacitor 12 are as shown in FIGS. At this time, the first resonance capacitor 8 is charged in a cosine waveform,
As shown in FIG. 2 (F), the voltage V _C1 across the first resonance capacitor 8 rises from 0V in a cosine waveform. At the same time, the voltage V _C2 across the second resonance capacitor 11 drops from the voltage E in a cosine wave as shown in FIG. The current I _TR1 flowing from the primary winding 2a of the transformer 2 during turn-on of the transistor 3 to the transistor 3 continue to linearly increase from zero as shown in FIG. 2 (D), in t ₄ of the transistor 3 When the current I _TR1 becomes equal to the current I _{0 of the} primary winding 2a of the transformer 2, the current thereafter increases in a sinusoidal manner. Therefore, transistor 3
At the time of turn-on, zero-current switching with little overlap between the voltage waveform and the current waveform is achieved. Several seconds after the transistor 3 is turned on, that is, several seconds after t _{3, the} control pulse signal voltage V _B2 applied to the base terminal of the auxiliary transistor 21 from the control circuit 7 becomes low as shown in FIG. From the off state to the on state.

[0015] Figure 2 as shown in (I), when the current I _L of the resonant reactor 12 becomes zero at t _5, the voltage across V _C1 of the first and second resonance capacitor 8, 11, V _C2
Become the voltages E and 0 V of the DC power supply 1 as shown in FIGS. 2 (F) and 2 (E), respectively. At this time, the resonance current component of the current I _TR1 of the transistor 3 is 0, is equal to the current I ₀ of the primary winding 2a of the transformer 2 as shown in FIG. 2 (D), t ₅ after the DC power supply 1 to primary winding 2a of transformer 2
The current I ₀ flows through the transistor 3. This allows
The energy is stored in the transformer 2 and the rectifier diode 4 is turned off, the smoothing capacitor 5 is discharged, and the current flows to the load 6.

As described above, in this embodiment, zero voltage or zero current switching is achieved when the transistor 3 is turned off and turned on, so that the power loss during the on / off operation of the transistor 3, ie, the switching loss, is reduced. be able to. In addition, the auxiliary transistor 21 is turned off from the on state at time Δt seconds after the charging voltage V _{C2 of} the second resonance capacitor 11 reaches the voltage E of the DC power supply 1 (t ₂ ), so that the transformer 2 When energy remains in the primary winding 2a, the current that continues to flow through the path of the primary winding 2a of the transformer 2, the diode 10, the resonance reactor 12, the diode 13, and the auxiliary transistor 21 is cut off. The power loss caused by the above can be reduced. Furthermore, the spike-like surge voltage and surge current generated when the transistor 3 is turned off and turned on are first and second surge voltages.
Is absorbed by the resonance action of the resonance capacitors 8 and 11 and the resonance reactor 12, and the rise and fall of the voltage and current waveforms of the transistor 3 become gentle. Surge current and noise can be reduced.

The transformer connection type DC of the embodiment shown in FIG.
-The DC converter can be changed. For example, in the transformer connection type DC-DC converter of the embodiment shown in FIG. 3, in the transformer connection type DC-DC converter shown in FIG.
Is changed between the primary winding 2a and the transistor 3. In this case, an ideally manufactured transformer having no leakage inductance may be used as the transformer 2. Other configurations are similar to those of the transformer connection type DC-
It is almost the same as a DC converter. Therefore, in the transformer connection type DC-DC converter of the embodiment shown in FIG. 3, substantially the same operation and effect as in the case of FIG. 1 can be obtained. In the DC-DC converter of the transformer connection type shown in FIG.
A surge current flowing from the primary winding 2a to the transistor 3 via the resonance reactor 12
, The current I _TR1 flowing through the transistor 3 gradually increases from zero. For this reason, the current limiting reactor required when the transformer 2 is an ideal transformer having no leakage inductance becomes unnecessary, and the number of components can be reduced. Therefore, the zero current switching at the time of turning on the transistor 3 can be more reliably performed with a small number of parts and the transistor 3
, Switching loss and noise at the time of turn-on can be further reduced.

The embodiments of the present invention are not limited to the above embodiments, and various modifications are possible. For example, in each of the above embodiments, the auxiliary transistor 21 determines the voltage V _C2 across the second resonance capacitor 11 as the voltage E _C of the DC power supply 1.
At (t ₂ ), Δt seconds later,
Although the embodiment in which the transistor 3 is turned on several seconds after being turned on has been described, when the voltage V _C2 across the second resonance capacitor 11 reaches the voltage E of the DC power supply 1 without providing a delay time. The auxiliary transistor 21 may be turned off, and the auxiliary transistor 21 may be turned on at the same time when the transistor 3 is turned on. In each of the embodiments described above, a mode in which a bipolar transistor is used as a switching element and an auxiliary switching element has been described. However, a MOS-FET (MOS field effect transistor), a J-FET (junction field effect transistor),
Other switching elements such as IGBTs (Insulated Gate 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 and smoothing circuit to each of the secondary windings to form a multi-output DC-DC converter. is there. Further, in each of the above-described embodiments, the form in which the rectifier diode 4 is applied to the flyback type DC-DC converter in which the rectifier diode 4 is in a non-conducting state when the transistor 3 is on is shown. Forward type DC- in which the rectifier diode 4 is in a conductive state
The present invention is also applicable to a DC converter.

[0019]

According to the present invention, the switching loss at the time of the ON / OFF operation of the switching element can be reduced, and the power loss generated by the residual energy on the primary side of the transformer can be reduced. Type D
The conversion efficiency of the C-DC converter can be greatly improved.

[Brief description of the drawings]

FIG. 1 shows a transformer connection 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 of a transformer connection type DC-DC converter showing another embodiment of the present invention.

FIG. 4 is an electric circuit diagram showing a conventional transformer-connected DC-DC converter.

[Explanation of symbols]

1. . . DC power supply, 2. . . Transformer, 2a. . . Primary winding, 2b. . . 2. secondary winding; . . 3. transistors (switching elements); . . Rectifier diode, 5. . .
5. smoothing capacitor; . . Load, 7. . . Control circuit,
8. . . 8. first resonance capacitor; . . Diode, 10. . . Diode (first rectifier), 1
1. . . 11. second resonance capacitor; . . 12. Resonance reactor; . . A diode (second rectifier),
21. . . Auxiliary transistor (auxiliary switching element)

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

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 connection type DC to take out DC output of constant voltage different from DC power supply voltage
-In a DC converter, a first resonance capacitor connected to a connection point between a primary winding of the transformer and the switching element, and a first resonance capacitor connected between the first resonance capacitor and one end of the DC power supply. An auxiliary switching element, a first rectifying element connected to a connection point between the first resonance capacitor and the switching element, and a second rectifying element connected between the first rectifying element and the other end of the DC power supply. A second resonance capacitor connected in series between a connection point between the auxiliary switching element and the first resonance capacitor and a connection point between the second resonance capacitor and the first rectifier element. The auxiliary switching element, when the charging voltage of the second resonance capacitor reaches the voltage of the DC power supply, or Descending the turned off state, the transformer connected DC-DC converter, wherein the switching element is turned on at the same time with or after turned on. 2. 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 to the switching element via a rectifying and smoothing circuit. Transformer connection type DC to take out DC output of constant voltage different from DC power supply voltage
-In a DC converter, a resonance reactor connected between a primary winding of the transformer and the switching element, and a second reactor having one end connected to a connection point between the primary winding of the transformer and the resonance reactor. One resonance capacitor, an auxiliary switching element connected between the other end of the first resonance capacitor and one end of the DC power supply, and one end connected to a connection point between the resonance reactor and the switching element. The first rectifier element, a second resonance capacitor connected between the other end of the first rectifier element and the other end of the DC power supply, the auxiliary switching element, and the first resonance element. And a second rectifier connected between a connection point of the second capacitor and a connection point of the second resonance capacitor and the first rectifier. A transformer characterized in that it is turned off when the charging voltage of the second resonance capacitor reaches the voltage of the DC power supply or thereafter, and turned on simultaneously with or after the switching element is turned on. Connection type DC-DC converter.