JP2006087284A - Dc/dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC/DC converter capable of efficiently recovering all the snubber energy. <P>SOLUTION: A primary winding N1 of a transformer T with a tap a and a main switch S1 are connected in series between both ends of a DC power source E. A snubber circuit 1, in which a snubber diode D1 and snubber capacitor C1 are connected, is connected in parallel to the main switch S1. A recovery circuit 2, in which a regenerative reactor L1, regenerative auxiliary switch S2, and regenerative diode D2 are connected in series, is connected between the tap a of the primary winding N1 and a connection point A between the snubber diode D1 and snubber capacitor C1. At least one clamping diode D3, connected in series by way of the regenerative reactor L1, is connected between the tap a of primary winding N1 and a return terminal of the DC power source E. The clamping diode D3 is connected back-to-back to the snubber capacitor C1, and a cathode is connected to the high-potential side of the regenerative reactor L1, with an anode connected to the return terminal of the DC power source E. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention connects a primary winding of a transformer and a switch in series to both ends of a DC power source, and supplies power to a load of a secondary winding insulated by the transformer while the switch is on. The present invention relates to a flyback type DC / DC converter such as a flyback type that stores electric power in a transformer while a switch is on and supplies electric power stored in the transformer to a load while the switch is off.

A DC / DC converter that uses a semiconductor element such as a MOSFET, IGBT, or thyristor as a switch and controls the flow of energy by turning this switch on and off can in principle control power without loss.
Further, by increasing the switching frequency, it is possible to reduce the size and weight of the apparatus and improve the control performance.
However, in practice, a semiconductor switch is not an ideal switch and has a finite turn-on and turn-off time.
In addition, the circuit to which the switch is connected includes parasitic inductance of wiring, leakage inductance of the transformer, stray capacitance, accumulated charge of the diode, and the like.
As a result, switching loss and surges occur, which adversely affects peripheral electronic devices due to deterioration in control performance and noise.

A fundamental solution to this problem is soft switching.
Soft switching reduces the loss and suppresses the occurrence of surge by reducing the current passing through the switch and the voltage applied to the switch to zero when the switch is turned on and off.
Soft switching includes a method based on resonance operation, but one basic method is to connect a snubber circuit to both ends of the switch, absorb the snubber energy when the switch is off, and supply the snubber energy when the switch is on or before Or a method of collecting it to the load.

As a method for recovering the snubber energy, for example, Japanese Patent Laid-Open No. 10-191632 proposes a method in which a second transformer is provided and the energy stored in the snubber capacitor is supplied to the load as part of output power when the switch is turned on. However, in this case, there is a problem that not all energy is recovered.
For example, Japanese Patent Laid-Open No. 2000-341947 proposes a method in which a second switch is provided to recover the energy stored in the snubber capacitor to the power supply when the second switch is turned on. In addition, there is a problem that if the voltage more than twice the power supply voltage is not charged, it cannot be recovered and hard switching is performed.
For example, Japanese Patent Laid-Open No. 2001-119944 proposes a method of providing a voltage source that is ½ of the power supply voltage and recovering the snubber energy that is charged above the power supply voltage. In order to create a source, it is necessary to use a large-capacity electrolytic capacitor having a life characteristic, which causes problems such as a complicated circuit configuration and an increased number of parts.
JP-A-10-191632 JP 2000-341947 A JP 2001-119944

  The problem to be solved is that the conventional method of recovering the snubber energy does not necessarily recover all the energy, and the circuit configuration such as the power source becomes complicated even if the energy is recovered. An object of the present invention is to provide a DC / DC converter that has a simple circuit configuration for soft switching and that can efficiently recover all snubber energy.

  Therefore, in the present invention, a primary winding N1 of a transformer T with a tap a and a main switch (first switch in claim 1) S1 are connected in series to both ends of a DC power supply E, and a snubber is connected in parallel with the main switch S1. In a single-ended converter formed by connecting a snubber circuit in which a diode D1 and a snubber capacitor C1 are connected in series, between the tap a of the primary winding N1 and the connection point of the snubber diode D1 and the snubber capacitor C1. Is connected to a regenerative circuit in which a regenerative reactor L1, a regenerative auxiliary switch (second switch in claim 1) S2, and a regenerative diode D2 are connected in series, and the energy when the main switch S1 is turned off is converted into a snubber capacitor C1. And when the main switch S1 is turned on or before that, the regenerative auxiliary switch S2 is turned on and the snubber controller is turned on. The most important feature that regenerated to the transformer T through resonance snubber energy charged in the capacitors C1.

The DC / DC converter of the present invention charges the snubber capacitor C1 with the energy when the main switch S1 is turned off, and turns on the auxiliary auxiliary switch S2 when the main switch S1 is turned on or before that to the snubber capacitor C1. Since the charged snubber energy is recovered to the transformer T by a resonance operation, the regeneration auxiliary switch S2 and its drive circuit are necessary, but the following effects are obtained.
1. Both the main switch S1 and the regenerative auxiliary switch S2 enable soft switching operation by ZVS (zero voltage switching) or ZCS (zero current switching). 2. Compared with a method of creating a voltage source that is ½ of the DC power source E in order to recover the energy of the snubber capacitor C1, the configuration is simple and the device is small and inexpensive.
3. Similarly, there is a method of recovering the energy of the snubber capacitor C1 to the DC power supply E. However, if the snubber voltage is not twice or more than the voltage of the DC power supply E, the energy is not recovered and hard switching is performed.
As described above, it is possible to provide an insulated DC / DC converter that can eliminate the switching loss in principle and reduce the generation of electromagnetic noise.

  Hereinafter, embodiments of the present invention will be described.

FIG. 1 shows a circuit diagram of a single-ended converter according to a first embodiment of the present invention.
In the basic circuit of the single-ended converter of the first embodiment, a primary winding N1 of a transformer T with a tap a and a main switch S1 are connected in series to both ends of a DC power supply E, and a snubber diode is connected in parallel with the main switch S1. A snubber circuit 1 in which D1 and a snubber capacitor C1 are connected in series is connected.
The converter according to the present invention includes a regenerative reactor L1, a regenerative auxiliary switch S2, and a regenerative diode between the connection point A of the snubber diode D1 and the snubber capacitor C1 of this basic circuit and the tap a of the primary winding N1. The regenerative circuit 2 in which D2 is connected in series is connected.

The combination of elements constituting the regeneration circuit 2 is arbitrary, and as shown in FIG. 5, (1) 2 (L1 + S2 + D2), (2) 2 (L1 + D2 + S2), (3) 2 (S2 + L1 + D2), (4) 2 (D2 + L1 + S2) ), (5) 2 (S2 + D2 + L1), and (6) 2 (D2 + S2 + L1).
However, when the regeneration auxiliary switch S2 is a reverse blocking type switch, the regeneration diode D2 is unnecessary, and the combination of the elements of the regeneration circuit 2 is (1) 2 (L1 + S2), (2 ) 2 (S2 + L1).

Further, at least one clamping diode D3 connected in series is connected between the tap a of the primary winding N1 and the return terminal of the DC power supply E via the regenerative reactor L1.
The clamping diode D3 is connected in antiparallel with the snubber capacitor C1, the cathode is connected to the high potential side of the regeneration reactor L1, and the anode is connected to the return terminal of the DC power source E.
Accordingly, there are a plurality of connection positions of the clamping diode D3, and the cathode in the regenerative circuit 2 is between L1 and S2 in the case of FIG. In the case of (3), it can be connected to one place between L1 and L2, and in the case of (4), one place between L1 and S2.
In the case of FIG. 6 (1), it can be connected to one place between L1 and S2.
Outside the regenerative circuit 2, the cathode can be connected between D2 and C1 on both sides of the snubber capacitor C1, between 2 and C1 and D1, between D1 and S1 on both sides of the main switch S1, and between S1 and N1. It is.
A plurality of clamping diodes D3 may be connected in the same circuit, and FIG. 1 shows an example in which they are connected at three locations between L1-S2, between D2-C1, and between S1-N1.
In this case, if the clamping diode D3 is connected between L1 and S2, that is, immediately after the regenerative reactor L1, the loss of L1 is minimized.
Note that the parasitic diode of the main switch S1 can be used as the clamping diode D3.
Further, the leakage inductance of the transformer T can be used as the regeneration reactor L1, and FIG. 2 shows a circuit diagram of a converter using the leakage inductance L0 of the transformer T.
Power is supplied to the load of the secondary winding N2 insulated by the transformer T by turning on and off the main switch S1 with the above circuit configuration.

FIG. 3 shows a circuit diagram of a single-ended converter according to a second embodiment in which the present invention is implemented.
The single-ended converter of the second embodiment includes a discharge circuit 3 in which a discharge diode D0 and a charge / discharge capacitor C0 are connected in series between the tap a of the primary winding N1 and the return terminal of the DC power supply E in FIG. Connect further.
A regenerative circuit 2 in which a regenerative reactor L1, a regenerative auxiliary switch S2, and a regenerative diode D2 are connected in series is a connection point A between a snubber diode D1 and a snubber capacitor C1, and a connection between a discharge diode D0 and a charge / discharge capacitor C0. Connect to point B.
Further, the leakage inductance of the transformer T can be used as the regenerative reactor L1, and a circuit diagram of a converter using the leakage inductance L0 of the transformer T is shown in FIG.
Power is supplied to the load of the secondary winding N2 insulated by the transformer T by turning on and off the main switch S1 with the above circuit configuration.

Next, the operation principle of the regenerative circuit 2 will be described in the case where the tap voltage is approximately half that of the DC power supply E.
Hereinafter, the tap voltage of the transformer T is Va, the charging voltage of the snubber capacitor C1 is Vc1, the charging voltage of the charging / discharging capacitor C0 is Vc0, and the resonance current flowing through the regeneration diode D2 and the regeneration reactor L1 is IL1.
The tap voltage Va is fixed to a voltage proportional to the number of turns of the primary winding N1 when the main switch S1 is turned on and a voltage is applied.
The LC resonance circuit as the snubber energy regenerative circuit of the first embodiment always discharges to zero when regenerating from the voltage Vc1 of the snubber capacitor C1 to a tap voltage Va less than half of that, and Va = Vc1 / 2. In this case, when Vc1 = 0, the resonance current IL1 = 0.
In the case of Va <Vc1 / 2, even if Vc1 = 0, the resonance current does not become IL1 = 0 and continues to flow until IL1 = 0 while linearly decreasing via the clamping diode D3.
As described above, the energy of the snubber capacitor C1 can be recovered to the transformer T if the voltage Vc1 of the snubber capacitor C1 becomes twice or more the tap voltage Va.
Further, if there is a clamp circuit including a clamp diode D3 in parallel with the snubber capacitor C1, the energy of the regeneration reactor L1 can be recovered to the transformer T.

The LC resonance circuit as the snubber energy regeneration circuit of the second embodiment always discharges to zero when the voltage Vc0 of the charging / discharging capacitor C0 is less than half of the voltage Vc1 of the snubber capacitor C1. When Vc1 / 2, the resonance current IL1 = 0 when Vc1 = 0.
In the case of Vc0 <Vc1 / 2, even if Vc1 = 0, the resonance current does not become IL1 = 0 and continues to flow until IL1 = 0 while linearly decreasing via the clamping diode D3.
As described above, if the voltage Vc1 of the snubber capacitor C1 is twice or more the voltage Vc0 of the charge / discharge capacitor C0, the energy of the snubber capacitor C1 can be recovered to the charge / discharge capacitor C0.
Further, if there is a clamp circuit including a clamp diode D3 in parallel with the snubber capacitor C1, the energy of the regenerative reactor L1 can be recovered to the charge / discharge capacitor C0.

FIG. 7 shows operating waveforms of a single-ended converter embodying the present invention.
Hereinafter, the current flowing through the main switch S1 is Is1, the voltage applied to the main switch S1 is Vs1, and the current flowing through the snubber capacitor C1 is Ic1.
In the figure, (a) is the drive waveform of the main switch S1, (b) is the drive waveform of the regeneration auxiliary switch S2, (c) is the waveform of Is1, (d) is the waveform of Vs1, (e) is the waveform of Ic1, (F) is the waveform of Vc1, and (g) is the waveform of IL1.

The operation of the single ended converter of the first embodiment will be described below.
Before t0 in FIG. 7, the main switch S1 is in an on state, and a current Is1 flows through the main switch S1. At this time, the charging voltage of the snubber capacitor C1 is set to Vc1 = 0.
Further, the regeneration auxiliary switch S2 is off, and the voltage Va ≦ Ve / 2 (hereinafter, the voltage of the DC power supply E is set to Ve) is applied to the tap a.
When the main switch S1 is turned off at time t0 in FIG. 7A in this state, the voltage Vs1 applied to the main switch S1 at the time of switch-off is the voltage Vc1 = 0 of the snubber capacitor C1, so that the snubber circuit is ideal. Then, it rises from zero regardless of the wiring on the load side and the inductance of the transformer T.
Therefore, the current Is1 of the main switch S1 in FIG. 7C is commutated to the snubber capacitor C1, and the charging current Ic1 in FIG. 7E flows.
Since the voltage Vc1 of the snubber capacitor C1 is 0 at this time, the voltage Vs1 applied to the main switch S1 is gentler than zero as shown in FIG. 7 (d), similarly to the voltage Vc1 of the snubber capacitor C1 in FIG. 7 (f). To rise.
As a result, ZVS (zero voltage switching) when the main switch S1 is turned off is achieved, and the switching loss at this time becomes extremely small.
Further, the spike voltage at the time of turn-off is absorbed, and the switching noise is also reduced.
In this way, the excitation energy accumulated in the transformer T while the main switch S1 is on is charged to the snubber capacitor C1 when the main switch S1 is turned off, and the energy charged to the snubber capacitor C1 is off of the main switch S1. Stored for the duration.
The snubber capacitor C1 is charged by the energy stored in the transformer T, but is charged at least up to the voltage Ve of the DC power supply E.

Before t1 in FIG. 7, the current flowing through the main switch S1 when the main switch S1 is off is Is1 = 0. At this time, the voltage Vc1 ≧ Ve is charged in the snubber capacitor C1.
Further, the regeneration auxiliary switch S2 is also off, and the voltage Va ≦ Ve / 2 is applied to the tap a.
In this state, when the main switch S1 is turned on at time t1 in FIG. 7A, the current of the DC power source E flows through the primary winding N1 of the transformer T and supplies power to the load of the secondary winding N2.
At time t1 in FIG. 7 (d), the voltage of the main switch S1 becomes Vs1 = 0, and an operation in which the current Is1 rises at time t1 in FIG. 7 (c) occurs at the same time, but actually due to the leakage inductance of the transformer T. The current Is1 rises from zero.
As a result, ZCS (zero current switching) of the main switch S1 is achieved, and no switching loss occurs at this time.
If the transformer T is close to the ideal transformer and the leakage inductance is insufficient, the ZCS operation can be surely performed by connecting an external reactor in series with the primary winding N1 of the transformer T.

When the regenerative auxiliary switch S2 is turned on simultaneously with or before the main switch S1 at time t1 in FIG. 7B, a resonance circuit including a snubber capacitor C1, a regenerative reactor L1, and a regenerative auxiliary switch S2 is formed. The
In this resonance circuit, if the difference between the charging voltage Vc1 ≧ Ve of the snubber capacitor C1 and the voltage Va ≦ Ve / 2 of the tap a is more than twice, as described in the operation principle of the regenerative circuit, the snubber capacitor C1 The energy is discharged to zero voltage.
Therefore, as shown in FIG. 7E, a sinusoidal discharge current Ic1 flows through the snubber capacitor C1 due to LC resonance, and the voltage Vc1 of the snubber capacitor C1 drops in a cosine waveform as shown in FIG. 7F. , Becomes zero at time t2. Further, the waveform of the resonance current IL1 rises from zero as shown in FIG.
When the regeneration auxiliary switch S2 is turned on, the resonance current IL1 rises from zero due to the effect of the regeneration reactor L1, and the ZCS operation is performed. Therefore, no switching loss occurs.

When the voltage of the snubber capacitor C1 becomes Vc1 = 0 at time t2 in FIG. 7 (f), the clamping diode D3 is turned on, and the remaining energy of the regenerative reactor L1 is the regenerative reactor L1 → transformer T → main. It is recovered by the transformer T through the path of the switch S1, the clamping diode D3, and the regenerative reactor L1.
In this way, the energy accumulated in the parasitic inductance of the wiring, the leakage inductance of the transformer T, and the excitation energy of the transformer T are first charged in the snubber capacitor C1, and then recovered in the transformer T, so there is no loss. , Prevent a decrease in efficiency and prevent heat generation.

Since the resonance current IL1 flowing through the regeneration auxiliary switch S2 naturally becomes zero as shown in FIG. 7 (g), the regeneration auxiliary switch S2 is turned off by a subsequent time point, for example, at time t3 in FIG. 7 (b). Just keep it.
The turn-off operation of the regeneration auxiliary switch S2 at this time is a ZCS operation similar to the on operation.
Therefore, since no switching loss occurs, there is almost no increase in loss due to the addition of the regeneration auxiliary switch S2.

The operation of the single ended converter of the second embodiment will be described below.
Before t0 in FIG. 7, the main switch S1 is in an on state, and a current Is1 flows through the main switch S1. At this time, the charging voltage of the snubber capacitor C1 is set to Vc1 = 0.
Further, the regeneration auxiliary switch S2 is OFF, and the voltage Vc0 ≦ Ve / 2 is charged in the charging / discharging capacitor C0.
When the main switch S1 is turned off at time t0 in FIG. 7A in this state, the voltage Vs1 applied to the main switch S1 at the time of switch-off is the voltage Vc1 = 0 of the snubber capacitor C1, so that the snubber circuit is ideal. Then, it rises from zero regardless of the wiring on the load side and the inductance of the transformer T.
Therefore, the current Is1 of the main switch S1 in FIG. 7C is commutated to the snubber capacitor C1, and the charging current Ic1 in FIG. 7E flows.
Since the voltage Vc1 of the snubber capacitor C1 is 0 at this time, the voltage Vs1 applied to the main switch S1 is gentler than zero as shown in FIG. 7 (d), similarly to the voltage Vc1 of the snubber capacitor C1 in FIG. 7 (f). To rise.
As a result, ZVS (zero voltage switching) when the main switch S1 is turned off is achieved, and the switching loss at this time becomes extremely small.
Further, the spike voltage at the time of turn-off is absorbed, and the switching noise is also reduced.
In this way, the excitation energy accumulated in the transformer T while the main switch S1 is on is charged to the snubber capacitor C1 when the main switch S1 is turned off, and the energy charged to the snubber capacitor C1 is off of the main switch S1. Stored for the duration.
The snubber capacitor C1 is charged by the energy stored in the transformer T, but is charged at least up to the voltage Ve of the DC power supply E.

Before t1 in FIG. 7, the current flowing through the main switch S1 when the main switch S1 is off is Is1 = 0. At this time, the voltage Vc1 ≧ Ve is charged in the snubber capacitor C1.
Further, the regeneration auxiliary switch S2 is also off, and the voltage Vc0 ≦ Ve / 2 is charged in the charging / discharging capacitor C0.
In this state, when the main switch S1 is turned on at time t1 in FIG. 7A, the current of the DC power source E flows through the primary winding N1 of the transformer T and supplies power to the load of the secondary winding N2.
At this time, when the voltage of the charging / discharging capacitor C0 becomes Vc0> Ve / 2, the energy of the charging / discharging capacitor C0 is supplied to the load of the secondary winding N2 of the transformer T in preference to the DC power source E.
At time t1 in FIG. 7 (d), the voltage of the main switch S1 becomes Vs1 = 0, and an operation in which the current Is1 rises at time t1 in FIG. 7 (c) occurs at the same time, but actually due to the leakage inductance of the transformer T. The current Is1 rises from zero.
As a result, ZCS (zero current switching) of the main switch S1 is achieved, and no switching loss occurs at this time.
If the transformer T is close to the ideal transformer and the leakage inductance is insufficient, the ZCS operation can be surely performed by connecting an external reactor in series with the primary winding N1 of the transformer T.

When the regenerative auxiliary switch S2 is turned on simultaneously with or before the main switch S1 at time t1 in FIG. 7B, the snubber capacitor C1, the regenerative reactor L1, the regenerative auxiliary switch S2, and the charge / discharge capacitor C0 A resonant circuit is formed.
In this resonance circuit, if the difference between the charging voltage Vc1 ≧ Ve of the snubber capacitor C1 and the charging voltage Vc0 ≦ Ve / 2 of the charging / discharging capacitor C0 is more than twice, as described in the operation principle of the regenerative circuit, the snubber The energy of the capacitor C1 is discharged to zero voltage.
Therefore, as shown in FIG. 7E, a sinusoidal discharge current Ic1 flows through the snubber capacitor C1 due to LC resonance, and the voltage Vc1 of the snubber capacitor C1 drops in a cosine waveform as shown in FIG. 7F. , Becomes zero at time t2. Further, the waveform of the resonance current IL1 rises from zero as shown in FIG.
When the regeneration auxiliary switch S2 is turned on, the resonance current IL1 rises from zero due to the effect of the regeneration reactor L1, and the ZCS operation is performed. Therefore, no switching loss occurs.
Thus, the snubber energy and the excitation energy stored in the snubber capacitor C1 are as follows: snubber capacitor C1, regenerative diode D2, regenerative auxiliary switch S2, regenerative reactor L1, charge / discharge capacitor C0, snubber capacitor. It is recovered by the charge / discharge capacitor C0 through the path C1.

When the voltage of the snubber capacitor C1 becomes Vc1 = 0 at time t2 in FIG. 7 (f), the clamping diode D3 is turned on, and the remaining energy of the regenerative reactor L1 is the regenerative reactor L1 → charge / discharge capacitor. It is subsequently recovered by the charge / discharge capacitor C0 through a path of C0 → clamping diode D3 → regenerative reactor L1.
The voltage Vc0 of the charging / discharging capacitor C0 is slightly increased by the energy of the snubber capacitor C1 and the regenerative reactor L1, and when Vc0> Ve / 2, the discharging diode D0 is turned on and charging / discharging is performed. It is recovered by the transformer T through a path of the capacitor C0 → the discharging diode D0 → the transformer T → the main switch S1 → the charging / discharging capacitor C0.
As described above, the energy accumulated in the parasitic inductance of the wiring, the leakage inductance of the transformer T, and the excitation energy of the transformer T are first charged in the snubber capacitor C1, and subsequently collected in the charge / discharge capacitor C0, and then the transformer T Therefore, it is not lost, prevents a decrease in efficiency and prevents heat generation.

Since the resonance current IL1 flowing through the regeneration auxiliary switch S2 naturally becomes zero as shown in FIG. 7 (g), the regeneration auxiliary switch S2 is turned off by a subsequent time point, for example, at time t3 in FIG. 7 (b). Just keep it.
The turn-off operation of the regeneration auxiliary switch S2 at this time is a ZCS operation similar to the on operation.
Therefore, since no switching loss occurs, there is almost no increase in loss due to the addition of the regeneration auxiliary switch S2.

The single-ended converter described above can be applied not only to the forward type but also to the flyback type by using a flyback transformer.
In this case, the polarity relationship between the primary winding N1 and the secondary winding N2 of the transformer T is reversed, but the same circuit configuration is obtained unless the start and end of winding are instructed.

FIG. 8 shows a circuit diagram of a push-pull converter embodying the present invention.
The basic circuit of the push-pull converter has one end of a DC power supply E connected to a tap b (generally used as a midpoint tap) of a primary winding N1 of a transformer T, and the other end connected to a pair of left and right main switches (claims). The first switch 6 is connected to both ends of the primary winding N1 of the transformer T via S1a and S1b, and the snubber diodes D1a and D1b and the snubber capacitors C1a and C1b are connected in series with the main switches S1a and S1b. The snubber circuits 1a and 1b connected to are connected.
The converter according to the present invention includes connection points A1 and A2 (approximately twice the potential of the DC power supply E) between the snubber diodes D1a and D1b and the snubber capacitors C1a and C1b of this basic circuit, one end of the DC power supply E, and the primary winding. Regenerative diodes D2a and D2b, regenerative reactors L1a and L1b, and a regenerative auxiliary switch between the connection point B of the line N1 and the tap b (substantially the same potential as that of the DC power supply E), respectively. Switch) Regenerative circuits 2a and 2b in which S2a and S2b are connected in series are connected.

Similarly, the combination of the elements constituting the regenerative circuits 2a and 2b is also arbitrary, and as shown in FIG. ) 2a (D2a + L1a + S2a) + 2b (S2b + L1b + D2b), (4) 2a (S2a + L1a + D2a) + 2b (D2b + L1b + S2b), (5) 2a (L1a + D2a + S2a) + 2b (S2b + D2) .
Similarly, when the regenerative auxiliary switches S2a and S2b are reverse blocking switches, the regenerative diodes D2a and D2b are not necessary, and the combination of the elements of the regenerative circuits 2a and 2b is (1) as shown in FIG. 2a (S2a + L1a) + 2b (L1b + S2b), (2) 2a (L1a + S2a) + 2b (S2b + L1b).

Further, at least one of the clamping diodes D3a and D3b connected in series is connected between the tap b of the primary winding N1 and the return terminal of the DC power supply E via the regenerative reactors L1a and L1b.
The clamping diodes D3a and D3b are connected in antiparallel with the snubber capacitors C1a and C1b, the cathode is connected to the high potential side of the regeneration reactors L1a and L1b, and the anode is connected to the return terminal of the DC power supply E.
Therefore, there are a plurality of connection positions of the clamping diodes D3a and D3b, and in the regenerative circuits 2a and 2b, the cathode is between L1a, L1b-S2a, S2b, and between S2a, S2b-D2a, D2b in FIG. In the case of (2), between L1a, L1b-D2a, D2b, four places between D2a, D2b-S2a, S2b, in the case of (3), two places between L1a, L1b-D2a, D2b, (4) In this case, it is possible to connect to two places between L1a, L1b-S2a, and S2b.
In the case of FIG. 11 (1), connection is possible at two locations between L1a, L1b-S2a, and S2b.
Outside the regenerative circuits 2a and 2b, the cathodes are connected to D2a on both sides of the snubber capacitors C1a and C1b, between D2a, D2b-C1a, and C1b, at four locations between C1a, C1b-D1a, and D1b, and on both sides of the main switches S1a and S1b , D1b-S1a, S1b, and S1a, S1b-N1.
A plurality of clamping diodes D3a and D3b may be connected in the same circuit, and FIG. 8 shows between L1a, L1b-S2a and S2b, between D2a, D2b-S2a and S2b, and between D1a, D1b-S1a and S1b. An example of connection to a location is shown.
Also in this case, when the clamping diodes D3a and D3b are connected between L1a, L1b-S2a and S2b, that is, immediately after the regenerative reactors L1a and L1b, the loss of L1 is minimized.
Similarly, the parasitic diodes of the main switches S1a and S1b can be used as the clamping diodes D3a and D3b.
Similarly, the leakage inductance of the transformer T can be used as the regenerative reactors L1a and L1b. FIG. 9 shows a circuit diagram of a converter using the leakage inductance L0 of the transformer T.
With the above circuit configuration, power is supplied to the load of the secondary winding N2 insulated by the transformer T by alternately turning on and off the two main switches S1a and S1b with a phase difference of 180 °.

Next, the operation of the push-pull converter will be described for a push-pull converter with a center tap.
First, when one of the main switches S1a is turned off, the current Is1 that has been flowing through the primary winding N1 of the transformer T until then to the main switch S1a is commutated to the snubber capacitor C1a via the snubber diode D1a. The voltage Vc1 of the snubber capacitor C1a is charged from 0V and a soft switching operation by ZVS is performed.
Next, when the other main switch S1b is turned on while the main switch S1a is turned off, a voltage 2Ve that is twice the voltage Ve of the DC power source E is induced at both ends of the primary winding N1 of the transformer T. The voltage Vc1 of the capacitor C1a is charged to at least 2Ve.
Next, when the regenerative auxiliary switch S2a is turned on when the main switch S1a is turned on, a resonance circuit including the snubber capacitor C1a, the regenerative reactor L1a, the regenerative auxiliary switch S2a, and the DC power source E is formed.
If the difference between the charging voltage Vc1 ≧ 2Ve of the snubber capacitor C1a and the voltage Ve of the DC power source E is more than twice in this resonance circuit, the energy of the snubber capacitor C1a is discharged to zero voltage.
Therefore, the energy accumulated in the snubber capacitor C1a becomes a resonance current IL1 with the regenerative reactor L1a and is recovered by the DC power source E.

When the main switch S1a is turned on, the current Is1 flowing through the main switch S1a increases from zero due to the leakage inductance of the transformer T, and the ZCS operation is performed.
When the regeneration auxiliary switch S2a is turned on, the resonance current IL1 rises from zero due to the effect of the regeneration reactor L1a, and similarly the ZCS operation is performed.

When the voltage of the snubber capacitor C1a becomes Vc1 = 0 due to the discharge, the clamping diode D3a is turned on, and the resonance current IL1 continues to flow through the regenerative reactor L1a.
The remaining energy of the regenerative reactor L1a is recovered by the DC power source E until the current IL1 flowing through the regenerative reactor L1a decreases linearly to zero.
Since the resonance current IL1 flowing through the regeneration auxiliary switch S2a naturally becomes zero, the regeneration auxiliary switch S2a may be turned off thereafter.
The off operation of the regeneration auxiliary switch S2a at this time is a ZCS operation as in the on operation.

As shown in FIG. 12, the two regenerative reactors L1a and L1b in FIG. 8 can be combined into one common reactor L1.
That is, the regenerative diodes D2a and D2b in FIG. 8 are actively used as reverse blocking diodes, and one end B1 of the shared reactor L1 is connected to the regenerative auxiliary switches S2a and S2b via the regenerative diodes D2a and D2b, respectively. Then, the other end B2 is connected to a connection point between the DC power source E and the tap b of the primary winding N1.
Thereby, one of the reactors L1a and L1b for regeneration can be easily saved.
FIG. 12 shows an example in which clamping diodes D3a and D3b are connected to two locations between D1a, D1b-S1a, and S1b.

Similarly, as shown in FIG. 13, the two auxiliary switches for regeneration S2a and S2b in FIG. 8 can be combined into one common switch S2.
In this case, one end B1 of the common switch S2 is connected to the regenerative reactors L1a and L1b via the regenerative diodes D2a and D2b, respectively, and the other end B2 is a connection point between the DC power source E and the tap b of the primary winding N1. Connect to.
Accordingly, one of the regeneration auxiliary switches S2a and S2b can be easily saved.
Similarly, FIG. 13 shows an example in which clamping diodes D3a and D3b are connected to two locations between D1a, D1b-S1a, and S1b.

Further, as shown in FIG. 14, the two regenerative reactors L1a and L1b and the two regenerative auxiliary switches S2a and S2b in FIG. 8 can be combined into one common reactor L1 and one common switch S2. .
In this case, one end B1 of the shared reactor L1 and the shared switch S2 connected in series is connected to the regenerative diodes D2a and D2b, respectively, and the other end B2 is connected to the connection point between the DC power source E and the tap b of the primary winding N1. To do.
Thereby, each of the reactors L1a and L1b for regeneration and the auxiliary switches S2a and S2b for regeneration can be easily reduced.
Similarly, FIG. 14 shows an example in which clamping diodes D3a and D3b are connected to two locations between D1a, D1b-S1a, and S1b.

FIG. 15 shows a circuit diagram in which a voltage clamp circuit is added to the single-ended converter of the first embodiment.
The voltage clamp circuit 4 has a winding N2b connected in series to the winding N2a of the secondary winding N2 of the transformer T via a tap c, and a rectifying diode Da, a freewheeling diode Db, a choke at both ends of the winding N2a. The coil La and the smoothing capacitor Ca are connected to form a choke input smoothing circuit. Further, a clamping diode Dc is connected between one end of the winding N2b and the connection point of the choke coil La and the smoothing capacitor Ca to form a voltage clamping circuit.
In the case of a forward converter having the above configuration, for example, when the main switch S1 is turned on, the rectifying diode Da is turned on, and power is supplied to the load through the choke coil La and the smoothing capacitor Ca. Excitation current flows through the transformer T, and excitation energy is accumulated.
When the main switch S1 is turned off, a counter electromotive force is generated in the winding N2a, the rectifying diode Da is turned off, the return diode Db is turned on, and current continues to flow through the choke coil La, so that power supply to the load is prevented. Will continue.
At this time, when the voltage Vc1 of the snubber capacitor C1 becomes higher than the output voltage, the clamping diode Dc is turned on to recover the snubber energy to the load.
As a result, the voltage Vc1 of the snubber capacitor C1 when the main switch S1 is OFF can be prevented from exceeding a certain value.

It is a circuit diagram of the single ended converter of the first embodiment. FIG. 2 is a circuit diagram of FIG. 1 using leakage inductance. It is a circuit diagram of the single ended converter of 2nd Example. FIG. 4 is a circuit diagram of FIG. 3 using leakage inductance. It is a figure which shows the combination of the element which comprises the regeneration circuit of FIG. It is a figure which shows the combination in the case of the reverse blocking type switch of FIG. It is an operation | movement waveform of the single ended converter which implemented this invention. It is a circuit diagram of the push pull converter which implemented this invention. FIG. 9 is a circuit diagram of FIG. 8 using leakage inductance. It is a figure which shows the combination of the element which comprises the regeneration circuit of FIG. It is a figure which shows the combination in the case of the reverse blocking type switch of FIG. It is the circuit diagram which shared the reactor for regeneration of FIG. It is the circuit diagram which shared the auxiliary switch for regeneration of FIG. It is the circuit diagram which shared the reactor for regeneration of FIG. 8, and the auxiliary switch for regeneration. FIG. 2 is a circuit diagram in which a voltage clamp circuit is added to FIG.

Explanation of symbols

C Capacitor D Diode E DC power supply L Reactor N1 Primary winding N2 Secondary winding S1 Main switch S2 Auxiliary switch T Transformer a, b, c Tap

Claims (11)

A primary winding N1 of a transformer T with a tap a and a first switch S1 are connected in series to both ends of a DC power supply E,
In a single-ended converter formed by connecting a snubber circuit in which a snubber diode D1 and a snubber capacitor C1 are connected in series in parallel with the first switch S1,
A regenerative circuit in which a regenerative reactor L1, a second switch S2, and a regenerative diode D2 are connected in series between the tap a of the primary winding N1 and the connection point of the snubber diode D1 and the snubber capacitor C1. connection,
When the first switch S1 is turned off, the snubber capacitor C1 is charged, and when the first switch S1 is turned on or before, the second switch S2 is turned on to charge the snubber capacitor C1. A DC / DC converter characterized by regenerating snubber energy to a transformer T by resonance operation. Between the high-potential side terminal of the regenerative reactor L1 and the low-potential side terminal of the DC power source E, at least one of the regenerative reactor L1 and the second switch S2, the regenerative diode D2, or the snubber diode D1. At least one clamping diode D3 that is indirectly connected in series with one in between, and further connected,
2. The DC / DC converter according to claim 1, wherein even when the voltage of the snubber capacitor C <b> 1 becomes zero, the energy when the current flows through the regeneration reactor L <b> 1 is regenerated to the transformer T. 3. A discharge diode D0 is connected between the tap a of the primary winding N1 and the regeneration circuit;
A discharge in which a charging / discharging capacitor C0 is connected between the connecting point of the discharging diode D0 and the regenerative circuit and the low potential side terminal of the DC power supply E, and the discharging diode D0 and the charging / discharging capacitor C0 are connected in series. Connect more circuits,
When the first switch S1 is turned off, the snubber capacitor C1 is charged, and when the first switch S1 is turned on or before, the second switch S2 is turned on to charge the snubber capacitor C1. 2. The DC / DC converter according to claim 1, wherein the snubber energy is temporarily moved to the charging / discharging capacitor C0 by a resonance operation, and the snubber energy moved to the charging / discharging capacitor C0 is regenerated to the transformer T by discharge.   2. The DC / DC converter according to claim 1, wherein the regeneration reactor L <b> 1 is omitted by utilizing a leakage inductance of the transformer T. 3.   2. The DC / DC converter according to claim 1, wherein a voltage clamp winding is additionally connected to the secondary winding N2 of the transformer T, and a voltage clamp circuit is connected to the voltage clamp winding. One end of the DC power source E is connected to the tap b of the primary winding N1 of the transformer T, and the other end is connected to both ends of the primary winding N1 of the transformer T via a pair of left and right first switches S1a and S1b. ,
In a push-pull converter formed by connecting a snubber circuit in which a snubber diode D1a, D1b and a snubber capacitor C1a, C1b are connected in series in parallel with the first switch S1a, S1b,
Between the tap b of the primary winding N1, the snubber diodes D1a and D1b, and the connection point of the snubber capacitors C1a and C1b, the regenerative reactors L1a and L1b, the second switches S2a and S2b, and the regenerative diode D2a , D2b is connected in series, a regenerative circuit is connected,
When the one first switch S1a is turned off, the other first switch S1b is turned on to charge the snubber energy to the one snubber capacitor C1a, and before or when the one first switch S1a is turned on. A DC / DC converter characterized in that the one second switch S2a is turned on and the snubber energy charged in one snubber capacitor C1a is regenerated to the DC power source E by a resonance operation. Between the high-potential side terminals of the regenerative reactors L1a and L1b and the low-potential side terminal of the DC power supply E, the regenerative reactors L1a and L1b directly or the second switches S2a and S2b, the regenerative diodes D2a and D2b, or At least one clamping diode D3a, D3b that is indirectly connected in series with at least one of the snubber diodes D1a, D1b in between, and further connected,
7. The DC / DC according to claim 6, wherein when the voltage of the snubber capacitors C1a and C1b becomes zero, the energy when the current flows through the regenerative reactors L1a and L1b is regenerated to the DC power source E. DC converter.   The DC / DC converter according to claim 6, wherein the regenerative reactors L1a and L1b are omitted by utilizing a leakage inductance of the transformer T. The two regenerative reactors L1a and L1b in the regenerative circuit are combined into one common reactor L1,
One end of the shared reactor L1 is connected to the second switches S2a and S2b via regenerative diodes D2a and D2b, respectively.
The DC / DC converter according to claim 6, wherein the other end is connected to a DC power source E. The two second switches S2a and S2b in the regenerative circuit are combined into one common switch S2,
One end of the shared switch S2 is connected to the regenerative reactors L1a and L1b via the regenerative diodes D2a and D2b, respectively.
The DC / DC converter according to claim 6, wherein the other end is connected to a DC power source E. The two regenerative reactors L1a and L1b and the two second switches S2a and S2b in the regenerative circuit are combined into one common reactor L1 and one common switch S2, respectively.
One end of a circuit in which the common reactor L1 and the common switch S2 are connected in series is connected to the regenerative diodes D2a and D2b, respectively.
The DC / DC converter according to claim 6, wherein the other end is connected to a DC power source E.

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