JP2001086750A - Power-supply unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power-supply unit that has a simple configuration and can reduce loss. SOLUTION: One end of secondary coil winding 12B of a transformer 12 is connected to the input end of an inverting circuit 42, and the output end of the inversion circuit 42 is connected to the gate of a MOSFET 38. Also, one end of a secondary coil winding 12B is connected to the input end of an inversion circuit 44, and the output end of the inversion circuit 44 is connected to the gate of an MOSFET 40, thus turning on the MOSFETs 38 and 40, even while no voltage is being applied to a primary coil winding 12A by a DC-to-AC inverter circuit 14, which allows current generated during the period through the energy accumulated in an inductance 48 of a smoothing circuit 18 to flow through the MOSFETs 38 and 40 in on-state, and hence allowing current to flow in body diodes 38a and 40a of the MOSFETs 38 and 40 for avoiding losses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly, to a method of intermittently applying a voltage to a primary winding of a transformer and rectifying and smoothing a voltage induced in a secondary winding having a center point of the transformer. And a power supply device for supplying power to the load.

[0002]

2. Description of the Related Art Conventionally, a DC voltage is intermittently applied to a primary winding of a transformer by a switching element, and a voltage induced in a secondary winding of the transformer provided with a center tap (middle point) is rectified. 2. Description of the Related Art A switching power supply (a so-called DC-DC converter) that obtains a predetermined DC voltage by performing rectification (full-wave rectification) and smoothing by a circuit is known. In a switching power supply of this type, a diode is generally used as a rectifying element of a rectifying circuit. However, a forward voltage drop of the diode (for example, 0.6 V
), Loss occurs in the rectifier circuit, and this loss hinders improvement in efficiency of the switching power supply device.

As one of the methods for reducing the loss in the rectifier circuit, a method using a Schottky diode as a rectifying element has been conventionally employed. However, this method depends on the performance of the element and is dramatically increased. No significant loss reduction can be expected. As another method, a method of reducing loss by a circuit technique is also known, and a method of using a synchronous rectifier circuit using a switching element such as a MOSFET as a rectifier element as a rectifier circuit is mainly used.

As a driving method of the MOSFET in the synchronous rectifier circuit, for example, a gate of a first MOSFET for turning on / off one end of a secondary winding of a transformer and a smoothing circuit is connected to the other end of the secondary winding. , A second MOSFET for turning on and off the conduction between the other end of the secondary winding and the smoothing circuit
Is connected to one end of the secondary winding (Japanese Patent Laid-Open No.
No. 337005) or a configuration in which a resistor is provided between the gate of the MOSFET and the secondary winding (Japanese Utility Model Application Laid-Open No. 7-239).
Japanese Patent Application Laid-Open No. 8-331841), and a configuration in which a resistor, a diode, and a capacitor are provided in parallel between the gate of a MOSFET and a secondary winding (see Japanese Patent Application Laid-Open No. 8-331841).

In each of the above-described configurations, any one of the MOSFETs is turned on and the synchronous rectification circuit operates during a period in which a voltage is applied to the primary winding of the transformer (rectification period). Loss reduction can be achieved. However, although the loss during the rectification period can be reduced, all the current generated by the inductance of the smoothing circuit during the commutation period (period when no voltage is applied to the primary winding of the transformer) is the body diode (MOSF) of the MOSFET.
Loss is generated by flowing through an internal diode of the ET (also referred to as a parasitic diode). In general, the body diode has a larger forward voltage drop than the fast recovery diode and the Schottky diode, so that the loss increases rather. For this reason, it is necessary to take measures to prevent a current from flowing through the body diode during the commutation period.

In order to reduce the loss during the commutation period, a method has been proposed in which the input voltage is controlled to shorten the commutation period. However, in order to effectively reduce the loss in this method, the commutation period is reduced. Needs to be very short, and the operating range of the switching power supply device becomes narrow.

In Japanese Patent Application Laid-Open No. 3-117364, a transformer having two sets of secondary windings with a center point is used, and a choke transformer is used as an inductance of a smoothing circuit. A configuration in which two switching elements are turned on, and a primary element of the choke transformer which is turned on by a voltage induced in the secondary winding of the choke transformer during the commutation period and short-circuits the input terminal of the smoothing circuit. A configuration for supplying the stored power of the winding to a load is disclosed. However, the above circuit has a disadvantage that the configuration of the transformer is complicated. Further, in a configuration in which a switching element is turned on and off using a choke transformer, there is a problem that a loss occurs due to a phase delay of a signal for turning the switching element on and off.

Further, in FIG. 7 and FIG. 9 of JP-A-8-322245, a current transformer is provided on the primary side of a transformer, and a current flowing through a switching element on the primary side is detected by the current transformer. A configuration is disclosed in which an auxiliary winding for a drive power supply is provided on the secondary side of the transformer and the switching element on the secondary side is also turned on during the commutation period. In the above configuration, a current transformer is provided on the primary side. Since it is necessary to provide an auxiliary winding in the transformer, the circuit configuration becomes complicated, which is disadvantageous in terms of cost and the like.

In Japanese Patent Application Laid-Open No. 9-149635, a full-bridge inverter having four switching elements is provided on the primary side of a transformer, and a synchronous rectifier circuit including a pair of switching elements is provided on the secondary side. In the configuration, during the commutation period, only one of the primary-side switching element pair that was in the on state during the rectification period up to that time is turned off, and one of the pair of secondary-side switching elements is also turned on. A technique for continuing is disclosed. Japanese Patent Application Laid-Open No. 9-149636 describes that a pair of secondary-side switching elements are turned on during a commutation period in a power supply device having a configuration similar to that of the above publication. However, each of the techniques described in the above publications has a disadvantage that the circuit configuration of a circuit that generates a drive signal for turning on and off a switching element becomes very complicated.

[0010]

As described above, in the conventional power supply devices including the center tap type synchronous rectifier circuit, current flows through the body diode of the switching element during the commutation period. However, there is a drawback that loss occurs or the circuit configuration becomes very complicated to prevent current from flowing through the body diode.

The present invention has been made in consideration of the above-described facts, and has as its object to provide a power supply device that can reduce a loss with a simple configuration.

[0012]

According to a first aspect of the present invention, there is provided a power supply device comprising: a primary winding;
A transformer having a secondary winding provided with a midpoint, and applying a voltage in one direction to the primary winding of the transformer, stopping the application of the voltage for a predetermined period, and applying a voltage in the other direction to the primary winding. And a pair of first switching elements respectively provided between both ends of a secondary winding of the transformer and a connection point, and A smoothing circuit provided between a middle point of the secondary winding and the connection point; and an inverting means for inverting the level of the potential of the end or the middle point of the secondary winding. The pair of first switching elements are turned on alternately during a period in which a voltage is applied to the line, and the pair of first switching elements are turned on in a period in which the application of the voltage to the primary winding is stopped. And control means.

According to the first aspect of the present invention, the voltage application is stopped for a predetermined period after the unidirectional voltage is applied to the primary winding of the transformer, and the voltage is applied after the unidirectional voltage is applied to the primary winding. A voltage application unit that repeats stopping for a predetermined period is provided. The voltage applying means includes a DC power supply, a state in which the voltage of the DC power supply is applied to the primary winding as a voltage in one direction, a state in which the voltage is applied as a voltage in the other direction, and a voltage applied to the primary winding. And a plurality of switching elements that can be switched to a state in which application is stopped. Specifically, for example, a half-bridge type or full-bridge type DC-AC inverter circuit can be used. it can.

According to the first aspect of the present invention, first switching elements are respectively provided between both ends of the secondary winding of the transformer and the connection point, and between the middle point and the connection point of the secondary winding. Since the smoothing circuit is provided, the control unit alternately turns on the pair of first switching elements during the period when the voltage is applied to the primary winding of the transformer (when the voltage is applied to the primary winding of the transformer). One of the pair of first switching elements is turned on during a certain period, and the first switching element to be turned on is switched each time a period during which the voltage is applied arrives, so that the primary winding and the secondary winding of the transformer are turned on. The voltage induced in the secondary winding according to the turns ratio of the wire is
It is rectified by the switching element and smoothed by the smoothing circuit, and can be supplied to the load.

By the way, during a period in which no voltage is applied to the primary winding of the transformer, the energy stored in the smoothing circuit flows as a current. When this current flows through the body diode of the first switching element, a loss occurs.
To reduce the loss, it is desirable to turn on each of the pair of first switching elements.

On the other hand, the potential of one end of the secondary winding of the transformer becomes high only while a voltage in one direction is applied to the primary winding, and the potential of the other end of the secondary winding is high. Is high only during the period when the voltage in the other direction is applied, and the potential at the middle point of the secondary winding is the period when the voltage in one direction is applied to the primary winding and the voltage in the other direction is applied. The potential becomes high during the period. That is, the potential of one end of the secondary winding of the transformer becomes low only during a period in which one of the first switching elements is to be turned on (including a period in which no voltage is applied to the primary winding). Of the other end is the first
The potential becomes low only during a period in which the switching element is to be turned on (including a period in which no voltage is applied to the primary winding), and the potential at the middle point of the secondary winding turns on each of the pair of first switching elements. The potential becomes low only during a power period (a period when no voltage is applied to the primary winding).

The present invention focuses on the above, and the control means according to the present invention includes an inverting means for inverting the level of the potential at the end or the middle point of the secondary winding, and a voltage is applied to the primary winding. , The pair of first switching elements are alternately turned on during a period in which the voltage is applied, and each of the pair of first switching elements is turned on while the application of the voltage to the primary winding is stopped. As described above, by using the potential at both ends of the secondary winding or the potential at the middle point of the secondary winding, each of the pair of first switching elements is turned on during a period in which no voltage is applied to the primary winding. This makes it possible to generate a signal for turning on and off the pair of first switching elements at appropriate timing with a very simple configuration.

As an example, when the control means is configured to include an inverting means for inverting the level of the potential of the end of the secondary winding, one of the pair of first switching elements is appropriately controlled by the inverting means. Since a signal to be turned on / off at a timing is output, the signal is input to a control signal input terminal (for example, a gate in a MOSFET) of the first switching element as it is, so that the first switching element can be set at an appropriate timing. Can be turned on and off.

In the case where the control means includes inversion means for inverting the level of the potential at the middle point of the secondary winding, the application of the voltage from the inversion means to the primary winding is stopped. Since the signal for turning on the first switching element is output during the period when the first switching element is turned on, the signal for turning on the first switching element during the period when the voltage is applied to the primary winding is controlled by the first switching element. The first switching element can be turned on and off at appropriate timing by a simple configuration in which the first switching element is input to a signal input terminal (for example, a gate in a MOSFET). The inverting means can also be realized by a simple circuit such as a NOT circuit.

Therefore, according to the first aspect of the present invention, it is possible to prevent an electric current from flowing through the body diodes of the pair of first switching elements by providing an auxiliary winding in the transformer or in the primary side of the transformer or in the smoothing circuit. Since this can be realized without providing a special circuit or element, the loss can be reduced with a simple configuration.

According to a second aspect of the present invention, there is provided a power supply apparatus comprising: a transformer having a primary winding, a secondary winding provided with a midpoint, and applying a unidirectional voltage to the primary winding of the transformer. After that, the application of the voltage is stopped for a predetermined period, and a voltage application unit that repeats stopping the application of the voltage for a predetermined period after applying the voltage in the other direction to the primary winding, and both ends of the secondary winding of the transformer. A pair of first pairs respectively provided between the connection points;
A switching element, a smoothing circuit provided between a middle point of the secondary winding and the connection point, and the pair of first switching elements alternately provided during a period in which a voltage is applied to the primary winding. Control means for turning on, a second switching element provided to short-circuit the middle point of the secondary winding and the connection point in the on state, and the potential of the middle point of the secondary winding or the connection point Or short-circuit control means for turning on the second switching element during a period in which application of voltage to the primary winding is stopped based on a current flowing through the second switching element. .

According to a second aspect of the present invention, a transformer, a voltage applying means, a pair of first switching elements, and a smoothing circuit similar to the first aspect of the present invention are provided. The pair of first switching elements are alternately turned on during a period in which a voltage is applied to the primary winding of the transformer. Thereby, the voltage induced in the secondary winding according to the turns ratio between the primary winding and the secondary winding of the transformer is rectified by the pair of first switching elements and smoothed by the smoothing circuit, and is applied to the load. It becomes possible to supply.

As described above, during a period in which no voltage is applied to the primary winding of the transformer, the energy stored in the smoothing circuit flows as a current, and this current is applied to the body of the first switching element. Loss occurs when flowing through a diode. According to the first aspect of the invention, the current is prevented from flowing through the body diode of the first switching element by turning on the pair of first switching elements during a period in which no voltage is applied to the primary winding. Blocking the current from flowing through the body diode can also be achieved by short-circuiting the middle point of the secondary winding and the connection point.

For this reason, according to the second aspect of the present invention, the second switching element is provided so as to short-circuit the middle point of the secondary winding and the connection point in the on state, and the short-circuit control means is provided with the secondary winding. The second switching element is turned on during a period in which the application of the voltage to the primary winding is stopped based on the potential at the middle point or the connection point, or the current flowing through the second switching element. As a result, the current due to the energy stored in the smoothing circuit is returned to the smoothing circuit through the second switching element, so that the current is prevented from flowing through the body diodes of the first switching element and the second switching element, and the loss is reduced. Can be reduced. Further, since current does not flow through the secondary winding of the transformer, loss (copper loss) caused by current flowing through the secondary winding can be eliminated.

As described above, the midpoint of the secondary winding (or the potential at the connection point) is low only during a period in which no voltage is applied to the primary winding (ie, a period during which the second switching element is to be turned on). The second switching element is turned on / off at an appropriate timing by using the potential of the middle point (or the potential of the connection point) of the secondary winding because the potential is at the potential (a period during which no voltage is applied to the primary winding). Only turned on) can be generated with a very simple configuration.

As an example, as described in claim 3,
If the short-circuit control means is configured to include a reversing means for reversing the level of the potential of the middle point or the connection point of the secondary winding, a signal for turning on and off the second switching element at an appropriate timing is provided from the reversing means. Since this signal is output, the second switching element can be turned on / off at appropriate timing by a simple configuration in which the signal is directly input to a control signal input terminal (for example, a gate in a MOSFET) of the second switching element. it can.

Further, if the second switching element is connected so that a forward voltage is applied to the body diode of the second switching element during a period when no voltage is applied to the primary winding, the voltage is applied to the primary winding. When a non-period starts, a current flows through the second switching element (specifically, a current flows through a body diode of the second switching element), and when a period in which no voltage is applied to the primary winding ends, the second switching is performed. Even when the element is in the ON state, the current stops flowing (in the case where the second switching element is a monopolar transistor or the like), and therefore, by using the current flowing through the second switching element,
A signal for turning on and off the second switching element at an appropriate timing can be generated with a very simple configuration.

As an example, as described in claim 4,
If the short-circuit control means includes a comparator that sets the output signal to a high potential when the current flowing through the body diode of the second switching element is equal to or more than a predetermined value, the comparator outputs the second signal.
Since a signal for turning on and off the switching element is output at an appropriate timing, the signal is directly input to a control signal input terminal (for example, a gate in a MOSFET) of the second switching element. The switching element can be turned on and off at appropriate timing.

In this embodiment, when a period in which no voltage is applied to the primary winding starts, a current flows through the body diode of the N-type MOSFET serving as the second switching element. After being turned on, no current flows through the body diode because the current flows through the channel of the N-type MOSFET. There is very little loss due to flowing.

As described above, according to the second aspect of the present invention, it is possible to prevent the current from flowing through the body diodes of the pair of first switching elements by providing an auxiliary winding in the transformer, or by connecting the primary side of the transformer or the primary side of the transformer. This can be realized without providing any special circuit or element in the smoothing circuit, and it is possible to prevent a steady current from flowing through the body diode of the second switching element. Therefore, the loss can be reduced with a simple configuration.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] FIG. 1 shows a power supply device 10 according to a first embodiment. The power supply device 10 includes a transformer 12 having a primary winding 12A and a secondary winding 12B provided with a middle point, a DC-AC inverter circuit 14 connected to the primary winding 12A of the transformer 12, Synchronous rectification circuit 16 connected to secondary winding 12B
, A smoothing circuit 18 connected to the synchronous rectifier circuit 16, and a feedback / control circuit 20 connected to the smoothing circuit 18 and the DC-AC inverter circuit 14.
A DC voltage is supplied to the load 22 connected to the power supply.

The DC-AC inverter circuit 14 corresponds to the voltage applying means of the present invention.
As the AC inverter circuit 14, a half-bridge type inverter circuit is used. That is, the DC-AC inverter circuit 14 includes the DC voltage source 26,
Are connected to the drain of the MOSFET 28 and one end of the capacitor 32, respectively. The DC voltage source 26 can be composed of, for example, a commercial AC voltage source, a rectifier circuit, and a smoothing circuit.

The source of the MOSFET 28 is the transformer 12
The other end of the capacitor 32 is connected to one end of the primary winding 12A and the drain of the MOSFET 30, and the other end of the capacitor 32 is connected to the other end of the primary winding 12A of the transformer 12 and one end of the capacitor. The source of MOSFET 30 and the other end of capacitor 34 are connected to the negative terminal of DC voltage source 26. The gates of the MOSFETs 28 and 30 are connected to the feedback / control circuit 20,
On / off of the feedback / control circuit 20 is controlled by the feedback / control circuit 20 (details will be described later).

The synchronous rectifier circuit 16 according to the first embodiment has N-type MOSFETs 38 and 40. In FIG. 1, the body diodes of the MOSFETs 38 and 40 are denoted by reference numerals "38a" and "40a", respectively. The drain of the MOSFET 38 is connected to one end of the secondary winding 12B of the transformer 12, and the MOSFET 40
Is connected to the other end of the secondary winding 12B.
The sources of the MOSFETs 38 and 40 are connected to each other at a connection point P. The MOSFETs 38 and 40 correspond to a pair of first switching elements according to the present invention.

In the following, for convenience of explanation, for convenience,
MOSFET3 of the secondary winding 12B of the transformer 12
8 is referred to as a “secondary winding 1” in a section from one end of the secondary winding 12B connected to the drain to the middle point of the secondary winding 12B.
2B ₀ ”, and the winding from the other end of the secondary winding 12B connected to the drain of the MOSFET 40 to the middle point of the secondary winding 12B is referred to as“ secondary winding 12B ₁ ”to distinguish each winding. I do.

Further, ends inverting circuit of the secondary winding 12B ₀ side of the secondary winding 12B of the transformer 12 (NOT circuit)
The output terminal of the inversion circuit 42 is connected to the gate of the MOSFET 38. Similarly, the ends of the secondary winding 12B ₁ side of the secondary winding 12B is connected to the input terminal of the inverting circuit 44, inverter circuit 44
Is connected to the gate of the MOSFET 40. The inverting circuits 42 and 44 correspond to the “inverting means for inverting the level of the potential at the end of the secondary winding” according to claim 1, and include the inverting circuits 42 and 44 and the inverting circuits 42 and 44. Connection line for connecting the winding 12B, and inversion circuits 42 and 44
The connection line connecting the MOSFETs 38 and 40 corresponds to the control means according to the first aspect.

The smoothing circuit 18 has an inductance 48 whose one end is connected to the middle point of the secondary winding 12B of the transformer 12.
And a capacitor 50 having one end connected to the other end of the inductance 50 and the other end connected to the connection point P. The load 22 as a DC voltage supply target by the power supply device 10 is connected to both ends of the capacitor 50.

The load 22 is connected to one end of the capacitor 50.
One end of a connection line 54 is connected in the middle of the feed line to the other end, and the other end of the connection line 54 is connected to the connection point P via the resistors 56 and 58 of the feedback / control circuit 20 connected in series. Have been. The connection point between the resistance 56 and the resistance 58 is the error amplifier 6
0, and is connected to the load 2
The DC voltage supplied to 2 is divided by resistors 56 and 58 and input to error amplifier 60. The error amplifier 60 inverts and amplifies the polarity of the error so that the difference (error) between the input voltage value and the target voltage value becomes zero.

The output terminal of the error amplifier 60 is a photocoupler 6
2 is connected to the input terminal of the variable frequency oscillation circuit 64, and the output terminal of the variable frequency oscillation circuit 64 is connected to the pulse generation circuit 66. Variable frequency oscillation circuit 64
Is a photo coupler 6 with respect to a predetermined reference frequency.
The oscillation frequency is changed in accordance with the voltage value of the signal input from the error amplifier 60 via the signal generator 2, and the signal of the oscillation frequency is input to the pulse generation circuit 66.

In this embodiment, the MOSFETs 28 and 30
By keeping the off time t _OFF (the predetermined period according to claim 1) constant and changing the on time t _ON , the MOSFET 2
By controlling the on / off duty ratio of 8, 30 to load 2
2 is controlled to be constant. MOSF
The off-time t _{OFF of the} ETs 28 and 30 is held in the one-shot timer 68, and a signal defining the off-time t _OFF is input from the one-shot timer 68 to the pulse generation circuit 66.

The pulse generating circuit 66 turns on only the MOSFET 28 for the ON time t _ON based on the signals input from the variable frequency oscillation circuit 64 and the one-shot timer 68, and then turns the MOSFETs 28 and 30 off for the OFF time t _OFF. The MOSFETs 28 and 30 are turned off, and then only the MOSFET 30 is turned on for the _ON time t _ON , and the MOSFETs 28 and 30 are turned off for the OFF time t _OFF.
Generate a drive signal (pulse signal) for turning on and off 0,
The generated drive signal is input to the gates of the MOSFETs 28 and 30, respectively.

Next, the operation of the power supply device 10 will be described as an operation of the first embodiment. In the DC-AC inverter circuit 14, when the MOSFET 28 is turned on, the DC voltage source 26 → the MOSFET 28 → the transformer 12
When a current flows through the path of the primary winding 12A → the capacitors 32 and 34 and the MOSFET 30 is turned on, the capacitors 32 and 34 → the primary winding 1 of the transformer 12
A current flows through a path of 2A → MOSFET 30 → DC voltage source 26.

Therefore, the direction of the current flowing through the primary winding 12A (the direction of the voltage applied to the primary winding 12A) is MO
When the SFET 28 is turned on and the MOSFET 30 is turned on, the direction is reversed. As shown in FIG. 2 as “primary winding voltage” and “primary winding current”, a constant Voltages having different polarities are alternately applied with a pause period (= off time t _OFF ) therebetween, and currents in opposite directions flow alternately. Incidentally, the primary winding voltage and the primary winding current shown in FIG.
Capacitors 32, 34 → primary winding 12A → MOSFET
The polarity when the current is flowing through the path of 30 → DC voltage source 26 is indicated as “positive”.

When the voltage is applied to the primary winding 12A of the transformer 12 as described above, the potential of the middle point of the secondary winding 12B (voltage V1) and the secondary winding 12B _{1 of the} secondary winding 12B are set.
The potential of the ends of the side (voltage V2), the potential of the ends of the secondary winding 12B ₀ side of the secondary winding 12B (voltage V3) is changing as shown in FIG. 2 over time . Note that the voltage V
1, V2 and V3 each have a reference potential of the potential V _{P of the} connection point _P.
It is. Further, the voltage V
2 (high level / low level) is inverted and input by the inverting circuit 44 (V4 shown in FIG. 2),
The level of the voltage V3 is inverted and input to the gate of the MOSFET 38 by the inverting circuit 42 (V5 shown in FIG. 2). Note that the voltages V4 and V5 are also the potential V _{P of the} connection point _P.
Is a reference potential.

Since the MOSFET 40 is turned on when the voltage V4 is at a high level and the MOSFET 38 is turned on when the voltage V5 is at a high level, the DC-AC inverter circuit 14 applies a positive voltage to the primary winding 12A. in the voltage in the secondary winding 12B ₀ is induced, the voltage V1 and the voltage V2 is ready voltage V3 at the high level is at a low level a (state in period a shown in FIG. 2),
When the voltage V4 goes low, the MOSFET 40 is turned off. When the voltage V5 goes high, the MOSFET 40 turns off.
T38 turns on.

Thus, the secondary winding 12 of the transformer 12
B middle point → inductance 48 → capacitor 50 and load 22 → connection point P → MOSFET 38 → secondary winding 12B
_A current flows through a path of _0, a DC voltage having a predetermined polarity is supplied to the load 22 via the smoothing circuit 18, and energy is accumulated in the inductance 48 of the smoothing circuit 18.

[0048] At this time MOSFET40 is off, since the secondary winding 12B ₁ in a state of reverse voltage is induced, the secondary winding 12B of the secondary winding 12B
The potential of the ends of the ₁ side is at a high potential compared to potential V _P of the connection point P. Therefore, from the connection point P to the MOSFET 40
No current flows through the body diode 40a, and no loss occurs due to the current flowing through the body diode 40a.

[0049] In FIG. 2, the secondary winding current I _B0 is the current flowing through the secondary winding 12B _0, the secondary winding current I _B1 is the current flowing through the secondary winding 12B _1, the secondary-side current I ₀ is Each of the currents flowing through the inductance 48 of the smoothing circuit 18 is shown,
Since no current flows in the state A, the secondary winding 12B _1, as described above (secondary winding current I _B1 = 0), the secondary-side current I ₀ is equal to the secondary winding current I _B0.

When a predetermined ON time elapses and DC-AC
When the inverter circuit 14 stops applying the voltage to the primary winding 12A, no voltage is induced in the secondary winding 12B, and the state B in which the voltages V1, V2, and V3 are each at a low level.
(The state in the period B shown in FIG. 2), and when the voltages V4 and V5 become high level, the MOSFET
38 and 40 are turned on.

Therefore, in this state B, the energy stored in the inductance 48 of the smoothing circuit 18 causes the inductance 48 → the capacitor 50 and the load 22 → the connection point P → the MOSFET 38 → the secondary winding 12B ₀ → the secondary winding 1
A current flows through the first path of the middle point of 2B → the inductance 48, and the inductance 48 → the capacitor 5
0 and load 22 → connection point P → MOSFET 40 → secondary winding 12B ₁ → middle point of secondary winding 12B → inductance 4
8, a current flows through the second path (secondary winding currents I _B0 , I _B1 and secondary side current I B during period B in FIG. 2).
₀ ), and a DC voltage having the same polarity as that in the state A is supplied to the load 22.

If the MOSFETs 38 and 40 are off in the state B, the secondary winding current I _B0 flows in the body diode 38a of the MOSFET 38 in the forward direction,
The secondary winding current I is applied to the body diode 38a of the ET 38.
_{When B1} flows in the forward direction, the body diodes 38a,
Loss is caused by the forward voltage drop of 38b. However, in the first embodiment, as described above, in the state B, the MOSFET
Since MOSFETs 38 and 40 are each on, MOSFET 38
No current flows through the body diode 38a of the MOSFET 40 and the body diode 40a of the MOSFET 40.
It is possible to avoid the occurrence of loss due to the current flowing through the body diodes 38a and 40a. In addition, state B
Since current flows through the secondary windings 12B ₀ and 12B ₁ respectively, the secondary side current I ₀ is equal to the sum of the secondary winding current I _B0 and the secondary winding current I _B1 (I ₀ = I _B0 + I _B1 ).

When a predetermined off time elapses and DC-AC
When the voltage in the secondary winding 12B ₁ by the inverter circuit 14 applies a negative voltage to the primary winding 12A is induced from the state B, which has been described above, the voltage V2 is a voltage V1, V3 at the High level Low The state is switched to the state C (the state in the period C shown in FIG. 2) in which the MOSFET 40 is turned on when the voltage V4 becomes the high level, and the voltage V4 is turned on.
The MOSFET 38 is turned off when the signal 5 goes low.

Thus, the secondary winding 12 of the transformer 12
B middle point → inductance 48 → capacitor 50 and load 22 → connection point P → MOSFET 40 → secondary winding 12B
A current flows through the path ₁ and a DC voltage having the same polarity as that in the state A and the state B is supplied to the load 22.
Energy is stored in the inductance 48 of the smoothing circuit 18.

At this time, since the MOSFET 38 is off and the secondary winding 12B ₀ is in a state where a reverse voltage is induced, the secondary winding 12B ₀
Potential end of the ₀ side is the higher potential as compared to potential V _P of the connection point P. Therefore, from the connection point P, the MOSFET 38
No current flows through the body diode 38a, and no loss occurs due to the current flowing through the body diode 38a. In state C, no current flows through the secondary winding 12B ₀ (secondary winding current I _B0 = 0), so the secondary current I ₀ is equal to the secondary winding current I _B1 .

As is clear from FIG. 2, the power supply circuit 10
(Synchronous rectifier circuit 16 and smoothing circuit 18)
Means that the state is A → B → C while the power supply circuit 10 is operating.
→ B → A →..., But as described above, in any of the states A to C, the MOSFET 3
Since no current flows through the body diodes 38a and 40a of the transistors 8 and 40, it is possible to avoid the occurrence of loss due to the current flowing through the body diodes.

In the first embodiment, the primary winding 12 of the transformer 12 is controlled by the DC-AC inverter circuit 14.
While the voltage is applied to A, the MOSFETs 38, 4
0 are alternately turned on, and the MOSFETs 38 and 40 are turned off while the application of the voltage to the primary winding 12A is stopped.
Are turned on by a simple configuration in which the potentials (voltages V2 and V3) at both ends of the secondary winding 12B are inverted by the inverting circuits 42 and 44 and input to the gates of the MOSFETs 38 and 40. Therefore, the configuration of the power supply device 10 can be simplified and the cost can be reduced.

The control means for controlling the on / off of the MOSFETs 38 and 40 can be configured as shown in FIG. 3 or FIG. For example, in the power supply device 72 shown in FIG. 3, the inverting circuit 42 that inverts the voltages V2 and V3,
Instead of 44, an inverting circuit 74 whose input terminal is connected to the middle point of the secondary winding 12B is provided. The output terminal of the inverting circuit 74 is connected to one of the two input terminals of the OR circuit 76 and the OR terminal.
Each of the two input terminals of the circuit 78 is connected to one of the two input terminals.

[0059] Two other input terminal of the OR circuit 76 is connected to an end of the secondary winding 12B ₁ side of the secondary winding 12B, the output terminal of the OR circuit 76 is connected to the gate of the MOSFET38 Have been. Also, two other input terminal is connected to an end of the secondary winding 12B ₀ side of the secondary winding 12B, the output terminal of the OR circuit 78 of the OR circuit 78 MO
It is connected to the gate of SFET40.

The OR circuit 76 receives the voltage V1 (see FIG. 2) which is inverted by the inverting circuit 74 and receives the voltage V2, and outputs a signal corresponding to the logical sum of the two signals. The signal output from 76 is shown in FIG.
Has the same waveform as the voltage V5 shown in FIG. Also, the OR circuit 7
8, the voltage V1 is inverted by the inverting circuit 74 and input, and the voltage V3 is input and outputs a signal corresponding to the logical sum of the two signals. It has the same waveform as the voltage V4 shown.

Therefore, the power supply circuit 72 shown in FIG.
The FETs 38 and 40 are turned on and off at the same timing as the MOSFETs 38 and 40 of the power supply circuit 10 shown in FIG. 1 when the DC-AC inverter circuit 14 applies a voltage to the primary winding 12A. As in the case of 10, it is possible to avoid the occurrence of loss due to the current flowing through the body diodes of the MOSFETs 38 and 40. Further, since the on / off control of the MOSFETs 38 and 40 is realized by a simple circuit configuration including the inversion circuit 74 and the OR circuits 76 and 78, the configuration of the power supply device 72 can be simplified and the cost can be reduced. .

The inverting circuit 74 of the power supply 72 corresponds to the "inverting means for inverting the level of the potential at the middle point of the secondary winding" according to the first aspect.
Reference numerals 6, 78 and the connection lines connecting these correspond to the control means according to the first aspect.

Further, in the power supply device 82 shown in FIG.
Instead of the OR circuits 76 and 78 shown in FIG.
A, 84B, 86A and 86B are used. That is, the output terminal of the inverting circuit 74 is connected to the anodes of the diodes 84A and 86A, respectively. Further, the diode 84B anode is connected to an end of the secondary winding 12B ₁ side of the secondary winding 12B, the diode 86B anode of the secondary winding 12B ₀ side of the secondary winding 12B Connected to the end. The cathodes of the diodes 84A and 84B are connected to the gate of the MOSFET 38, and the cathodes of the diodes 86A and 86B are connected to the MOSFET 40.
Connected to the gate.

With the above configuration, the signal input to the gate of the MOSFET 38 has the same waveform as the voltage V5 shown in FIG. 2, and the signal input to the gate of the MOSFET 40 has the same waveform as the voltage V4 shown in FIG. , The MOSFETs 38 and 40 of the power supply circuit 82 are also DC-AC
When voltage is applied to the primary winding 12A by the inverter circuit 14, the MOSFET 3 of the power supply circuit 10 shown in FIG.
It will be turned on and off at the same timing as 8 and 40. Therefore, it is possible to avoid a loss caused by a current flowing through the body diodes of the MOSFETs 38 and 40.

The on / off control of the MOSFETs 38 and 40 is controlled by an inverting circuit 74, a diode 84A,
Since the power supply device 82 is realized with a simple circuit configuration including 84B, 86A, and 86B, the configuration of the power supply device 82 can be simplified and the cost can be reduced.

The inverting circuit 74 of the power supply 82 also corresponds to the "inverting means for inverting the level of the potential at the middle point of the secondary winding" according to claim 1, and includes the inverting circuit 74, the diode 84A, 84B, 86A, 86B and the connection lines connecting them also correspond to the control means of the first aspect.

[Second Embodiment] Next, a second embodiment of the present invention will be described. The same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. FIG. 5 shows a power supply device 90 according to the second embodiment.

In the power supply device 90, the control unit 92A that outputs a drive signal for turning on and off the MOSFET 38 is a MOS transistor.
It is connected to the gate of FET38 and MOSFET4
A control unit 92B that outputs a drive signal for turning on and off 0 is connected to the gate of the MOSFET 40. Control unit 9
2A and 92B are, for example, MOSF
The ET 38 is turned on only during a period A (see FIG. 2) in which a voltage is induced in the secondary winding 12B ₀ , and the MOSFET 40 is turned on.
It is possible to adopt a configuration for generating a drive signal for turning on only in the period C the voltage induced in the secondary winding 12B _1.

The above-described structure is such that the secondary winding 12B is connected so that the voltage V2 is input to the gate of the MOSFET 38, for example.
Constitute a control section 92A by a connection line which connects the gate of the ends of the secondary winding 12B ₁ side and the MOSFET38 of, so that the voltage V3 is input to the gate of the MOSFET 40, two of the secondary winding 12B It can be realized by configuring the controller 92B by the connection line that connects the gate of the winding 12B ₀ side end and the MOSFET 40. The control units 92A and 92B correspond to the control unit according to the second aspect.

The middle point of the secondary winding 12B is an N-type M
The drain of the OSFET 94 is connected and the MOSF
The source of the ET94 is connected to the connection point P. In addition,
In FIG. 5, the body diode of the MOSFET 94 is set to "94".
a ". Also, the secondary winding 12B
The input terminal of the inversion circuit 96 is connected to the middle point, and the output terminal of the inversion circuit 96 is connected to the gate of the MOSFET 94.

Since the MOSFET 94 shorts the connection point P to the middle point of the secondary winding 12B in the ON state.
Corresponds to the second switching element. Also,
The inverting circuit 96 corresponds to inverting means for inverting the level of the “potential at the middle point of the secondary winding” according to claim 3, and the inverting circuit 96 and a connection line connecting the inverting circuit 96 are described in claim 2. Corresponds to the short-circuit control means (specifically, the short-circuit control means according to claim 3) for controlling on / off of the second switching element based on the "potential at the middle point of the secondary winding".

Next, the operation of the second embodiment will be described. MOSFET 38 of the power supply device 90 according to the second embodiment,
40 is turned off when no voltage is applied to the primary winding 12A (that is, during the period B).
During a period B in which no voltage is applied to 2A, the smoothing circuit 18
The energy stored in the inductance 48 of M
The body diodes 38a, 40 of the OSFETs 38, 40
A current flows through a.

On the other hand, the high / low level (high level / low level) of the voltage V1 at the middle point of the secondary winding 12B is inverted and input to the gate of the MOSFET 94 by the inverting circuit 96. As is clear from the change in V1, the MOSFET 94 turns on only during the period B when no voltage is applied to the primary winding 12A. As a result, the middle point of the secondary winding 12B and the connection point P are short-circuited, and the current due to the energy stored in the inductance 48 is reduced from the inductance 48 to the capacitor 50 and the load 2
It flows through a path of 2 → MOSFET 94 → inductance 48.

Therefore, current is prevented from flowing through the body diodes 38a, 40a of the MOSFETs 38, 40 and the body diode 94a of the MOSFET 94, and
It is possible to prevent a loss from being caused by a current flowing through the body diodes of the OSFETs 38, 40, and 94. Further, in the power supply device 90 according to the second embodiment, the current is also prevented from flowing through the secondary winding 12B during the period B when no voltage is applied to the primary winding 12A. , The occurrence of copper loss can be avoided, and the efficiency of the power supply device can be further improved as compared with the power supply device described in the first embodiment. In addition, to prevent the current from flowing through the body diodes of the MOSFETs 38, 40 and 94, the MOSF
Since this is realized with a simple circuit configuration including the ET 94 and the inverting circuit 94, the configuration of the power supply device 90 can be simplified and the cost can be reduced.

For example, the inverting circuit 94 includes resistors 100, 102, 104 and a transistor 1 as shown in FIG.
06. That is, one end of the resistor 100 is connected between the inductance 48 and the load 22, and the other end of the resistor 100 is connected to the gate of the MOSFET 94. One end of the resistor 102 is MOSFE
The other end of the resistor 102 is connected to one end of the resistor 104 and the base of the transistor 106, respectively. The collector of the transistor 106 is connected to the gate of the MOSFET 94, and the emitter of the transistor 106 and the other end of the resistor 104 are connected to a MOSF.
Connected to the source of ET94.

In the inverting circuit having the above configuration, the resistance 1
A path leading to the gate of the MOSFET 94 via the line 00 corresponds to a power supply line of the inverting circuit, and a DC voltage supplied to the load 22 is input to the gate of the MOSFET 94 via the resistor 100.

Here, during the period in which the DC-AC inverter circuit 14 applies a voltage to the primary winding 12A (period A and period C), the voltage V1 at the middle point of the secondary winding 12B is set to a high potential. Therefore, the base of the transistor 106 has the voltage V1
Is divided by the resistors 102 and 104 and a current flows to the base, so that the transistor 106 is turned on and the potential of the power supply line is set to a low potential. Therefore, while the voltage V1 at the middle point of the secondary winding 12B is kept at a high potential, the MOSFET 9
4 is turned off.

During the period (period B) during which the DC-AC inverter circuit 14 stops applying the voltage to the primary winding 12A, the voltage V1 at the middle point of the secondary winding 12B is set to a low potential. Therefore, when the transistor 106 is turned off, the potential of the power supply line is set to a high potential, and when the MOSFET 94 is turned on, the middle point of the secondary winding 12B and the connection point P are short-circuited. Since the inversion circuit 94 can be realized with a very simple circuit configuration as described above, the configuration of the power supply device 90 can be simplified and the cost can be reduced.

Although FIG. 5 shows an example in which the drains of the MOSFETs 38 and 40 are connected to the secondary winding 12B, the present invention is not limited to this, and as shown in FIG.
The source of the SFET 38 is connected to the secondary winding 12 of the secondary winding 12B.
While connected to the end portion of the B ₀ side, it may be connected to a source of MOSFET40 the end of the secondary winding 12B ₁ side of the secondary winding 12B. In the power supply device 110 shown in FIG. 7, the drains of the MOSFETs 38 and 40 are connected to each other via a connection point.
The drain of T94, the input terminal of the inverting circuit 96, and one end of the inductance 48 are connected. Also, MOSFE
The source of T94 is connected to the middle point of the secondary winding 12B.

This power supply device 110 has a secondary winding 12B ₀
During the period A (see FIG. 2) in which a voltage is induced in the MOSFET,
38 is turned on, the secondary winding 12B ₀ → MOSF
ET38 → midpoint of the connection point P → inductance 48 → capacitor 50 and load 22 → secondary winding 12B, a current flows through a path that turns on the MOSFET40 the period C the voltage induced in the secondary winding 12B ₁ The secondary winding 12B ₁ → MOSFET 40 → connection point P → inductance 48 → capacitor 50 and load 22 → secondary winding 12B
The operation other than the point at which the current flows through the middle point is the same as that of the power supply device 90.

The inverting circuit 96 of the power supply device 110 corresponds to the inverting means for inverting the level of the “potential at the connection point” according to the third aspect, and the inverting circuit 96 and the connection line connecting the inverting circuit 96 are The present invention corresponds to a short-circuit control unit (more specifically, a short-circuit control unit according to the third embodiment) that controls on / off of the second switching element based on the “potential at the connection point” according to the second embodiment.

Further, the short-circuit control means according to the second aspect of the present invention may employ the configuration shown in FIG. 8 instead of the configuration shown in FIGS. That is, the power supply device 114 shown in FIG. 8 includes a resistor 116 having one end connected to the source of the MOSFET 94 and the other end connected to the connection point P (or the middle point of the secondary winding 12B), and a minus terminal connected to the connection point. A reference voltage source 118 connected to P (or the middle point of the secondary winding 12B), one of the two input terminals is connected to the plus terminal of the reference voltage source 118, the other is connected to the source of the MOSFET 94, and the output terminal And a comparator 120 connected to the gate of the MOSFET 94.

The comparator 120 outputs the signal when the voltage input through the input terminal connected to the source of the MOSFET 94 is higher than the voltage input through the input terminal connected to the reference voltage source 118. The level (potential) of the signal output through the end is set to the high level (high potential), and the level (potential) of the output signal is set to the low level (low potential) except in the above case.

Incidentally, the MOSFET 94 corresponds to the second switching element according to the second aspect of the present invention.
Corresponds to the comparator according to claim 4. The short-circuit control means having the above configuration controls the on / off of the second switching element based on the “current flowing through the second switching element” according to claim 2 (specifically, according to claim 4). Short-circuit control means).

In the power supply device 114, when the application of the voltage to the primary winding 12A is stopped, the current due to the energy stored in the inductance 48 is applied to the MOSFET 94.
Flows through the body diode 94a of the MOSFET 9
The potential of the source No. 4 is higher than a predetermined value by the resistor 116. Here, when the voltage input to the comparator 120 via the input terminal connected to the source of the MOSFET 94 becomes higher than the voltage input to the comparator 120 via the input terminal connected to the reference voltage source 118. , The level of the signal output from the comparator 120 becomes high and the MOSF
ET94 turns on.

As a result, the middle point of the secondary winding 12B and the connection point P are short-circuited, so that the current due to the energy stored in the inductance 48 is changed from the inductance 48 → the capacitor 50 and the load 22 → the resistor 116 → the MOSFET 94.
→ It flows through the path of inductance 48. Therefore, M
The body diodes 38a, 40 of the OSFETs 38, 40
a, and current is prevented from flowing through the body diode 94a of the MOSFET 94, and the MOSFETs 38, 40,
It is possible to avoid a loss caused by a current flowing through the body diode 94.

Further, it is possible to prevent the current from flowing through the body diodes of the MOSFETs 38, 40 and 94.
Since it is realized with a simple circuit configuration including the MOSFET 94, the resistor 116, the reference voltage source 118, and the comparator 120, the configuration of the power supply device 114 can be simplified and the cost can be reduced.

Note that the short-circuit control means of the power supply 114
Since it is detected that a current has flowed through the body diode 94a of the MOSFET 94 and the MOSFET 94 is turned on, the MOSFET is turned on until the MOSFET 94 is turned on.
The current flows through the body diode 94a of the T94. The length of time from when the current starts flowing through the body diode 94a of the MOSFET 94 to when the level of the output signal of the comparator 120 is switched depends on the value of the resistor 116 and the reference voltage. By properly selecting parameters such as the voltage generated by the source 118, the length can be made very short, and the loss due to the current flowing through the body diode can be made extremely small.

In the above description, the case where the N-type MOSFET is applied as the first switching element and the second switching element has been described. However, the present invention is not limited to this. A P-type MOSFET or another transistor may be used.

In the above description, an example in which a half-bridge type inverter circuit is used as the voltage applying means has been described.
The invention is not limited to this, and it goes without saying that, for example, a full-bridge type inverter circuit or the like may be applied.

[0091]

As described above, according to the first aspect of the present invention, the potential at both ends of the secondary winding of the transformer provided with the middle point or the potential at the middle point of the secondary winding is inverted. Inverting means is provided, and while a voltage is applied to the primary winding of the transformer, a pair of first switching elements provided between both ends of the secondary winding and the connection point are alternately turned on,
Since the pair of first switching elements are turned on while the application of the voltage to the primary winding is stopped, there is an excellent effect that the loss can be reduced with a simple configuration.

According to a second aspect of the present invention, in the ON state, the second switching element is short-circuited between the middle point of the secondary winding of the transformer and a connection point to which the pair of first switching elements are connected. During the period in which the application of the voltage to the primary winding of the transformer is stopped based on the potential of the middle point or connection point of the secondary winding or the current flowing through the second switching element. Since the element is turned on, the loss can be reduced with a simple configuration.
It has an excellent effect.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an example of a configuration of a power supply device according to a first embodiment.

FIG. 2 is a timing chart for explaining an operation of the power supply device according to the first embodiment.

FIG. 3 is a circuit diagram illustrating another configuration example of the power supply device according to the first embodiment.

FIG. 4 is a circuit diagram illustrating another configuration example of the power supply device according to the first embodiment.

FIG. 5 is a circuit diagram illustrating an example of a configuration of a power supply device according to a second embodiment.

6 is a circuit diagram showing details of an inversion circuit in the power supply device shown in FIG.

FIG. 7 is a circuit diagram illustrating another configuration example of the power supply device according to the second embodiment.

FIG. 8 is a circuit diagram showing another configuration example of the power supply device according to the second embodiment.

[Explanation of symbols]

10, 72, 82, 90, 110, 114 Power supply device 12 Transformer 14 DC-AC inverter circuit (voltage applying means) 38, 40 MOSFET (first switching element) 42, 44, 74 Inverting circuit (control means) 84, 86 Diode (control means) 94 MOSFET (second switching element) 96 Inverting circuit (short-circuit control means) 100, 102, 104, 116 Resistance (short-circuit control means) 106 Transistor (short-circuit control means) 118 Reference voltage source (short-circuit control means) 120 comparator (short circuit control means)

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 14, 2000 (2000.8.1)
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Power supply unit

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device, and more particularly, to a method of intermittently applying a voltage to a primary winding of a transformer and rectifying and smoothing a voltage induced in a secondary winding having a center point of the transformer. And a power supply device for supplying power to the load.

[0002]

2. Description of the Related Art Conventionally, a DC voltage is intermittently applied to a primary winding of a transformer by a switching element, and a voltage induced in a secondary winding of the transformer provided with a center tap (middle point) is rectified. 2. Description of the Related Art A switching power supply (a so-called DC-DC converter) that obtains a predetermined DC voltage by performing rectification (full-wave rectification) and smoothing by a circuit is known. In a switching power supply of this type, a diode is generally used as a rectifying element of a rectifying circuit. However, a forward voltage drop of the diode (for example, 0.6 V
), Loss occurs in the rectifier circuit, and this loss hinders improvement in efficiency of the switching power supply device.

As one of the methods for reducing the loss in the rectifier circuit, a method using a Schottky diode as a rectifying element has been conventionally employed. However, this method depends on the performance of the element and is dramatically increased. No significant loss reduction can be expected. As another method, a method of reducing loss by a circuit technique is also known, and a method of using a synchronous rectifier circuit using a switching element such as a MOSFET as a rectifier element as a rectifier circuit is mainly used.

As a driving method of the MOSFET in the synchronous rectifier circuit, for example, a gate of a first MOSFET for turning on / off one end of a secondary winding of a transformer and a smoothing circuit is connected to the other end of the secondary winding. , A second MOSFET for turning on and off the conduction between the other end of the secondary winding and the smoothing circuit
Is connected to one end of the secondary winding (Japanese Patent Laid-Open No.
No. 337005) or a configuration in which a resistor is provided between the gate of the MOSFET and the secondary winding (Japanese Utility Model Application Laid-Open No. 7-239).
Japanese Patent Application Laid-Open No. 8-331841), and a configuration in which a resistor, a diode, and a capacitor are provided in parallel between the gate of a MOSFET and a secondary winding (see Japanese Patent Application Laid-Open No. 8-331841).

In each of the above-described configurations, any one of the MOSFETs is turned on and the synchronous rectification circuit operates during a period in which a voltage is applied to the primary winding of the transformer (rectification period). Loss reduction can be achieved. However, although the loss during the rectification period can be reduced, all the current generated by the inductance of the smoothing circuit during the commutation period (period when no voltage is applied to the primary winding of the transformer) is the body diode (MOSF) of the MOSFET.
Loss is generated by flowing through an internal diode of the ET (also referred to as a parasitic diode). In general, the body diode has a larger forward voltage drop than the fast recovery diode and the Schottky diode, so that the loss increases rather. For this reason, it is necessary to take measures to prevent a current from flowing through the body diode during the commutation period.

In order to reduce the loss during the commutation period, a method has been proposed in which the input voltage is controlled to shorten the commutation period. However, in order to effectively reduce the loss in this method, the commutation period is reduced. Needs to be very short, and the operating range of the switching power supply device becomes narrow.

In Japanese Patent Application Laid-Open No. 3-117364, a transformer having two sets of secondary windings with a center point is used, and a choke transformer is used as an inductance of a smoothing circuit. A configuration in which two switching elements are turned on, and a primary element of the choke transformer which is turned on by a voltage induced in the secondary winding of the choke transformer during the commutation period and short-circuits the input terminal of the smoothing circuit. A configuration for supplying the stored power of the winding to a load is disclosed. However, the above circuit has a disadvantage that the configuration of the transformer is complicated. Further, in a configuration in which a switching element is turned on and off using a choke transformer, there is a problem that a loss occurs due to a phase delay of a signal for turning the switching element on and off.

Further, in FIG. 7 and FIG. 9 of JP-A-8-322245, a current transformer is provided on the primary side of a transformer, and a current flowing through a switching element on the primary side is detected by the current transformer. A configuration is disclosed in which an auxiliary winding for a drive power supply is provided on the secondary side of the transformer and the switching element on the secondary side is also turned on during the commutation period. In the above configuration, a current transformer is provided on the primary side. Since it is necessary to provide an auxiliary winding in the transformer, the circuit configuration becomes complicated, which is disadvantageous in terms of cost and the like.

In Japanese Patent Application Laid-Open No. 9-149635, a full-bridge inverter having four switching elements is provided on the primary side of a transformer, and a synchronous rectifier circuit including a pair of switching elements is provided on the secondary side. In the configuration, during the commutation period, only one of the primary-side switching element pair that was in the on state during the rectification period up to that time is turned off, and one of the pair of secondary-side switching elements is also turned on. A technique for continuing is disclosed. Japanese Patent Application Laid-Open No. 9-149636 describes that a pair of secondary-side switching elements are turned on during a commutation period in a power supply device having a configuration similar to that of the above publication. However, each of the techniques described in the above publications has a disadvantage that the circuit configuration of a circuit that generates a drive signal for turning on and off a switching element becomes very complicated.

[0010]

As described above, in the conventional power supply devices including the center tap type synchronous rectifier circuit, current flows through the body diode of the switching element during the commutation period. However, there is a drawback that loss occurs or the circuit configuration becomes very complicated to prevent current from flowing through the body diode.

The present invention has been made in consideration of the above-described facts, and has as its object to provide a power supply device that can reduce a loss with a simple configuration.

[0012]

According to a first aspect of the present invention, there is provided a power supply device comprising: a primary winding;
A midpoint is provided and the winding from one end to the midpoint and forward from the other end
And a secondary winding which windings up serial in point is the phase, and the transformer with a voltage application was stopped for a predetermined time period after applying a unidirectional voltage to the primary winding of the transformer, the primary and voltage applying means for repeating that predetermined period stops applying the voltage after applying the other direction voltage to the winding, and one end of the transformer secondary winding, between the connection point to be a reference potential a first switching element was set <br/> vignetting, secondary of the transformer
A second switch provided between the other end of the winding and the connection point.
A switching element , a smoothing circuit provided between a middle point of the secondary winding and the connection point, and the first switching element.
Off while the potential at one end of the secondary winding is at a high level.
When the potential at one end is turned on while the potential at the one end is low level,
In both cases, the second switching element is connected to the other
The terminal at the other end is turned off during the high level, and the potential at the other end is turned off.
And control means for turning on during the low level .

According to the first aspect of the present invention, the voltage application is stopped for a predetermined period after the unidirectional voltage is applied to the primary winding of the transformer, and the voltage is applied after the unidirectional voltage is applied to the primary winding. A voltage application unit that repeats stopping for a predetermined period is provided. The voltage applying means includes a DC power supply, a state in which the voltage of the DC power supply is applied to the primary winding as a voltage in one direction, a state in which the voltage is applied as a voltage in the other direction, and a voltage applied to the primary winding. And a plurality of switching elements that can be switched to a state in which application is stopped. Specifically, for example, a half-bridge type or full-bridge type DC-AC inverter circuit can be used. it can.

Further, according to the first aspect of the present invention, the first terminal is connected between one end of the secondary winding of the transformer and a connection point set to the reference potential .
The switching element is set vignetting, other transformer secondary winding
A second switching element is provided between the end and the connection point;
In addition, since the smoothing circuit is provided between the middle point of the secondary winding and the connection point, during a period in which a voltage is applied to the primary winding of the transformer, the control unit controls the first switching element and the second switching element . S
The switching elements are turned on alternately (while the voltage is applied to the primary winding of the transformer , the first switching element
And one of the second switching elements is turned on,
Turn on each time the period when the voltage is applied
Luz switching switch the device) that is, the voltage induced in the secondary winding in accordance with the turns ratio of the primary winding and the secondary winding of the transformer, the first switching element and the second switching
It is rectified by the element and smoothed by the smoothing circuit, and can be supplied to the load.

By the way, in the period in which no voltage is applied to the primary winding of the transformer, the energy stored in the smoothing circuit flows as a current, for loss reduction, before
The first switching element and the second switching element
It is desirable to turn on each child .

By the way, during the period when no voltage is applied to the primary winding of the transformer, the energy stored in the smoothing circuit flows as a current. When this current flows through the body diodes of the first switching element and the second switching element, a loss occurs. Therefore, it is desirable to turn on the first switching element and the second switching element , respectively, in order to reduce the loss.

On the other hand, the potential of one end of the secondary winding of the transformer becomes high only while a voltage in one direction is applied to the primary winding, and the potential of the other end of the secondary winding becomes high. Is high only during the period when the voltage in the other direction is applied, and the potential at the middle point of the secondary winding is the period when the voltage in one direction is applied to the primary winding and the voltage in the other direction is applied. The potential becomes high during the period. That is, the potential of one end of the secondary winding of the transformer becomes low only during a period in which one of the first switching elements is to be turned on (including a period in which no voltage is applied to the primary winding). Of the other end is the first
The potential becomes low only during a period in which the switching element is to be turned on (including a period in which no voltage is applied to the primary winding), and the potential at the middle point of the secondary winding turns on each of the pair of first switching elements. The potential becomes low only during a power period (a period when no voltage is applied to the primary winding).

According to the first aspect of the present invention, both the secondary windings of the transformer are provided.
Paying attention to the change in the potential of the terminal, the control means according to the first aspect of the present invention comprises a first control circuit connected to one end of the secondary winding of the transformer.
When the potential at one end of the secondary winding is high
Off during the level, and the potential at the one end is at the low level.
And turn on the other end of the transformer secondary winding.
Connected to the other end of the secondary winding
Is turned off while the potential of the other end is high level, and the potential of the other end is
Turn on all the time during low level. As a result, the first switch
The timing element and the second switching element should be properly timed.
On and off.

As an example, when the control means includes an inversion means for inverting the level of the potential of the end of the secondary winding, the inversion means outputs the first switching element and the second switch .
Since a signal for turning on or off one of the switching elements at an appropriate timing is output, the signal is directly input to a control signal input terminal (for example, a gate in a MOSFET) of the first switching element or the second switching element. With a simple configuration, the first switching element or the second switching element can be turned on and off at appropriate timing.

More specifically, for example, as described in claim 2
As described above, the control means is connected to one end of the secondary winding and the first switch.
Connected between the switching element and the control signal input terminal of the switching element.
A first inverting circuit for inverting the potential at one end, and the secondary winding;
And a control signal input terminal of the second switching element.
And a second inversion circuit for inverting the potential of the other end.
Road and can be configured with a very simple configuration
Turn the first switching element on and off at the right time
Can be made.

Further, for example , when the control means includes an inversion means for inverting the level of the potential at the middle point of the secondary winding, the application of the voltage to the primary winding from the inversion means is stopped. The first switching element and the second switch during
Since the signal for turning on the switching element is output, the first switching element and the second switching element are alternately switched while the signal and the voltage are applied to the primary winding.
The signal for turning on the first switching element and the second Sui
Respectively inputted to the control signal input terminal of the switching element (e.g., a gate in MOSFET), it is possible to turn on and off the first switching element and second switching element at a proper timing by the simple configuration of. In addition,
The inversion means can also be realized by a simple circuit such as a NOT circuit.

[0022] Thus, according to the invention of claim 1, Trang
While no voltage is applied to the primary winding of the switch,
Since the switching element and the second switching element can be turned on without providing an auxiliary winding in the transformer or providing a special circuit or element on the primary side of the transformer or the smoothing circuit, a simple configuration is achieved. Thus, the loss can be reduced.

[0023] In the first aspect of the present invention, the third aspect of the present invention provides
In the on state, the middle point of the secondary winding and the front
A third switch provided to short-circuit the connection point
And the potential of the middle point or connection point of the secondary winding.
And the output from the inversion means.
Input the control signal to the third switching element.
Input to the terminal stops the application of voltage to the primary winding.
Turn on the third switching element during the stopped period
And a short-circuit control means.
As described above, in the ON state, the connection between the middle point of the secondary winding and the connection
And a point is short-circuited, and a voltage is applied to the primary winding.
A diode to which a forward voltage is applied during the period when no voltage is applied
A third switching element provided in parallel with
The current flowing through the third switching element is equal to or greater than a predetermined value
In this case, the comparator
And outputs the signal output from the comparator to the third switch.
Input to the control signal input terminal of the
During the period when the voltage application to the line is stopped, the third switch
Short-circuit control means for turning on the switching element.
Is preferred.

As described above, in the on state, the midpoint of the secondary winding
Third switch provided so as to short-circuit the connection point and the connection point
During the period when the application of voltage to the primary winding is stopped.
By turning on the third switching element in the meantime,
The current due to the energy stored in the smooth circuit
Since the current flows back to the smoothing circuit side through the switching element, no current flows to the secondary winding of the transformer, and the loss (copper loss) due to the current flowing through the secondary winding can be eliminated.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] FIG. 1 shows a power supply device 10 according to a first embodiment. The power supply device 10 includes a transformer 12 having a primary winding 12A and a secondary winding 12B provided with a middle point, a DC-AC inverter circuit 14 connected to the primary winding 12A of the transformer 12, Synchronous rectification circuit 16 connected to secondary winding 12B
, A smoothing circuit 18 connected to the synchronous rectifier circuit 16, and a feedback / control circuit 20 connected to the smoothing circuit 18 and the DC-AC inverter circuit 14.
A DC voltage is supplied to the load 22 connected to the power supply.

The DC-AC inverter circuit 14 corresponds to the voltage applying means of the present invention.
As the AC inverter circuit 14, a half-bridge type inverter circuit is used. That is, the DC-AC inverter circuit 14 includes the DC voltage source 26,
Are connected to the drain of the MOSFET 28 and one end of the capacitor 32, respectively. The DC voltage source 26 can be composed of, for example, a commercial AC voltage source, a rectifier circuit, and a smoothing circuit.

The source of the MOSFET 28 is the transformer 12
The other end of the capacitor 32 is connected to one end of the primary winding 12A and the drain of the MOSFET 30, and the other end of the capacitor 32 is connected to the other end of the primary winding 12A of the transformer 12 and one end of the capacitor. The source of MOSFET 30 and the other end of capacitor 34 are connected to the negative terminal of DC voltage source 26. The gates of the MOSFETs 28 and 30 are connected to the feedback / control circuit 20,
On / off of the feedback / control circuit 20 is controlled by the feedback / control circuit 20 (details will be described later).

The synchronous rectifier circuit 16 according to the first embodiment includes N-type MOSFETs 38 and 40. In FIG. 1, the body diodes of the MOSFETs 38 and 40 are denoted by reference numerals "38a" and "40a", respectively. The drain of the MOSFET 38 is connected to one end of the secondary winding 12B of the transformer 12, and the MOSFET 40
Is connected to the other end of the secondary winding 12B.
The sources of the MOSFETs 38 and 40 are connected to each other at a connection point P. MOSFET38,40 are respectively corresponding to the engaging Ru first switching element or the second switching element <br/> the present invention.

In the following, for convenience of explanation, for convenience,
MOSFET3 of the secondary winding 12B of the transformer 12
8 is referred to as a “secondary winding 1” in a section from one end of the secondary winding 12B connected to the drain to the middle point of the secondary winding 12B.
2B ₀ ”, and the winding from the other end of the secondary winding 12B connected to the drain of the MOSFET 40 to the middle point of the secondary winding 12B is referred to as“ secondary winding 12B ₁ ”to distinguish each winding. I do.

Further, ends inverting circuit of the secondary winding 12B ₀ side of the secondary winding 12B of the transformer 12 (NOT circuit)
The output terminal of the inversion circuit 42 is connected to the gate of the MOSFET 38. Similarly, the ends of the secondary winding 12B ₁ side of the secondary winding 12B is connected to the input terminal of the inverting circuit 44, inverter circuit 44
Is connected to the gate of the MOSFET 40. The first inversion circuit according to claim 2 , wherein the inversion circuits (42, 44) are provided .
And a second inverting circuit.
4, connection lines connecting the inversion circuits 42 and 44 to the secondary winding 12B, and the inversion circuits 42 and 44 and the MOSFET 38;
The connection line connecting the terminals 40 corresponds to the control unit according to the first aspect.

The smoothing circuit 18 has an inductance 48 whose one end is connected to the middle point of the secondary winding 12B of the transformer 12.
And a capacitor 50 having one end connected to the other end of the inductance 50 and the other end connected to the connection point P. The load 22 as a DC voltage supply target by the power supply device 10 is connected to both ends of the capacitor 50.

The load 22 is connected from one end of the capacitor 50 to the load 22.
One end of a connection line 54 is connected in the middle of the feed line to the other end, and the other end of the connection line 54 is connected to the connection point P via the resistors 56 and 58 of the feedback / control circuit 20 connected in series. Have been. The connection point between the resistance 56 and the resistance 58 is the error amplifier 6
0, and is connected to the load 2
The DC voltage supplied to 2 is divided by resistors 56 and 58 and input to error amplifier 60. The error amplifier 60 inverts and amplifies the polarity of the error so that the difference (error) between the input voltage value and the target voltage value becomes zero.

The output terminal of the error amplifier 60 is a photocoupler 6
2 is connected to the input terminal of the variable frequency oscillation circuit 64, and the output terminal of the variable frequency oscillation circuit 64 is connected to the pulse generation circuit 66. Variable frequency oscillation circuit 64
Is a photo coupler 6 with respect to a predetermined reference frequency.
The oscillation frequency is changed in accordance with the voltage value of the signal input from the error amplifier 60 via the signal generator 2, and the signal of the oscillation frequency is input to the pulse generation circuit 66.

In this embodiment, the MOSFETs 28 and 30
By keeping the off time t _OFF (the predetermined period according to claim 1) constant and changing the on time t _ON , the MOSFET 2
By controlling the on / off duty ratio of 8, 30 to load 2
2 is controlled to be constant. MOSF
The off-time t _{OFF of the} ETs 28 and 30 is held in the one-shot timer 68, and a signal defining the off-time t _OFF is input from the one-shot timer 68 to the pulse generation circuit 66.

The pulse generating circuit 66 turns on only the MOSFET 28 for the ON time t _ON and then turns off the MOSFETs 28 and 30 for the OFF time t _OFF based on the signals input from the variable frequency oscillation circuit 64 and the one-shot timer 68. The MOSFETs 28 and 30 are turned off, and then only the MOSFET 30 is turned on for the _ON time t _ON , and the MOSFETs 28 and 30 are turned off for the OFF time t _OFF.
Generate a drive signal (pulse signal) for turning on and off 0,
The generated drive signal is input to the gates of the MOSFETs 28 and 30, respectively.

Next, the operation of the power supply device 10 will be described as an operation of the first embodiment. In the DC-AC inverter circuit 14, when the MOSFET 28 is turned on, the DC voltage source 26 → the MOSFET 28 → the transformer 12
When a current flows through the path of the primary winding 12A → the capacitors 32 and 34 and the MOSFET 30 is turned on, the capacitors 32 and 34 → the primary winding 1 of the transformer 12
A current flows through a path of 2A → MOSFET 30 → DC voltage source 26.

Therefore, the direction of the current flowing through the primary winding 12A (the direction of the voltage applied to the primary winding 12A) is MO
When the SFET 28 is turned on and the MOSFET 30 is turned on, the direction is reversed. As shown in FIG. 2 as “primary winding voltage” and “primary winding current”, a constant Voltages having different polarities are alternately applied with a pause period (= off time t _OFF ) therebetween, and currents in opposite directions flow alternately. Incidentally, the primary winding voltage and the primary winding current shown in FIG.
Capacitors 32, 34 → primary winding 12A → MOSFET
The polarity when the current is flowing through the path of 30 → DC voltage source 26 is indicated as “positive”.

When the voltage is applied to the primary winding 12A of the transformer 12 as described above, the potential of the middle point of the secondary winding 12B (voltage V1), and the secondary winding 12B _{1 of the} secondary winding 12B.
The potential of the ends of the side (voltage V2), the potential of the ends of the secondary winding 12B ₀ side of the secondary winding 12B (voltage V3) is changing as shown in FIG. 2 over time . Note that the voltage V
1, V2 and V3 each have a reference potential of the potential V _{P of the} connection point _P.
It is. Further, the voltage V
2 (high level / low level) is inverted and input by the inverting circuit 44 (V4 shown in FIG. 2),
The level of the voltage V3 is inverted and input to the gate of the MOSFET 38 by the inverting circuit 42 (V5 shown in FIG. 2). Note that the voltages V4 and V5 are also the potential V _{P of the} connection point _P.
Is a reference potential.

Since the MOSFET 40 is turned on when the voltage V4 is at a high level and the MOSFET 38 is turned on when the voltage V5 is at a high level, the DC-AC inverter circuit 14 applies a positive voltage to the primary winding 12A. in the voltage in the secondary winding 12B ₀ is induced, the voltage V1 and the voltage V2 is ready voltage V3 at the high level is at a low level a (state in period a shown in FIG. 2),
When the voltage V4 goes low, the MOSFET 40 is turned off. When the voltage V5 goes high, the MOSFET 40 turns off.
T38 turns on.

Thus, the secondary winding 12 of the transformer 12
B middle point → inductance 48 → capacitor 50 and load 22 → connection point P → MOSFET 38 → secondary winding 12B
_A current flows through a path of _0, a DC voltage having a predetermined polarity is supplied to the load 22 via the smoothing circuit 18, and energy is accumulated in the inductance 48 of the smoothing circuit 18.

[0042] At this time MOSFET40 is off, since the secondary winding 12B ₁ in a state of reverse voltage is induced, the secondary winding 12B of the secondary winding 12B
The potential of the ends of the ₁ side is at a high potential compared to potential V _P of the connection point P. Therefore, from the connection point P to the MOSFET 40
No current flows through the body diode 40a, and no loss occurs due to the current flowing through the body diode 40a.

[0043] In FIG. 2, the secondary winding current I _B0 is the current flowing through the secondary winding 12B _0, the secondary winding current I _B1 is the current flowing through the secondary winding 12B _1, the secondary-side current I ₀ is Each of the currents flowing through the inductance 48 of the smoothing circuit 18 is shown,
Since no current flows in the state A, the secondary winding 12B _1, as described above (secondary winding current I _B1 = 0), the secondary-side current I ₀ is equal to the secondary winding current I _B0.

When a predetermined ON time elapses and DC-AC
When the inverter circuit 14 stops applying the voltage to the primary winding 12A, no voltage is induced in the secondary winding 12B, and the state B in which the voltages V1, V2, and V3 are each at a low level.
(The state in the period B shown in FIG. 2), and when the voltages V4 and V5 become high level, the MOSFET
38 and 40 are turned on.

Therefore, in this state B, the energy stored in the inductance 48 of the smoothing circuit 18 causes the inductance 48 → the capacitor 50 and the load 22 → the connection point P → the MOSFET 38 → the secondary winding 12B ₀ → the secondary winding 1
A current flows through the first path of the middle point of 2B → the inductance 48, and the inductance 48 → the capacitor 5
0 and load 22 → connection point P → MOSFET 40 → secondary winding 12B ₁ → middle point of secondary winding 12B → inductance 4
8, a current flows through the second path (secondary winding currents I _B0 , I _B1 and secondary side current I B during period B in FIG. 2).
₀ ), and a DC voltage having the same polarity as that in the state A is supplied to the load 22.

[0046] Assuming the case where MOSFET38,40 was turned off in a state B, the body diode 38a of MOSFET38 flow secondary winding current I _B0 is in the forward direction, MOSF
The secondary winding current I is applied to the body diode 38a of the ET 38.
_{When B1} flows in the forward direction, the body diodes 38a,
Loss is caused by the forward voltage drop of 38b. However, in the first embodiment, as described above, in the state B, the MOSFET
Since MOSFETs 38 and 40 are each on, MOSFET 38
No current flows through the body diode 38a of the MOSFET 40 and the body diode 40a of the MOSFET 40.
It is possible to avoid the occurrence of loss due to the current flowing through the body diodes 38a and 40a. In addition, state B
Since current flows through the secondary windings 12B ₀ and 12B ₁ respectively, the secondary side current I ₀ is equal to the sum of the secondary winding current I _B0 and the secondary winding current I _B1 (I ₀ = I _B0 + I _B1 ).

When a predetermined off time has passed and DC-AC
When the voltage in the secondary winding 12B ₁ by the inverter circuit 14 applies a negative voltage to the primary winding 12A is induced from the state B, which has been described above, the voltage V2 is a voltage V1, V3 at the High level Low The state is switched to the state C (the state in the period C shown in FIG. 2) in which the MOSFET 40 is turned on when the voltage V4 becomes the high level, and the voltage V4 is turned on.
The MOSFET 38 is turned off when the signal 5 goes low.

Thus, the secondary winding 12 of the transformer 12
B middle point → inductance 48 → capacitor 50 and load 22 → connection point P → MOSFET 40 → secondary winding 12B
A current flows through the path ₁ and a DC voltage having the same polarity as that in the state A and the state B is supplied to the load 22.
Energy is stored in the inductance 48 of the smoothing circuit 18.

At this time, since the MOSFET 38 is off and the secondary winding 12B ₀ is in a state where a reverse voltage is induced, the secondary winding 12B
Potential end of the ₀ side is the higher potential as compared to potential V _P of the connection point P. Therefore, from the connection point P, the MOSFET 38
No current flows through the body diode 38a, and no loss occurs due to the current flowing through the body diode 38a. In state C, no current flows through the secondary winding 12B ₀ (secondary winding current I _B0 = 0), so the secondary current I ₀ is equal to the secondary winding current I _B1 .

As is apparent from FIG.
(Synchronous rectifier circuit 16 and smoothing circuit 18)
Means that the state is A → B → C while the power supply circuit 10 is operating.
→ B → A →..., But as described above, in any of the states A to C, the MOSFET 3
Since no current flows through the body diodes 38a and 40a of the transistors 8 and 40, it is possible to avoid the occurrence of loss due to the current flowing through the body diodes.

In the first embodiment, the primary winding 12 of the transformer 12 is controlled by the DC-AC inverter circuit 14.
While the voltage is applied to A, the MOSFETs 38, 4
0 are alternately turned on, and the MOSFETs 38 and 40 are turned off while the application of the voltage to the primary winding 12A is stopped.
Are turned on by a simple configuration in which the potentials (voltages V2 and V3) at both ends of the secondary winding 12B are inverted by the inverting circuits 42 and 44 and input to the gates of the MOSFETs 38 and 40. Therefore, the configuration of the power supply device 10 can be simplified and the cost can be reduced.

The control means for controlling the on / off of the MOSFETs 38 and 40 can be configured as shown in FIG. 3 or FIG. For example, in the power supply device 72 shown in FIG. 3, the inverting circuit 42 that inverts the voltages V2 and V3,
Instead of 44, an inverting circuit 74 whose input terminal is connected to the middle point of the secondary winding 12B is provided. The output terminal of the inverting circuit 74 is connected to one of the two input terminals of the OR circuit 76 and the OR terminal.
Each of the two input terminals of the circuit 78 is connected to one of the two input terminals.

[0053] Two other input terminal of the OR circuit 76 is connected to an end of the secondary winding 12B ₁ side of the secondary winding 12B, the output terminal of the OR circuit 76 is connected to the gate of the MOSFET38 Have been. Also, two other input terminal is connected to an end of the secondary winding 12B ₀ side of the secondary winding 12B, the output terminal of the OR circuit 78 of the OR circuit 78 MO
It is connected to the gate of SFET40.

The OR circuit 76 receives the voltage V1 (see FIG. 2) inverted by the inverting circuit 74 and receives the voltage V2, and outputs a signal corresponding to the logical sum of the two signals. The signal output from 76 is shown in FIG.
Has the same waveform as the voltage V5 shown in FIG. Also, the OR circuit 7
8, the voltage V1 is inverted by the inverting circuit 74 and input, and the voltage V3 is input and outputs a signal corresponding to the logical sum of the two signals. It has the same waveform as the voltage V4 shown.

Therefore, the power supply circuit 72 shown in FIG.
The FETs 38 and 40 are turned on and off at the same timing as the MOSFETs 38 and 40 of the power supply circuit 10 shown in FIG. 1 when the DC-AC inverter circuit 14 applies a voltage to the primary winding 12A. As in the case of 10, it is possible to avoid the occurrence of loss due to the current flowing through the body diodes of the MOSFETs 38 and 40. Further, since the on / off control of the MOSFETs 38 and 40 is realized by a simple circuit configuration including the inversion circuit 74 and the OR circuits 76 and 78, the configuration of the power supply device 72 can be simplified and the cost can be reduced. .

[0056] Incidentally, inverting circuit 74, OR power supply 72
The circuits 76 and 78 and the connection lines connecting them correspond to the control means according to claim 1.

In the power supply device 82 shown in FIG.
Instead of the OR circuits 76 and 78 shown in FIG.
A, 84B, 86A and 86B are used. That is, the output terminal of the inverting circuit 74 is connected to the anodes of the diodes 84A and 86A, respectively. Further, the diode 84B anode is connected to an end of the secondary winding 12B ₁ side of the secondary winding 12B, the diode 86B anode of the secondary winding 12B ₀ side of the secondary winding 12B Connected to the end. The cathodes of the diodes 84A and 84B are connected to the gate of the MOSFET 38, and the cathodes of the diodes 86A and 86B are connected to the MOSFET 40.
Connected to the gate.

With the above configuration, the signal input to the gate of MOSFET 38 has the same waveform as voltage V5 shown in FIG. 2, and the signal input to the gate of MOSFET 40 has the same waveform as voltage V4 shown in FIG. , The MOSFETs 38 and 40 of the power supply circuit 82 are also DC-AC
When voltage is applied to the primary winding 12A by the inverter circuit 14, the MOSFET 3 of the power supply circuit 10 shown in FIG.
It will be turned on and off at the same timing as 8 and 40. Therefore, it is possible to avoid a loss caused by a current flowing through the body diodes of the MOSFETs 38 and 40.

The on / off control of the MOSFETs 38 and 40 is controlled by an inverting circuit 74, a diode 84A,
Since the power supply device 82 is realized with a simple circuit configuration including 84B, 86A, and 86B, the configuration of the power supply device 82 can be simplified and the cost can be reduced.

[0060] Incidentally, inversion circuit 74 of the power supply 82, diodes 84A, 84B, 86A, 86B, and also connecting lines for connecting these, and corresponds to the control means of claim 1.

[Second Embodiment] Next, a second embodiment of the present invention will be described. The same portions as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. FIG. 5 shows a power supply device 90 according to the second embodiment.

In the power supply device 90, the control unit 92A that outputs a drive signal for turning on and off the MOSFET 38 is a MOS transistor.
It is connected to the gate of FET38 and MOSFET4
A control unit 92B that outputs a drive signal for turning on and off 0 is connected to the gate of the MOSFET 40. Control unit 9
2A and 92B are, for example, MOSF
The ET 38 is turned on only during a period A (see FIG. 2) in which a voltage is induced in the secondary winding 12B ₀ , and the MOSFET 40 is turned on.
It is possible to adopt a configuration for generating a drive signal for turning on only in the period C the voltage induced in the secondary winding 12B _1.

The above-described configuration is such that, for example, the secondary winding 12B is set so that the voltage V2 is input to the gate of the MOSFET 38.
Constitute a control section 92A by a connection line which connects the gate of the ends of the secondary winding 12B ₁ side and the MOSFET38 of, so that the voltage V3 is input to the gate of the MOSFET 40, two of the secondary winding 12B the connecting line which connects the gate of the winding 12B ₀ side end and MOSFET40 Ru can be realized by configuring the control unit 92B.

Further, an N-type M
The drain of the OSFET 94 is connected and the MOSF
The source of the ET94 is connected to the connection point P. In addition,
In FIG. 5, the body diode of the MOSFET 94 is set to "94".
a ". Also, the secondary winding 12B
The input terminal of the inversion circuit 96 is connected to the middle point, and the output terminal of the inversion circuit 96 is connected to the gate of the MOSFET 94.

[0065] Since MOSFET94 to short the connection point P and center point of the secondary winding 12B in the ON state, claim 3
Corresponds to the third switching element. Also,
The inverting circuit 96 corresponds to inverting means for inverting the level of the “potential at the middle point of the secondary winding” according to claim 3, and the inverting circuit 96 and a connection line connecting the inverting circuit 96 are provided in claim 3. corresponds to the short絡制your hand stages described in.

Next, the operation of the second embodiment will be described. MOSFET 38 of the power supply device 90 according to the second embodiment,
40 is turned off when no voltage is applied to the primary winding 12A (that is, during the period B).
During a period B in which no voltage is applied to 2A, the smoothing circuit 18
The energy stored in the inductance 48 of M
The body diodes 38a, 40 of the OSFETs 38, 40
A current flows through a.

On the other hand, the high / low level (high level / low level) of the voltage V1 at the middle point of the secondary winding 12B is inverted and input to the gate of the MOSFET 94 by the inverting circuit 96. As is clear from the change in V1, the MOSFET 94 turns on only during the period B when no voltage is applied to the primary winding 12A. As a result, the middle point of the secondary winding 12B and the connection point P are short-circuited, and the current due to the energy stored in the inductance 48 is reduced from the inductance 48 to the capacitor 50 and the load 2
It flows through a path of 2 → MOSFET 94 → inductance 48.

Therefore, current is prevented from flowing through the body diodes 38a and 40a of the MOSFETs 38 and 40 and the body diode 94a of the MOSFET 94, and
It is possible to prevent a loss from being caused by a current flowing through the body diodes of the OSFETs 38, 40, and 94. Further, in the power supply device 90 according to the second embodiment, the current is also prevented from flowing through the secondary winding 12B during the period B when no voltage is applied to the primary winding 12A. , The occurrence of copper loss can be avoided, and the efficiency of the power supply device can be further improved as compared with the power supply device described in the first embodiment. In addition, to prevent the current from flowing through the body diodes of the MOSFETs 38, 40 and 94, the MOSF
ET94 and so are realized by a simple circuit structure comprising inverting circuit 9 6, it can be realized simplification and cost reduction of the configuration of the power supply device 90.

[0069] For example inverting circuit 9 6, resistor as shown in FIG. 6 as an example 100, 102, 104 and the transistor 1
06. That is, one end of the resistor 100 is connected between the inductance 48 and the load 22, and the other end of the resistor 100 is connected to the gate of the MOSFET 94. One end of the resistor 102 is MOSFE
The other end of the resistor 102 is connected to one end of the resistor 104 and the base of the transistor 106, respectively. The collector of the transistor 106 is connected to the gate of the MOSFET 94, and the emitter of the transistor 106 and the other end of the resistor 104 are connected to a MOSF.
Connected to the source of ET94.

In the inverting circuit having the above configuration, the resistance 1
A path leading to the gate of the MOSFET 94 via the line 00 corresponds to a power supply line of the inverting circuit, and a DC voltage supplied to the load 22 is input to the gate of the MOSFET 94 via the resistor 100.

Here, during a period in which the DC-AC inverter circuit 14 applies a voltage to the primary winding 12A (period A and period C), the voltage V1 at the middle point of the secondary winding 12B is set to a high potential. Therefore, the base of the transistor 106 has the voltage V1
Is divided by the resistors 102 and 104 and a current flows to the base, so that the transistor 106 is turned on and the potential of the power supply line is set to a low potential. Therefore, while the voltage V1 at the middle point of the secondary winding 12B is kept at a high potential, the MOSFET 9
4 is turned off.

During the period (period B) during which the DC-AC inverter circuit 14 stops applying the voltage to the primary winding 12A, the voltage V1 at the middle point of the secondary winding 12B is set to a low potential. Therefore, when the transistor 106 is turned off, the potential of the power supply line is set to a high potential, and when the MOSFET 94 is turned on, the middle point of the secondary winding 12B and the connection point P are short-circuited. Since the inverting circuit 9 6 can be realized by a very simple circuit configuration as described above, it can be achieved simplification and cost reduction of the configuration of the power supply device 90.

Although FIG. 5 shows an example in which the drains of the MOSFETs 38 and 40 are connected to the secondary winding 12B, the present invention is not limited to this, and as shown in FIG.
The source of the SFET 38 is connected to the secondary winding 12 of the secondary winding 12B.
While connected to the end portion of the B ₀ side, it may be connected to a source of MOSFET40 the end of the secondary winding 12B ₁ side of the secondary winding 12B. In the power supply device 110 shown in FIG. 7, the drains of the MOSFETs 38 and 40 are connected to each other via a connection point.
The drain of T94, the input terminal of the inverting circuit 96, and one end of the inductance 48 are connected. Also, MOSFE
The source of T94 is connected to the middle point of the secondary winding 12B.

This power supply device 110 has a secondary winding 12B ₀
During the period A (see FIG. 2) in which a voltage is induced in the MOSFET,
38 is turned on, the secondary winding 12B ₀ → MOSF
ET38 → midpoint of the connection point P → inductance 48 → capacitor 50 and load 22 → secondary winding 12B, a current flows through a path that turns on the MOSFET40 the period C the voltage induced in the secondary winding 12B ₁ The secondary winding 12B ₁ → MOSFET 40 → connection point P → inductance 48 → capacitor 50 and load 22 → secondary winding 12B
The operation other than the point at which the current flows through the middle point is the same as that of the power supply device 90.

The inverting circuit 96 of the power supply device 110 corresponds to the inverting means for inverting the level of the “potential at the connection point” according to claim 3, and the inverting circuit 96 and the connection line connecting the inverting circuit 96 are corresponds to short絡制his hand stage of claim 3.

[0076] Also, short絡制control means, instead of the configuration shown in FIGS. 5 to 7, it is also possible to adopt the configuration shown in FIG. That is, the power supply 114 shown in FIG.
A resistor 1 having one end connected to the source of the MOSFET 94 and the other end connected to the connection point P (or the middle point of the secondary winding 12B)
16 and the negative terminal is connected to the connection point P (or the secondary winding 12B
), One of the two input terminals is connected to the plus terminal of the reference voltage source 118, and the other is connected to M
The output terminal is connected to the source of OSFET 94
And a comparator 120 connected to the gate of the ET94.

The comparator 120 outputs the signal when the voltage input through the input terminal connected to the source of the MOSFET 94 is higher than the voltage input through the input terminal connected to the reference voltage source 118. The level (potential) of the signal output through the end is set to the high level (high potential), and the level (potential) of the output signal is set to the low level (low potential) except in the above case.

Note that the MOSFET 94 corresponds to the third switching element according to the fourth aspect , and
Corresponds to the comparator according to claim 4. The short circuit control unit of the above configuration, the short絡制your hands of claim 4
Corresponds to the column .

In the power supply device 114, when the application of the voltage to the primary winding 12A is stopped, the current due to the energy stored in the inductance 48 is reduced by the MOSFET 94.
Flows through the body diode 94a of the MOSFET 9
The potential of the source No. 4 is higher than a predetermined value by the resistor 116. Here, when the voltage input to the comparator 120 via the input terminal connected to the source of the MOSFET 94 becomes higher than the voltage input to the comparator 120 via the input terminal connected to the reference voltage source 118. , The level of the signal output from the comparator 120 becomes high and the MOSF
ET94 turns on.

As a result, the middle point of the secondary winding 12B and the connection point P are short-circuited, so that the current due to the energy stored in the inductance 48 is changed from the inductance 48 → the capacitor 50 and the load 22 → the resistor 116 → the MOSFET 94
→ It flows through the path of inductance 48. Therefore, M
The body diodes 38a, 40 of the OSFETs 38, 40
a, and current is prevented from flowing through the body diode 94a of the MOSFET 94, and the MOSFETs 38, 40,
It is possible to avoid a loss caused by a current flowing through the body diode 94.

Further, it is possible to prevent the current from flowing through the body diodes of the MOSFETs 38, 40 and 94.
Since it is realized with a simple circuit configuration including the MOSFET 94, the resistor 116, the reference voltage source 118, and the comparator 120, the configuration of the power supply device 114 can be simplified and the cost can be reduced.

Note that the short-circuit control means of the power supply 114
Since it is detected that a current has flowed through the body diode 94a of the MOSFET 94 and the MOSFET 94 is turned on, the MOSFET is turned on until the MOSFET 94 is turned on.
The current flows through the body diode 94a of the T94. The length of time from when the current starts flowing through the body diode 94a of the MOSFET 94 to when the level of the output signal of the comparator 120 is switched depends on the value of the resistor 116 and the reference voltage. By properly selecting parameters such as the voltage generated by the source 118, the length can be made very short, and the loss due to the current flowing through the body diode can be made extremely small.

In the above description, the first switching element and the
N as the second switching element and the third switching element
Although the case where a MOSFET of the type is applied has been described, the present invention is not limited to this, and the first switching element and the second
As a switching element, a P-type MOSFET or another transistor may be used.

In the above description, an example in which a half-bridge type inverter circuit is used as the voltage applying means has been described.
The invention is not limited to this, and it goes without saying that, for example, a full-bridge type inverter circuit or the like may be applied.

[0085]

As described above, the present invention provides a transformer.
Between one end of the secondary winding of
The provided first switching element is connected to one of the secondary windings.
The terminal at the one end is turned off during the high level, and the potential at the one end is turned off.
Is turned on during the low level, and the secondary
A second switch provided between the other end of the winding and the connection point.
The potential of the other end of the secondary winding to a high level.
Off while the potential at the other end is at a low level.
Since so as to down, it is possible to reduce the loss with a simple structure, it has an excellent effect that.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an example of a configuration of a power supply device according to a first embodiment.

FIG. 2 is a timing chart for explaining an operation of the power supply device according to the first embodiment.

FIG. 3 is a circuit diagram illustrating another configuration example of the power supply device according to the first embodiment.

FIG. 4 is a circuit diagram illustrating another configuration example of the power supply device according to the first embodiment.

FIG. 5 is a circuit diagram illustrating an example of a configuration of a power supply device according to a second embodiment.

6 is a circuit diagram showing details of an inversion circuit in the power supply device shown in FIG.

FIG. 7 is a circuit diagram illustrating another configuration example of the power supply device according to the second embodiment.

FIG. 8 is a circuit diagram showing another configuration example of the power supply device according to the second embodiment.

[Description of Signs] 10, 72, 82, 90, 110, 114 Power supply device 12 Transformer 14 DC-AC inverter circuit (voltage applying means) 38, 40 MOSFET (first and second switching elements) 42, 44, 74 inversion Circuit (control means) 84, 86 Diode (control means) 94 MOSFET ( third switching element) 96 Inverting circuit (short-circuit control means) 100, 102, 104, 116 Resistance (short-circuit control means) 106 Transistor (short-circuit control means) 118 Reference voltage source (short-circuit control means) 120 Comparator (short-circuit control means)

Claims (4)

[Claims] A transformer having a primary winding and a secondary winding provided with a midpoint; applying a voltage in one direction to the primary winding of the transformer, and stopping application of the voltage for a predetermined period. Voltage applying means for repeating application of a voltage in the other direction to the primary winding and then stopping application of the voltage for a predetermined period, and provided between both ends of the secondary winding of the transformer and a connection point. A pair of first switching elements, a smoothing circuit provided between a middle point of the secondary winding and the connection point, and an inversion for inverting a level of a potential at an end or a middle point of the secondary winding. Means for turning on the pair of first switching elements alternately during a period in which voltage is applied to the primary winding, and during a period in which application of voltage to the primary winding is stopped. Control means for turning on each of the pair of first switching elements , A power supply device including a. 2. A transformer having a primary winding and a secondary winding provided with a middle point, and after applying a unidirectional voltage to the primary winding of the transformer, stopping the application of the voltage for a predetermined period. Voltage applying means for repeating application of a voltage in the other direction to the primary winding and then stopping application of the voltage for a predetermined period, and provided between both ends of the secondary winding of the transformer and a connection point. A pair of first switching elements; a smoothing circuit provided between a middle point of the secondary winding and the connection point; and a pair of first switching elements during a period in which a voltage is applied to the primary winding. Control means for turning on the elements alternately; a second switching element provided to short-circuit the middle point of the secondary winding and the connection point in the on state; and a middle point of the secondary winding or the second switching element. Potential at the connection point or flow through the second switching element And a short-circuit control means for turning on the second switching element during a period in which the application of the voltage to the primary winding is stopped based on the current. 3. The power supply device according to claim 2, wherein said short-circuit control means includes an inversion means for inverting a level of a potential at a middle point or a connection point of said secondary winding. . 4. The short-circuit control means includes a comparator for setting an output signal to a high potential when a current flowing through the second switching element is equal to or more than a predetermined value. Item 3. The power supply device according to Item 2.