JPH05199744A - Synchronously rectifying method, and switching power source with synchronous rectifier circuit - Google Patents

Abstract

PURPOSE:To reduce voltage fall at the time of rectification or commutation to reduce a loss, regarding a switching power source provided with a synchronous rectifier circuit for rectifying to be synchronized with switching on a primary side. CONSTITUTION:In a switching power source having a switching element 11 on the first side of a transformer 1, a rectifying element 12 to be electrified to be ON-worked with a positive electromotive force on a secondary side, and a commutating element 13 to be electrified to be ON-worked with a counter electromotive force, for the rectifying element 12 and the commutating element 13, insulation gate type field-effect transistors are used, and are synchronized with the ON/OFF of switching on the primary side, and even in a zero period, the rectifying element 12 and the commutating element 13 are composed to be retained in an ON-state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply provided with a synchronous rectification circuit which rectifies in synchronization with switching on the primary side.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 10, a switching power supply has a transformer 1 having a primary winding 1a and a secondary winding 1a.
In addition to b, auxiliary windings 1c and 1d are provided on the secondary side, and a resistor 2 is inserted in series at one end of the auxiliary winding 1c for rectification FE.
The gate of a T (field effect transistor, the same applies hereinafter) is connected, and the gate of a commutating FET 5 is connected to one end of the auxiliary winding 1d via a resistor 4 in series.

The source side of the FET 3 is connected to the other end of the auxiliary winding 1c, and the drain side of the FET 3 is connected to a connection terminal 7a for a load 7 via an inductance 6. Further, a diode 8 which is parasitic between the source and the drain of the FET 3 is connected in parallel. Auxiliary winding 1d
The source side of the FET 5 is connected to the other end of, and the drain side of the FET 3 is connected to the connection terminal 7a for the load 7 via the reactance 6. Further, a diode 9 which is parasitic between the source and the drain of the FET 5 is connected in parallel. The source side of the FET 5 is further connected to the connection terminal 7b for the load 7, and the smoothing capacitor 10 is connected in parallel between the connection terminal 7a and the connection terminal 7b.

The waveform of each part in such a circuit is as shown in FIG. Here, when the drive waveform shown in FIG. 11A is output, the rectifying FET 3 has a waveform as shown in FIG. 11B between the gate and the source and between the source and the drain. Then, FIG. 11 (c)
The waveform is as shown in. Further, in the FET 5 for commutation, the waveform between the gate and the source is as shown in FIG. 11D, and the waveform between the source and the drain is as shown in FIG.
The waveform is as shown in (e).

This synchronous rectifier circuit, as shown in FIG. 12 (a), has periods of one pattern of drive waveforms I, II, III.
, The rectifying circuit functions as a circuit configured as shown in FIGS. 12B, 12C, and 12D, and the rectifying FET 3 is turned on by the positive electromotive force generated in the auxiliary winding 1c on the secondary side. It is controlled to turn on (ON) and turn on the commutating FET 5 by the counter electromotive force generated in the auxiliary winding 1d.

[0006]

In the above conventional technique, no electromotive force is generated in the auxiliary windings 1c and 1d during the zero period when the switching is OFF, and the FETs 3 and 5 are not generated.
There is a problem in that the diode 8 or 9 parasitized by the element functions as a rectifying element or a commutating element, the voltage drop during rectification or commutation becomes large, and the loss becomes large.

The present invention is intended to solve the above-mentioned problems in the prior art, and an object thereof is to provide a synchronous rectification circuit capable of reducing loss without voltage drop during rectification or commutation. It is to provide a switching power supply equipped with the same.

[0008]

In order to achieve the above-mentioned object, the present invention has a switching element 11 on the primary side of a transformer 1 and a positive electromotive force on the secondary side in a synchronous rectification method. Rectifying element 1 that turns on and energizes
In a switching power supply having a commutation element 13 that is turned on and energized by a back electromotive force, an insulated gate field effect transistor is used for the rectification element 12 and / or the commutation element 13, and switching on the primary side is performed. The rectifying element 12 is synchronized with the on / off of the
And / or holding the commutation element 13 in an ON state, and in the device configuration, as shown in FIG. 1, a control circuit using a rectification field effect transistor or a commutation field effect transistor is provided. The configuration.

As a device configuration, in the switching power supply provided with the synchronous rectification circuit when the control circuit using the rectification field effect transistor is provided, the transformer 1 is used.
A rectifying element 12 which has a switching element 11 on the primary side thereof and is turned on by a positive electromotive force on the secondary side to conduct current; and a commutation element 13 which is turned on by a counter electromotive force on the secondary side to conduct current. Insulating gate type field effect transistors are used as the rectifying element 12 and the commutating element 13, respectively, and a voltage is applied to the gate side of the rectifying element 12 during a zero period to provide the rectifying element. 12 is provided with a rectification control circuit 15 using an insulated gate field effect transistor for maintaining the ON state of the rectification control circuit 12, and the rectification control circuit 15 is turned off during the zero period of switching to maintain the rectification element 12 in the ON state. Characterize.

Further, in a switching power supply provided with a synchronous rectification circuit in the case of providing a control circuit using a field effect transistor for commutation, a switching element 11 is provided on the primary side of the transformer and a positive electromotive force on the secondary side is used. A switching power supply having a rectifying element 12 that is turned on and energized, and a commutation element 13 that is turned on and energized by a counter electromotive force on the secondary side, the rectifying element 12 and the commutation element 13 being provided. , And each of them uses an insulated gate field effect transistor, and a commutation control using an insulated gate field effect transistor that maintains the ON state of the commutation element 13 by applying a voltage to the gate side of the commutation element 13 during the zero period. A circuit 16 is provided, and the commutation control circuit 16 is turned off during the zero period of switching to maintain the rectifying element 13 in an on state. And wherein the door.

Furthermore, in a switching power supply provided with a synchronous rectification circuit in the case of providing a control circuit using a rectification field effect transistor and a commutation field effect transistor, a switching element 11 is provided on the primary side of the transformer. 1. A switching power supply comprising: a rectifying element 12 that is turned on by a positive electromotive force on the secondary side and is energized; and a commutation element 13 that is turned on by a counter electromotive force on the secondary side and is energized. 12 and the commutation element 13
And a rectification control circuit using the insulated gate field effect transistor for applying a voltage to the gate side of the rectifying element 12 in the zero period to maintain the rectifying element 12 in the ON state. 1
5, a commutation control circuit 16 using an insulated gate field effect transistor for applying a voltage to the gate side of the commutation element 13 in the zero period to maintain the ON state of the commutation element 13, and the rectification element And a capacitor 17 that is charged by the electromotive force of the rectification side auxiliary winding 1c when 12 is in the on state, and the commutation element 1 is provided during the zero period of switching.
3 is activated by the commutation control circuit 16 to maintain the ON state, and the rectifying element 12 causes the rectifying element 12 to
The discharge voltage of No. 7 maintains the ON state.

A metal oxide semiconductor field effect transistor is used as the insulated gate field effect transistor.

[0013]

With this configuration, in the synchronous rectification method, the rectification element 12 and / or the commutation element 13 are in the ON state even in the zero period in synchronization with ON / OFF of the switching on the primary side. To prevent rectification or commutation by a parasitic diode, reduce voltage drop during rectification or commutation, and reduce power loss.

In a switching power supply provided with a synchronous rectification circuit when a control circuit using a field effect transistor for rectification is provided, the rectification control circuit 15 is operated during the zero period of switching, and the insulated gate electric field of the rectification control circuit 15 is applied. By applying a gate voltage from the effect transistor to the rectifying element 12 to maintain the rectifying element 12 in the ON state, normal rectification is continued and rectification by the parasitic diode of the rectifying element 12 is prevented, and at the time of rectification It reduces the voltage drop of the DC power supply, reduces the loss, and improves the efficiency of the DC power supply.

In a switching power supply provided with a synchronous rectification circuit in the case of providing a control circuit using a field effect transistor for commutation, the commutation control circuit 16 is operated during the zero period of switching, and the insulated gate of the commutation control circuit 16 is operated. Voltage is applied to the commutation element 13 from the field effect transistor to maintain the commutation element 13 in the ON state, so that normal commutation is continued and commutation by the parasitic diode of the commutation element 13 is prevented. At the same time, there is no voltage drop during commutation, which reduces loss and improves the efficiency of the DC power supply.

In a switching power supply having a synchronous rectification circuit in the case of providing a control circuit using a rectification field effect transistor and a commutation field effect transistor, the commutation element 13 causes the commutation control circuit 16 to operate during the zero period of switching. Is turned off and remains on,
Since the rectifying element 12 is maintained in the ON state by the voltage of the capacitor 17, each parasitic diode is prevented from functioning as an element related to rectification or commutation, and a highly efficient DC power supply is realized.

When a metal oxide semiconductor field effect transistor is used, its charge capacity is used to charge the metal oxide semiconductor field effect transistor before the zero period, and the charged electric charge is applied during the zero period of switching. By not discharging, the metal oxide semiconductor field effect transistor as a rectifying element and / or the metal oxide semiconductor field effect transistor as a commutation element is supplied to the gate side to turn on the rectifying element and / or the commutating element. Hold the state.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described separately for the case where control circuits are provided for rectification, commutation, and both rectification and commutation.

FIG. 2 is a diagram showing a structure of a synchronous rectification circuit having a control circuit for maintaining rectification in the zero period of the first embodiment. Here, 101 is a transistor (Tr), and 1
It is provided for a switch for energizing the secondary side. 102 is a winding on the primary side, and is a transistor 101
When is turned on (energized state), an electromotive force is generated on the secondary side. A secondary winding 103 generates a rated electromotive force to the load side. Reference numeral 104 denotes an auxiliary winding on the rectifying side, which generates an electromotive force for applying a starting voltage to the gate side of a rectifying MOSFET (metal oxide semiconductor field effect transistor) 106 (described later). Reference numeral 105 denotes an auxiliary winding on the commutation side, which is an MO for commutation.
The electromotive force is supplied to the gate side of the SFET.

Reference numeral 106 is a rectifying MOSFET,
The gate (G) side is connected to one end of the auxiliary winding 104 via the resistor (R1) 107, and the source (S) side is connected to the secondary winding 1
03 is connected to one end located on the side to which the auxiliary winding 104 is connected, and the drain (D) side is connected to the inductance (L) 10
8 is connected to the connection terminal 109a on the load side via 8 so that when a positive voltage is applied to the gate, current is supplied between the source and drain for rectification.

111 is a control MOSFET,
The gate (G) side is connected via a resistor (R4) 112 to one end of the secondary winding 103 located on the side to which the auxiliary winding 105 is connected, and the source (S) side is connected to the source side of the MOSFET 106, Resistor (R3) 11 on the drain (D) side
3 is connected to the gate side of the MOSFET 106, and when a positive voltage is applied to the gate, current is supplied between the source and drain, and a positive voltage is applied to the gate side of the MOSFET 106 to turn on the MOSFET 106.

Reference numeral 114 is a MOSFET for commutation,
The gate (G) side is connected to one end of the auxiliary winding 105 opposite to the secondary winding connection side via a resistor (R2) 115, and the source (S) side is connected to the resistor (R2) of the secondary winding 103. R4)
It is connected to one end located on the connection side, the drain (D) side is connected to the drain side of the MOSFET 106, and when the counter electromotive force of the auxiliary winding 105 is applied to the gate, it is energized between the source and drain to turn on. It works.

Reference numeral 116 is a capacitor (C), which is connected to the load side connection terminals 109a and 109b in parallel with the load to smooth the voltage to the load side.

In the first embodiment constructed as described above, as shown in FIG.
The output waveform is the same as before, but
At T106, the transistor 101 is off, and even if the zero period is reached, the MOSFET1 that has been charged up to that point
11 is discharged to perform start control, the gate voltage of the MOSFET 106 is supplied, and the ON state of the MOSFET 106 is maintained.

FIG. 4 is a diagram showing the structure of a synchronous rectification circuit having a control circuit for maintaining commutation in the zero period of the second embodiment. Here, 118 is a control MOSFET,
The gate (G) side is connected to one end of the secondary winding 103 located on the side to which the auxiliary winding 104 is connected via a resistor (R5) 119, and the source (S) side is connected to the resistor 11 of the secondary winding 103.
9 is connected to one end on the side opposite to the side connected thereto, the drain (D) side is connected to one end on the side opposite to the side to which the resistor 115 of the auxiliary winding 105 is connected, and the secondary winding 103 is connected. The MOSFET 118 is not directly connected to the auxiliary winding 105.
The source and drain of the MOSFET 118 are connected to each other, and when a counter electromotive force is applied to the gate of the MOSFET 118,
Is turned off and the on operation of the MOSFET 114 is maintained.

Others are the MOSFE in the first embodiment.
The configuration is similar to that without T111 and resistors 112 and 113.

In the second embodiment constructed as described above, as shown in FIG.
With respect to the above, the counter electromotive force of the auxiliary winding 104 does not energize, and the voltage between the source and the drain has an output waveform of 0 V while the transistor 101 is off.
Then, when the transistor 101 is off and the period is zero, the voltage charged in the odd capacitance C between G and S of the MOSFET 114 by that time causes the MOSFET 118
Is off, the output waveform holds the on state of the MOSFET 114.

FIG. 6 is a diagram showing the construction of a synchronous rectification circuit having a control circuit for maintaining rectification and a control circuit for maintaining commutation in the zero period of the third embodiment. Reference numeral 121 denotes a diode for rectifying the auxiliary winding 104 system, which rectifies the auxiliary winding 104 system. A diode 122 rectifies the auxiliary power system in the zero period. A capacitor 123 is charged when the transistor 101 is off and discharged when the transistor 101 is on. A diode 124 rectifies the auxiliary current system in the zero period. 125 is a current limiting resistor (R
6).

Others are the same as those of the combination of the first and second embodiments. That is, M on the rectification side
A control MOSFET 111 is provided in the OSFET 106,
The commutation MOSFET 114 is a control MOSFET.
115 is provided for starting control in the zero period.

In the third embodiment thus constructed, as shown in FIG. 7, the transistor 10 is applied to the drive waveform.
When 1 is off and the zero period is reached, the MOSFET 10
6, the gate voltage of the MOSFET 106 is supplied by the control of the control MOSFET 111,
The ON state of the SFET 114 is maintained, and the conduction waveform between the source and the drain is maintained.
At T114, the gate voltage of the MOSFET 114 is supplied by the control of the control MOSFET 118, and the MOS
An output waveform is obtained in which the ON state of the FET 114 is retained and the conduction state between the source and drain is retained.

FIG. 8 is a diagram showing a configuration of another aspect of the third embodiment. Here, 121 is a diode for rectifying the auxiliary winding 104 system, which rectifies the auxiliary winding 104 system. 123 is a capacitor, which is the transistor 10
It is charged when 1 is on and discharged when 1 is off. 126 is a resistor (R7), which is a diode 121
Is connected to the diode 121 side from the connection point of the capacitor 123 between the resistor 114 and the resistor 107.
It is for setting the resistance value for adjusting the supply voltage to the gate of the. A diode 127 rectifies the auxiliary winding 105 system in the zero period.

Otherwise, the configuration is the same as that of the combination of the first and second embodiments. That is, M on the rectification side
A control MOSFET 111 is provided in the OSFET 106,
The commutation MOSFET 114 is a control MOSFET.
118 is provided for starting control in the zero period.

In another aspect of the third embodiment thus constructed, the output waveforms of the respective parts with respect to the drive waveform are as shown in FIG. 9 for the MOSFET 106 when the transistor 101 is off and the period is zero. MO for control
The gate voltage of the MOSFET 106 is supplied by the control of the SFET 111, the ON state of the MOSFET 114 is held, the conduction state between the source and the drain is held, and the charging waveform of the capacitor 123 is maintained, resulting in an output waveform. MOSFET 1
By the control of 18, the gate voltage of the MOSFET 114 is supplied, the ON state of the MOSFET 114 is held,
The output waveform is such that the conduction state between the source and the drain is maintained and the charging voltage of the capacitor 113 is maintained.

As described above, in each embodiment, the rectifying MOS is used.
Regarding the FET 106, the control MOSFET 111 can maintain the gate voltage by maintaining the gate voltage in the zero period, and regarding the commutation MOSFET 114, the control MOSFET 118 maintains the gate voltage in the zero period and the on state. By making it possible to hold the diode, the diode does not function as an element for rectification and commutation, the voltage drop at the time of rectification can be suppressed small, the loss becomes small, and the low voltage large current A synchronous rectification circuit that is suitable for rectification and that can be downsized can be realized.

In the third embodiment, the control MOSF is used.
In addition to the discharge voltage from ET111, capacitor 123
Can be supplied to the rectifying MOSFET 106, the load on the startup of the MOSFET 106 is lightened, and even if the waveform in the zero period is distorted, the rectifying M
The ON state of the OSFET 106 can be maintained.

[0036]

As described above, according to the present invention, in the synchronous rectification method, the rectification element 12 and / or the commutation element 13 are synchronized with ON / OFF of the switching on the primary side even during the zero period. By making it possible to keep it in the ON state, rectification or commutation via a parasitic diode is avoided, the voltage drop during rectification or commutation can be reduced, and power loss can be reduced. The efficiency of the DC power supply can be increased.

In a switching power supply provided with a synchronous rectification circuit in the case where a control circuit is provided in the rectification circuit, the rectification control circuit 15 causes the rectification element 1 to operate during the zero period of switching.
By applying the gate voltage of 2 so that the rectifying element 12 can be maintained in the ON state, normal rectification can be continued and rectification by the parasitic diode of the rectifying element 12 can be prevented. The voltage drop during rectification can be reduced, the loss can be reduced, and the efficiency of the DC power supply can be improved.

Further, in the switching power supply provided with the synchronous rectification circuit when the control circuit is provided in the commutation circuit,
During the zero period of switching, by applying the gate voltage of the commutation element 13 from the commutation control circuit 16 so as to maintain the ON state of the commutation element 13, normal commutation is continued, It is possible to prevent commutation due to the parasitic diode of the commutation element 13, and
It is possible to eliminate the voltage drop during commutation, reduce the loss, and improve the efficiency of the DC power supply.

Furthermore, in the switching power supply provided with the synchronous rectification circuit in the case where the control circuit is provided in the rectification circuit and the commutation circuit, the commutation control circuit 16 supplies the gate voltage during the zero period of switching. Since the commutation element 13 is maintained in the on state and the rectification element 12 is maintained in the on state by the discharge voltage of the capacitor 17, the parasitic diodes of the rectification element 12 and the commutation element 13 are rectified. Alternatively, it is possible to avoid functioning as a commutation element, and it is possible to realize a highly efficient DC power supply that suppresses a voltage drop during power supply.

When the metal oxide semiconductor field effect transistor is used, its charge capacity is used to charge the metal oxide semiconductor field effect transistor before the zero period, and the charged electric charge is switched. Of the metal oxide film semiconductor field effect transistor as a rectifying element and / or the metal oxide film semiconductor field effect transistor as a commutating element by supplying no gate voltage to the rectifying element and / or
Alternatively, by making it possible to maintain the ON state of the commutation element, the configuration of the control circuit can be simplified, and the ON state of the rectification element and / or the commutation element can be easily maintained with a small electric power. Can be maintained.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of a first embodiment.

FIG. 3 is a waveform diagram showing waveforms of respective parts of the synchronous rectification circuit of the first embodiment.

FIG. 4 is a configuration diagram of a second embodiment.

FIG. 5 is a waveform diagram showing waveforms of respective parts of the synchronous rectification circuit of the second embodiment.

FIG. 6 is a configuration diagram of a third embodiment.

FIG. 7 is a waveform diagram showing waveforms of respective parts of the synchronous rectification circuit of the third embodiment.

FIG. 8 is a configuration diagram of another aspect of the third embodiment.

FIG. 9 is a waveform diagram showing waveforms of respective parts in another mode of the third embodiment.

FIG. 10 is a configuration diagram showing a conventional synchronous rectification circuit.

FIG. 11 is a waveform diagram showing waveforms of respective parts of a conventional synchronous rectification circuit.

FIG. 12 is an operation explanatory view showing a state of a conventional synchronous rectification circuit.

[Explanation of symbols]

 1 Transformer 1a Primary winding 1b Secondary winding 1c Rectification side auxiliary winding 1d Commutation side auxiliary winding 11 Switching element 12 Rectification element 13 Commutation element 14 Smoothing capacitor 15 Rectification control circuit 16 Commutation control Circuit 17 Capacitor

Claims (5)

[Claims] 1. A rectifying element (12) which has a switching element (11) on the primary side of a transformer (1) and which is turned on by a positive electromotive force and conducts electricity on the secondary side, and is turned on by a counter electromotive force. A rectifying element (12) and / or a commutating element (13) in a switching power supply having a commutating element (13) that operates and conducts electricity.
An insulated gate field effect transistor is used for the rectification element (12) and / or the commutation element (1) in synchronization with ON / OFF of the switching on the primary side even during the zero period.
3) A synchronous rectification method, characterized in that (3) is held in an ON state. 2. A transformer (1) has a switching element (11) on a primary side thereof, and a secondary side has a rectifying element (12) which is turned on by a positive electromotive force and is energized, and a reverse electromotive force. A switching power supply having a commutation element (13) for operating and energizing, the commutation element (12) and the commutation element (13).
Insulated gate type field effect transistors are used as the insulating gate type field effect transistors for maintaining the ON state of the rectifying element (12) by applying a voltage to the gate side of the rectifying element (12) during the zero period. The rectification control circuit (15) is provided, and the rectification control circuit (15) is operated during the zero period of switching to supply the gate voltage of the rectification element (12) to turn on the rectification element (12). A switching power supply equipped with a synchronous rectification circuit, characterized in that 3. A rectifying element (12), which has a switching element (11) on the primary side of the transformer 1, is turned on by a positive electromotive force and conducts electricity, and is turned on by a counter electromotive force on the secondary side. A switching power supply having a commutation element (13) which is energized by a current, the commutation element (12) and the commutation element (13).
Insulated gate type field effect transistors are used as the insulating gate type field effect transistors for maintaining the ON state of the commutation element (13) by applying a voltage to the gate side of the commutation element (13) during the zero period. The commutation control circuit (16) is provided, and the commutation control circuit (16) is operated during the zero period of switching to supply the gate voltage of the commutation element (13) to supply the rectification element (13). A switching power supply provided with a synchronous rectification circuit characterized by maintaining an ON state. 4. A transformer (1) has a switching element (11) on a primary side thereof, and a rectifying element (12) which is turned on by a positive electromotive force and is energized on a secondary side, and is turned on by a counter electromotive force. A switching power supply having a commutation element (13) for operating and energizing, the commutation element (12) and the commutation element (13).
Insulated gate type field effect transistors are used as the insulating gate type field effect transistors for maintaining the ON state of the rectifying element (12) by applying a voltage to the gate side of the rectifying element (12) during the zero period. The rectification control circuit (15) and the switching using the insulated gate field effect transistor for applying a voltage to the gate side of the commutation element (13) during the zero period to maintain the ON state of the commutation element (13). A flow control circuit (16) and a capacitor (1) charged by an electromotive force of a rectification side auxiliary winding (1c) when the rectification element (12) is in an ON state.
7), the commutation element (13) is activated by the commutation control circuit (16) to maintain the ON state during the zero period of switching, and the rectification element (12) is the capacitor (12). A switching power supply provided with a synchronous rectification circuit, which is maintained in an on state by the discharge voltage of 17). 5. A switching power supply provided with a synchronous rectification circuit according to claim 2, wherein a metal oxide semiconductor field effect transistor is used as said insulated gate field effect transistor.