JP3346543B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a synchronous rectification type switching power supply.

[0002]

2. Description of the Related Art In a switching power supply, a DC input voltage supplied through an input winding of a power conversion transformer is switched by a switch element included in a switch circuit, and a switching output is output from the output winding of the power conversion transformer. The output rectifier circuit and the output smoothing circuit connected to the line convert the output voltage into an arbitrary DC output voltage.

As means for reducing the loss of the output rectifier circuit, a switch element having a lower voltage drop and a smaller loss, typically a field effect transistor (hereinafter referred to as FET), is used instead of the rectifier diode. There is known a synchronous rectifier circuit used as a rectifier.

In a synchronous rectifier circuit using an FET as a rectifying element, a DC voltage required for operation must be supplied to the rectifying FET. Conventionally, the following first to fourth circuit systems are known as such means.

The first circuit system employs a circuit system in which the ON / OFF timing of the rectifying FET and the driving power are supplied from the secondary winding of the power conversion transformer.

The second circuit system employs a circuit system in which a third winding is provided on a power conversion transformer, and the third winding obtains ON / OFF timing of a rectifying FET and driving power. .

A third circuit system is disclosed in Japanese Patent Publication No. 58-409.
As disclosed in Japanese Patent Application Publication No. 15-2005, etc., a second winding is connected to a magnetic element connected in series with a secondary winding of a power conversion transformer, specifically, a choke coil constituting an output smoothing circuit. This is a method of obtaining the ON / OFF timing and drive power of the rectifying FET from the second winding. Even when a control circuit is provided on the secondary side of the power conversion transformer, power is similarly obtained from the second winding of the magnetic element.

The fourth circuit system employs a circuit system for supplying driving power and power for the secondary side control circuit from another power source.

[0009]

A problem with the first and second circuit systems is that, when the input voltage changes, the voltage generated in the secondary winding of the power conversion transformer changes, so that That is, the drive voltage changes in proportion to the input voltage.

A problem with the third circuit system is that when the output terminals of the switching power supply are short-circuited, the rectifying FE
That is, the voltage for driving the rectifying FET changes when the voltage for driving the T decreases and when the output voltage is changed. The problem when the voltage for driving the rectifying FET changes is that it deviates from the voltage for driving the rectifying FET most efficiently, and the loss of the rectifying FET increases. Gate. If the source withstand voltage is exceeded and the rectifying FET is damaged, and if the gate voltage is too low, the rectifying F
ET cannot be conducted, current flows through the parasitic diode of the rectifying FET, and the loss of the rectifying FET increases.

A problem of the fourth circuit system is that since it is necessary to provide a separate power supply, the number of components increases, and it is difficult to reduce the size and cost.

An object of the present invention is to provide a switching power supply device capable of supplying a stable drive voltage to a circuit for driving a rectifying switch element included in a synchronous rectifier circuit even when an input voltage or an output voltage fluctuates. To provide.

Another object of the present invention is to provide a switching power supply capable of supplying a stable drive voltage to a circuit for driving a rectifying switch element included in a synchronous rectifier circuit even when an output short circuit occurs. To provide.

[0014]

In order to solve the above-mentioned problems, a switching power supply according to the present invention comprises a transformer, a switch circuit, a synchronous rectifier circuit, a smoothing circuit, a control circuit, and an insulating coupling circuit. , A drive circuit, and an auxiliary power supply circuit. The transformer includes an input winding and an output winding. The switch circuit includes at least one switch element, and the switch element switches a DC input voltage supplied through the input winding.

[0015] The synchronous rectifier circuit includes at least one rectifying switch element having a control electrode as a rectifier element, and rectifies and outputs a voltage induced in the output winding of the transformer. The smoothing circuit smoothes and outputs a rectified voltage output from the synchronous rectification circuit.

The control circuit supplies a control signal to the switch element to control the switching operation.

The drive circuit supplies a drive signal generated based on the control signal supplied from the control circuit via the insulating coupling circuit to the control electrode of the rectifying switch element, The rectifying switch element is controlled in synchronization with the switch element of the switch circuit.

The auxiliary power supply circuit rectifies and smoothes the control signal supplied from the control circuit via the insulating coupling circuit to generate a DC voltage, and uses the DC voltage as an operating voltage to supply the drive circuit with the DC voltage. Supply.

In the above switching power supply,
DC input voltage supplied through the input winding of the transformer,
Switching is performed by a switch element included in the switch circuit, and a switching output can be converted to a DC output voltage by a synchronous rectification circuit and an output smoothing circuit provided in an output winding of the transformer. The switching operation of the switch element is controlled by a control signal supplied from a control circuit. By this control operation, a stabilized DC output voltage can be obtained. The DC output voltage is supplied to a load.

The drive circuit controls the rectifying switch element in synchronization with the switch element of the switch circuit by a drive signal generated based on a control signal supplied from the control circuit via the insulating coupling circuit. By this synchronous rectification, a synchronous rectification type switching power supply device in which the loss is reduced as compared with a rectifier circuit using a rectifier diode can be obtained.

The above-described switching operation, synchronous rectification operation, and the like are conventionally known. A feature of the switching power supply according to the present invention is that it includes an auxiliary power supply circuit. The auxiliary power supply circuit rectifies and smoothes a control signal supplied from the control circuit via the insulating coupling circuit to generate a DC voltage, and supplies the DC voltage to the drive circuit as an operating voltage. That is, an operation voltage for the drive circuit is generated using a control signal for controlling the rectifying switch element. Therefore, even when the input voltage or the output voltage fluctuates, a stable drive voltage can be supplied to the drive circuit.

Further, since power can be supplied from the primary side having the switch circuit to the secondary side having the synchronous rectification circuit and the drive circuit via the insulating coupling circuit, the drive can be performed even at the time of start-up or output short-circuit. A stable drive voltage can be supplied to the circuit.

In the switching power supply according to the present invention, various circuit configurations can be adopted as the synchronous rectifier circuit. For example, the synchronous rectifier circuit may be configured to include two rectifier elements, and both of the two rectifier elements may be configured as switch elements. One of the two rectifier elements may be a switch element, and the other may be a rectifier diode. Good. The synchronous rectification circuit may be either a full-wave rectification system or a half-wave rectification system. Further, the smoothing circuit may be either a choke input type or a capacitor input type.

Further, the synchronous rectifier circuit may include only one rectifier. In this case, it is obvious that one provided rectifying element becomes a rectifying switch element. In the case of this configuration, the synchronous rectification circuit is of a flyback rectification type that rectifies and outputs a flyback voltage induced in the secondary winding of the transformer.

The switching power supply according to the present invention comprises:
As one mode, a second auxiliary power supply circuit may be included. According to this configuration, in the normal state, the operating voltage can be supplied to the drive circuit through the second auxiliary power supply circuit. In this case, the DC voltage output from the second auxiliary power supply circuit is set to be higher than the DC voltage output from the auxiliary power supply circuit.

As another aspect, the switching power supply according to the present invention may include a delay circuit. The delay circuit delays a rise of a control signal supplied from the control circuit to a control electrode of the switch element. In this case,
In a switch circuit, a switch element serving as a main switch is turned on. Even when the pulse width becomes small, a stable voltage can be supplied to the drive circuit.

Other objects, features, advantages, and the like of the present invention will be described in more detail with reference to the accompanying drawings which are embodiments. The accompanying drawings are merely examples.

[0028]

FIG. 1 is an electric circuit diagram of a switching power supply according to the present invention. The illustrated switching power supply includes a transformer 1, a switch circuit 3, a synchronous rectifier circuit 5, a smoothing circuit 7, a control circuit 9, an insulating coupling circuit 11, a drive circuit 13, an auxiliary power supply circuit 15, including.

The transformer 1 includes an input winding 101 and an output winding 102. The switch circuit 3 includes at least one switch element 31. The switch element 31 is
DC input voltage Vin supplied through input winding 101
Switching. The DC input voltage Vin is supplied from the DC power supply 17 to the input terminals T1 and T2. DC power supply 1
Reference numeral 7 includes a DC power supply such as a battery or various AC / DC power supplies for converting AC to DC.

The switch element 31 is constituted by an FET, a bipolar transistor or the like. Switch element 3
One main electrode 311 is connected to one end of the input winding 101 of the transformer 1, and the other end of the input winding 101 of the transformer 1 is led to the input terminal T <b> 1. The other main electrode 312 of the switch element 31 is connected to the input terminal T2.

Unlike the illustrated embodiment, the switching circuit 3
May include a plurality of switch elements. For example,
A circuit configuration may be used in which four switch elements are bridge-connected and two switch elements are set as one set to perform switching operation alternately.

The synchronous rectifier circuit 5 includes at least one rectifying switch element 51, and the output winding 101 of the transformer 1.
Rectifies and outputs the voltage induced in the circuit. The rectifying switch element 51 has a control electrode 513. Such a rectifying switch element 51 is configured by an FET, a bipolar transistor, or the like.

The smoothing circuit 7 smoothes the rectified voltage output from the synchronous rectification circuit 5 and outputs the rectified voltage. The smoothing circuit 7 can be realized by a known circuit configuration.

The control circuit 9 supplies a control signal CS11 to the switch element 31 to control the switching operation.
The illustrated control circuit 9 includes a control electrode 31 of the switch element 31.
3 is given a control signal CS11. The control signal CS11 is a pulse train signal with a controlled pulse width. In the embodiment, a signal transmission circuit 19 for appropriately driving the control electrode 313 is provided between the control circuit 9 and the control electrode 313 of the switch element 31. The signal transmission circuit 19 supplies the control electrode 313 with a control signal CS11 having a pulse width substantially equal to the pulse width (ON duty) of the control signal CS1 supplied from the control circuit 9. Therefore, regarding the driving of the switch element 31, the control signal CS1 and the control signal CS11 can be regarded as substantially the same signal.

The control circuit 9 further includes output terminals T3, T4
Monitor the DC output voltage V0 appearing at the switch element 31
Is given pulse width modulation control for stabilizing the DC output voltage V0. Reference numeral CS3 in FIG.
Indicates a monitoring signal of the DC output voltage V0. Although not shown, the control circuit 9 is electrically insulated from the secondary side.

The drive circuit 13 converts the drive signal CS2 generated based on the control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11 into a rectifying switch element 5.
Rectifying switch element 5
1 is controlled in synchronization with the switch element 31 of the switch circuit 3. The drive signal CS2 is a pulse train signal.

The insulated coupling circuit 11 typically includes a pulse transformer. Insulation coupling means other than the pulse transformer may be used. The insulating coupling circuit 11 outputs a control signal CS12 having a pulse width substantially equal to the pulse width (ON duty) of the control signal CS1 supplied from the control circuit 9. Therefore, as the pulse train signal, the control signal C
S1 and control signal CS12 can be regarded as substantially the same signal.

The auxiliary power supply circuit 15 rectifies and smoothes the control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11, generates a DC voltage Vc1, and generates a DC voltage Vc1.
Is supplied to the drive circuit 13 as an operating voltage.

In the switching power supply device described above,
The DC input voltage Vin supplied through the input winding 101 of the transformer 1 is switched by the switch element 31 included in the switch circuit 3 to generate a high-frequency voltage,
The switching output is transmitted from the input winding 101 of the transformer 1 to the output winding 102, and is converted into a DC output voltage V0 by the synchronous rectification circuit 5 and the output smoothing circuit 7 connected to the output winding 102. The DC output voltage V0 is applied to the output terminal T3,
From T4, it is supplied to the load L.

The switching operation of the switch element 31 is controlled by the control signal CS11 supplied from the control circuit 9 to the control electrode 313 via the signal transmission circuit 19. By this control operation, a stabilized DC output voltage V0 can be obtained.

The drive circuit 13 drives the rectifying switch element 51 included in the synchronous rectifier circuit 5 by the drive signal CS2 generated based on the control signal CS11 supplied from the control circuit 9 via the insulating coupling circuit 11. Control is performed in synchronization with the switch element 31 included in the switch circuit 3. By providing the synchronous rectifier circuit 5 described above, a synchronous rectification type switching power supply device in which loss is reduced as compared with a rectifier circuit using a rectifier diode can be obtained.

The above-described switching operation, synchronous rectification operation and the like are conventionally known. A feature of the present invention is to include the auxiliary power supply circuit 15. The auxiliary power supply circuit 15
The control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11 is rectified and smoothed to generate a DC voltage Vc1.
To supply. That is, the DC voltage Vc for operating the drive circuit 13 using the control signal CS12 for controlling the rectifying switch element 51 included in the synchronous rectifier circuit 5 is used.
1 is generated. Therefore, the input voltage Vin and the output voltage V
Even when 0 fluctuates, a stable drive voltage can be supplied to the drive circuit 13.

Further, since power can be supplied from the primary side of the switch element 31 to the secondary side of the synchronous rectifier circuit 5, the drive circuit 13, and the auxiliary power supply circuit 15 via the insulating coupling circuit 11, The stable drive voltage Vc1 can be supplied to the drive circuit 13 even at the time of start-up or output short-circuit.

FIG. 2 is a more specific circuit diagram of the switching power supply according to the present invention shown in FIG. In the figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals. In the embodiment of FIG. 2, the synchronous rectification circuit 5 includes a first rectification switch element 51.
And a second rectifying switch element 52. The first and second rectifying switch elements 51 and 52 are constituted by FETs or bipolar transistors or the like. The first rectifying switch element 51 has a main electrode 511 connected to one end of the output winding 102 of the transformer 1. The second rectifying switch element 52 has a main electrode 521 connected to the other end of the output winding 102 of the transformer 1, and a main electrode 522 connected to a main electrode 512 of the first rectifying switch element 51. .

Unlike the illustrated embodiment, one of the first rectifying switch element 51 and the second rectifying switch element 52 may be constituted by a rectifying diode.

The input side of the smoothing circuit 7 is connected to the main electrodes 521 and 522 of the second rectifying switch element 52.

The drive circuit 13 uses the drive signals CS21 and CS22 generated based on the control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11 to generate a first signal.
The rectifying switch element 51 and the second rectifying switch element 52 are controlled in synchronization with the switch element 31. The drive signals CS21 and CS22 are pulse train signals.

In the synchronous rectifier circuit 5 of the switching power supply device described above, the first and second rectifying switch elements 51 and 52 are turned on by the drive signals CS21 and CS22 supplied from the drive circuit 13. At this time, the first rectifying switch element 51 is turned on, and the second
Is controlled so that the rectifying switch element 52 is turned off. When the switch element 31 is off, control is performed so that the first rectification switch element 51 is turned off and the second rectification switch element 52 is turned on. By providing the synchronous rectifier circuit 5 described above, a synchronous rectification type switching power supply device in which loss is reduced as compared with a rectifier circuit using a rectifier diode can be obtained.

The auxiliary power supply circuit 15 rectifies and smoothes the control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11, generates a DC voltage Vc1, and generates a DC voltage Vc1.
Is supplied to the drive circuit 13 as an operating voltage. That is,
A DC voltage Vc1 for operating the drive circuit 13 is generated using a control signal CS12 for controlling the first and second rectifying switch elements 51 and 52. Therefore, even when the input voltage Vin or the output voltage V0 fluctuates, a stable drive voltage can be supplied to the drive circuit 13.

Power is supplied from the primary side having the switch element 31 to the secondary side having the first rectifying switch element 51 and the second rectifying switch element 52 via the insulating coupling circuit 11. Accordingly, a stable drive voltage can be supplied to the first and second rectifying switch elements 51 and 52 constituting the synchronous rectifier circuit 5 even at the time of startup or when the output is short-circuited.

FIG. 3 is an electric circuit diagram showing a more specific circuit configuration of the switching power supply according to the present invention shown in FIG. In the drawings, the same components as those shown in FIGS. 1 and 2 are denoted by the same reference numerals.
In the embodiment, the switch element 31 included in the switch circuit 3 and the first and second rectifying switch elements 51, 5
Reference numeral 2 denotes an FET. The main electrode 311 of the switch element 31 is connected to one end of the input winding 101 of the transformer 1, and the other end of the input winding 101 of the transformer 1 is led to the input terminal T1. The main electrode 312 of the switch element 31 is connected to the input terminal T2.

In the synchronous rectifier circuit 5, the first rectifying switch element 51 has a main electrode 511 connected to one end of the output winding 102 of the transformer 1. The second rectifying switch element 52 is configured such that the main electrode 521 is connected to the output winding 102 of the transformer 1.
The main electrode 522 is connected to the main electrode 512 of the first rectifying switch element 51.

The smoothing circuit 7 is of a choke input type including a choke coil 71 as a magnetic element and a capacitor 72. One end of the choke coil 71 is connected to a connection point between the output winding 102 of the transformer 1 and the main electrode 521 of the second rectifying switch element 52. Capacitor 7
2 is connected to the other end of the choke coil 71 and the main electrodes 512 and 522 of the first rectifying switch element 51 and the second rectifying switch element 52. DC output voltage V0
Is taken out from both ends of the capacitor 72.

The insulating coupling circuit 11 includes a signal transmission circuit 111
And an insulating transformer 112. Signal transmission circuit 111
And an insulating transformer 112 for electrically insulating the drive circuit 13 and the auxiliary power supply circuit 15 on the secondary side of the transformer 1 from the switch element 31 and the control circuit 9 provided on the primary side, and 13 and an auxiliary power supply circuit 15 for supplying a control signal CS12 having substantially the same pulse width as the control signal CS1 supplied from the control circuit 9.

The drive circuit 13 includes a first drive circuit 131
And a second drive circuit 132. The first drive circuit 131 drives the control electrode 513 of the first rectifying switch element 51. The second drive circuit 132 drives the control electrode 523 of the second rectifying switch element 52. The first drive circuit 131 and the second drive circuit 132 are commonly connected on the input side, and the control signal CS12 is commonly supplied. The first drive circuit 131 is a logic gate that performs a non-inverted logic operation on the input control signal CS12. That is, when the input control signal CS12 has the logical value 1 (high level), the output signal of the first drive circuit 131 has the logical value 1 (high level). Second drive circuit 132
Is a logic gate that performs an inversion logic operation on the input control signal CS12. That is, the input control signal C
When S12 has the logical value 1 (high level), the output signal has the logical value 0 (low level).

The auxiliary power supply circuit 15 includes a rectifier diode 15
1 and a smoothing capacitor 152. The control signal CS12 generated in the output winding of the insulating transformer 112 included in the insulating coupling circuit 11 is rectified by the rectifier diode 151 and smoothed by the smoothing capacitor 152. As a result, the DC voltage Vc1 is generated. This DC voltage Vc1 is supplied to the first drive circuit 131 and the second drive circuit 1
The first drive circuit 131 and the second drive circuit 132 stably perform a predetermined logic operation because the operation voltage is supplied to the drive circuit 32.

The auxiliary power supply circuit 15 is not limited to the illustrated embodiment. For example, a voltage stabilizing circuit that generates a stabilized voltage may be included. Specifically, a circuit configuration in which a third winding is provided in the transformer 112 and supplied from the winding via a voltage stabilizing circuit can be given.

The control operation of the first and second rectifying switch elements 51 and 52 by the first and second drive circuits 131 and 132 is as follows. First, control signals CS1, CS
11 is a logical value 1 (high level) and the switch circuit 3
Is turned on, the driving signal CS21 supplied from the first driving circuit 131 to the first rectifying switch element 51 has a logical value of 1 (high level). The switch element 51 turns on. Second
The rectifying switch element 52 is turned off because the drive signal CS22 has the logical value 0 (low level) by the inverted logic operation of the second drive circuit 132.

Next, when the control signals CS1 and CS11 have the logical value 0 (low level) and the switch element 31 included in the switch circuit 3 is off, the first drive circuit 131 outputs the first rectifying switch. Since the drive signal CS21 supplied to the element 51 has the logical value 0 (low level), the first rectifying switch element 51 is turned off. The second rectifying switch element 52 is turned on because the drive signal CS22 has the logical value 1 (high level) due to the inverted logic operation of the second drive circuit 132. By the synchronous rectification operation described above, a synchronous rectification type switching power supply device in which the loss is reduced as compared with a rectifier circuit using a rectifier diode is obtained.

The illustrated auxiliary power supply circuit 15 has a rectifier diode 151 and a smoothing capacitor 152, and thus operates as a kind of peak hold circuit. Since the control signal CS12 is a pulse signal having a constant peak value, the DC voltage Vc1 has a substantially constant voltage value. Therefore, even when the input voltage or the output voltage fluctuates, the first and second rectifying switch elements 5 constituting the synchronous rectifier circuit 5
A stable drive voltage can be supplied to the first and the second 52.

Since power can be supplied from the primary side of the switch element 31 to the secondary side of the first and second rectifying switch elements 51 and 52 via the insulating coupling circuit 11, A stable drive voltage can be supplied to the first and second drive circuits 131 and 132 even at the time of startup or output short-circuit.

FIG. 4 is an electric circuit diagram showing still another specific embodiment of the switching power supply according to the present invention shown in FIG. In the drawings, the same components as those shown in FIGS. 1 to 3 are denoted by the same reference numerals.
The feature of this embodiment is that a secondary side control circuit 21 is provided, and the DC voltage Vc1 generated by the auxiliary power supply circuit 15 is supplied to the secondary side control circuit 21 as an operation voltage. It is that you are. The secondary side control circuit 21 includes, for example, an output voltage detection circuit and the like. An insulating coupler 22 such as a transformer is provided between the secondary side control circuit 21 and the control circuit 9, and electrically connects the primary side with the control circuit 9 and the secondary side control circuit 21 to each other. The monitoring signal CS3 is supplied to the control circuit 9 in the insulated state.

FIG. 5 is an electric circuit diagram showing still another specific embodiment of the switching power supply according to the present invention shown in FIG. In the drawings, the same components as those shown in FIGS. 1 to 4 are denoted by the same reference numerals.
The feature of this embodiment is that a second auxiliary power supply circuit 23 is included. As means for configuring the second auxiliary power supply circuit 23, in the embodiment, the choke coil 7 of the smoothing circuit 7 is used.
1 includes a first winding 73 and a second winding 74. First winding 73 is connected in series with output winding 102 of transformer 1.

The second auxiliary power supply circuit 23 converts the voltage induced in the second winding 74 of the choke coil 71 into a DC voltage V
Generate c2. Second winding 74 of choke coil 71
Is proportional to the DC output voltage V0. Second
The auxiliary power supply circuit 23 generates a DC voltage Vc2 using the induced voltage.

The illustrated second auxiliary power supply circuit 23 includes a rectifier diode 25, and an anode of the rectifier diode 25.
Is connected to one end of the second winding 74, and the cathode is connected to the cathode of the rectifier diode 151 of the auxiliary power supply circuit 15. The smoothing capacitor 152 included in the auxiliary power supply circuit 15 is also used as a smoothing capacitor in the second auxiliary power supply circuit 23. According to this configuration,
Under normal conditions, the operating voltage Vc2 can be supplied to the drive circuit 13 through the second auxiliary power supply circuit 23.

The DC voltage Vc2 output from the second auxiliary power supply circuit 23 is set to be higher than the DC voltage Vc1 output from the auxiliary power supply circuit 15. According to this configuration, the rectifier diode 151 does not conduct during the normal operation, and the power passing through the insulating coupling circuit 11 can be reduced, so that the loss due to the signal transmission circuit 111 and the transformer 112 constituting the insulating coupling circuit 11 is reduced. Thus, downsizing can be achieved.

Although not shown, as means for constituting the second auxiliary power supply circuit 23, a third winding is provided in the transformer 1, and a voltage induced in the third winding is rectified and smoothed. The operating voltage Vc2 may be generated.

FIG. 6 is an electric circuit diagram showing still another specific embodiment of the switching power supply according to the present invention shown in FIG. In the drawings, the same components as those shown in FIGS. 1 to 5 are denoted by the same reference numerals. The feature of this embodiment is that a delay circuit 27 is included. The delay circuit 27 delays the rise of the control signal CS11 supplied to the control electrode 313 of the switch element 31.

FIG. 7 is a time chart for explaining the delay operation by the delay circuit 27. FIG. 7A shows the control circuit 9.
7B is a waveform diagram of the control signal CS1 output from the delay circuit 27 and supplied to the delay circuit 27 and the insulating coupling circuit 11, and the control signal C12 output from the insulating coupling circuit 11, and FIG. Control signal CS10 and control signal CS supplied to control electrode 313 of switch element 31
11 shows a waveform diagram of FIG.

As shown in the figure, the control circuit 9 outputs a control signal CS1 which is a pulse signal having a pulse width TW and a period Tf.
Is supplied (see FIG. 7A), the delay circuit 27
Generates a control signal CS10 whose rising is delayed by a delay time Td (ON delay) (see FIG. 7B). The fall of the control signal CS10 is the same as the control signal CS1. Due to this delay operation, a narrow ON-state suitable for driving the control electrode 313 of the switch element 31 is obtained. The control signal CS11 having the pulse width Ts is obtained.

The control signal C supplied from the control circuit 9 to the secondary-side auxiliary power supply circuit 15 through the insulating coupling circuit 11
S12 has the same pulse width TW as the control signal CS1 output from the control circuit 9 (see FIG. 7A). Therefore, the switch element 31 which is the main switch is turned on. Even when the pulse width becomes very small, a stable drive voltage Vc1 can be supplied to the first and second rectifying switch elements 51 and 52 constituting the synchronous rectifier circuit 5.

Although not shown, the configuration described in this specification and the embodiments shown in FIGS. 3 to 6 can be arbitrarily combined.

FIG. 8 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention shown in FIG. In the figure, the same components as those described above in the drawings are denoted by the same reference numerals.

In the embodiment shown in FIG. 8, the synchronous rectifier circuit 5
Rectifying switch element 51 and a second rectifying switch element 52. The first rectifying switch element 51 has a main electrode 511 connected to one end of the output winding 102 of the transformer 1. The second rectifying switch element 52 is connected to the main electrode 5.
21 is connected to the other end of the output winding 102 of the transformer 1, and the main electrode 522 is connected to the main electrode 5 of the first rectifying switch element 51.
12 is connected.

In the transformer 1, the output winding 102 has an intermediate tap CT. In the synchronous rectification circuit 5, the main electrodes 512 and 522 connected to each other and the intermediate tap CT among the main electrodes of the first and second rectification switch elements 51 and 52 are connected to the input side of the smoothing circuit 7. Has been. The circuit system of the synchronous rectifier circuit 5 is a full-wave rectifier system.

In the switching power supply described above,
The control operation of the first and second rectifying switch elements 51 and 52 by the drive circuit 13 is substantially the same as that described with reference to FIG. That is, the first and second rectifying switch elements 5
1 and 52 are controlled in synchronization with the switch element 31 such that when the switch element 31 is on, the first rectifying switch element 51 is on and the second rectifying switch element 52 is off. . In addition, when the switch element 31 is off, control is performed in synchronization with the switch element 31 so that the first rectification switch element 51 is turned off and the second rectification switch element 52 is turned on. By providing the synchronous rectifier circuit 5 described above, a synchronous rectification type switching power supply device in which loss is reduced as compared with a rectifier circuit using a rectifier diode can be obtained.

Although not shown, in the embodiment shown in FIG. 8, the first and second rectifying switch elements 51, 5
Either one of the two can be replaced with a rectifying diode, and the circuit configuration as shown in FIGS. 3 to 6 can be adopted.

FIG. 9 is an electric circuit diagram showing still another embodiment of the switching power supply according to the present invention shown in FIG. In the figure, the same components as those described above in the drawings are denoted by the same reference numerals.

In the illustrated embodiment, the synchronous rectifier circuit 5
Only one rectifying switch element 51 is included, and the rectifying switch element 51 rectifies and outputs a flyback voltage induced in the secondary winding 102 of the transformer 1. The rectifying switch element 51 is configured by an FET, a bipolar transistor, or the like. The rectifying switch element 51 is configured such that the main electrode 511 has the output winding 102 of the transformer 1.
Is connected to one end. The input side of the smoothing circuit 7 is connected between the main electrode 512 of the first rectifying switch element 51 and the other end of the output winding 102 of the transformer 1.

The drive circuit 13 synchronizes the rectifying switch element 51 with the switch element 31 by the drive signal CS2 generated based on the control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11. Control. The drive signal CS2 is a pulse train signal.

More specifically, the rectifying switch element 51
Is controlled in synchronization with the switch element 31 so that the switch element 31 included in the switch circuit 3 is turned off when the switch element 31 is on and turned on when the switch element 31 is off. The energy stored in the transformer 1 during the ON period of the switch element 31 is released when the switch element 31 is turned off and the rectifying switch element 51 is turned on. By providing the synchronous rectifier circuit 5 described above, a synchronous rectification type switching power supply device in which loss is reduced as compared with a rectifier circuit using a rectifier diode can be obtained.

In the embodiment shown in FIG.
5 generates a DC voltage Vc1 by rectifying and smoothing the control signal CS12 supplied from the control circuit 9 via the insulating coupling circuit 11, and supplies the DC voltage Vc1 to the drive circuit 13 as an operating voltage. Therefore, even when the input voltage Vin or the output voltage V0 fluctuates, a stable drive voltage can be supplied to the drive circuit 13.

Power is supplied from the primary side having the switch element 31 to the secondary side having the first rectifying switch element 51 and the second rectifying switch element 52 via the insulating coupling circuit 11. Therefore, a stable drive voltage can be supplied to the drive circuit 13 even at the time of start-up or output short-circuit.

FIG. 10 is an electric circuit diagram showing a more specific embodiment of the switching power supply device shown in FIG. In the figure, the same components as those shown in FIG. 9 are denoted by the same reference numerals. In the synchronous rectifier circuit 5, the main electrode 511 of the rectifying switch element 51 is connected to one end of the output winding 102 of the transformer 1.

The drive circuit 13 drives the control electrode 513 of the rectifying switch element 51. The drive circuit 13 is a logic gate that performs an inversion logic operation on the input control signal CS12. That is, when the input control signal CS12 has the logical value 1 (high level), the drive circuit 13 outputs the drive signal CS2 having the logical value 0 (low level), and outputs the control signal CS12.
Is a logical value 0 (low level) and a logical value 1 (high level)
Is output.

The auxiliary power supply circuit 15 includes a rectifier diode 15
1 and a smoothing capacitor 152. The control signal CS12 generated in the output winding of the insulating transformer 112 included in the insulating coupling circuit 11 is rectified by the rectifier diode 151 and smoothed by the smoothing capacitor 152. As a result, the DC voltage Vc1 is generated. This DC voltage Vc1 is supplied to the drive circuit 13 as an operation voltage.

The auxiliary power supply circuit 15 is not limited to the illustrated embodiment. For example, a voltage stabilizing circuit that generates a stabilized voltage may be included. Specifically, a circuit configuration in which a third winding is provided in the transformer 112 and supplied from the winding via a voltage stabilizing circuit can be given.

Since the illustrated auxiliary power supply circuit 15 has the rectifier diode 151 and the smoothing capacitor 152, it operates as a kind of peak hold circuit. Since the control signal CS12 is a pulse signal having a constant peak value, the DC voltage Vc1 has a substantially constant voltage value. Therefore, even when the input voltage or the output voltage fluctuates, a stable drive voltage can be supplied to the rectifying switch element 51 included in the synchronous rectifier circuit 5.

Also, from the primary side of the switch circuit 3,
Since power can be supplied to the secondary side including the synchronous rectifier circuit 5, the drive circuit 13, and the auxiliary power supply circuit 15 via the insulating coupling circuit 11, even at the time of startup or output short-circuit,
A stable drive voltage can be supplied to the drive circuit 13.

FIG. 11 is a diagram showing still another embodiment of the switching power supply device shown in FIG. In the drawings, the same components as those shown in FIGS. 9 and 10 are denoted by the same reference numerals.

In this embodiment, a second auxiliary power supply circuit 23 is included. As means for configuring the second auxiliary power supply circuit 23,
Transformer 1 includes third winding 103. The second auxiliary power supply circuit 23 generates a DC voltage Vc2 from a voltage induced in the third winding 103 of the transformer 1. The output terminal of the second auxiliary power supply circuit 23 is connected to the output terminal of the auxiliary power supply circuit 15.

The illustrated second auxiliary power supply circuit 23 includes a rectifier diode 25,
Is connected to one end of the third winding 103, and the cathode is connected to the cathode of the rectifier diode 151 of the auxiliary power supply circuit 15. The smoothing capacitor 152 included in the auxiliary power supply circuit 15 is also used as a smoothing capacitor in the second auxiliary power supply circuit 23. According to this configuration, the operating voltage Vc2 can be supplied to the drive circuit 13 through the second auxiliary power supply circuit 23 in a normal state.

The DC voltage Vc2 output from the second auxiliary power supply circuit 23 is set to be higher than the DC voltage Vc1 output from the auxiliary power supply circuit 15. According to this configuration, the rectifier diode 151 does not conduct during the normal operation, and the power passing through the insulating coupling circuit 11 can be reduced, so that the loss due to the signal transmission circuit 111 and the transformer 112 constituting the insulating coupling circuit 11 is reduced. Thus, downsizing can be achieved.

FIG. 12 is an electric circuit diagram showing still another specific embodiment of the switching power supply according to the present invention shown in FIG. In the drawings, the same components as those shown in FIGS. 9 to 11 are denoted by the same reference numerals. The feature of this embodiment is that a delay circuit 27 is included. The delay circuit 27 delays the rise of the control signal CS11 supplied to the control electrode 313 of the switch element 31.

The details of the operation of delay circuit 27 are almost the same as the operation characteristics shown in FIG. Therefore, when the switch element 31 which is the main switch is turned on. Even when the pulse width becomes small, a stable drive voltage Vc1 can be supplied to the first rectifying switch element 51 constituting the synchronous rectifier circuit 5.

Although not shown, the configuration described in this specification and the embodiments shown in FIGS. 10 to 12 can be arbitrarily combined.

[0097]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a switching power supply device capable of supplying a stable drive voltage to a circuit for driving a rectifying switch element included in a synchronous rectifier circuit even when an input voltage or an output voltage fluctuates. (B) It is possible to provide a switching power supply device capable of supplying a stable drive voltage to a circuit for driving a rectifying switch element included in a synchronous rectification circuit even when an output short circuit occurs.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a switching power supply device according to the present invention.

FIG. 2 is a more specific electric circuit diagram of the switching power supply according to the present invention shown in FIG.

FIG. 3 is a more specific electric circuit diagram of the switching power supply according to the present invention shown in FIG. 2;

FIG. 4 is still another specific electric circuit diagram of the switching power supply device according to the present invention shown in FIG. 2;

FIG. 5 is still another specific electric circuit diagram of the switching power supply according to the present invention shown in FIG. 2;

FIG. 6 is still another specific electric circuit diagram of the switching power supply according to the present invention shown in FIG. 2;

FIG. 7 is a time chart for explaining a delay operation by a delay circuit in the switching power supply device shown in FIG. 6;

FIG. 8 is an electric circuit diagram showing still another specific embodiment of the switching power supply according to the present invention shown in FIG. 1;

FIG. 9 is an electric circuit diagram showing still another specific embodiment of the switching power supply according to the present invention shown in FIG. 1;

FIG. 10 is an electric circuit diagram showing a more specific embodiment of the switching power supply device shown in FIG.

11 is an electric circuit diagram showing still another specific embodiment of the switching power supply device shown in FIG.

FIG. 12 is an electric circuit diagram showing still another specific embodiment of the switching power supply device shown in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transformer 3 Switch element 5 Synchronous rectifier circuit 51 1st rectifier switch element 52 2nd rectifier switch element 7 Smoothing circuit 9 Control circuit 11 Insulation coupling circuit 13 Drive circuit 15 Auxiliary power supply circuit 21 Secondary side control circuit 23 Second auxiliary power supply circuit 25 Rectifier diode 27 Delay circuit

Continuation of the front page (56) References JP-A-8-322245 (JP, A) JP-A-6-78526 (JP, A) JP-A-64-57820 (JP, A) JP-A-6-113540 (JP, A) JP-A-11-178335 (JP, A) JP-A-11-69802 (JP, A) JP-A-10-191629 (JP, A) JP-A-11-55944 (JP, A) 5-18292 (JP, U) Japanese Utility Model 55-158685 (JP, U) Japanese Utility Model Application 54-104029 (JP, U) Japanese Utility Model Application No. 3-124779 (JP, U) Japanese Utility Model Application No. 4-97478 (JP, U.S.A.) U) (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 7/21

Claims (10)

(57) [Claims] 1. A switching power supply device including a transformer, a switch circuit, a synchronous rectifier circuit, a smoothing circuit, a control circuit, an insulation coupling circuit, a drive circuit, an auxiliary power supply circuit, and a delay circuit. Wherein the transformer includes an input winding and an output winding; the switch circuit includes at least one switch element, wherein the switch element is a DC input voltage supplied through the input winding. Wherein the synchronous rectifier circuit includes at least one rectifying switch element having a control electrode, rectifies and outputs a voltage induced in the output winding of the transformer, and wherein the smoothing circuit performs the synchronization. A rectifying circuit that smoothes and outputs a rectified voltage output from the rectifier circuit; the control circuit supplies a control signal to the switch element to control a switching operation thereof; A drive signal generated based on the control signal supplied from the control circuit via the insulating coupling circuit is supplied to the control electrode of the rectifying switch element, and the rectifying switch element is connected to the switch circuit. The auxiliary power supply circuit generates a DC voltage by rectifying and smoothing the control signal supplied from the control circuit via the insulating coupling circuit, and generates the DC voltage. The operating voltage is supplied to the drive circuit and supplied to the auxiliary power circuit.
The pulse width of the control signal (CS12)
The pulse width (TW) of the output control signal (CS1)
And the delay circuit is provided from the control circuit to the switch circuit.
Supplied to the control electrode of the switch element included in
The rise of the control signal by the delay time (Td)
The control being delayed and supplied to the control electrode of the switch element
The pulse width (Ts) of the signal (CS11) is determined by the control circuit
From the control signal (CS
12) The pulse width TW is equal to the delay time (Td).
Narrow switching power supply. 2. The switching power supply device according to claim 1, wherein the synchronous rectifier circuit includes a first rectifying switch element and a second rectifying switch element, and the first rectifying switch. In the element, one of the main electrodes is connected to one end of the output winding of the transformer, and the second rectifying switch element has one of the main electrodes connected to the other end of the output winding of the transformer. And the other of the main electrodes is connected to the other of the main electrodes of the first rectifying switch element. 3. The switching power supply device according to claim 2, wherein the synchronous rectifier circuit includes one main electrode of one of the first rectifier switch element and the second rectifier switch element. Is a switching power supply device guided to the input side of the smoothing circuit. 4. The switching power supply device according to claim 2, wherein the transformer has the output winding having an intermediate tap, and the synchronous rectifier circuit has the first and second windings. A switching power supply device wherein, among main electrodes of a rectifying switch element, a main electrode connected to each other and the intermediate tap are guided to an input side of the smoothing circuit. 5. The switching power supply device according to claim 1, wherein the synchronous rectification circuit includes two rectification elements, one of the two rectification elements is a rectification switch element, and the other is a rectification switch element. A switching power supply that is a rectifier diode. 6. The switching power supply device according to claim 1, further comprising: a second auxiliary power supply circuit; wherein the smoothing circuit includes at least one magnetic element; The element includes a first winding and a second winding, wherein the first winding is connected in series with the output winding of the transformer, and wherein the second auxiliary power supply circuit A switching power supply device that generates a DC voltage from a voltage induced in the second winding of the magnetic element and has an output terminal connected to an output terminal of the auxiliary power supply circuit. 7. The switching power supply device according to claim 1, further comprising: a second auxiliary power supply circuit; wherein the transformer includes a third winding; The switching power supply device according to claim 2, wherein the auxiliary power supply circuit generates a DC voltage from a voltage induced in the third winding of the transformer, and has an output terminal connected to the output terminal of the auxiliary power supply circuit. 8. The switching power supply according to claim 1, wherein the synchronous rectifier circuit includes one rectifier element, wherein the rectifier element is the rectifying switch element, A switching power supply that rectifies and outputs the flyback voltage induced in the secondary winding. 9. The switching power supply device according to claim 8, further comprising: a second auxiliary power supply circuit; wherein the transformer includes a third winding; Is a switching power supply device that generates a DC voltage from a voltage induced in the third winding of the transformer, and has an output terminal connected to an output terminal of the auxiliary power supply circuit. 10. The switching power supply device according to claim 6, wherein a DC voltage output from the second auxiliary power supply circuit is lower than a DC voltage output from the auxiliary power supply circuit. High switching power supply.