JP2004215356A - Switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a witching power supply in which voltage drop of a battery and damage of a switching element for synchronous rectification can be prevented. <P>SOLUTION: A capacitor 14-2 is charged from a constant current source 14-1 and the voltage level Vss at point A is increased gradually. When the voltage level Vss exceeds Vt1, an output signal V1 from a comparator 13-2 transits from off to on and a signal Vpwm is delivered as a signal V2 from an AND circuit 13-5. When the voltage level Vss further increases to exceed Vt2, an output signal V3 from a comparator 13-1 transits from off to on and a synchronous rectification control signal outputted from a control circuit 12 is fed to a synchronous rectification circuit 44 from AND circuits 13-6 and 13-7. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply including a rectifier circuit having a switching element.
[0002]
[Prior art]
FIG. 4A is a diagram illustrating a general switching power supply device.
The switching power supply device 40 shown in FIG. 4A includes a power supply 41, a full bridge circuit 42 including a MOSFET (Metal-Oxide Semiconductor Field Effect Transistor) 42-1 to 42-4, a transformer 43, a MOSFET 44-1 and a MOSFET 44-1. A synchronous rectifier circuit 44 composed of 44-2, a coil 45, a capacitor 46, and a battery 47 are provided.
[0003]
The switching power supply device 40 is configured to alternately turn on and off a set of MOSFETs 42-1 and 42-3 and a set of MOSFETs 42-2 and 42-4 of the full bridge circuit 42, thereby obtaining the DC power of the power supply 41. , And the converted AC power is rectified by the synchronous rectifier circuit 44 via the transformer 43, the power rectified by the coil 45 and the capacitor 46 is smoothed, and the smoothed power is To store electricity.
[0004]
In general, a MOSFET can suppress a voltage drop during conduction more than a diode, and a synchronous rectifier circuit 44 using a MOSFET can suppress power loss more than a rectifier circuit using a diode. Therefore, the switching power supply circuit 40 using the synchronous rectifier circuit 44 can achieve higher efficiency and smaller size than the switching power supply circuit using the diode.
[0005]
In addition, a synchronous rectifier circuit configured using a switching element such as a MOSFET has a self-excited type in which drive control of each MOSFET is performed based on a secondary voltage of a transformer, and a control circuit independent of its own device. There is a separately-excited type in which drive control of each MOSFET is performed based on a control signal (for example, see Patent Document 1). In either method, two MOSFETs are controlled so as not to short-circuit the secondary voltage of the transformer. There is a need to.
[0006]
[Patent Document 1]
JP-A-2001-145348 (pages 2 to 4, FIG. 1)
[0007]
[Problems to be solved by the invention]
However, the switching power supply device 40 including the separately-excited synchronous rectifier circuit has the following problems.
(1) As shown in FIG. 4B, when all the MOSFETs 42-1 to 42-4 of the full bridge circuit 42 are off, and when the MOSFETs 44-1 and 44-2 are simultaneously on (2). In the next short mode, there is a problem that the charge stored in the battery 47 flows out through the MOSFET 44-1, the MOSFET 44-2, and the coil 45, thereby lowering the voltage of the battery 47. Further, when the electric charge of the battery 47 flows out, if an overcurrent flows through the MOSFET 44-1, the MOSFET 44-2, and the coil 45, the MOSFETs 44-1 and 44-2 may be damaged.
[0008]
(2) Also, as shown in FIG. 4C, when all of the MOSFETs 42-1 to 42-4 of the full bridge circuit 42 are off, and one of the MOSFETs 44-1 and 44-2 is turned off. When turned on (regeneration mode), the charge stored in the battery 47 flows through the transformer 43 to each of the parasitic diodes of the MOSFETs 42-1 to 42-4, thereby decreasing the voltage of the battery 47. There is. Further, an overcurrent may flow through the MOSFET 44-1 or 44-2 and the MOSFETs 42-1 to 42-4, and may damage each element.
[0009]
As described above, when the battery 47 is connected to the output side of the switching power supply 40 and the synchronous rectifier circuit 44 is turned on, the charge of the battery 47 is transferred to the secondary side of the switching power supply 40 (in FIG. (The circuit on the right side), and the voltage of the battery 47 is reduced. Further, the outflow of the electric charge of the battery 47 may damage the MOSFETs 42-1 to 42-4 and the MOSFETs 44-1 and 44-2.
[0010]
The present invention has been made in consideration of the above problems, and has as its object to provide a switching power supply device capable of preventing a voltage drop of a power supply connected as a load and damage of a switching element.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is configured as follows.
That is, a switching power supply device of the present invention includes a first switching element, and converts a power of an input power supply into a predetermined power in accordance with ON / OFF of the first switching element; A first control circuit that controls on / off of the first switching element; and a second switching element, rectifies the power converted by the power conversion circuit, and uses the rectified power as a power supply as a load. A rectifying circuit for charging, a second control circuit for controlling on / off of the second switching element, and a third control circuit for controlling start or stop of driving of the first and second control circuits; Wherein the third control circuit starts driving the first control circuit and then starts driving the second control circuit, and stops driving the second control circuit and then stops driving the second control circuit. First control Characterized in that stops the driving of the road.
[0012]
As a result, only the second control circuit is not driven, so that the second switching element is turned on and off, so that the charge charged in the power supply as a load can be prevented from flowing out, and the load can be prevented. As a result, it is possible to prevent a voltage drop of the power supply and breakage of the switching element.
[0013]
Further, the third control circuit of the switching power supply device outputs a voltage whose voltage value gradually increases when the switching power supply device starts, and gradually decreases when the switching power supply device stops. When the voltage value of the voltage output from the step-up / step-down circuit rises above a first reference voltage value, the driving of the first control circuit is started and the voltage is output from the step-up / step-down circuit. When the voltage value of the voltage drops below the first reference voltage value, a first comparison circuit for stopping the driving of the first control circuit, and a voltage value of the voltage output from the voltage step-up / step-down circuit are changed to a second voltage value. When the voltage of the voltage output from the step-up / step-down circuit drops below the second reference voltage value, the second control circuit starts driving. Stop driving of control circuit Second and a comparator circuit for said second reference voltage value, may be configured to be higher than the first reference voltage value.
[0014]
As described above, since the second reference voltage value is higher than the first reference voltage value, the third control circuit does not always drive the second control circuit when the first control circuit is not driven. Can be controlled as follows. Thus, since only the second control circuit is not driven, it is possible to prevent the charge charged in the power supply as a load from flowing out by turning on and off the second switching element. This makes it possible to prevent a voltage drop of the power supply as a load and damage of the switching element.
[0015]
Further, since the first and second comparison circuits can be constituted by semiconductor elements such as MOSs, for example, it is possible to suppress an increase in the size of the switching power supply device.
In addition, the switching power supply device includes a soft start circuit that gradually increases or decreases the on-time of each of the plurality of first switching elements and the plurality of second switching elements according to the amount of charge charged to a capacitor. The third control circuit may be configured to start or stop driving of the first and second control circuits based on an amount of charge charged in the capacitor.
[0016]
As described above, by using the capacitor provided for suppressing the overcurrent to the switching element generated at the start of driving of the switching power supply device also for controlling the driving of the first and second control circuits, In addition, it is possible to prevent only the second control circuit from being driven without newly providing a capacitor. Thus, it is possible to suppress an increase in the size of the switching power supply device.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a switching power supply device 10 according to an embodiment of the present invention. In the switching power supply device 10 shown in FIG. 1, the same components as those of the switching power supply device 40 shown in FIG. 4A are denoted by the same reference numerals, and description thereof will be omitted.
[0018]
As shown in FIG. 1, the switching power supply device 10 includes a power supply 41 (input power supply), a full bridge circuit 42 (power conversion circuit), a transformer 43, a synchronous rectification circuit 44 (rectification circuit), a coil 45, The control circuit 11 (first control circuit) for controlling the driving of the capacitor 46, the battery 47 (power supply as a load), the full bridge circuit 42, and the control circuit 12 (second for controlling the driving of the synchronous rectification circuit 44) ) And a control circuit 13 (third control circuit) for controlling the start or stop of driving of the control circuits 11 and 12. Note that the synchronous rectifier circuit 44 may include a switching element and a diode.
[0019]
The control circuit 13 includes a soft start circuit 14 (soft start circuit, step-up / step-down circuit), a comparator 13-1 (second comparison circuit), a comparator 13-2 (first comparison circuit), and a comparator 13- 3, an amplifier 13-4, an AND circuit 13-5, an AND circuit 13-6, an AND circuit 13-7, and a reference signal generator 13-8 for generating a reference signal such as a triangular wave. Is done. Note that each MOSFET of the full bridge circuit 42 and each MOSFET of the synchronous rectifier circuit 44 have a PWM (Pulse Width Modulation) based on a reference signal generated from the reference signal generator 13-8 and a signal output from the amplifier 13-4. ) Controlled.
[0020]
The soft start circuit 14 includes a constant current source 14-1, a capacitor 14-2, a resistor 14-3, and a switch 14-4. The output signal Vss of the soft start circuit 14 is used not only for driving the full bridge circuit 42 and for controlling the driving of the synchronous rectification circuit 44 but also for the MOSFETs 132-1 to 13-4. It is also used to gradually increase the on-time of 42-4 and MOSFETs 44-1 and 44-2. As described above, by gradually increasing the on-time of the MOSFETs 42-1 to 42-4 and the MOSFETs 44-1 and 44-2, an overcurrent (rush current) to each MOSFET generated at the start of driving of the switching power supply device 10 is obtained. Can be suppressed. The soft start circuit 14 gradually reduces the on-time of the MOSFETs 42-1 to 42-4 and the MOSFETs 44-1 and 44-2 when the switching power supply 10 stops driving. (Soft down)
The switching power supply device 10 is controlled by the control circuit 11 so that the set of MOSFETs 42-1 and 42-3 of the full bridge circuit 42 and the set of MOSFETs 42-2 and 42-4 are turned on and off alternately. Then, the control circuit 12 controls the MOSFET 44-1 and the MOSFET 44-2 of the synchronous rectification circuit 44 to be turned on and off alternately, so that the battery is charged with desired power. In the present embodiment, the MOSFETs 42-1 to 42-4 are the first switching elements, and the MOSFETs 44-1 and 44-2 are the second switching elements.
[0021]
Next, the operation of the control circuit 13 will be described.
2 and 3 are diagrams for explaining the operation of the control circuit 13. FIG. 2 shows input / output signal waveforms (I / O signal waveforms of each element in the control circuit 13 when the driving of the switching power supply 10 is started). FIG. 3 is a diagram showing input / output signal waveforms (voltage values) of each element in the control circuit 13 when driving of the switching power supply device 10 is stopped.
[0022]
First, the operation of the control circuit 13 when the driving of the switching power supply circuit 10 is started will be described.
The first waveform from the top in FIG. 2 is a signal start / stop for controlling ON / OFF of the switch 14-4, and the second waveform is input to the plus terminal side of the amplifier 13-4. The third waveform indicates the signal Vsens, the third waveform indicates the voltage value Vss input to the plus terminal side of the comparator 13-2, and the fourth waveform is output from the amplifier 13-4, and the plus terminal of the comparator 13-3. _{Shows the} signal V _EAOUT input to the comparator 13-2, and the fifth waveform shows the signal V _EAOUT , the signal Vosc output from the reference signal generator 13-8, and the voltage input to the minus terminal side of the comparator 13-2. The relationship between the value Vt1 (first reference voltage) and the voltage value Vt2 (second reference voltage) input to the minus terminal of the comparator 13-1 is shown. The seventh waveform indicates the signal V1 output from the comparator 13-2, and the eighth waveform indicates the signal V2 output from the AND circuit 13-5. The ninth waveform shows the signal V3 output from the comparator 13-1.
[0023]
First, the switch 14-4 of the soft start circuit 14 is opened to start driving the switching power supply device 10. Then, the charge of the constant current source 14-1 is charged in the capacitor 14-2, and the voltage value Vss at the point A gradually increases.
Then, when the voltage value Vss rises above the voltage value Vt1, the signal V1 output from the comparator 13-2 switches from off to on. Then, the signal Vpwm is output from the AND circuit 13-5 as the signal V2, and the full bridge circuit 42 is driven by the signal V2.
[0024]
Next, when the voltage value Vss further rises and rises above the voltage value Vt2, the signal V3 output from the comparator 13-1 switches from off to on. Then, the synchronous rectification control signal output from the control circuit 12 is input to the synchronous rectification circuit 44 from the AND circuits 13-6 and 13-7, and the synchronous rectification circuit 44 is driven.
[0025]
Next, the operation of the control circuit 13 when stopping the driving of the switching power supply circuit 10 will be described. Note that the waveforms shown in FIG. 3 show the same output waveforms as the waveforms shown in FIG. 2, and a description of each waveform will be omitted.
First, to stop the switching power supply 10, the switch 14-4 of the soft start circuit 14 is closed. Then, the charge stored in the capacitor 14-2 is released, and the voltage value Vss at the point A gradually decreases.
[0026]
When the voltage value Vss falls below the voltage value Vt2, the signal V3 output from the comparator 13-1 switches from on to off. Then, the output of the synchronous rectification control signal output from the AND circuits 13-6 and 13-7 stops, and the synchronous rectification circuit 44 stops.
[0027]
Next, when the voltage value Vss further decreases and drops below the voltage value Vt1, the signal V1 output from the comparator 13-2 switches from on to off. Then, the signal V2 output from the AND circuit 13-5 stops, and the full bridge circuit 42 stops.
[0028]
That is, when the voltage value of the signal Vss output from the soft start circuit 14 becomes larger than the voltage value Vt1 of the comparator 13-2, the control circuit 13 starts driving the full bridge circuit 42 and starts the switching power supply circuit 10. Then, when the voltage value of the signal Vss becomes larger than the voltage value Vt2 of the comparator 13-1, the driving of the synchronous rectification circuit 44 is started. When the voltage value of the signal Vss becomes smaller than the voltage value Vt2 of the comparator 13-1, the control circuit 13 stops driving the synchronous rectification circuit 44, and furthermore, the voltage value of the signal Vss becomes the voltage of the comparator 13-2. When the value becomes smaller than the value Vt1, the driving of the full bridge circuit 42 is stopped, and the driving of the switching power supply circuit 10 is stopped.
[0029]
As described above, the synchronous rectifier circuit 44 is driven after the full bridge circuit 42 is driven, and the full bridge circuit 42 is stopped after the synchronous rectifier circuit 44 is stopped. Since the circuit 44 is not driven, the charge is prevented from flowing out of the battery 47, and the voltage of the battery 47 can be prevented from being reduced and the MOSFET can be prevented from being damaged.
[0030]
Also, in order to prevent an overcurrent from flowing through the MOSFETs 42-1 to 42-4 and the MOSFETs 44-1 and 44-2 when the switching power supply 10 is started, a soft start capacitor originally provided in the switching power supply 10 is provided. Are used to make the timings of driving or stopping the control circuits 11 and 12 different from each other, so that the switching power supply device 10 can be prevented from being enlarged.
[0031]
<Other embodiments>
The present invention is not limited to the above embodiment, and various configurations can be adopted within the scope described in each claim. For example, the following configuration changes are possible.
[0032]
(1) In the above embodiment, a MOSFET is used as a switching element constituting the full bridge circuit 42. However, as another switching element, a bipolar transistor or an IGBT (Insulated Gate Bipolar) is used.
Transistor) may be adopted.
[0033]
(2) In the above-described embodiment, the full bridge circuit 42 including four MOSFETs is configured as a power conversion circuit for converting the power of the power supply 41 into AC. However, the power conversion circuit includes two switching elements (for example, MOSFETs). May be employed as a power conversion circuit.
[0034]
(3) The switching power supply device 10 may be configured by employing a forward converter, a flyback converter, or the like.
(4) The switching power supply 10 has a configuration in which the battery 47 is connected to the output side, but may have a configuration in which a load other than the battery 47, such as a converter or a motor, is connected.
[0035]
(5) The switching power supply device 10 may be configured as a non-insulated converter without the transformer 43.
(6) Further, the switching power supply device 10 is not limited to a boost converter, and may be configured as a buck converter or a polarity inversion converter.
[0036]
【The invention's effect】
According to the present invention, since the rectifier circuit does not operate while the power conversion circuit is stopped, it is possible to prevent the charge of the charging power supply from leaking out, and to suppress a voltage drop of the charging power supply. . In addition, since the outflow of the electric charge of the charging power supply can be prevented, it is possible to prevent the MOSFETs constituting the power conversion circuit, the rectifier circuit, and the like from being damaged.
[Brief description of the drawings]
FIG. 1 is a diagram showing a switching power supply device according to an embodiment of the present invention.
FIG. 2 is a diagram showing input / output signal waveforms of each element in a control circuit when driving of a switching power supply device is started.
FIG. 3 is a diagram showing input / output signal waveforms of respective elements in a control circuit when driving of a switching power supply is stopped.
FIG. 4 is a diagram showing a conventional switching power supply device.
[Explanation of symbols]
10 Switching power supply circuit 11 Control circuit 12 Control circuit 13 Control circuit 13-1 Comparator 13-2 Comparator 13-3 Comparator 13-4 Amplifier 13-5 AND circuit 13-6 AND circuit 13-7 AND circuit 13-8 Reference signal generation Unit 14 Soft start circuit 14-1 Constant current source 14-2 Capacitor 14-3 Resistance 14-4 Switch 40 Switching power supply circuit 41 Power supply 42 Full bridge circuit 43 Transformer 44 Synchronous rectification circuit 45 Coil 46 Capacitor 47 Battery

Claims (3)

A power conversion circuit that includes a first switching element, and converts power of an input power supply into a predetermined power in accordance with ON / OFF of the first switching element;
A first control circuit for controlling on / off of the first switching element;
A rectifier circuit including a second switching element, rectifying the power converted by the power conversion circuit, and charging the rectified power to a power supply as a load;
A second control circuit for controlling on / off of the second switching element;
A third control circuit that controls driving start or driving stop of the first and second control circuits;
With
The third control circuit starts driving the second control circuit after starting driving the first control circuit, and stops driving the first control circuit after stopping driving the second control circuit. A switching power supply, wherein driving of a control circuit is stopped. The switching power supply device according to claim 1,
The third control circuit includes:
When the switching power supply is started, the voltage value gradually increases, and when the switching power supply stops, a step-up / down circuit that outputs a voltage whose voltage value gradually decreases,
When the voltage value of the voltage output from the step-up / step-down circuit rises above a first reference voltage value, the driving of the first control circuit is started, and the voltage value of the voltage output from the step-up / step-down circuit becomes A first comparison circuit that stops driving the first control circuit when the voltage drops below a first reference voltage value;
When the voltage value of the voltage output from the step-up / step-down circuit rises above a second reference voltage value, the driving of the second control circuit is started, and the voltage value of the voltage output from the step-up / step-down circuit becomes A second comparison circuit that stops driving the second control circuit when the voltage drops below a second reference voltage value;
With
The switching power supply device, wherein the second reference voltage value is higher than the first reference voltage value. The switching power supply device according to claim 1,
A soft start circuit that gradually increases or decreases the on-time of each of the first switching element and the second switching element according to the amount of charge charged to the capacitor;
The switching power supply device according to claim 3, wherein the third control circuit starts or stops driving the first and second control circuits based on an amount of charge charged in the capacitor.

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