Switching power supply device

Abstract

To provide a switching power supply device capable of improving response characteristics at startup.SOLUTION: A switching power supply device includes a DC-DC converter and a pulse signal generating unit that generates a pulse signal for driving a switch element of a switching circuit such that one of the voltage, current, or power thereof reaches a predetermined target value, and the pulse signal generating unit checks whether the initial voltage of a constant voltage load connected to the output terminal of the switching power supply device exceeds a predetermined threshold before startup, starts up in a first switching mode when it does not exceed the threshold, and starts up in a second switching mode when it does exceed the threshold, and the pulse signal generating unit monitors the output voltage during normal use after startup, and controls in the first switching mode when the output voltage is equal to or lower than the predetermined threshold, and controls in the second switching mode when the output voltage exceeds the predetermined threshold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a switching power supply device that operates by combining a plurality of switching methods. [Background technology]

[0002] Switching power supply devices that operate by combining multiple switching methods are known. For example, Patent Document 1 describes a switching power supply device that can switch between pulse width modulation control (PWM control) and pulse frequency modulation control (PFM control). Also, Patent Document 2 describes an LLC converter that first starts in PWM mode and then changes to resonant mode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-209180 [Patent Document 2] Special Publication No. 2013-516955 Summary of the Invention [Problem to be solved by the invention]

[0004] An example of a switching power supply that switches between switching methods is the LLC converter, which, as its name suggests, has two coils and one capacitor. It is a DC-DC converter that is capable of soft switching with little noise due to the current resonance phenomenon caused by these elements. LLC converters control the output voltage using the frequency of the switching pulse. They are basically pulse frequency modulation (PFM) converters, but can also operate using pulse width modulation (PWM) under certain conditions. By switching between pulse width modulation (PWM) and pulse frequency modulation (PFM) control, the LLC converter can expand its output gain range. Note that output gain is an index corresponding to the voltage, current, and power output by the DC-DC converter, and there is a direct correlation between the output gain and each output amount. However, at startup, operation is first initiated using the PWM control method, so it takes time for the DCDC output to be able to output a voltage higher than the battery voltage, and it takes a long time to reach the target value.

[0005] The present invention has been made in view of the above circumstances, and its object is to provide a switching power supply device that operates by combining a plurality of switching methods, and that can reduce the time it takes for the electrical quantity to be controlled, such as voltage, current, or power, to reach a target value, and can improve the response characteristics at startup. [Means for solving the problem]

[0006] In order to achieve this object, the technical means according to the present invention is a switching power supply device having at least the following configuration.

[0007] A switching power supply includes a DC-DC converter with a switching circuit for power conversion between input and output, and a pulse signal generator that generates a pulse signal to drive a switch element of the switching circuit so that one of the voltage, current, or power of the DC-DC converter reaches a predetermined target value. The pulse signal generator has a first switching mode and a second switching mode as pulse generation modes. The pulse signal generator checks whether the initial voltage of a constant-voltage load connected to the output terminal of the switching power supply exceeds a predetermined threshold before startup. If the initial voltage does not exceed a predetermined threshold, the switching power supply starts in the first switching mode. If the initial voltage exceeds a predetermined threshold, the switching power supply starts in the second switching mode. The pulse signal generator monitors the output voltage during normal operation after startup, and controls the power supply in the first switching mode if the output voltage is below the predetermined threshold, and controls the power supply in the second switching mode if the output voltage exceeds the predetermined threshold. Here, the "pulse signal generator" can be implemented, for example, by a digital controller such as a microcomputer. The "predetermined threshold" need not necessarily be a fixed value, as long as it can be determined by any suitable method. [Effects of the Invention]

[0008] By virtue of these characteristics, the present invention can reduce the time required to reach the target voltage and improve the response characteristics at startup in a switching power supply device that operates using a combination of multiple switching methods. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a circuit diagram of a DC-DC converter included in a switching power supply device according to a first embodiment of the present invention. [Figure 2] 3 is a graph showing waveforms and the like applied to switch inputs of a DC-DC converter included in the switching power supply device according to the first embodiment of the present invention. [Figure 3]5 is a graph illustrating the response characteristics of the switching power supply device according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a circuit diagram of a DC-DC converter included in a switching power supply device according to a second embodiment of the present invention. [Figure 5] 6 is a graph showing waveforms and the like applied to switch inputs of a DC-DC converter included in a switching power supply device according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an example of an embodiment of a switching power supply device according to the present invention will be described with reference to the drawings. However, the drawings have been created for the purpose of explanation, and for the sake of clarity, components unnecessary for the explanation may not be shown. In the following description, the same reference numerals in different drawings indicate parts with the same function, and duplicated explanations in each drawing will be omitted as appropriate.

[0011] First Embodiment (Configuration of switching power supply unit) FIG. 1 is a circuit diagram of an example of a DC-DC converter included in a switching power supply device according to a first embodiment of the present invention. As shown in FIG. 1, the DC-DC converter is a half-bridge LLC converter generally composed of a power switch, a resonant circuit, a transformer, and a rectifying / smoothing circuit. A control signal generated by a digital controller (not shown) is input to the gate of the MOSFET in the switch circuit, and the switching power supply device performs switching control using a PFM control method or a PWM control method. Note that the DC-DC converter shown in FIG. 1 is merely an example, and the type of DC-DC converter may be a full-bridge converter, and the topology is not limited. Any suitable converter can be used as long as it can be configured to operate by switching between multiple switching methods.

[0012] As shown in Figure 1, a DC power supply, for example, a 300V lithium-ion battery, is connected to the input side of the DC-DC converter, and a battery, for example, a 12V lead battery, which acts as a constant voltage load, is connected to the output side of the DC-DC converter, with a monitor circuit for detecting the current I0 and voltage V0 interposed as appropriate. Note that the constant voltage load may be other means capable of storing voltage, such as a lithium-ion capacitor, in addition to a battery.

[0013] The digital controller (not shown) is programmed to check whether the initial voltage of the constant-voltage load detected by the monitor circuit exceeds a predetermined threshold before starting switching control, and if it does not exceed the threshold, start up using PWM control, and if it does exceed the threshold, start up using PFM control. The digital controller is also programmed to monitor the output voltage during normal use after startup of the switching power supply, and control using PWM control if the output voltage is below the predetermined threshold, and control using PFM control if the output voltage exceeds the threshold. The digital controller can be a microcomputer, FPGA, ASIC, or other suitable device.

[0014] FIG. 2 is a graph showing waveforms applied to the switch input of the DC-DC converter included in the switching power supply device according to the first embodiment of the present invention. In the PFM region shown on the left, as indicated by the switching pulse waveform, the duty ratio is 1, control is performed at a low switching frequency, and the detected voltage and current are large. While the graph is for a fixed frequency, qualitatively, the output gain decreases as the switching frequency increases. Note that the duty cycle in the graph represents an internal value of the digital controller. In this example, when the duty cycle is 1, the ON duty cycle of the pulse signal applied to the gate terminal of the MOSFET is set to 0.5. Unless otherwise specified, the duty cycle values will be described below using the internal values of the digital controller. In the PWM region shown on the right, as the switching pulse waveform shows, the duty ratio is set to less than 0.5, while the switching frequency is controlled at a high level, resulting in small detected voltages and currents. The graph shows a fixed duty ratio, but qualitatively, as the duty ratio decreases, the output gain also decreases.

[0015] (Output waveform of switching power supply) One of the features of the switching power supply according to the first embodiment of the present invention is that it performs startup using the PFM control method when the initial voltage of the constant voltage load detected by the monitor circuit exceeds a predetermined threshold before starting switching control. The contribution of this feature to the response characteristics of the switching power supply at startup will now be described. Figure 3 is a graph illustrating the response characteristics, etc., of the switching power supply according to the first embodiment of the present invention. From the top, the waveforms of the first embodiment and the conventional technology are shown for comparison with respect to changes in duty ratio, switching frequency, output voltage, and output current. Regarding the duty ratio, in the prior art shown by the dotted line, as shown by the waveform of the duty ratio change, in the first half region, control is performed in the "PWM region" where the duty ratio gradually increases from 0.0 to 1.0. On the other hand, in the first embodiment shown by the solid line, control is performed in the "PFM region" over the entire region under the condition that the initial voltage of the constant voltage load detected by the monitor circuit exceeds a predetermined threshold, so the duty ratio is 1.0 over the entire region. Regarding the switching frequency, in the prior art shown by the dotted line, control is performed in the "PWM region" in the first half region, so the switching frequency is constant, and the switching frequency gradually decreases in the second half region. On the other hand, in the first embodiment shown by the solid line, control is performed in the "PFM region" where the switching frequency gradually decreases immediately after startup, under the condition that the initial voltage of the constant voltage load detected by the monitor circuit exceeds a predetermined threshold. As can be seen from the waveforms of the output voltage change and the output current change, the first embodiment shown at the top significantly reduces the time it takes to reach the output target value compared to the conventional technology shown at the bottom. As described above, LLC converters that switch switching modes generally operate using pulse frequency modulation (PFM) control, but also pulse width modulation (PWM) control under certain conditions. As the switching frequency increases, the output gain becomes difficult to reduce at a certain point. After that point, the output gain is reduced using PWM control, for example, using a digital controller. Considering this as the reverse of the startup process, PWM control is performed first, followed by a switch to PFM control. However, if the output target is known to be high, slowly increasing the output gain using PWM control is a waste of time. Therefore, in the first embodiment, the initial voltage of the constant-voltage load detected by a monitor circuit is monitored. If the initial voltage is higher than a predetermined threshold, the digital controller switches to PFM control from the beginning.

[0016] So far, we have used a 300V lithium-ion input voltage as an example. However, because it is a battery, voltage variations are inevitable. Generally, in a DC-DC converter, if the switching mode control variables, such as the switching frequency and duty ratio, remain the same, the absolute value of the output voltage also increases as the input voltage increases. As mentioned above, there are limitations on the switching mode control variables, such as the fact that increasing the switching frequency makes it difficult for the output gain to decrease. Therefore, it is preferable to set a different threshold value for the output voltage that determines the switching point between the first and second switching modes depending on the input voltage. Therefore, it is recommended to provide a table containing information on threshold values appropriate for different input voltages, and configure the digital controller to control the digital controller based on that information. Of course, methods other than tables can be used, such as formulas.

[0017] Second Embodiment (Configuration of switching power supply unit) Fig. 4 is a circuit diagram of an example of a DC-DC converter included in a switching power supply according to a second embodiment of the present invention. As shown in Fig. 4, the DC-DC converter is a dual active bridge (DAB) converter in which bridge circuits are provided on the primary and secondary sides of a transformer. Control signals generated by a digital controller (not shown) are input as first and second pulses to the gates of the MOSFETs in the switch circuits on the primary and secondary sides, respectively, and the switching power supply performs switching control in a pulse width modulation mode that involves changing the pulse width applied to the switch elements or in a pulse width modulation mode that involves a phase shift between the bridge circuits.

[0018] Before starting switching control, a digital controller (not shown) checks whether the initial voltage of the constant-voltage load detected by the monitor circuit exceeds a predetermined threshold. If the initial voltage does not exceed the predetermined threshold, the digital controller starts the switching power supply in a pulse-width modulation mode that changes the pulse width applied to the switching elements. If the initial voltage exceeds the predetermined threshold, the digital controller starts the switching power supply in a pulse-width modulation mode that changes the pulse width applied to the switching elements. If the output voltage exceeds the predetermined threshold, the digital controller controls the switching power supply in a pulse-width modulation mode that changes the pulse width applied to the switching elements. If the output voltage exceeds the predetermined threshold, the digital controller controls the switching power supply in a pulse-width modulation mode that changes the pulse width applied to the switching elements. The digital controller can be a microcomputer, FPGA, ASIC, or other suitable device.

[0019] 5 is a graph showing waveforms applied to the switch input of the DC-DC converter included in the switching power supply device according to the second embodiment of the present invention. In the graph of the switching pulse waveform shown on the left, the double-headed arrow indicates that the pulse width is changed. In the graph of the switching pulse waveform shown on the right, the single-headed arrow indicates that a phase difference is applied to the switches between the bridge circuits. As the waveforms of the output voltage and output current show, it can be seen that control in pulse-width modulation mode with a phase shift between the bridge circuits provides a greater output gain than control in pulse-width modulation mode with a change in the pulse width applied to the switching elements. This relationship is the same as the relationship between PFM control and PWM control in the first embodiment. When starting up in pulse-width modulation mode with a change in the pulse width applied to the switching elements, the response characteristics are limited, as in the first embodiment. Therefore, if the initial voltage of the constant-voltage load detected by the monitor circuit exceeds a predetermined threshold, control is performed in pulse-width modulation mode with a phase shift between the bridge circuits from the beginning of startup, thereby improving the response characteristics.

[0020] Although the switching power supply according to the embodiments of the present invention has been described above in detail, the specific configuration is not limited to these embodiments, and design modifications within the scope of the present invention are also included. For example, in the embodiments, the predetermined threshold is described as varying depending on the input voltage. However, the change condition is not limited to the input voltage and may be changed in reference to other characteristic quantities. Furthermore, in addition to the examples described in the first and second embodiments, the first and second switching modes may be pulse density modulation (PDM) or pulse amplitude modulation (PAM). Any combination can be adopted as long as two switching modes with different amounts of change relative to the output gain are combined to increase the output gain. It should be properly recognized that the present invention is based on the technical idea that, based on the premise that the switching power supply has a first switching mode and a second switching mode to increase the output gain, if the initial voltage of a constant-voltage load connected to the output terminal of the switching power supply exceeds a predetermined threshold before startup, the switching power supply is started in the second switching mode, thereby increasing the output gain and improving response characteristics.

Claims

1. a DC-DC converter including a switching circuit for performing power conversion at input and output; a pulse signal generating unit that generates a pulse signal for driving a switch element of the switching circuit so that any one of a voltage, a current, and a power of the DC-DC converter reaches a predetermined target value, The pulse signal generating unit has a first switching mode and a second switching mode as pulse generation modes, the pulse signal generating unit checks whether an initial voltage of a constant voltage load connected to an output terminal of the switching power supply device exceeds a predetermined threshold before startup, and performs startup in a first switching mode if the initial voltage does not exceed the predetermined threshold, and performs startup in a second switching mode if the initial voltage exceeds the predetermined threshold; The pulse signal generating unit monitors the output voltage during normal use after startup, and controls in a first switching mode when the output voltage is equal to or less than the predetermined threshold, and controls in a second switching mode when the output voltage exceeds the predetermined threshold. A switching power supply device characterized by:

2. The first switching mode is a pulse width modulation mode, and the second switching mode is a pulse frequency modulation mode.

2. The switching power supply device according to claim 1.

3. The first switching mode is a pulse width modulation mode involving varying the pulse width applied to a switch element, and the second switching mode is a pulse width modulation mode involving a phase shift between legs of a bridge circuit.

2. The switching power supply device according to claim 1.

4. The predetermined threshold value varies depending on the voltage on the input side of the switching power supply device.

2. The switching power supply device according to claim 1.

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