Switching power supply device

Abstract

The invention provides a switching power supply device which reduces output voltage fluctuation generated in an operation state in which a normal driving mode and an intermittent driving mode frequently change. This switching power supply device is provided with: a DC / DC converter having a switching circuit for performing power conversion by input / output; and a pulse signal generation unit that generates a pulse signal for driving a switching element of the switching circuit such that any one of the voltage, current, and power of the DC / DC converter becomes a predetermined target value, the switching power supply device has a normal driving mode in which a switching pulse is repeated at a constant interval in accordance with predetermined threshold values of parameters relating to the operating state of the switching power supply device, and an intermittent driving mode in which the switching pulse is divided at a predetermined division rate, and a plurality of predetermined threshold values are set. A plurality of intermittent driving modes are prepared, and any one of the plurality of intermittent driving modes having different division rates is selected according to a plurality of threshold values.

Description

Technical Field

[0001] The present invention relates to a switching power supply device capable of operating in an intermittent drive mode of switching pulses. Background Art

[0002] In order to reduce the loss of a switching power supply device during light load, a switching power supply device capable of operating in an intermittent drive mode of switching pulses is known. For example, Patent Document 1 discloses a switching power supply device that can perform an operation of intermittently driving switching pulses depending on the load state.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-129482

[0004] The intermittent drive mode of switching pulses is a mode for reducing switching losses associated with the operation of a switching power supply device during light load, and is an operation method called burst mode (registered trademark) in which switching pulses are intermittently driven. Compared with the normal drive mode in which switching pulses are not intermittent, the intermittent drive mode, which is a method of reducing the switching frequency under specified threshold conditions, also helps to reduce switching noise.

[0005] However, in an operating state where the normal drive mode and the intermittent drive mode frequently change around the threshold value, the output voltage fluctuation of the converter becomes large. A state of large output voltage fluctuation may cause adverse effects such as malfunction of electronic devices connected to the subsequent stage. In addition, the output voltage fluctuation here does not refer to the switching fluctuation generated corresponding to the period of the switching operation, but refers to the fluctuating voltage generated corresponding to the mode change and generated during a period longer than the switching period. Summary of the Invention

[0006] The present invention has been completed in view of such circumstances, and an object thereof is to provide a switching power supply device that reduces output voltage fluctuations generated in an operating state where the normal drive mode and the intermittent drive mode frequently change.

[0007] In order to achieve such an object, the technical solution of the present invention is a switching power supply device having at least the following structure.

[0008] A switching power supply device includes: a DC / DC converter having a switching circuit for power conversion through input / output; and a pulse signal generation unit that generates a pulse signal for driving a switching element of the switching circuit such that any one of the voltage, current, and power of the DC / DC converter becomes a predetermined target value. The switching power supply device is characterized in that it has a normal driving mode and an intermittent driving mode. The normal driving mode is a mode in which switching pulses are repeated at a constant interval according to a specified threshold value of a parameter related to the operating state of the switching power supply device. The intermittent driving mode is a mode in which the switching pulses are intermittently removed at a specified intermittent rate. A plurality of the specified threshold values are set, and a plurality of the intermittent driving modes are also prepared. Any one of the plurality of intermittent driving modes with different intermittent rates is selected according to the plurality of threshold values.

[0009] Here, the "intermittent rate" refers to the ratio of the number of switching pulses after intermittent removal to the number of original switching pulses within the repetition period.

[0010] By having such a feature, according to the present invention, it is possible to reduce the output voltage fluctuation generated in an operating state where the normal driving mode and the intermittent driving mode frequently change. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a circuit diagram of the DC / DC converter included in the switching power supply device according to an embodiment of the present invention.

[0012] Figure 2 is a system configuration diagram of the microcomputer control device included in the switching power supply device according to an embodiment of the present invention.

[0013] Figure 3 is a conceptual block diagram for explaining the case of generating a PWM signal in the microcomputer control device.

[0014] Figure 4 is a graph showing the characteristics of the duty ratio in the DC / DC converter with respect to the output current.

[0015] Figure 5 is a graph showing the operating waveforms in a state where the normal driving mode and the intermittent driving mode frequently change in a conventional switching power supply device.

[0016] Figure 6 is a graph showing the operating waveforms in a state where the intermittent driving mode in a region where the intermittent rate is set to 33% and the intermittent driving mode in a region where the intermittent rate is set to 50% frequently change in the switching power supply device according to an embodiment of the present invention.

[0017] Figure 7It is an explanatory diagram conceptually showing the mode transition in the switching power supply device according to an embodiment of the present invention and the mode transition in the switching power supply device as the prior art.

[0018] Reference numeral description

[0019] A: Microcomputer control device; 1: AD conversion unit; 2: Duty ratio calculation unit; 3: PWM signal output unit; 4: Frequency change unit; 5: Storage unit. Specific embodiments

[0020] Hereinafter, examples of embodiments of the switching power supply device of the present invention will be described based on the drawings. However, the following drawings are made for the purpose of explanation, and for ease of understanding, parts that are not required in the explanation are sometimes intentionally not shown. In addition, for the purpose of explanation, parts are sometimes intentionally shown large or small, and the drawings do not represent an accurate scale. In the following description, the same reference numerals in different drawings denote parts having the same function, and repeated explanations in each drawing are appropriately omitted.

[0021] <Embodiment>

[0022] (Structure of switching power supply device)

[0023] Figure 1 It is a circuit diagram of an example of a DC / DC converter included in the switching power supply device according to an embodiment of the present invention. As Figure 1 shown, the DC / DC converter is generally a full-bridge converter composed of a switching circuit, a transformer circuit, and a rectifying and smoothing circuit. The gate of the MOSFET in the switching circuit is input with a PWM (Pulse Width Modulation) control signal generated by a digital controller described later, and the switching power supply device performs switching control based on the PWM control method. In addition, Figure 1 the DC / DC converter shown is an example. As the type of the DC / DC converter, it can be a half-bridge converter, or a non-isolated synchronous rectification type converter. As long as a switching power supply device capable of performing PWM control can be constructed, an appropriate converter can be adopted.

[0024] Figure 2 It is a system configuration diagram of a microcomputer control device as a digital controller. Figure 3 It is a conceptual block diagram for explaining the case of generating a PWM signal in the microcomputer control device. The microcomputer control device A has an AD conversion unit 1, a duty ratio calculation unit 2, a PWM signal output unit 3, a frequency change unit 4, and a storage unit 5. The AD conversion unit 1 is input with a monitoring signal from a control object, such as the value of the output voltage. The duty ratio is calculated based on the value of the monitored signal after AD conversion, and a PWM control signal is generated. Specifically, as Figure 3As shown, the difference between the monitored output voltage and the target voltage is obtained by feedback control, and an appropriate duty ratio is obtained such that the difference becomes zero. A PWM control signal based on this duty ratio is output from the PWM signal output unit 3 and input to the switching circuit of the DC / DC converter. In addition, as the digital controller, it may not be a microcomputer but may be constructed by an FPGA, ASIC, etc. Further, the monitored signal to be controlled may not be the monitored voltage but may be the monitored current or power.

[0025] In the switching power supply device according to the embodiment of the present invention, when the duty ratio is lower than a specified threshold value, it changes from the normal drive mode to the intermittent drive mode. Here, if the mode change is frequently performed between the normal drive mode and the intermittent drive mode, it becomes a major cause of increased fluctuations. However, as long as the method of setting a threshold value for mode change is adopted, this problem cannot be essentially avoided. Therefore, in the switching power supply device according to the embodiment of the present invention, a plurality of specified threshold values are set, and a plurality of intermittent drive modes are also set. That is, a plurality of intermittent modes with different duty ratios are selected according to the plurality of threshold values. For example, the duty ratio is selected as shown in [Table 1].

[0026] [Table 1]

[0027] Duty cycle condition Operation mode Intermittent mode Duty cycle ≥ 10% Normal drive operation (intermittent rate 0%) None 7% ≤ Duty cycle < 10% Intermittent drive operation · Intermittent rate 10% 0111111111 4% ≤ Duty cycle < 7% Intermittent drive operation · Intermittent rate 25% 0111 Duty cycle < 4% Intermittent drive operation · Intermittent rate 33% 011

[0028] Regarding the notation of the duty mode in [Table 1], O indicates that the pulse is duty-cycled, and 1 indicates that it is not duty-cycled. In addition, the relationship between the duty ratio and the duty mode shown in Table 1 is stored in the storage unit 5. When the duty ratio is less than 10%, the selected duty mode is transmitted to the PWM signal output unit 3, and a PWM control signal for intermittent drive operation is generated.

[0029] The switching power supply device according to the embodiment of the present invention determines whether it is in a state where the connected device is operating and the current is larger than that in the light load state and a state where most of the connected devices are not operating and intermittent drive operation should be performed under normal load according to the duty ratio when generating the PWM control signal. Using the duty ratio created inside the microcomputer control device means that no special monitoring function is required, so the circuit structure becomes simple.

[0030] The switching power supply device can be configured to determine the load rate by monitoring the load current. However, in such a configuration, the switching power supply device needs to have a current sensor. When the current error is large under light load, although it should be transferred to the intermittent drive mode, it may not be possible to appropriately perform the mode change. As described above, in the switching power supply device according to the embodiment of the present invention, the duty ratio is automatically determined according to the deviation between the monitored output voltage and the target voltage. As Figure 4As shown, the DC / DC converter has a region called discontinuous conduction mode, in which the duty ratio gradually decreases as the current decreases, but at a certain current value, the duty ratio decreases sharply. According to this property, the switching power supply device can determine whether it is in a light load state even without a sensor for detecting the load current. Thus, the device structure of the switching power supply device according to an embodiment of the present invention having a function of calculating the duty ratio is simple, and there is no malfunction in the mode transition during light load caused by current sensor error, which is advantageous. However, the present invention does not exclude the method of providing a sensor to monitor the load current.

[0031] (Output waveform of switching power supply device)

[0032] Figure 5 is a graph showing the operation waveforms in a state where the normal drive mode and the intermittent drive mode frequently transition in an existing switching power supply device. From the top, the situation of the change in the duty ratio, the output voltage waveform, and the switching pulse waveform are shown. The dashed line in the middle of the change in the duty ratio represents the mode transition threshold between the normal drive mode and the intermittent drive mode. The dashed line in the middle of the output voltage waveform represents the target voltage. In addition, since the change in the duty ratio is automatically generated inside the microcomputer through feedback control, in Figure 5 , the change in the duty ratio becomes an image diagram, but the waveforms of the output voltage and the switching pulse are measured values.

[0033] Used in Figure 5 The four regions labeled (1) to (4) in the shown switching pulse waveform are used to explain the behavior of the duty ratio. In the region (1), the duty ratio is above the mode transition threshold, so it is the normal drive mode, and to increase the output voltage smaller than the target value, the duty ratio increases. In the region (2), the duty ratio is also above the mode transition threshold, so although it is the normal drive mode, to decrease the output voltage larger than the target value, the duty ratio decreases. In the region (3), the duty ratio is less than the mode transition threshold, so it is the intermittent drive mode, and to decrease the output voltage larger than the target value, the duty ratio decreases. In the region (4), the duty ratio is also less than the mode transition threshold, so although it is the intermittent drive mode, to increase the output voltage smaller than the target value, the duty ratio increases. Due to the duty ratio showing such behavior, there are output voltage fluctuations of a non-negligible magnitude in the output voltage.

[0034] Figure 6 is a graph showing the operation waveforms in a state where the intermittent drive mode with a duty cycle set to 33% and the intermittent drive mode with a duty cycle set to 50% frequently transition in the switching power supply device according to an embodiment of the present invention. In addition, Figure 6 The output voltage in Figure 5displayed with the same resolution scale of the output voltage. Additionally, in Figure 6 the change in the duty ratio is an image diagram, and the waveforms of the output voltage and the switching pulse are measured values, which is also the same as Figure 5 The behavior of the duty ratio near the threshold value forming the boundary between the 33% duty cycle and the 50% duty cycle is qualitatively the same as the behavior of (1) to (4) described using Figure 5 However, since Figure 5 and Figure 6 are displayed with the same resolution scale, it can be seen that the output voltage fluctuation becomes extremely small.

[0035] However, Figure 6 only one scenario of the behavior in the switching power supply device of the embodiment of the present invention is taken out to verify the effect of reducing the output fluctuation voltage. That is, as shown on the left side of Figure 7 In the switching power supply device of the embodiment of the present invention, multiple intermittent drive modes are prepared, and any one of the multiple intermittent drive modes with different duty cycles is selected according to multiple threshold values. Figure 6 The state of switching back and forth between two specific intermittent drive modes is verified. On the other hand, as shown on the right side of Figure 7 Figure 5 is a diagram verifying the state of switching back and forth between the normal drive mode and the intermittent drive mode in the prior art with only one intermittent drive mode. Comparing Figure 6 and Figure 5 It is easy to understand from the comparison results that in order to reduce the change amount of the duty cycle, by setting the duty cycle to increase stepwise as the duty ratio decreases, the output voltage fluctuation can be reduced. At this time, the relationship between the duty cycle and the duty ratio can be freely set. That is, no matter how the relationship is set, as long as the change amount of the duty cycle between adjacent modes is made smaller by setting it to be a stepwise change, the desired effect can be obtained.

[0036] As described above, the switching power supply device according to the embodiments of the present invention has been described in detail. However, the specific structure is not limited to these embodiments, and design changes and the like within the scope not departing from the gist of the present invention are also included in the present invention. For example, in the embodiments, the determination of whether it is a light load is configured not to require a special sensor but to be based on the duty ratio generated in the microcomputer control device. However, a current sensor may be provided to monitor the load current, or control may be performed by an analog control circuit. However, in the case of being constituted by an analog control circuit, a special unit for monitoring the duty ratio needs to be provided. As described in this specification, the present invention is not based on the type of DC / DC converter or the difference in the feedback control method, and it should be correctly recognized that it is based on the following technical idea: on the basis of setting an intermittent drive operation mode that generates output voltage fluctuations, setting a plurality of thresholds for mode transition, and preparing a plurality of operation modes with different duty ratios, thereby reducing the output fluctuation voltage.

Claims

1. A switching power supply device, comprising: A DC / DC converter having a switching circuit for power conversion through input / output; and A pulse signal generation unit that generates a pulse signal for driving a switching element of the switching circuit so that any one of the voltage, current, and power of the DC / DC converter becomes a predetermined target value. It is characterized in that The switching power supply device has a normal driving mode and an intermittent driving mode. The normal driving mode is a mode in which switching pulses are repeated at a constant interval according to a specified threshold value of a parameter related to the operating state of the switching power supply device. The intermittent driving mode is a mode in which switching pulses are intermittently removed at a specified intermittent rate. A plurality of the specified threshold values are set. A plurality of the intermittent driving modes are also prepared, and any one of the plurality of intermittent driving modes with different intermittent rates is selected according to the plurality of threshold values.

2. The switching power supply device according to claim 1, characterized in that The parameter is the current flowing in the switching power supply device.

3. The switching power supply device according to claim 1, characterized in that The parameter is the duty ratio of the switching pulse.

4. The switching power supply device according to claim 2 or 3, characterized in that The pulse signal generation unit is a digital controller. The digital controller calculates the duty ratio required for the operation of the switching power supply device and generates a desired pulse signal through pulse width modulation control.

5. The switching power supply device according to claim 4, characterized in that The digital controller has a table storing the intermittent rate corresponding to the parameter, and generates a pulse signal at the intermittent rate determined by referring to the table.

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