Switching power supply device

Abstract

To provide a switching power supply device with reduced output voltage ripples to be generated in an operation state in which a normal drive mode and an intermittent drive mode frequently transit.SOLUTION: A switching power supply device comprises a microcomputer controller comprising: a DC / DC converter with a switching circuit for converting power; and a pulse signal generation unit which generates a pulse signal for driving the switching circuit so that any one of voltage, current, and power of the DC / DC converter becomes a predetermined target value, has a normal drive mode in which switching pulses are repeated at fixed intervals and intermittent drive modes in which the switching pulses are thinned at predetermined thinning ratio according to predetermined thresholds of a parameter regarding an operation state of the switching power supply device, wherein a plurality of predetermined thresholds are set, a plurality of intermittent drive modes are also prepared, and any of the plurality of intermittent drive modes with different thinning ratio is selected according to the plurality of thresholds.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a switching power supply device operable 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 operable in an intermittent drive mode of switching pulses is known. For example, Patent Document 1 describes a switching power supply device that enables an operation of thinning out switching pulses and driving them depending on the load state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[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, also called so-called burst mode (registered trademark), in which switching pulses are thinned out and operated. The intermittent drive mode, which is a method of reducing the switching frequency under predetermined threshold conditions with respect to the normal drive mode in which switching pulses are not thinned out, also contributes to reducing switching noise. However, in operating conditions where there are frequent transitions between normal drive mode and intermittent drive mode around the threshold, the converter's output voltage ripple becomes large. Large output voltage ripple can have adverse effects, such as causing malfunctions in electronic devices connected downstream. Note that the output voltage ripple here does not refer to the switching ripple that occurs in response to the switching operation cycle, but rather to the ripple voltage that occurs in response to mode transitions and that occurs for a period longer than the switching cycle.

[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 reduces output voltage ripple that occurs in an operating state in which there are frequent transitions between normal drive mode and intermittent drive mode. [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 device comprising: a DC / DC converter with a switching circuit for converting power between input and output; and a pulse signal generating unit that generates a pulse signal for driving 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 switching power supply device having a normal drive mode in which switching pulses are repeated at regular intervals according to a predetermined threshold value for a parameter related to the operating state of the switching power supply device; and an intermittent drive mode in which the switching pulses are thinned out at a predetermined thinning rate, with a plurality of predetermined threshold values being set and a plurality of intermittent drive modes being prepared, and one of a plurality of intermittent drive modes with different thinning rates being selected according to the plurality of threshold values. Here, the "thinning-out rate" means the ratio of the number of thinned-out switching pulses to the original number of switching pulses within a repetition period. [Effects of the Invention]

[0008] By having such characteristics, according to the present invention, it is possible to reduce the output voltage ripple generated in an operating state where the normal drive mode and the intermittent drive mode frequently transition.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0010] Hereinafter, an example of an embodiment of the switching power supply device according to the present invention will be described with reference to the drawings. However, the following drawings are created for the purpose of explanation, and in some cases, members unnecessary for the explanation may not be intentionally illustrated for clarity. Also, for the purpose of explanation, members may be intentionally illustrated larger or smaller, and the drawings do not show the exact scale. In the following description, the same reference numerals in different figures indicate parts having the same function, and duplicate descriptions in each figure are omitted as appropriate.

[0011] <Embodiment> (Configuration of the Switching Power Supply Device) FIG. 1 is a circuit diagram as an example of a DC / DC converter included in the switching power supply device according to an embodiment of the present invention. As shown in FIG. 1, the DC / DC converter is generally a full-bridge converter composed of a switch circuit, a transformer circuit, and a rectifying and smoothing circuit. A PWM control signal generated by a digital controller described later is input to the gate of the MOSFET of the switch circuit, and the switching power supply device performs switching control by the PWM control method. Note that the DC / DC converter shown in FIG. 1 is an example, and as the type of the DC / DC converter, a half-bridge converter may be used, or a non-isolated synchronous rectification type converter may be used. As long as a switching power supply device capable of performing PWM control can be constructed, an appropriate converter can be adopted as appropriate.

[0012] FIG. 2 is a system configuration diagram of a microcomputer control device as a digital controller. FIG. 3 is a conceptual block diagram for explaining how a PWM signal is generated in the microcomputer control device. The microcomputer control device A includes 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. A monitor signal from a control target, for example, a value of an output voltage, is input to the AD conversion unit 1. Based on the value of the AD-converted monitor signal, a duty ratio is calculated and a PWM control signal is generated. Specifically, as shown in FIG. 3, an appropriate duty ratio at which the difference between the monitored output voltage and the target voltage becomes zero is obtained by feedback control, and a PWM control signal based on the duty ratio is output from the PWM signal output unit 3 and input to the switch circuit of the DC / DC converter. Note that as the digital controller, instead of a microcomputer, it may be configured with an FPGA, an ASIC, or the like. Also, the monitor signal to be controlled may monitor not only voltage but also current or power.

[0013] The switching power supply device according to an embodiment of the present invention transitions from a normal drive mode to an intermittent drive mode when the duty ratio falls below a predetermined threshold value. Here, if frequent mode transitions occur between the normal drive mode and the intermittent drive mode, it becomes a major factor in increasing the ripple. However, as long as the method of setting a threshold value to cause mode transition is adopted, this problem cannot be essentially avoided. Therefore, the switching power supply device according to an embodiment of the present invention sets a plurality of predetermined threshold values and also sets a plurality of intermittent drive modes. That is, a plurality of intermittent modes with different thinning ratios are selected according to the plurality of threshold values. For example, as shown in [Table 1], a thinning ratio is selected.

Table 1

[0014] The switching power supply device according to the embodiment of the present invention determines whether the device is in a normal drive mode under normal load conditions, where the connected devices are operating and the current is higher than that of a light load, or in an intermittent drive mode under light load conditions, where most of the connected devices are not operating, based on the duty ratio used to generate the PWM control signal. The use of a duty ratio generated within the microcomputer control device means that no special monitoring function is required, and therefore the circuit configuration can be simplified.

[0015] It is possible to configure a switching power supply to determine the load factor by monitoring the load current. However, such a configuration requires the switching power supply to be equipped with a current sensor. Furthermore, if a current error is large under light load conditions, there is a risk that the mode transition will not be performed properly even when the intermittent drive mode should be selected. As described above, in the switching power supply according to the embodiment of the present invention, the duty ratio is automatically determined based on the deviation between the monitored output voltage and the target voltage. As shown in FIG. 4, the duty ratio of a DC / DC converter gradually decreases as the current decreases. However, the DC / DC converter has a region called discontinuous conduction mode, where the duty ratio suddenly decreases at a certain current value. This property allows the switching power supply to determine whether the load is light or not, even without a sensor for detecting the load current. Thus, the switching power supply according to the embodiment of the present invention, which has the function of calculating the duty ratio, has the advantages of a simple configuration and no malfunction of mode transition under light load conditions due to current sensor error. However, the present invention does not exclude the use of a sensor to monitor the load current.

[0016] (Output waveform from switching power supply) Figure 5 is a graph showing the operating waveforms of a conventional switching power supply in a state where it frequently transitions between normal drive mode and intermittent drive mode. From the top, the graph shows the change in duty ratio, the output voltage waveform, and the switching pulse waveform. The dotted line in the middle of the duty ratio change indicates the mode transition threshold between normal drive mode and intermittent drive mode. The dotted line in the middle of the output voltage waveform indicates the target voltage. Note that because the change in duty ratio occurs automatically within the microcontroller through feedback control, the change in duty ratio in Figure 5 is shown as an image, but the output voltage and switching pulse waveforms are actual measured values.

[0017] The behavior of the duty ratio will be explained using four regions labeled (1) to (4) in the switching pulse waveform shown in Figure 5. In region (1), the duty ratio is equal to or greater than the mode transition threshold, indicating normal drive mode. The duty ratio increases in an attempt to raise the output voltage, which is lower than the target value. In region (2), the duty ratio is equal to or greater than the mode transition threshold, indicating normal drive mode, but the duty ratio decreases in an attempt to lower the output voltage, which has become higher than the target value. In region (3), the duty ratio is less than the mode transition threshold, indicating intermittent drive mode, and the duty ratio decreases in an attempt to lower the output voltage, which is higher than the target value. In region (4), the duty ratio is less than the mode transition threshold, indicating intermittent drive mode, but the duty ratio increases in an attempt to raise the output voltage, which has become lower than the target value. When the duty ratio exhibits these behaviors, a non-negligible output voltage ripple occurs in the output voltage.

[0018] 6 is a graph showing operating waveforms in a switching power supply device according to an embodiment of the present invention, where the device frequently transitions between an intermittent drive mode in a region where the thinning rate is set to 33% and an intermittent drive mode in a region where the thinning rate is set to 50%. The output voltage in FIG. 6 is displayed on the same resolution scale as the output voltage in FIG. 5. Also, as in FIG. 5, FIG. 6 shows an image of the change in duty ratio, while the output voltage and switching pulse waveforms are actual measured values. The behavior of the duty ratio near the threshold value that forms the boundary between the 33% and 50% thinning rates is qualitatively the same as the behaviors (1) to (4) described using FIG. 5. However, since FIG. 5 and FIG. 6 are displayed on the same resolution scale, it can be seen that the output voltage ripple is significantly smaller. FIG. 6 illustrates the effect of reducing the output ripple voltage by extracting only one behavioral scenario of a switching power supply according to an embodiment of the present invention. Specifically, as shown on the left side of FIG. 7, the switching power supply according to an embodiment of the present invention has multiple intermittent drive modes, and one of the multiple intermittent drive modes with different thinning rates is selected according to multiple thresholds. FIG. 6 illustrates the state of switching between two specific intermittent drive modes. Meanwhile, FIG. 5 illustrates the state of switching between the normal drive mode and the intermittent drive mode in a conventional technology with only one intermittent drive mode, as shown on the right side of FIG. 7. Comparing the results of FIGS. 6 and 5, it is easy to see that the output voltage ripple can be reduced by gradually increasing the thinning rate as the duty ratio decreases in order to reduce the change in the thinning rate. In this case, the relationship between the thinning rate and the duty ratio can be freely set. Regardless of the relationship, the desired effect can be achieved as long as the change in the thinning rate between adjacent modes is reduced by gradually changing the thinning rate.

[0019] Although the switching power supply according to the present invention has been described in detail above, the specific configuration is not limited to these embodiments, and the present invention encompasses design modifications within the spirit and scope of the present invention. For example, in the embodiments, the determination of whether or not a light load is present is based on a duty ratio generated within a microcomputer control device without the use of a special sensor. However, a current sensor may be provided to monitor the load current, or control may be performed using an analog control circuit. However, if an analog control circuit is used, a special means for monitoring the duty ratio is required. As described herein, it should be properly recognized that the present invention is not based on the type of DC / DC converter or the feedback control method, but is based on the technical idea of reducing output ripple voltage by setting multiple thresholds for mode transition and providing multiple operating modes with different thinning rates, assuming that an intermittent drive operating mode in which output voltage ripple occurs is set. [Explanation of symbols]

[0020] A Microcomputer Control Device 1 AD conversion section 2 Duty ratio calculation section 3 PWM signal output section 4 Frequency change section 5 Storage section

Claims

1. A DC / DC converter including a switching circuit for performing power conversion by input and output, A pulse signal generation unit for generating a pulse signal for driving a switch 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, and a switching power supply device comprising: Depending on a predetermined threshold value for a parameter related to the operating state of the switching power supply device, it has a normal drive mode in which switching pulses are repeated at regular intervals and an intermittent drive mode in which switching pulses are thinned out at a predetermined thinning rate. A plurality of the predetermined threshold values are set. A plurality of the intermittent drive modes are also prepared, and any one of a plurality of intermittent drive modes with different thinning rates is selected according to a plurality of threshold values. A switching power supply device characterized by the above.

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

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

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

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

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