CN113424422A

CN113424422A - Switching power supply device

Info

Publication number: CN113424422A
Application number: CN201980091698.3A
Authority: CN
Inventors: 中村胜
Original assignee: Sanken Electric Co Ltd
Current assignee: Sanken Electric Co Ltd
Priority date: 2019-03-29
Filing date: 2019-03-29
Publication date: 2021-09-21
Anticipated expiration: 2039-03-29
Also published as: CN113424422B; WO2020202335A1; JPWO2020202335A1; JP7184168B2

Abstract

The present invention has: a voltage detection unit (1) that detects an output voltage and converts the detected output voltage into a digital value having a predetermined number of bits; a digital filter (4) that performs a predetermined operation based on an error between a target value and an output of the voltage detection unit; a drive unit (5) that drives the switching element at a predetermined duty ratio during a filter characteristic analysis period, and controls the main switching element at a duty ratio based on the calculation result of the digital filter after the filter characteristic analysis period ends; a current detection unit (6) that detects a current flowing through the inductor and outputs the detected current as a current detection signal; a filter characteristic analysis unit (7) that analyzes filter characteristics composed of the inductor and the output capacitor in accordance with a generation period of an inrush current that flows through the inductor during the filter analysis period, based on a current detection signal of the current detection unit; and a constant storage unit (8) having a plurality of digital filter constant tables in which a plurality of filter constants corresponding to a plurality of filter characteristics are stored, wherein, after the filter characteristic analysis period is completed, an appropriate filter constant is selected from the plurality of digital filter tables according to the filter characteristics, and supplied to the digital filter.

Description

Switching power supply device

Technical Field

The present invention relates to a switching power supply device applied to a non-insulated step-down chopper circuit or the like.

Background

As a method of generating a stable voltage lower than an input voltage, a non-insulated step-down chopper circuit is widely used. In particular, POL (Point of Load) module power is widely used in communication infrastructure and the like.

The module power supply has a control circuit, a power mosfet (power mosfet), and an inductor mounted on a single substrate. An output capacitor is added between the output terminal of the module and GND by the user, and the output capacitor value is adjusted. This makes it possible to suppress the output ripple voltage associated with the switching operation, and to adjust the output voltage to a variation within a standard range when the output load current fluctuates abruptly.

Generally, the larger the output capacitor value is adjusted, the less the output ripple voltage and the output voltage variation at load ramp. However, in the control circuit, the control constant of the digital filter is set so as to be able to perform a stable operation within an assumed range. Therefore, for example, when the output capacitor is increased more than supposed, the control band (crossover frequency) of the feedback control is decreased, and the response characteristic is degraded. Therefore, it is not possible to suppress the output voltage variation at the time of load sudden change as expected, and there is a problem that the operation becomes unstable due to insufficient phase margin at worst.

In contrast, the switching power supply device described in patent document 1 extracts the filter characteristic of the control target based on the fluctuation of the output voltage generated in the filter characteristic analysis period after the output voltage starts to increase and reaches the predetermined value after the power supply is started. The device analyzes the filter characteristics by comparing the extracted filter characteristics with a plurality of model frequency characteristics set in advance. Then, this apparatus can secure a wide operation range by automatically selecting a control constant (control response characteristic) of the digital filter corresponding to the model frequency characteristic.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 5925724

Disclosure of Invention

Problems to be solved by the invention

However, the model frequency characteristic of patent document 1 is optimized when the output voltage reaches the set voltage after the power supply has risen. Therefore, the filter characteristic analysis period must be set at a timing after the output voltage reaches the set voltage. Therefore, in a state where the output voltage immediately after the power supply is started is low, the filter characteristics cannot be analyzed, and the filter constant setting is not completed. Therefore, the feedback control becomes unstable during the rise period until the output voltage reaches the set voltage.

In this way, the switching power supply device of patent document 1 extracts the filter characteristic of the controlled object based on the fluctuation of the output voltage generated in the filter characteristic analysis period after the output voltage starts to rise and reaches the set voltage after the power supply is started, and sets the optimal control constant of the digital filter. Therefore, the control constant is not set completely during the rise period until the output voltage reaches the set voltage, and unstable operation occurs.

The invention provides a switching power supply device capable of preventing unstable operation in a rising period until an output voltage reaches a set voltage.

Means for solving the problems

In order to solve the above problem, a switching power supply device according to the present invention is a switching power supply device that turns on and off a switching element to convert a 1 st dc voltage supplied from a power supply into a 2 nd dc voltage via an inductor and an output capacitor and supply an output voltage to an output load, the switching power supply device including: a voltage detector that detects the output voltage and converts the detected output voltage into a digital value having a predetermined number of bits; a digital filter that performs a predetermined operation based on an error between a target value and an output of the voltage detection unit; a driving unit that drives the switching element at a predetermined duty ratio during a filter characteristic analysis period, and controls the main switching element at a duty ratio based on a calculation result of the digital filter after the filter characteristic analysis period ends; a current detection unit that detects a current flowing through the inductor and outputs the detected current as a current detection signal; a filter characteristic analysis unit that analyzes a filter characteristic including the inductor and the output capacitor in accordance with a generation period of an inrush current flowing through the inductor during the filter analysis period, based on a current detection signal of the current detection unit; and a constant storage unit having a plurality of digital filter constant tables in which a plurality of filter constants corresponding to a plurality of filter characteristics are stored, wherein after the filter characteristic analysis period is completed, an appropriate filter constant is selected from the plurality of digital filter tables according to the filter characteristic, and supplied to the digital filter.

Further, a switching power supply device according to the present invention is a switching power supply device that turns on and off a switching element to convert a 1 st dc voltage supplied from a power supply into a 2 nd dc voltage via an inductor and an output capacitor and supply an output voltage to an output load, the switching power supply device including: a voltage detector that detects the output voltage and converts the detected output voltage into a digital value having a predetermined number of bits; a digital filter that performs a predetermined operation based on an error between a target value and an output of the voltage detection unit; a driving unit that drives the switching element at a predetermined duty ratio during a filter characteristic analysis period, and controls the main switching element at a duty ratio based on a calculation result of the digital filter after the filter characteristic analysis period ends; a current detection unit that detects a current flowing through the inductor and outputs the detected current as a current detection signal; a filter characteristic analysis unit that analyzes a filter characteristic including the inductor and the output capacitor in accordance with a generation period of an inrush current flowing through the inductor during the filter analysis period, based on a current detection signal of the current detection unit; and a filter constant calculation unit that calculates a filter constant from the filter characteristic after the filter characteristic analysis period is completed, and supplies the filter constant to the digital filter.

Effects of the invention

According to the present invention, the filter characteristic analysis unit extracts the filter characteristic of the control target determined by the output capacitor and the inductor at a time based on the inrush current generation period flowing in the filter characteristic analysis period immediately after the power supply is started and before the output voltage starts to rise. The constant storage unit selects an optimum digital filter constant from a plurality of digital filter constant tables set and stored in advance and applies the selected digital filter constant to the digital filter.

Therefore, the setting of the output capacitor and the inductor in the manual operation does not need to be considered. Then, by performing the soft start operation, the output voltage is gradually increased to the set voltage.

Since the filter constant setting is completed before the output voltage rises to the set voltage, the feedback control during the soft start period can be stabilized. Therefore, it is possible to prevent the unstable operation from being entered during the rise period of the output voltage.

Drawings

Fig. 1 is a circuit configuration diagram of a switching power supply device of embodiment 1.

Fig. 2 is a diagram showing the frequency characteristics of a general voltage-mode DC/DC converter.

Fig. 3 is a diagram showing the frequency characteristics of the digital filter and the converter obtained by decomposing the frequency characteristics shown in fig. 2 for each element.

Fig. 4 is a diagram showing frequency characteristics in a case where the output capacitor has a small value and a sufficient phase margin can be secured.

Fig. 5 is a graph showing frequency characteristics in the case where the output capacitor has a large value and the phase margin is insufficient.

Fig. 6 is a timing chart of each part for explaining the operation of the switching power supply device of embodiment 1.

Fig. 7 is a graph showing frequency characteristics when the Crossover frequency (cross frequency) and the phase margin are decreased in the case where the output capacitor is a large value and the resonance frequency is lower than the zero point frequency.

Fig. 8 is a graph showing frequency characteristics when the zero point frequency is shifted to a lower frequency and the gain is decreased as the resonance frequency becomes lower as the output capacitor has a larger value.

Fig. 9 is a circuit configuration diagram of a switching power supply device of embodiment 2.

Fig. 10 is a circuit configuration diagram of a switching power supply device of embodiment 3.

Fig. 11 is a diagram showing rising waveforms of an output voltage and an inductor current in a case where an input voltage is high in the switching power supply device of embodiment 1.

Fig. 12 is a diagram showing rising waveforms of an output voltage and an inductor current in a case where an input voltage is high in the switching power supply device of embodiment 3.

Detailed Description

Hereinafter, an embodiment of a switching power supply device according to the present invention will be described with reference to the drawings.

(example 1)

Fig. 1 is a circuit configuration diagram of a switching power supply device of embodiment 1. The switching power supply device of embodiment 1 shown in fig. 1 includes a voltage detection unit 1, a target value generation unit 2, a subtractor 3, a digital filter 4, a drive unit 5, a current detection unit 6, a filter characteristic analysis unit 7, a constant storage unit 8, a high-side MOSFET 101, a low-side MOSFET 102, an inductor 103, an output capacitor 104, and an output load 105. The high-side MOSFET 101 and the low-side MOSFET 102 correspond to switching elements of the present invention.

The switching power supply device converts a 1 st dc voltage supplied from a power supply Vi into a 2 nd dc voltage via an inductor 103 and an output capacitor 104 by alternately turning on and off a high-side MOSFET 101 and a low-side MOSFET 102, and supplies an output voltage Vo to an output load 105.

The positive terminal of the power supply Vi is connected to the drain of the N-channel high-side MOSFET 101, and the source of the high-side MOSFET 101 and the drain of the N-channel low-side MOSFET 102 are connected to one end of the inductor L. The source of the low side MOSFET 102 is connected to ground.

The other end of the inductor L is connected to one end of the output capacitor 104 and one end of the load 105. The other end of the output capacitor 104 and the other end of the output load 105 are grounded.

The driver 5 alternately performs a switching operation of the high-side MOSFET 101 and the low-side MOSFET 102, thereby generating a rectangular wave voltage at the SW terminal (a connection point between the high-side MOSFET 101 and the low-side MOSFET 102). The output filter including the inductor 103 and the output capacitor 104 smoothes the rectangular wave voltage, thereby supplying an output voltage Vo formed of a stable dc voltage to the load 105.

The voltage detector 1 is connected to one end of the output capacitor 104, detects the output voltage Vo, converts the detected output voltage Vo into a digital voltage value having a predetermined number of bits, and outputs the converted digital voltage value to the subtractor 3.

The target value generation unit 2 generates a target value of the output voltage Vo, converts the target value into a digital value having a predetermined number of bits, and outputs the converted digital value to the subtractor 3. Further, the target value is gradually changed from the 1 st target value to the 2 nd target value within a predetermined period from the end time of a filter characteristic analysis period described later, and the output voltage Vo is gradually increased from the 1 st output voltage to the 2 nd output voltage. Thereby, an overshoot and an excessive inrush current (Rush current) flowing from the power supply Vi through the output capacitor 104 via the high-side MOSFET 101 and the inductor 103 are suppressed.

The subtractor 3 calculates an error between the digital voltage value from the voltage detection unit 1 and the target value generated by the target value generation unit 2, and outputs the obtained error to the digital filter 4.

The digital filter 4 outputs a predetermined analysis signal during the filter characteristic analysis period Tr, and after the filter characteristic analysis period Tr is completed, performs mainly PID (proportional/integral/derivative) operation on the error from the subtractor 3, and outputs the operation result to the drive unit 5.

The drive unit 5 alternately drives the high-side MOSFET 101 and the low-side MOSFET 102 to be turned on and off based on the calculation result from the digital filter 4. The on and off duty ratios of the high-side MOSFET 101 and the low-side MOSFET 102 are controlled according to the operation result of the digital filter 4.

The driver 5 drives the high-side MOSFET 101 and the low-side MOSFET 102 at a predetermined duty ratio during the filter characteristic analysis period, and controls the high-side MOSFET 101 and the low-side MOSFET 102 at a duty ratio based on the calculation result of the digital filter 4 after the filter characteristic analysis period ends.

The current detection unit 6 detects a current value flowing through the inductor 103, converts the detected current value into a current detection signal having a digital voltage value of a predetermined number of bits, and outputs the current detection signal to the filter characteristic analysis unit 7.

The filter characteristic analysis unit 7 analyzes the filter characteristic (LC resonance frequency f) determined by the inductor 103 and the output capacitor 104 to be controlled, based on the current detection signal from the current detection unit 6, based on the generation period of the inrush current flowing through the inductor 103 in the filter characteristic analysis period Tr₀) The filter characteristics thus analyzed are output to the constant storage unit 8.

The constant storage unit 8 is configured to store the filter characteristic analysis result (LC resonance frequency f) analyzed by the filter characteristic analysis unit 7 after the filter characteristic analysis period ends₀) The optimum digital filter constant is selected from a plurality of digital filter constant tables set and stored in advance in the constant storage unit 8, and the selected digital filter constant is supplied to the digital filter 4.

Next, the feedback control will be described. The digital filter 4 receives an error between the output voltage Vo and the target value VREF, and performs a predetermined operation. The drive section 5 controls the duty ratio of the high-side MOSFET 101 and the low-side MOSFET 102. Thereby, the feedback control is performed so that the error between the output voltage Vo and the comparison value VREF is reduced.

As a method of determining the stability of the feedback loop, a bode diagram is widely used. Fig. 2 is a graph of a bode plot of a general voltage mode DC/DC converter. The higher the frequency, the larger the gain and phase variations, and finally the gain becomes 1 time (0 dB). The frequency at this time is referred to as a crossover frequency fc.

If the phase at the crossover frequency fc has a sufficient margin with respect to the oscillation limit (-180deg), it can be determined that the feedback control is stable. This margin is referred to as a phase margin PM, and the higher the margin is, the more the stability is improved. Generally, the phase margin of about 60deg is set to an optimum value that can achieve both stability and responsiveness. The gain and phase have inflection points with respect to the change in frequency, and in the region I where the frequency is low, the gain decreases by-20 dB/dec with the increase in frequency.

Frequency fz₁The zero point 1 is set to a gain of +20dB/dec and the phase is advanced by +90 deg. Therefore, in region II, there is no change in gain, and the phase is advanced to 0deg at maximum.

Frequency f₀Is the LC resonance frequency determined by the inductor 103 and the output capacitor 104, and is given by equation (1). The gain is lowered by-40 dB/dec with the increase in frequency, and the phase is delayed by-180 deg. Thus, in region III, the gain is varied at-40 dB/dec with a phase delay of up to-180 deg.

Frequency fz₂Is zero 2, and zero 1 fz₁Similarly, the gain is increased by +20dB/dec, and the phase is advanced by +90 deg. Thus, in region IV, the gain is varied by-20 dB/dec, and in region III, a phase is returned with a maximum delay of-180 deg. This can secure a phase margin at the crossover frequency fc.

Fig. 3 is a diagram obtained by decomposing the frequency characteristic of fig. 2 for each element. The digital filter characteristic is a characteristic determined by the digital filter 4 of fig. 1, and the converter characteristic is a characteristic determined by a component other than the digital filter 4. The digital filter 4 has an integration characteristic of decreasing the gain by-20 dB/dec in accordance with the frequency, and two zeros fz₁And fz₂And is suitably configured so as to have an LC resonance frequency f of the converter characteristic₀The slope of the lower gain drop is gentle.

Furthermore, the digital filter 4 generatesTwo zeros fz₁And fz₂To return a phase of-180 deg maximum delay. By appropriately configuring the zero point fz₁And fz₂The phase margin PM can be sufficiently ensured. In general, the 1 st zero fz₁Set to be lower than the resonance frequency f₀Zero point 2 fz₂Preferably at LC resonance frequency f₀To the crossover frequency fc.

However, most users of the module power supply add a capacitor between the output terminal of the module power supply and GND to adjust the capacitor value. Thus, the output ripple voltage accompanying the switching operation is suppressed, and the output voltage is adjusted so that the variation of the output voltage when the output load current abruptly varies falls within the standard range. Therefore, the LC resonance frequency f given by equation (1)₀The change is caused, and the load response performance is deteriorated due to the shift in the direction in which the crossover frequency fc becomes lower, and therefore, even if the output capacitor value is increased, a sufficient effect of suppressing the output voltage variation cannot be obtained. At worst, the feedback action sometimes becomes unstable. This is explained in detail with reference to fig. 4.

For example, as shown in fig. 4, it is considered that the 1 st zero point fz is set so that a sufficient phase margin PM can be secured with a small output capacitor 104₁And zero point 2 fz₂Conditions for optimization were performed. When only the output capacitor 104 is increased in a state where the filter condition is maintained, as shown in fig. 5, the LC resonance frequency moves below f₀F of (a)₀'. Therefore, the 1 st zero fz₁And resonance point f₀The positional relationship of' is reversed, and particularly, in the region II, becomes-60 dB/dec, and the slope becomes very steep.

As a result, the crossover frequency fc' becomes low, and thus the load response performance deteriorates. Moreover, the zero point fz based on 2 nd point cannot be obtained sufficiently₂The phase advancing effect of (2). Therefore, the phase margin PM' is insufficient, and unstable operation is caused. In order to solve this problem, it is necessary to determine the LC resonance frequency f determined by the inductor 103 and the output capacitor 104₀Based on the result, the 1 st zero point fz₁And zero point 2 fz₂Optimization is performed.

Therefore, the present inventionIt is clear that an inrush current flowing through the inductor 103 is actively generated during a filter characteristic analysis period immediately after the power supply Vi is turned on, and the LC resonance frequency f determined by the output capacitor and the inductor is estimated from the generation period of the inrush current₀Optimally setting the zero point fz₁And fz₂. Therefore, the setting of the output capacitor and the inductor in the manual operation does not need to be considered. This situation is explained in detail with reference to fig. 6.

After the input voltage Vi is turned on, the digital filter 4 outputs a predetermined analysis signal to the drive unit 5 in the filter characteristic analysis period Tr in the region I, thereby turning on and off the high-side MOSFET 101 and the low-side MOSFET 102 at a predetermined duty ratio.

The predetermined duty ratio is much lower than the duty ratio of the steady operation period Tc (region IV). Thus, the output capacitor 104 is charged, and the inductor 103 actively generates an inrush current during a period until the output voltage Vo reaches the 1 st output voltage Vo1 determined by the input voltage Vi and the predetermined duty ratio. In addition, the 1 st output voltage Vo1 is given by the following equation. D denotes a duty ratio.

Vo1＝Vi·D……(2)

The envelope ELP of the inrush current generated in the inductor 103 is substantially similar to a half wave of free oscillation of the LC determined by the inductor 103 and the output capacitor 104.

Therefore, the filter characteristic analysis unit 7 calculates the resonance frequency f determined by the inductor 103 and the output capacitor 104 by measuring the time Tr from the start of the filter characteristic analysis period to the vicinity of the top of the envelope ELP₀. A period Tr and an LC resonance frequency f from the start of the filter characteristic analysis period to the vicinity of the vertex of the envelope ELP₀The relationship (c) is given by the equation (3).

f₀≒1/(4·Tr)……(3)

In a constant setting period Ts (region II) of fig. 6, the filter characteristic analysis unit 7 calculates the resonance frequency f from the calculated resonance frequency₀Value to select optimum digital filter constant from a plurality of digital filter constant tables preset and stored in constant storage unit 8 and apply the selected digital filter constant to the numberA word filter 4. Specifically, as shown in table 1, the filter characteristic analysis unit 7 selects the LC resonance frequency f₀The lower the value is, the 1 st zero fz₁And zero point 2 fz₂The lower the digital filter setting table.

[ Table 1]

Thus, as shown in fig. 7, the 1 st zero point fz is set before the zero point adjustment₁And resonance point f₀The positional relationship of (3) is reversed. Particularly, in the region II, the slope becomes very steep at-60 dB/dec, and therefore the crossover frequency fc becomes low, and the load response performance is degraded. Moreover, the zero point fz based on 2 nd cannot be obtained₂The phase advancing effect of (2) and the phase margin PM is insufficient.

In contrast, after the zero point adjustment, as shown in fig. 8, the LC resonance frequency f is determined₀So that the 1 st zero fz₁' and 2 nd zero fz₂' go down. Thus, by sufficiently securing the phase margin PM 'and increasing the crossover frequency fc', it is possible to construct a power supply with high load response performance and stability.

In the soft start Tss (region III) of fig. 6, the target value generation unit 2 gradually increases the target value from the 1 st target value to the 2 nd target value, thereby realizing a soft start operation of the output voltage Vo and preventing overshoot. When the output voltage Vo reaches the set voltage determined by the 2 nd target value, the operation transitions to the region IV, and the steady operation starts.

In addition, in the conventional technique, since the filter characteristic is set after the soft start operation period is ended, there is a problem that the feedback operation becomes unstable during the soft start operation period.

In contrast, in the present invention, the digital filter 4 is set before the soft start operation of the output voltage Vo is started, and therefore, there is an advantage that the same problem does not occur.

In addition, in Table 1, the resonant frequency f is determined by the LC₀And the zero point is adjusted to form the balance of load responsePower supply of performance and stability, in contrast, even according to LC resonance frequency f₀The same effect can be obtained by adjusting the gain by the value. And, even according to the LC resonance frequency f₀The same effect can be obtained by adjusting both the zero point and the gain.

The current flowing through the inductor 103 may be detected directly by using a shunt resistance, indirectly by using a DCR (direct current resistance) of the inductor 103, or contactlessly by using a hall element.

As described above, according to the switching power supply device of embodiment 1, the filter characteristic analyzing unit extracts the filter characteristic of the control target determined by the output capacitor 104 and the inductor 103 at a time in accordance with the inrush current generation period flowing in the filter characteristic analyzing period immediately after the power supply is started and before the output voltage starts to rise. Constant storage unit 8 selects an optimum digital filter constant from a plurality of digital filter constant tables set and stored in advance, and applies the selected digital filter constant to digital filter 4.

Therefore, it is not necessary to consider the settings of the output capacitor 104 and the inductor 103 in the manual operation. Then, by performing the soft start operation, the output voltage is gradually increased to the set voltage.

(example 2)

Fig. 9 is a structural diagram of a switching power supply device of embodiment 2. In example 2, the constant calculation unit 9 is provided instead of the constant storage unit 8 in example 1. Since the other configuration of embodiment 2 is the same as that of embodiment 1, only the constant calculation unit 9 will be described.

The constant calculation unit 9 analyzes the filter characteristics (LC resonance frequency f) from the filter characteristics analysis unit 7₀Value), target crossover frequency fca, target phase margin PMa, and other information necessary for setting, and calculates filter constants satisfying the conditionsThe calculated filter constant is applied to the digital filter 4. An example of the calculation method in the constant calculation unit 9 will be described.

When it is assumed that the optimized filter characteristic satisfies fz₁<<f ₀<fz₂<<fca, when the target crossover frequency is fca and the target phase margin is PMa, the 2 nd zero fz can be estimated by equation (4)₂。

fz₂≒－fca·tan(PMa+90deg)－fz₁……(4)

In addition, due to fz₁<<fz₂As a prerequisite, therefore fz is set₁Is represented by the formula (5).

fz₁≒fz₂/10……(5)

The 1 st zero fz is calculated from the above-described equations (4) and (5)₁2 nd zero point fz₂And applied to the digital filter 4, whereby a good feedback control with a high load response performance and sufficient stability can be realized.

In example 1, the constant storage unit 8 calculates the LC resonance frequency f from the filter characteristic analysis unit 7₀And the best constant is selected from a stored table of filter constants. Therefore, the allowable LC resonance frequency f₀To a certain extent, is limited.

In contrast, in embodiment 2, since the constant calculation unit 9 calculates the control constant by calculation, the LC resonance frequency f is also calculated₀Even if the deviation occurs in a wider range, favorable feedback control can be achieved.

As described above, according to the switching power supply device of embodiment 2, the filter characteristic analyzing unit 7 extracts the filter characteristic of the control target determined by the output capacitor 104 and the inductor 103 at a time in accordance with the inrush current generation period flowing in the filter characteristic analyzing period immediately after the power supply is started and before the output voltage starts to rise. The constant calculation unit 9 calculates an optimum constant corresponding to the filter characteristic, and applies the calculated filter constant to the digital filter 4.

(example 3)

Fig. 10 is a structural diagram of a switching power supply device of embodiment 3. The switching power supply device of example 3 is added with an input voltage detection unit 10 to the switching power supply device of example 2. The digital filter 4 is changed to a digital filter 4 b. The other configuration shown in fig. 10 is the same as that shown in fig. 1, and therefore only a different configuration will be described.

The input voltage detector 10 detects the input voltage Vi and outputs the detected input voltage Vi as a digital value to the digital filter 4 b. The digital filter 4b outputs an analysis signal to the drive unit 5, the analysis signal changing in accordance with the value of the input voltage Vi detected by the input voltage detection unit 10 during the filter characteristic analysis period Tr. The drive unit 5 turns on and off the high-side MOSFET 101 and the low-side MOSFET 102 at a duty ratio corresponding to the input voltage Vi, specifically, at a duty ratio that becomes narrower as the input voltage Vi becomes higher, based on the analysis signal from the digital filter 4 b.

Fig. 11 shows that the 1 st output voltage Vo generated when the input voltage Vi is high in embodiment 1 shown in fig. 1. In contrast, fig. 12 shows that the 1 st output voltage Vo1 is low when the input voltage Vi is high in embodiment 2 shown in fig. 10. Since the 1 st output voltage Vo1 is low, it is possible to prevent malfunction of the FPGA or CPU serving as a load.

As described above, according to the switching power supply device of embodiment 3, by controlling the duty ratio in the filter characteristic analysis period based on the input voltage Vi, it is possible to prevent the 1 st output voltage (offset voltage) generated in the filter characteristic analysis period from becoming excessively high as shown in fig. 12, and to realize smooth soft start characteristics.

The current flowing through inductor 103 may be detected directly by using a shunt resistor, indirectly by using DCR (direct current resistance) of inductor 103, or contactlessly by using a hall element.

Industrial applicability

The present invention can be applied to a non-insulated step-down chopper circuit and the like.

Description of the reference symbols

1: a voltage detection unit;

2: a target value generation unit;

3: a subtractor;

4: a digital filter;

5: a drive section;

6: a current detection unit;

7: a filter characteristic analysis unit;

8: a constant storage unit;

9: a constant calculation unit;

10: an input voltage detection unit;

101: a high side MOSFET;

102: a low side MOSFET;

103: an inductor;

104: an output capacitor;

105: an output load;

and Vi: a power source.

Claims

1. A switching power supply device which supplies an output voltage to an output load by converting a 1 st DC voltage supplied from a power supply into a 2 nd DC voltage via an inductor and an output capacitor by turning on and off a switching element, the switching power supply device comprising:

a voltage detector that detects the output voltage and converts the detected output voltage into a digital value having a predetermined number of bits;

a digital filter that performs a predetermined operation based on an error between a target value and an output of the voltage detection unit;

a driving unit that drives the switching element at a predetermined duty ratio during a filter characteristic analysis period, and controls the main switching element at a duty ratio based on a calculation result of the digital filter after the filter characteristic analysis period ends;

a current detection unit that detects a current flowing through the inductor and outputs the detected current as a current detection signal;

a filter characteristic analysis unit that analyzes a filter characteristic including the inductor and the output capacitor in accordance with a generation period of an inrush current flowing through the inductor during the filter analysis period, based on a current detection signal of the current detection unit; and

and a constant storage unit having a plurality of digital filter constant tables in which a plurality of filter constants corresponding to a plurality of filter characteristics are stored, wherein after the filter characteristic analysis period is completed, an appropriate filter constant is selected from the plurality of digital filter tables according to the filter characteristic, and supplied to the digital filter.

2. Switching power supply unit according to claim 1,

the switching power supply device has an input voltage detection unit that detects an input voltage of the power supply,

the driving unit drives the main switching element at a duty ratio that changes in accordance with a voltage signal from the input voltage detection unit during the filter characteristic analysis period.

3. Switching power supply unit according to claim 1 or 2,

the filter characteristic analysis unit obtains a resonance frequency of the inductor and the capacitor from a generation period of the inrush current, and selects the filter constant from the resonance frequency.

4. A switching power supply device which supplies an output voltage to an output load by converting a 1 st DC voltage supplied from a power supply into a 2 nd DC voltage via an inductor and an output capacitor by turning on and off a switching element, the switching power supply device comprising:

and a filter constant calculation unit that calculates a filter constant from the filter characteristic after the filter characteristic analysis period is completed, and supplies the filter constant to the digital filter.

5. Switching power supply unit according to claim 4,

6. Switching power supply unit according to claim 4 or 5,