JP7184168B2 - switching power supply - Google Patents

Description

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

A non-isolated step-down chopper circuit is widely used as a method of generating a stable voltage lower than the input voltage. In particular, POL (Point of Load) module power supplies are often used in communication infrastructure and the like.

This module power supply has a control circuit, a Power MOSFET, and an inductor mounted on a single board. The user adds an output capacitor between the output terminal of the module and GND, and adjusts the output capacitor value. As a result, the output ripple voltage associated with the switching operation can be suppressed, and the fluctuation of the output voltage when the output load current fluctuates rapidly can be adjusted to fall within the standard range.

In general, the larger the output capacitor value is adjusted, the smaller the output ripple voltage and the output voltage fluctuation when the load suddenly changes. However, the control constant of the digital filter is set so that the control circuit can operate stably within an assumed range. Therefore, for example, when the output capacitor is made larger than expected, the control band (crossover frequency) of the feedback control is lowered and the response characteristic is degraded. For this reason, there is a problem that the output voltage fluctuation at the time of sudden load change cannot be suppressed as expected, and in the worst case, the phase margin is insufficient, resulting in unstable operation.

On the other hand, in the switching power supply device described in Patent Document 1, after the output voltage starts to rise after the power supply is started and reaches a predetermined value, the fluctuation of the output voltage generated during the filter characteristic analysis period is used as the control target. Extract filter characteristics. The device analyzes the filter characteristics by comparing the extracted filter characteristics with a plurality of preset model frequency characteristics. After that, the device can ensure a wide operating range by automatically selecting the control constant (control response characteristic) of the digital filter corresponding to the model frequency characteristic.

Japanese Patent No. 5925724

However, the model frequency characteristic of Patent Document 1 is optimized when the output voltage reaches the set voltage after the power is turned on. Therefore, the filter characteristic analysis period must be set at a timing after the output voltage reaches the set voltage. Therefore, when the output voltage is low immediately after the power is turned on, the filter characteristics cannot be analyzed, and the filter constant setting is not completed. Therefore, the feedback control becomes unstable during the rising period until the output voltage reaches the set voltage.

As described above, the switching power supply device of Patent Document 1 extracts the filter characteristics of the controlled object from the fluctuations in the output voltage that occur during the filter characteristic analysis period after the output voltage starts to rise after the power is turned on and reaches the set voltage. to set the optimal digital filter control constant. For this reason, during the rising period until the output voltage reaches the set voltage, setting of the control constant is not completed, resulting in unstable operation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switching power supply device capable of preventing unstable operation during the rising period until the output voltage reaches a set voltage.

In order to solve the above problems, a switching power supply device of the present invention converts a first DC voltage supplied from a power supply into a second DC voltage via an inductor and an output capacitor by turning on and off a switching element. A switching power supply device that supplies an output voltage to an output load, comprising: a voltage detection unit that detects the output voltage and converts the detected output voltage into a digital value of a predetermined number of bits; a target value and the voltage detection a digital filter that performs a predetermined calculation based on an error from the output of the unit; a duty that drives the switching element with a predetermined duty during the filter characteristic analysis period and a duty based on the calculation result of the digital filter after the filter characteristic analysis period ends; a drive unit for controlling the switching element, a current detection unit for detecting the current flowing through the inductor and outputting the detected current as a current detection signal, and the filter based on the current detection signal of the current detection unit a filter characteristic analysis unit that analyzes the characteristics of a filter composed of the inductor and the output capacitor from the occurrence period of the inrush current flowing through the inductor during the analysis period; a constant storage unit having a digital filter constant table, selecting a suitable filter constant from the plurality of digital filter constant tables according to the filter characteristic after the filter characteristic analysis period ends, and supplying the filter constant to the digital filter; an input voltage detection unit that detects an input voltage of a power supply, wherein the drive unit drives the switching element with a duty that varies according to the voltage signal from the input voltage detection unit during the filter characteristic analysis period. characterized by

Further, the switching power supply device of the present invention converts the first DC voltage supplied from the power supply to the second DC voltage via the inductor and the output capacitor by turning on and off the switching element, and outputs the output voltage to the output load. A switching power supply device for supplying power, comprising: a voltage detection unit that detects the output voltage and converts the detected output voltage into a digital value of a predetermined number of bits; and an error between a target value and the output of the voltage detection unit. and a digital filter for performing a predetermined calculation based on the above, driving the switching element with a predetermined duty during the filter characteristic analysis period, and driving the switching element with a duty based on the calculation result of the digital filter after the filter characteristic analysis period. a drive unit that controls the switching element; a current detection unit that detects the current flowing through the inductor and outputs the detected current as a current detection signal; and the filter analysis period based on the current detection signal of the current detection unit. a filter characteristic analysis unit that analyzes a filter characteristic composed of the inductor and the output capacitor from a period during which an inrush current flowing through the inductor is generated; and after the filter characteristic analysis period ends, a filter constant is calculated according to the filter characteristic. and an input voltage detection unit that detects the input voltage of the power supply. The switching element is driven with a duty that changes accordingly.

According to the present invention, the filter characteristics analysis unit obtains the filter characteristics of the controlled object determined by the output capacitor and the inductor at once from the inrush current generation period that flows during the filter characteristics analysis period before the output voltage starts to rise immediately after the power is turned on. Extract. The constant storage unit selects an optimum one from among a plurality of preset and stored digital filter constant tables and applies it to the digital filter.

This eliminates the need to manually set the output capacitor and inductor. After that, a soft start operation is performed to slowly increase the output voltage 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. As a result, it is possible to prevent unstable operation during the rising period of the output voltage.

FIG. 1 is a circuit configuration diagram of a switching power supply device according to a first embodiment. FIG. 2 is a diagram showing frequency characteristics of a general voltage mode DC/DC converter. FIG. 3 is a diagram showing frequency characteristics of a digital filter and a converter obtained by decomposing the frequency characteristics shown in FIG. 2 for each element. FIG. 4 is a diagram showing frequency characteristics when a sufficient phase margin can be ensured with a small output capacitor value. FIG. 5 is a diagram showing frequency characteristics when the value of the output capacitor is large 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 the first embodiment. FIG. 7 is a diagram showing frequency characteristics when the crossover frequency and the phase margin decrease when the value of the output capacitor is large and the resonance frequency is low with respect to the zero point frequency. FIG. 8 is a diagram showing frequency characteristics when the zero-point frequency is shifted to a lower frequency and the gain is lowered as the resonant frequency is lowered with a large value of the output capacitor. FIG. 9 is a circuit configuration diagram of a switching power supply device according to a second embodiment. FIG. 10 is a circuit configuration diagram of a switching power supply device according to the third embodiment. FIG. 11 is a diagram showing rising waveforms of the output voltage and the inductor current when the input voltage is high in the switching power supply device of the first embodiment. FIG. 12 is a diagram showing rising waveforms of the output voltage and the inductor current when the input voltage is high in the switching power supply device of the third embodiment.

Embodiments of the switching power supply device of the present invention will be described below with reference to the drawings.

(Example 1)
FIG. 1 is a circuit configuration diagram of a switching power supply device according to a first embodiment. The switching power supply device of the first embodiment shown in FIG. 8, a high-side MOSFET 101, a low-side MOSFET 102, an inductor 103, an output capacitor 104, and an output load 105; A high-side MOSFET 101 and a low-side MOSFET 102 correspond to switching elements of the present invention.

The switching power supply alternately turns on and off the high-side MOSFET 101 and the low-side MOSFET 102 to convert the first DC voltage supplied from the power supply Vi into the second DC voltage via the inductor 103 and the output capacitor 104 and output the voltage. It supplies the output voltage Vo to the load 105 .

The drain of the N-channel high-side MOSFET 101 is connected to the positive electrode of the power source Vi, 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 low-side MOSFET 102 is grounded.

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 driving unit 5 alternately switches the high-side MOSFET 101 and the low-side MOSFET 102 to generate a rectangular wave voltage at the SW terminal (connection point between the high-side MOSFET 101 and the low-side MOSFET 102). An output filter composed of an inductor 103 and an output capacitor 104 smoothes the square wave voltage to supply a load 105 with an output voltage Vo consisting of a stable DC voltage.

The voltage detection unit 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 of a predetermined number of bits, and converts the converted digital voltage value into a subtractor. Output to 3.

The target value generator 2 generates a target value of the output voltage Vo, converts the target value into a digital value of a predetermined number of bits, and outputs the converted digital value to the subtractor 3 . In a predetermined period from the end of the filter characteristic analysis period described later, the target value is slowly changed from the first target value to the second target value, and the output voltage Vo is changed from the first output voltage to the second output voltage. Bring up slowly. This suppresses overshoot and excessive rush current flowing from the power supply Vi to the output capacitor 104 via the high-side MOSFET 101 and the inductor 103 .

The subtractor 3 calculates the error between the digital voltage value from the voltage detector 1 and the target value generated by the target value generator 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 outputs the calculation result to the drive unit 5 .

The driving unit 5 alternately turns on and off the high-side MOSFET 101 and the low-side MOSFET 102 based on the calculation result from the digital filter 4 . The on/off duty ratios of the high-side MOSFET 101 and the low-side MOSFET 102 are controlled according to the calculation result of the digital filter 4 .

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

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

Based on the current detection signal from the current detection unit 6, the filter characteristic analysis unit 7 determines a filter determined by the inductor 103 to be controlled and the output capacitor 104 from the occurrence period of the inrush current flowing through the inductor 103 during the filter characteristic analysis period Tr. The characteristics (LC resonance frequency f ₀ ) are analyzed, and the analyzed filter characteristics are output to the constant storage unit 8 .

The constant storage unit 8 stores a plurality of values preset and stored in the constant storage unit 8 according to the filter characteristic analysis result (LC resonance frequency f ₀ ) analyzed by the filter characteristic analysis unit 7 after the end of the filter characteristic analysis period. An optimum one is selected from the digital filter constant table and the selected digital filter constant is supplied to the digital filter 4. - 特許庁

Next, feedback control will be described. The digital filter 4 inputs the error between the output voltage Vo and the target value VREF and performs a predetermined calculation. A drive unit 5 controls the duty ratios of the high-side MOSFET 101 and the low-side MOSFET 102 . As a result, feedback control is performed so that the error between the output voltage Vo and the comparison value VREF is reduced.

A Bode diagram is widely used as a method of determining the stability of a feedback loop. FIG. 2 is an image of a Bode diagram of a typical voltage-mode DC/DC converter. As the frequency becomes higher, the gain and phase change, and eventually the gain becomes 1 (0 dB). The frequency at this time is called a crossover frequency fc.

If the phase at the crossover frequency fc has a sufficient margin with respect to the oscillation limit (-180 deg), it can be determined that the feedback control is stable. This margin is called a phase margin PM, and the higher the margin, the better the stability. Generally, a phase margin of about 60 degrees is considered to be the best value for achieving both stability and responsiveness. The gain and phase have an inflection point with respect to frequency change, and in the low frequency region I, the gain decreases at -20 dB/dec as the frequency increases.

Frequency fz ₁ is the first zero, increasing the gain by +20 dB/dec and advancing the phase by +90 degrees. Therefore, there is no change in gain in region II, and the phase advances up to 0 deg.

A frequency _f0 is an LC resonance frequency determined by the inductor 103 and the output capacitor 104, and is given by equation (1). As the frequency rises, the gain is lowered by -40dB/dec and the phase is delayed by -180deg. Therefore, in region III, the gain changes at −40 dB/dec, and the phase is delayed up to −180 deg.

f ₀ =1/(2·π·√(L·C)) (1)
Frequency fz ₂ is the second zero and, like the first zero fz ₁ , raises the gain by +20 dB/dec and advances the phase by +90 degrees. Therefore, the gain changes at −20 dB/dec in region IV, and the phase is delayed up to −180 degrees in region III. Thereby, the phase margin can be ensured at the crossover frequency fc.

FIG. 3 is a diagram in which the frequency characteristics of FIG. 2 are decomposed for each element. A digital filter characteristic is a characteristic determined by the digital filter 4 in FIG. 1, and a converter characteristic is a characteristic determined by something other than the digital filter 4. The digital filter 4 has an integration characteristic that lowers the gain by -20 dB/dec depending on the frequency. In addition, two zero points fz ₁ and fz ₂ are added and arranged appropriately to obtain the LC resonance frequency f of the converter characteristic. Soften the slope of the gain drop at _zero .

Also, the digital filter 4 generates two zero points fz ₁ and fz ₂ to return a phase that is delayed by -180 degrees at maximum. By properly arranging the zero points _fz1 and _fz2 , a sufficient phase margin PM can be ensured. In general, _{it is desirable to set the first zero point fz1 lower than the resonance frequency f0 and the second zero point fz2 between the} LC resonance frequency _f0 and the crossover frequency fc.

However, many users of module power supplies add a capacitor between the output terminal of the module power supply and GND and adjust the capacitor value. This suppresses the output ripple voltage associated with the switching operation, and adjusts the fluctuation of the output voltage when a rapid fluctuation of the output load current occurs so that it falls within the standard range. As a result, the LC resonance frequency _f0 given by equation (1) changes, and the crossover frequency fc shifts downward, degrading the load response performance. Therefore, it is not possible to obtain an effective output voltage fluctuation suppression effect. In the worst case, the feedback operation may become unstable. This will be described in detail with reference to FIG.

For example, as shown in FIG. 4, consider a condition in which the first zero point fz ₁ and the second zero point fz ₂ are optimized so that a sufficient phase margin PM can be secured with a small value of the output capacitor 104 . If only the output capacitor 104 is increased while maintaining this filter condition, the LC resonance frequency moves to f _{0 ′} , which is lower than f ₀ , as shown in FIG. For this reason, the positional relationship between the first zero point fz ₁ and the resonance point f ₀ ′ is reversed, and in particular, in the region II, it becomes −60 dB/dec and the slope becomes very steep.

As a result, the crossover frequency fc' becomes low, degrading the load response performance. Furthermore, a sufficient phase advance effect cannot be obtained by the second zero point _fz2 . As a result, the phase margin PM' becomes insufficient, resulting in unstable operation. To solve this problem, it is necessary to obtain the LC resonance frequency f ₀ ′ determined by the inductor 103 and the output capacitor 104 and optimize the first zero point fz ₁ and the second zero point fz ₂ based on this result.

Therefore, according to the present invention, the inrush current flowing through the inductor 103 is actively generated during the filter characteristic analysis period immediately after the power supply Vi is turned on, and the LC resonance frequency _f0 determined by the output capacitor and the inductor is estimated from the period during which the inrush current is generated. and optimally set the zeros _fz1 and _fz2 . This eliminates the need to manually set the output capacitor and inductor. This state will be described in detail with reference to FIG.

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

The predetermined duty is sufficiently low with respect to the duty of steady operation period Tc (region IV). As a result, a rush current is actively generated in the inductor 103 during the period until the output capacitor 104 is charged and the output voltage Vo reaches the first output voltage Vo1 determined by the input voltage Vi and a predetermined duty. Note that the first output voltage Vo1 is given by the following equation. D represents duty.

Vo1=Vi.D (2)
The envelope ELP of the rush current generated in the inductor 103 is roughly similar to the half wave of the LC free oscillation determined by the inductor 103 and the output capacitor 104 .

Therefore, the filter characteristic analysis unit 7 calculates the resonance frequency _f0 determined by the inductor 103 and the output capacitor 104 by measuring the time Tr from the start of the filter characteristic analysis period until reaching the vicinity of the apex of the envelope ELP. The relationship between the period Tr from the start of the filter characteristic analysis period until reaching the vicinity of the apex of the envelope ELP and the LC resonance frequency _f0 is given by equation (3).

f ₀ ≈1/(4·Tr) (3)
In the constant setting period Ts (area II) in FIG. 6, the filter characteristic analysis unit 7 performs a plurality of digital filter constant tables preset and stored in the constant storage unit ₈ according to the obtained resonance frequency f0 value. The optimum one is selected from among them and applied to the digital filter 4. - 特許庁Specifically, as shown in Table 1, the filter characteristic analysis unit 7 uses a digital filter setting table such that the lower the LC resonance frequency _f0 value, the lower the first zero point _fz1 and the second zero point _fz2 . to select.

As a result, as shown in FIG. 7, the positional relationship between the first zero point _fz1 and the resonance point _f0 is reversed before the zero point adjustment. In particular, since the slope is extremely steep at -60 dB/dec in region II, the crossover frequency fc is lowered and the load response performance is degraded. Furthermore, the phase margin PM is insufficient because the phase lead effect by the second zero point _fz2 is not obtained.

On the other hand, after the zero point adjustment, the first zero point fz _{1 ′} and the second zero point fz ₂ ′ are lowered according to the LC resonance frequency f ₀ as shown in FIG. Thus, by increasing the crossover frequency fc' while ensuring a sufficient phase margin PM', a power supply with high load response performance and stability can be configured.

In the soft start Tss (region III) of FIG. 6, the target value generation unit 2 slowly increases the target value from the first target value to the second target value, thereby realizing a soft start operation of the output voltage Vo and over Prevent shoots. After that, when the output voltage Vo reaches the set voltage determined by the second target value, it shifts to region IV and starts steady operation.

In the prior art, since the filter characteristics are set after the soft start operation period ends, there is a problem that the feedback operation becomes unstable during the soft start operation period.

In contrast, in the present invention, setting of the digital filter 4 is completed before the soft start operation of the output voltage Vo starts, so there is an advantage that similar problems do not occur.

In Table 1, the zero point _is adjusted according to the LC resonance frequency _f0 to configure a power supply that achieves both load response performance and stability. A similar effect can be obtained by adjusting. Furthermore, the same effect can be obtained by adjusting both the zero point and the gain according to the LC resonance frequency _f0 .

In addition, the current flowing through the inductor 103 can be detected directly using a shunt resistor or indirectly using the DCR (direct current resistance) of the inductor 103, using a Hall element. Any method is fine.

As described above, according to the switching power supply device of the first embodiment, the filter characteristic analysis unit detects the output capacitor 104 and the inductor from the inrush current occurrence period before the output voltage starts to rise immediately after the power is turned on. The filter characteristics of the controlled object determined by 103 are extracted at once. The constant storage unit 8 selects the optimum one from among a plurality of preset and stored digital filter constant tables and applies it to the digital filter 4 .

Therefore, manual setting considering the output capacitor 104 and the inductor 103 becomes unnecessary. After that, a soft start operation is performed to slowly increase the output voltage 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. As a result, it is possible to prevent unstable operation during the rising period of the output voltage.

(Example 2)
FIG. 9 is a configuration diagram of a switching power supply device according to a second embodiment. The second embodiment has a constant calculator 9 instead of the constant storage 8 in contrast to the first embodiment. Other configurations of the second embodiment are the same as those of the first embodiment, so only the constant calculator 9 will be described.

Based on the filter characteristic analysis result (LC resonance frequency _f0 value) from the filter characteristic analysis unit 7, the target crossover frequency fca, the target phase margin PMa, and other information necessary for setting Then, the filter constant that satisfies the conditions is calculated, and the calculated filter constant is applied to the digital filter 4 . An example of the calculation method in the constant calculator 9 will be described.

Assuming that the filter characteristic after optimization satisfies fz ₁ <<f ₀ <fz ₂ <<fca, the second zero point fz ₂ is expressed by the formula ( 4).
fz ₂ ≈−fca·tan (PMa+90deg)−fz ₁ (4)
In addition, since fz ₁ <<fz ₂ is a precondition, _fz 1 is represented by formula (5).

_fz1≈fz2 / ₁₀ (5)
By calculating the first zero point fz ₁ and the second zero point fz ₂ from the equations (4) and (5) shown above and applying them to the digital filter 4, high load response performance and sufficient stability Good feedback control can be realized.

In the first embodiment, the constant storage unit 8 selects an optimum constant from the stored filter constant table according to the LC resonance frequency f ₀ calculated by the filter characteristic analysis unit 7 . Therefore, the allowable variation range of the LC resonance frequency _f0 is limited to some extent.

On the other hand, in the second embodiment, since the constant calculator 9 calculates the control constant, good feedback control can be realized even if the LC resonance frequency _f0 varies in a wider range.

The current flowing through the inductor 103 can be detected either directly using a shunt resistor or indirectly using a DCR (direct current resistance) of the inductor 103 without contact using a Hall element. A detection method may be used.

As described above, according to the switching power supply device of the second embodiment, the filter characteristic analysis unit 7 detects the output capacitor from the inrush current generation period that flows in the filter characteristic analysis period immediately after the power supply is started and before the output voltage starts to rise. The filter characteristics of the controlled object determined by 104 and inductor 103 are extracted at once. A constant calculator 9 calculates an optimum constant corresponding to the filter characteristic and applies the calculated filter constant to the digital filter 4 .

Therefore, manual setting considering the output capacitor 104 and the inductor 103 becomes unnecessary. After that, a soft start operation is performed to slowly increase the output voltage 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. As a result, it is possible to prevent unstable operation during the rising period of the output voltage.

(Example 3)
FIG. 10 is a configuration diagram of a switching power supply device according to the third embodiment. The switching power supply device of the third embodiment has an input voltage detection unit 10 added to the switching power supply device of the second embodiment. Also, the digital filter 4 is changed to a digital filter 4b. Since other configurations shown in FIG. 10 are the same as those shown in FIG. 1, only different configurations will be described.

The input voltage detection unit 10 detects the input voltage Vi and outputs the detected input voltage Vi to the digital filter 4b as a digital value. The digital filter 4b outputs an analysis signal to the drive unit 5 that varies according to the value of the input voltage Vi detected by the input voltage detection unit 10 during the filter characteristic analysis period Tr. Based on the analysis signal from the digital filter 4b, the drive unit 5 turns on and off the high-side MOSFET 101 and the low-side MOSFET 102 with a duty corresponding to the input voltage Vi, specifically, with a duty that narrows as the input voltage Vi increases.

FIG. 11 shows that the first output voltage Vo generated when the input voltage Vi is high in the first embodiment shown in FIG. 1 is high. In contrast, FIG. 12 shows that the first output voltage Vo1 is low when the input voltage Vi is high in the second embodiment shown in FIG. Since the first output voltage Vo1 is low, it is possible to prevent malfunction of the FPGA and CPU, which are loads.

As described above, according to the switching power supply device of the third embodiment, by controlling the duty during the filter characteristic analysis period according to the input voltage Vi, as shown in FIG. 12, the first output generated during the filter characteristic analysis period It is possible to prevent the voltage (offset voltage) from becoming too high, and realize smooth soft-start characteristics.

The current flowing through the inductor 103 can be detected directly using a shunt resistor or indirectly using a DCR (direct current resistance) of the inductor 103, using a Hall element without contact. A detection method may be used.

INDUSTRIAL APPLICABILITY The present invention is applicable to a non-isolated step-down chopper circuit and the like.

1 voltage detection unit 2 target value generation unit 3 subtractor 4 digital filter 5 drive unit 6 current detection unit 7 filter characteristic analysis unit 8 constant storage unit 9 constant operation unit 10 input voltage detection unit 101 high side MOSFET
102 Low side MOSFET
103 inductor 104 output capacitor 105 output load Vi power supply

Claims (4)

A switching power supply for supplying an output voltage to an output load by converting a first DC voltage supplied from a power supply to a second DC voltage via an inductor and an output capacitor by turning on and off a switching element,
A voltage detection unit that detects the output voltage and converts the detected output voltage into a digital value of a predetermined number of bits, and a digital filter that performs a predetermined calculation based on an error between a target value and the output of the voltage detection unit. a driving unit that drives the switching element with a predetermined duty during the filter characteristic analysis period, and controls the switching element with a duty based on the calculation result of the digital filter after the filter characteristic analysis period ends; and the inductor a current detection unit that detects a current flowing through and outputs the detected current as a current detection signal;
a filter characteristic analysis unit that analyzes the characteristics of a filter composed of the inductor and the output capacitor from a period during which a rush current flowing through the inductor occurs during the filter analysis period based on a current detection signal from the current detection unit; and a plurality of filters. It has a plurality of digital filter constant tables storing a plurality of filter constants corresponding to characteristics, and selects a suitable filter constant from among the plurality of digital filter constant tables according to the filter characteristics after the filter characteristic analysis period ends. and a constant storage unit for supplying to the digital filter;
an input voltage detection unit that detects the input voltage of the power supply,
The switching power supply device, wherein the drive section drives the switching element with a duty that varies according to the voltage signal from the input voltage detection section during the filter characteristic analysis period. The filter characteristic analysis unit analyzes the inductor and the
2. The switching power supply according to claim 1, wherein a resonance frequency with an output capacitor is obtained, and said filter constant is selected according to said resonance frequency. A switching power supply that turns on and off a switching element to convert a first DC voltage supplied from a power supply into a second DC voltage via an inductor and an output capacitor and supplies an output voltage to an output load,
a voltage detection unit that detects the output voltage and converts the detected output voltage into a digital value of a predetermined number of bits;
a digital filter that performs a predetermined calculation based on the error between the target value and the output of the voltage detection unit;
a driving unit that drives the switching element with a predetermined duty during the filter characteristic analysis period, and controls the switching element with a duty based on the 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 the characteristics of a filter composed of the inductor and the output capacitor from a period during which an inrush current flowing through the inductor occurs during the filter analysis period, based on a current detection signal from the current detection unit;
a filter constant calculation unit that calculates a filter constant according to the filter characteristic after the filter characteristic analysis period ends and supplies the filter constant to the digital filter;
an input voltage detection unit that detects the input voltage of the power supply,
The switching power supply device, wherein the drive section drives the switching element with a duty that varies according to the voltage signal from the input voltage detection section during the filter characteristic analysis period. The filter characteristic analysis unit analyzes the inductor and the
4. The switching power supply according to claim 3, wherein a resonance frequency with an output capacitor is obtained, and the filter constant is selected according to the resonance frequency.

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