WO2018150572A1

WO2018150572A1 - Switching power supply device

Info

Publication number: WO2018150572A1
Application number: PCT/JP2017/006127
Authority: WO
Inventors: 中村　勝
Original assignee: サンケン電気株式会社
Priority date: 2017-02-20
Filing date: 2017-02-20
Publication date: 2018-08-23
Also published as: CN210351013U

Abstract

A switching power supply device of the present invention is provided with: a comparison value generation unit 2 that generates a first comparison value after starting up a power supply and raises a comparison value from the first comparison value up to a second comparison value larger than the first comparison value after an output voltage Vo reaches a first output voltage corresponding to the first comparison value; a digital filter 4 that performs a predetermined calculation on the error between the comparison value and the output voltage; a filter characteristic analysis unit 7 that analyzes, on the basis of a current detection signal output from a current detection unit 6 for detecting the current flowing through an inductor 103, the first output voltage, and a filter characteristic analysis period, a filter characteristic determined by the inductor and an output capacitor 104; and a filter constant storage unit 8 that selects, with reference to a plurality of digital filter constant tables 81, in a period during which the comparison value makes a transition from the first comparison value to the second comparison value, a filter constant according to the filter characteristic obtained from the filter characteristic analysis unit and supplies the selected filter constant to the digital filter.

Description

Switching power supply

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

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

This module power supply has a control circuit, a power MOSFET, and an inductor mounted on a single substrate. The user adjusts the output capacitor value by adding an output capacitor between the output terminal of the module and GND. As a result, the output ripple voltage associated with the switching operation can be suppressed, and the output voltage fluctuation when the output load current suddenly fluctuates 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 during a sudden load change. However, the filter constant is set so that the control circuit can operate stably within an assumed range. For this reason, for example, when the output capacitor is made larger than expected, there is a problem that the phase margin is insufficient and the operation becomes unstable in the worst case.

On the other hand, the switching power supply device described in Patent Document 1 obtains the filter characteristics from the fluctuation of the output voltage generated during the filter characteristic analysis period after the output voltage starts to rise and reaches a predetermined value after the power is turned on. Extract. The apparatus analyzes the filter characteristic by comparing the extracted filter characteristic with a plurality of preset model frequency characteristics. Thereafter, the apparatus can ensure a wide operating range by automatically selecting a filter constant (control response characteristic) 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 supply is turned on. For this reason, the filter characteristic analysis period must be provided at a timing after the output voltage reaches the set voltage. For this reason, the filter characteristics cannot be analyzed in a state where the output voltage is low immediately after the power is turned on, and the filter constant setting is not completed. For this reason, feedback control becomes unstable during the rising period until the output voltage reaches the set voltage.

As described above, the switching power supply device disclosed in Patent Document 1 extracts the filter characteristic from the fluctuation of the output voltage generated during the filter characteristic analysis period after the output voltage starts to rise and reaches the set voltage after the power supply is started. Set the appropriate filter constant. For this reason, the filter setting is not completed during the rising period until the output voltage reaches the set voltage, resulting in an unstable operation.

An object of the present invention is to provide a switching power supply device that can prevent an unstable operation during a rising period until an output voltage reaches a set voltage.

In order to solve the above-described problem, 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. A switching power supply that supplies an output voltage to an output load, having a first comparison value and a second comparison value that is larger than the first comparison value, generating the first comparison value after the power supply is activated, Generated by the comparison value generator and the comparison value generator for increasing the comparison value from the first comparison value to the second comparison value after the output voltage reaches the first output voltage corresponding to the first comparison value A digital filter that performs a predetermined calculation on an error between the output voltage and the first comparison value or the second comparison value, and an on / off state of the switching element according to a calculation result of the digital filter. A drive unit that controls a duty of the current detection unit, a current detection unit that detects a current flowing through the inductor and outputs the detected current as a current detection signal, the current detection signal, the first output voltage, and the first comparison value. A filter characteristic analysis unit that analyzes a filter characteristic determined by the inductor and the output capacitor based on a filter characteristic analysis period from when the output voltage reaches the first output voltage to a time when the output voltage reaches the first output voltage; A plurality of digital filter constant tables storing a plurality of filter constants corresponding to filter characteristics, and the plurality of digital filter constants during a period until the comparison value shifts from the first comparison value to the second comparison value; Referring to the table, select and select the filter constant according to the filter characteristic analyzed by the filter characteristic analysis unit It said filter constants and a filter constant storing unit to be supplied to the digital filter.

Also, 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 apparatus for supplying, having a first comparison value and a second comparison value larger than the first comparison value, generating the first comparison value after the power is turned on, and the output voltage being the first comparison value After reaching the first output voltage corresponding to the comparison value, the comparison value generation unit that raises the comparison value from the first comparison value to the second comparison value, and the first comparison generated by the comparison value generation unit A digital filter that performs a predetermined calculation on an error between a value or the second comparison value and the output voltage, and an on / off duty of the switching element is controlled according to a calculation result of the digital filter. A drive unit that detects the current flowing through the inductor and outputs the detected current as a current detection signal; and from the time when the current detection signal, the first output voltage, and the first comparison value are generated A filter characteristic analyzer for analyzing a filter characteristic determined by the inductor and the output capacitor based on a filter characteristic analysis period until the output voltage reaches the first output voltage; and the comparison value is the first value In the period from the comparison value to the second comparison value, a filter constant is calculated according to the filter characteristic analyzed by the filter characteristic analysis unit, and the calculated filter constant is supplied to the digital filter. And a filter constant calculation unit.

According to the present invention, the filter characteristic analysis unit analyzes the filter characteristic based on the inrush current value flowing in the filter characteristic analysis period immediately after starting the power supply and before the output voltage starts to rise. The filter constant storage unit refers to a plurality of stored digital filter constant tables, selects a filter constant corresponding to the analyzed filter characteristic, and applies the selected filter constant to the digital filter.

Thereafter, the comparison value generation unit increases the comparison value from the first comparison value to the second comparison value after the output voltage reaches the first output voltage. That is, the soft start operation causes the output voltage to slowly rise to the set voltage.

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

FIG. 1 is a circuit configuration diagram of the switching power supply device according to the 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 secured with a small output capacitor. FIG. 5 is a diagram showing frequency characteristics when 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 according to the first embodiment. FIG. 7 is a diagram showing frequency characteristics when the crossover frequency and the phase margin are lowered when the output capacitor is large and the resonance frequency is lower than 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 resonance frequency is lowered with a large output capacitor value. FIG. 9 is a circuit configuration diagram of the switching power supply device according to the second embodiment. FIG. 10 is a circuit configuration diagram of the switching power supply device according to the third embodiment.

Hereinafter, embodiments of the switching power supply device of the present invention will be described with reference to the drawings.

Example 1
FIG. 1 is a circuit configuration diagram of the switching power supply device according to the first embodiment. 1 includes a voltage detection unit 1, a comparison 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, and a filter constant storage. Unit 8, high-side MOSFET 101, low-side MOSFET 102, inductor 103, output capacitor 104, and output load 105. The high side MOSFET 101 and the low side MOSFET 102 correspond to the switching element of the present invention.

The switching power supply device 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 source Vi into a second DC voltage via the inductor 103 and the output capacitor 104, and outputs it. An output voltage Vo is supplied 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 the low side MOSFET 102 is grounded.

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

The drive unit 5 generates a rectangular wave voltage at the SW terminal (a connection point between the high-side MOSFET 101 and the low-side MOSFET 102) by alternately switching the high-side MOSFET 101 and the low-side MOSFET 102. An output filter including the inductor 103 and the output capacitor 104 supplies the output voltage Vo composed of a stable DC voltage to the load 105 by smoothing the rectangular wave voltage.

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 of a predetermined number of bits, and subtracts the converted digital voltage value 3 is output.

The comparison value generation unit 2 has a first comparison value of the output voltage Vo and a second comparison value larger than the first comparison value, generates a first comparison value after the power is turned on, and generates the generated comparison value as a predetermined value. The digital value is converted into a bit number digital value, and the converted digital value is output to the subtractor 3. The comparison value generating unit 2 increases the comparison value from the first comparison value to the second comparison value after the output voltage reaches the first output voltage corresponding to the first comparison value.

Specifically, the comparison value generation unit 2 slowly changes the comparison value from the first comparison value to the second comparison value in a predetermined period from the end of the filter characteristic analysis period, which will be described later, and changes the output voltage Vo. Slowly rise from the first output voltage to the second output voltage. As a result, overshoot and excessive rush current flowing from the power source Vi to 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 comparison value generated by the comparison value generation unit 2 and outputs the obtained error to the digital filter 4.

The digital filter 4 mainly performs PID (proportional / integral / derivative) operation on the error from the subtractor 3 and outputs the operation result to the drive unit 5.

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

The current detection unit 6 detects the current value flowing through the 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 the filter characteristic analysis unit 7. To do.

The filter characteristic analysis unit 7 is a filter characteristic analysis period from when the current detection signal from the current detection unit 6, the first output voltage, and the first comparison value are generated to when the output voltage reaches the first output voltage value. Based on Tr, the filter characteristic (LC resonance frequency f ₀ ) determined by the inductor 103 and the output capacitor 104 is analyzed, and the analyzed filter characteristic is output to the filter constant storage unit 8.

The filter constant storage unit 8 includes a plurality of digital filter constant tables 81 that store a plurality of filter constants corresponding to a plurality of filter characteristics. The filter constant storage unit 8 refers to the plurality of digital filter constant tables 81 during the period until the comparison value shifts from the first comparison value to the second comparison value, and the filter characteristics ( A filter constant corresponding to the LC resonance frequency f ₀ ) is selected, and the selected filter constant is supplied to the digital filter 4.

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

The Bode diagram is widely used as a method for determining the stability of the feedback loop. FIG. 2 is an image of a Bode diagram of a general voltage mode DC / DC converter. As the frequency increases, the gain and phase change, and eventually the gain becomes 1 time (0 dB). This frequency 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), the feedback control can be determined to be stable. This margin is referred to as phase margin PM, and the higher the margin, the higher the stability. Generally, a phase margin of about 60 degrees is the best value that can achieve both stability and responsiveness. The gain and phase have an inflection point with respect to the change in frequency, and in the region I where the frequency is low, the gain decreases at −20 dB / dec as the frequency increases.

The frequency fz ₁ is the first zero point, the gain is increased by +20 dB / dec, and the phase is advanced by +90 deg. For this reason, there is no gain change in the region II, and the phase advances to 0 deg at the maximum.

The frequency f ₀ is an LC resonance frequency determined by the inductor 103 and the output capacitor 104, and is given by Expression (1). As the frequency increases, the gain is decreased by −40 dB / dec and the phase is delayed by −180 deg. For this reason, 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)
The frequency fz ₂ is the second zero, and similarly to the first zero fz ₁ , the gain is increased by +20 dB / dec and the phase is advanced by +90 deg. Therefore, in region IV, the gain changes at −20 dB / dec, and the phase delayed up to −180 deg in region III is restored. As a result, the phase margin can be ensured at the crossover frequency fc.

FIG. 3 is an exploded view of the frequency characteristics of FIG. 2 for each element. The digital filter characteristic is a characteristic determined by the digital filter 4 in FIG. 1, and the converter characteristic is a characteristic determined by other than the digital filter 4. The digital filter 4 adds two zeros fz ₁ and fz ₂ in addition to the integral characteristic that decreases the gain by −20 dB / dec in accordance with the frequency, and appropriately arranges them, thereby arranging the LC resonance frequency f of the converter characteristic. Reduce the slope of the gain drop at _zero .

Also, the digital filter 4 generates two zeros fz ₁ and fz ₂ in order to return the phase delayed by −180 deg at the maximum. By appropriately arranging the zeros fz ₁ and fz ₂ , the phase margin PM can be sufficiently secured. In general, it is desirable that the first zero point fz ₁ is set lower than the resonance frequency f ₀ and the second zero point fz ₂ is arranged between the LC resonance frequency f ₀ and the crossover frequency fc.

However, many 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. As a result, the output ripple voltage associated with the switching operation is suppressed, and adjustment is made so that the fluctuation of the output voltage when the sudden fluctuation of the output load current occurs falls within the standard range. For this reason, the LC resonance frequency f ₀ given by the equation (1) may change and the feedback operation may become unstable. This will be described in detail with reference to FIG.

For example, as shown in FIG. 4, a condition is considered in which the first zero point fz ₁ and the second zero point fz ₂ are optimized so that the output capacitor 104 can secure a sufficient phase margin PM with a small value. If only the output capacitor 104 is increased while maintaining this filter condition, the LC resonance frequency moves to f ₀ ′ 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, −60 dB / dec, and the slope becomes very steep.

As a result, since the crossover frequency fc ′ is lowered, the phase advance effect by the second zero point fz ₂ cannot be sufficiently obtained. For this reason, the phase margin PM ′ is insufficient, resulting in unstable operation. In order to solve this problem, it is necessary to obtain the LC resonance frequency f ₀ ′ after measuring the value of the output capacitor 104 and to optimize the first zero point fz ₁ and the second zero point fz ₂ based on this result.

Accordingly, the present invention provides a filter from the time immediately after the power source Vi is turned on until the first output voltage determined by the first comparison value is reached by causing the comparison value generating unit 2 to generate a small offset (first comparison value) in the comparison value. Inrush current is actively generated during the characteristic analysis period. The present invention calculates the value of the output capacitor 104 and the resonance frequency f ₀ by measuring the inrush current value and the filter characteristic analysis period Tr (inrush current generation period). In the present invention, the zeros fz ₁ and fz ₂ are optimally set according to the calculated resonance frequency f ₀ . This will be described with reference to FIG.

First, after the power source Vi is turned on, the comparison value generator 2 generates a first comparison value (small offset) in the filter characteristic analysis period Tr. For this reason, the output voltage Vo rises rapidly to the first output voltage determined by the first comparison value. At this time, an inrush current having a current value higher than that of the subsequent filter setting period Tf flows in the inductor current IL.

The current detection unit 6 calculates a peak current and a bottom current (in the example of FIG. 6, peak currents: IL ₁ and IL ₃ , bottom current: IL ₂ ) in a rush current generation period (filter characteristic analysis period Tr) with a predetermined number of bits. Convert to digital value. Specifically, the average value of the inrush current is obtained by applying to the equation (2).

ILave = (IL ₁ + IL ₂ + IL ₃ +... + IL _n ) / n (2)
Next, the filter characteristic analysis unit 7 obtains the value of the output capacitor 104 by substituting the inrush current average value ILave, the filter characteristic analysis period (inrush current generation period) Tr, and the first output voltage Vo1 into Expression (3). .

C = ILave × Tr / Vo1 (3)
The filter characteristic analysis unit 7 obtains the resonance frequency f ₀ by applying the capacitance value C of the output capacitor 104 and the inductor value L of the inductor 103 obtained in Expression (3) to Expression (1).

f ₀ = 1 / (2 · π · √ (L · C)) (1)
In the filter setting period Tf shown in FIG. 6, the resonance frequency f ₀ determined by the filter characteristic analysis unit 7 from the plurality of digital filter constant tables 81 set and stored in advance in the filter constant storage unit 8 is used. A filter constant is selected, and the selected filter constant is applied to the digital filter 4. Filter constant is composed of a first zero point fz ₁ and the second zero point fz ₂ and gain Aac. Specifically, the digital filter constant table 81 is selected such that the first zero point fz ₁ , the second zero point fz _2, and the gain Aac decrease as the LC resonance frequency f ₀ value decreases.

Here, the reason why the gain Aac needs to be adjusted will be described. If only the zero point is set to be low, the crossover frequency fc is high. The crossover frequency fc indicates the maximum frequency that can be controlled by the feedback control loop. The higher the crossover frequency fc, the higher the response performance of the feedback control. However, if the crossover frequency fc is excessively high, it becomes sensitive to noise. Therefore, in general, the crossover frequency fc is adjusted to be about 1/10 of the switching frequency.

Therefore, in the present invention, as shown in Table 1 below, the first zero point fz ₁ , the second zero point fz _2, and the gain Aac are set to work together. Table 1 shows a setting relationship between the resonance frequency and the digital filter constants of the plurality of digital filter constant tables 81.

As a result, as shown in FIG. 7, before the zero adjustment, the positional relationship between the first zero fz ₁ and the resonance point f ₀ is reversed. In particular, in the region II, the gain becomes −60 dB / dec, and the inclination is very small. It becomes steep. For this reason, the crossover frequency fc becomes low, the phase advance effect by the second zero point fz ₂ cannot be obtained, and the phase margin PM is insufficient.

However, after the zero point adjustment, as shown in FIG. 8, the first zero point fz ₁ ′, the second zero point fz ₂ ′, and the gain Aac are lowered according to the LC resonance frequency f ₀ . Accordingly, it is possible to configure a power supply with higher stability by preventing the crossover frequency fc ′ from becoming too high while sufficiently securing the phase margin PM.

In the soft start period Ts in FIG. 6, the comparison value generation unit 2 slowly increases the comparison value from the first comparison value to the second comparison value, thereby realizing a soft start operation of the output voltage Vo and preventing overshoot. To do. After that, when the output voltage Vo reaches the set voltage determined by the second comparison value, the steady operation period Tc is started and the steady operation is started.

In the prior art, since the filter characteristics are set after the soft start operation period, the feedback operation becomes unstable during the soft start operation period. On the other hand, in the present invention, since the setting of the digital filter 4 is completed before the output voltage Vo starts the soft start operation, the above problem does not occur.

As a method of detecting the inductor current IL, a method of directly detecting using the shunt resistor, a method of detecting indirectly using the DCR (DC resistance) of the inductor 103, or a non-contact detecting using the Hall element. You may use the method to do.

Further, the filter characteristic analysis unit 7 may end the filter characteristic analysis period when the output voltage Vo detected by the voltage detection unit 1 reaches a predetermined voltage lower than the first output voltage. The filter characteristic analysis unit 7 may end the filter characteristic analysis period when the peak value of the inductor current detected by the current detection unit 1 reaches a predetermined current or less.

As described above, according to the switching power supply device of the first embodiment, the filter characteristic analysis unit 7 performs filtering based on the inrush current value that flows in the filter characteristic analysis period immediately after starting the power supply and before the output voltage starts to increase. Analyze the characteristics. The filter constant storage unit 8 refers to a plurality of stored digital filter constant tables, selects a filter constant according to the analyzed filter characteristics, and applies the selected filter constant to the digital filter.

Thereafter, the comparison value generator 2 increases the comparison value from the first comparison value to the second comparison value after the output voltage reaches the first output voltage. That is, the soft start operation causes the output voltage to slowly rise 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 an unstable operation during the rising period of the output voltage.

(Example 2)
FIG. 9 is a configuration diagram of the switching power supply device according to the second embodiment. The second embodiment is different from the first embodiment in that a filter constant calculation unit 9 is provided instead of the filter constant storage unit 8. Since the other configuration of the second embodiment is the same as that of the first embodiment, only the filter constant calculation unit 9 will be described.

The filter constant calculation unit 9 uses the filter characteristic analysis result (LC resonance frequency f ₀ value) from the filter characteristic analysis unit 7, the target crossover frequency fca, the target phase margin PMa, and other information necessary for setting. Based on this, a filter constant satisfying the condition is calculated, and the calculated filter constant is applied to the digital filter 4. An example of a calculation method in the filter constant calculation unit 9 will be described.

Assuming that the optimized filter characteristics satisfy fz ₁ << f ₀ <fz ₂ << fca, the second zero point fz ₂ is expressed by an equation ( ₂₎ where the target crossover frequency is fca and the target phase margin is PMa. It can be estimated in 4).

fz ₂ ≈−fca · tan (PMa + 90 deg) −fz ₁ (4)
Further, the gain can be approximated by Expression (5), where Aac is a gain at an arbitrary frequency f (for example, a low frequency of about 10 Hz).

_{_{Aac ≒ fca · fz 1 · fz}} 2 / (f · f 0 · f 0) ··· (5)
Further, fz ₁ is expressed by Expression (6) because fz ₁ << fz ₂ is a precondition.

_{_{fz 1 ≒ fz 2/10 ···}} (6)
The filter constant calculation unit 9 calculates the first zero point fz ₁ , the second zero point fz ₂ , and the gain Aac from the equations (4), (5), and (6) shown above, and applies them to the digital filter 4. . Thereby, feedback control with sufficient stability can be realized. In the first embodiment, the filter constant storage unit 8 selects an optimal constant from the stored filter constant table in accordance with the LC resonance frequency f ₀ calculated by the filter characteristic analysis unit 7. Therefore, the variation range of acceptable LC resonance frequency f ₀ will be limited to some extent.

On the other hand, in the second embodiment, since the filter constant calculation unit 9 calculates the filter constant by calculation, stable feedback control can be realized even if the LC resonance frequency f ₀ varies in a wider range.

As described above, according to the switching power supply device of the second embodiment, the filter characteristic analysis unit 7 performs the filter characteristic based on the inrush current value that flows in the filter characteristic analysis period immediately after starting the power supply and before the output voltage starts to increase. Analyze. The filter constant calculation unit 9 calculates an optimum filter constant corresponding to the filter characteristic and applies it to the digital filter.

(Example 3)
FIG. 10 is a configuration diagram of the switching power supply device according to the third embodiment. In the switching power supply device according to the third embodiment, the overcurrent protection unit 10 is added to the switching power supply device according to the second embodiment, and the driving unit 5 is changed to the driving unit 5b. Since the other configuration shown in FIG. 10 is the same as the configuration shown in FIG. 9, only the different configuration will be described.

The overcurrent protection unit 10 compares the peak value of the current detection signal detected by the current detection unit 6 with the overcurrent threshold IOCP, and when the peak value reaches the overcurrent threshold IOCP, the overcurrent protection unit 10 is off-triggered. Output a signal. That is, the overcurrent protection unit 10 limits the ON period of the switching element.

The driving unit 5b receives the off-trigger signal from the overcurrent protection unit 10 and stops the high-side MOSFET 101 in a pulse-by-pulse manner. As a result, the inrush current flowing during the filter characteristic analysis period can be limited by the overcurrent threshold IOCP. For this reason, in the second embodiment, the peak current and the bottom current in the inrush current generation period Tr (filter characteristic analysis period) are measured and the inrush current average value ILave is obtained using the equation (2). Then, since the peak value of the inrush current is limited by the overcurrent threshold IOCP, a certain amount of inrush current average value ILave can be predicted without measurement, and the configuration can be simplified.

Further, the filter characteristic analysis unit 7 may end the filter characteristic analysis period when the output voltage Vo detected by the voltage detection unit 1 reaches a predetermined voltage lower than the first output voltage. The filter characteristic analysis unit 7 may end the filter characteristic analysis period when the peak current value of the inductor current detected by the current detection unit 1 falls below the overcurrent threshold.

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

DESCRIPTION OF SYMBOLS 1 Voltage detection part 2 Comparison value generation part 3 Subtractor 4

Digital filter

5, 5b Drive part 6 Current detection part 7 Filter characteristic analysis part 8 Filter constant storage part 9 Filter operation part 10 Overcurrent protection part 81 Several digital filter constant table 101 high-side MOSFET
102 Low-side MOSFET
103 Inductor 104 Output capacitor 105 Output load Vi Power supply

Claims

A switching power supply device that converts a first DC voltage supplied from a power supply by turning on and off a switching element into a second DC voltage via an inductor and an output capacitor and supplies the output voltage to an output load,
A first output voltage having a first comparison value and a second comparison value greater than the first comparison value, generating the first comparison value after the power is turned on, and the output voltage corresponding to the first comparison value A comparison value generating unit that raises the comparison value from the first comparison value to the second comparison value after reaching
A digital filter that performs a predetermined operation on an error between the first comparison value or the second comparison value generated by the comparison value generation unit and the output voltage;
A drive unit for controlling on / off duty of the switching element in accordance with a calculation result of the digital filter;
A current detection unit that detects a current flowing through the inductor and outputs the detected current as a current detection signal;
The inductor, the output capacitor, and the output capacitor based on a filter characteristic analysis period from when the current detection signal, the first output voltage, and the first comparison value are generated to when the output voltage reaches the first output voltage. A filter characteristic analysis unit for analyzing the filter characteristic determined by
A plurality of digital filter constant tables storing a plurality of filter constants corresponding to a plurality of filter characteristics, and the plurality of digital filters in a period until the comparison value shifts from the first comparison value to the second comparison value; A filter constant storage unit that refers to a filter constant table, selects the filter constant according to the filter characteristic analyzed by the filter characteristic analysis unit, and supplies the selected filter constant to the digital filter;
A switching power supply device comprising:
The filter characteristic is a resonance frequency determined by the inductor and the output capacitor,
The filter constant storage unit stores a plurality of the resonance frequencies and zeros in the gain of the Bode diagram for determining the stability of the feedback loop, and stores the filter characteristic analysis unit from the plurality of zeros. The switching power supply device according to claim 1, wherein a zero point corresponding to the resonance frequency from is selected and supplied to the digital filter.
The switching power supply device according to claim 2, wherein the filter constant storage unit sets at least one of the zeros to a frequency lower than the resonance frequency.
The current detection unit calculates an average value based on a peak value and a bottom value of the current flowing through the inductor during the filter characteristic analysis period, and outputs the calculated average value as the current detection signal. The switching power supply device described in 1.
An overcurrent protection unit that limits an on period of the switching element by limiting a peak value of the current flowing through the inductor during the filter characteristic analysis period with an overcurrent threshold;
2. The current detection unit according to claim 1, wherein the current detection unit predicts an average value of a current flowing through the inductor during the filter characteristic analysis period based on the overcurrent threshold and outputs the predicted average value as the current detection signal. Switching power supply.
6. The switching power supply device according to claim 4, wherein the filter characteristic analysis unit ends the filter characteristic analysis period when the output voltage reaches a predetermined voltage lower than the first output voltage.
The switching according to claim 4 or 5, wherein the filter characteristic analysis unit ends the filter characteristic analysis period when the peak value of the inductor current detected by the current detection unit reaches a predetermined current or less. Power supply.
A switching power supply device that converts a first DC voltage supplied from a power supply by turning on and off a switching element into a second DC voltage via an inductor and an output capacitor and supplies the output voltage to an output load,
A first output voltage having a first comparison value and a second comparison value greater than the first comparison value, generating the first comparison value after the power is turned on, and the output voltage corresponding to the first comparison value A comparison value generating unit that raises the comparison value from the first comparison value to the second comparison value after reaching
A digital filter that performs a predetermined operation on an error between the first comparison value or the second comparison value generated by the comparison value generation unit and the output voltage;
A drive unit for controlling on / off duty of the switching element in accordance with a calculation result of the digital filter;
A current detection unit that detects a current flowing through the inductor and outputs the detected current as a current detection signal;
The inductor, the output capacitor, and the output capacitor based on a filter characteristic analysis period from when the current detection signal, the first output voltage, and the first comparison value are generated to when the output voltage reaches the first output voltage. A filter characteristic analysis unit for analyzing the filter characteristic determined by
In the period until the comparison value shifts from the first comparison value to the second comparison value, a filter constant is calculated according to the filter characteristic analyzed by the filter characteristic analysis unit, and the calculated filter constant is A filter constant calculator for supplying to the digital filter;
A switching power supply device comprising:
The filter characteristic is a resonance frequency determined by the inductor and the output capacitor,
The filter constant calculation unit is configured to filter the filter characteristics based on the resonance frequency, a target crossover frequency in a gain of a Bode diagram for determining stability of a feedback loop, and a target phase margin in a phase of the Bode diagram. The switching power supply according to claim 8, wherein the calculated filter characteristic is supplied to the digital filter.
The switching power supply device according to claim 9, wherein the filter constant calculation unit performs calculation so that at least one zero point in the gain of the Bode diagram is lower than the resonance frequency.
The current detection unit outputs the average value calculated by calculating an average value from a peak value and a bottom value of the current flowing through the inductor during the filter characteristic analysis period as the current detection signal. The switching power supply device described.
An overcurrent protection unit that limits an on period of the switching element by limiting a peak value of the current flowing through the inductor during the filter characteristic analysis period with an overcurrent threshold;
The switching according to claim 8, wherein the current detection unit predicts an average value of a current flowing through the inductor during the filter characteristic analysis period from the overcurrent threshold and outputs the predicted average value as the current detection signal. Power supply.
The switching power supply device according to claim 11 or 12, wherein the filter characteristic analysis unit ends the filter characteristic analysis period when the output voltage reaches a predetermined voltage lower than the first output voltage.
The switching according to claim 11 or 12, wherein the filter characteristic analysis unit ends the filter characteristic analysis period when the peak value of the inductor current detected by the current detection unit reaches a predetermined current or less. Power supply.