JP6971102B2 - Lighting power supply and program that can execute PWM control by a microcomputer - Google Patents

Description

The present invention relates to a power supply device for lighting capable of performing PWM control by a microcomputer.

Lighting fixtures using light emitters such as LED elements are widespread in the field of general-purpose lighting fixtures. In particular, many LED elements can maintain lighting even with a small current, and even though the actual lighting current is small, it does not feel so dark to human vision, so a wide range from near zero to 100%. There is a need for lighting fixtures that enable continuous dimming in.

The power supply device of the lighting equipment basically requires constant current control due to the characteristics of the forward voltage and the forward current of the LED element. Then, in order to supply a stable continuous current to the illumination light source (LED element), a configuration of a switching power supply circuit including a power storage element such as an inductance element, a switching element and an electrolytic capacitor is generally used as a power supply device.

Further, as a control circuit for controlling the operation of the switching element of the switching power supply circuit, a PWM control circuit is usually used. The PWM control circuit repeatedly oscillates a rectangular wave signal (referred to as a PWM signal) having a variable on period to operate the switching element on and off. Then, by changing the on-duty of the PWM signal in conjunction with the dimming signal from the outside, the light output of the lighting equipment corresponding to the dimming signal can be obtained.

Recently, an increasing number of PWM control circuits have a digital control configuration. In the conventional PWM signal by analog control, the control characteristics vary due to the error of the characteristics of each element such as a capacitor and a resistor in the control circuit. On the other hand, in the case of a digital control configuration, since the characteristics of the control circuit are determined by setting the coefficients, there is almost no variation in the characteristics of each control circuit.

The digital PWM control circuit is usually composed of an A / D conversion unit, a digital arithmetic unit (CPU), a PWM timer unit, a storage unit, and the like, and all of them are called a microcontroller unit (MCU). In this book, it is abbreviated as microcomputer. For example, by executing a program by the CPU, the A / D converter reads a dimming signal from the outside, a feedback signal such as a load voltage of a power supply device, and the like as digital values. The digital arithmetic unit calculates the on-duty value of switching based on the read input value. Then, the PWM timer unit repeatedly executes a timekeeping process based on the on-duty value to repeatedly create a rectangular wave for a desired on-period, and outputs it as a PWM signal. The PWM signal is sent to the driver IC of the switching element or the like, and is used for the on / off operation of the switching element. Patent Document 1 is given as an example of such a digital PWM control circuit. In Patent Document 1, the microcomputer determines the on-width of the on / off signal by numerical calculation of a program based on the detected voltage values from a plurality of detection points on the switching power supply circuit, and executes constant current control of the LED element. The power supply is shown.

Japanese Unexamined Patent Publication No. 2014-032748 (see FIG. 3)

By the way, when executing PWM control using a microcomputer, a microcomputer equipped with a CPU having a large number of bits and its peripheral devices may be used, but for the purpose of simplifying the system design and suppressing the manufacturing cost, the number of bits is reduced. There are also cases where you want to actively use a general-purpose microcomputer such as a suppressed 8-bit or 16-bit microcomputer. Here, the "number of bits" is usually defined by the data width of the data bus of the CPU or the data width that the CPU can process at one time.

On the other hand, when a general-purpose microcomputer as described above is used, it is difficult to maintain a high on-duty resolution of the generated PWM signal while supporting a high switching frequency of, for example, around 100 KHz, and the performance of the microcomputer to be used. Depending on the case, the on-duty resolution may be low. For example, when an 8-bit microcomputer is used to execute a switching frequency of 100 KHz, if the number of clocks for 8 bits (0 to 255 clocks) is assigned to one switching cycle (10 μsec cycle), one clock is processed. The time is 10 μs ÷ 256 = about 39 n seconds, which is a guideline for the processing speed (clock frequency) required for the microcomputer. As for the on-duty resolution of the PWM signal in one cycle of the square wave, since the number of 8-bit clocks is 256, the on-duty width that can be adjusted in one clock is 100% ÷ 256 = about 0. It will be 39%. Adjusting the on-duty in increments of about 0.39% is the limit of the on-duty resolution.

In this way, regarding the on-duty resolution at the time of PWM signal generation, no matter how finely the on-duty is adjusted, the amount of increase / decrease for one clock determined by the number of bits of the microcomputer (for example, about 0.39%) is set as one unit. The limit was to adjust. Therefore, in order to adjust the switching on-duty with higher resolution, it was necessary to select a microcomputer with high specifications (clock frequency and number of bits).
The PWM control may adjust the on-duty or the off-duty, and in either case, it is difficult to adjust the duty with higher resolution if the processing capacity of the microcomputer remains the same.

The present invention has been made in view of the above problems, and an object thereof is lighting capable of digitally adjusting the duty at the time of PWM signal generation with high resolution even with the processing capacity of a conventional microcomputer. The purpose is to provide a power supply device and a program.

That is, the power supply device for lighting of the present invention is
A switching power supply circuit that supplies power to the illumination light source,
A PWM control circuit that oscillates a pulse width modulation (PWM) signal to a switching element provided in the switching power supply circuit to control the switching element by PWM.
Is configured with
The PWM control circuit generates a digital calculation unit for determining a duty command value (for example, 39.9%) of the PWM signal according to a dimming signal from the outside, and a square wave corresponding to the duty command value. Has a square wave generator for
The digital calculation unit obtains an approximate duty value (for example, 40%) that can be generated at the resolution according to the duty command value based on the resolution of the duty determined by the number of bits of the digital calculation unit (for example, 1%). Configured to calculate
The square wave generation unit is configured to repeatedly generate a square wave based on the estimated duty value (40%).
The digital arithmetic unit further uses the estimated duty value (40%) to compensate for the difference (0.1%) between the estimated duty value (39.9%) and the estimated duty value (40%). The generated square wave sequence is grouped into a plurality of (for example, 10) square waves, and the duty of at least one of the plurality of square waves in each group is set to the resolution (1%) of the duty. ) Is increased or decreased (for example, the duty of one square wave in a group is reduced by 1% by 1%) .
In order to further lower the lower limit of the duty, the digital arithmetic unit further groups a sequence of square waves composed of the units of the resolution into a plurality of square waves, and at least one of the plurality of square waves in each group. It is characterized in that it is configured to thin out two square waves.

The numbers in parentheses are examples. Here, the "switching power supply circuit" includes, but is not limited to, various chopper circuits composed of an inductance element, a switching element, and a power storage element, a flyback type power conversion circuit, and the like, but at least switching. It is assumed that a circuit capable of supplying desired power to the illumination light source by turning the element on and off is included.
Further, the present invention can be applied both when adjusting the on-duty of the PWM signal and when adjusting the off-duty.

Next, the program of the present invention is for generating a pulse width modulation (PWM) signal to a switching power supply circuit for lighting.
For a computer configured with a digital arithmetic unit and a square wave generator
A command value determination step for determining a duty command value of the PWM signal according to a dimming signal from the outside, and a command value determination step.
An approximate value calculation step for calculating a duty approximate value that can be generated at the resolution according to the duty command value based on the duty resolution determined by the number of bits of the digital calculation unit.
A square wave generation step instructing the square wave generation unit to repeatedly generate a square wave based on the estimated duty value, and a square wave generation step.
At the same time as the square wave generation step, a difference compensation step that compensates for the difference between the duty command value and the estimated duty value, and
To execute,
In the difference compensation step, a sequence of square waves generated by the estimated duty value is grouped into a plurality of square waves, and at least among the plurality of square waves in each group for the square wave generation unit. Command the duty of one square wave to be increased or decreased by the unit of the resolution of the duty .
In the difference compensation step, in order to further lower the lower limit of the duty, a row of rectangular waves composed of the units of the resolution is grouped into a plurality of square waves, and each group is referred to the square wave generation unit. It is characterized in that at least one square wave is instructed to be thinned out from a plurality of square waves in the box.

In the present invention, even if the duty command value (for example, 39.9%) at the time of generating the PWM signal is at a level that cannot be generated by the resolution of the duty (for example, 1%) determined by the number of bits of the microcomputer, first of all, the duty command value is the same. We decided to generate a square wave by calculating an approximate value of duty (for example, 40%) at a level that can be generated with resolution. Then, in order to compensate for the difference (0.1%) between the duty command value (39.9%) and the estimated duty value (40%), the rectangular wave columns are grouped and within the group as follows. I decided to perform some square wave duty increase / decrease processing. That is, the sequence of square waves generated by the estimated duty value (40%) is grouped by a plurality of square waves, and the duty of at least one of the plurality of square waves in each group is the resolution ( It is increased or decreased in units of 1%). For example, if 10 square waves are regarded as one group and only the duty of one of them is 39%, the average duty of the group is (40% × 9 + 39% × 1) ÷ 10 = 39.9%. , Same as the duty command value. By using such a row of square waves as a PWM signal, the average duty for each group becomes the same level as the duty command value, and even with the processing capacity of the conventional microcomputer, the duty for generating the PWM signal can be increased. Digital adjustment becomes possible with high resolution. In addition, the lower limit of on-duty (dimming lower limit) can be made smaller than before.

It is a schematic block diagram of the power supply device for lighting which concerns on 1st Embodiment of this invention. It is a processing flow diagram of the said embodiment. It is an image diagram of the conventional PWM control. It is an image diagram of the PWM control of the said embodiment. It is a figure for demonstrating the improvement of the resolution of the PWM control in the said Embodiment. It is an image diagram of the dimming control which concerns on the 2nd Embodiment of this invention. It is a figure for demonstrating the thinning process of a pulse (rectangular wave) in the said embodiment. It is a graph which shows the relationship between the optical output (%) and on-duty (%) of switching in the said embodiment. The graph which shows the relationship between the light output (%) and the dimming signal (%) in the said embodiment.

(First Embodiment)
FIG. 1 shows a schematic configuration of an LED power supply for lighting according to the first embodiment of the present invention. The lighting LED power supply 10 oscillates a pulse width modulation (PWM) signal toward the switching power supply circuit 4, the driver IC 6 that turns on and off the switching element 5 provided in the switching power supply circuit 4, and the driver IC 6. It is configured to include a digital PWM control circuit 8 that PWM-controls the switching element 5. The switching power supply circuit 4 receives electric power from an external AC power supply 3 and supplies a predetermined current to the LED element 2 which is an illumination light source.

FIG. 1 shows a configuration of a switching power supply circuit of a method of switching the high side side of the LED element 2, but the present invention is not limited to this, and a power supply circuit of a method of switching the low side side may be used. Further, as the switching power supply circuit, various chopper circuits including an inductance element, a switching element, and a power storage element, a flyback type power conversion circuit, and the like may be adopted.

The digital PWM control circuit 8 is composed of a one-chip microcomputer or the like, and a dimming signal from an external dimming controller or the like is input. Further, a voltage value or the like at a detection point (not shown) of the switching power supply circuit 4 is input as a feedback (FB) signal.

The digital PWM control circuit 8 includes an A / D conversion unit 12 that digitally converts a dimming signal, a digital calculation unit (CPU) 14 that handles various digital calculations, a square wave generation unit (PWM timer, etc.) 16, programs, and various parameters. It is composed of a storage unit 18 and the like for storing.

The digital arithmetic unit 14 is configured to realize each function such as determining the on-duty command value of the PWM signal by executing the program of the storage unit 18. Specifically, the digital calculation unit 14 compensates for the difference between the on-duty command value (duty command value) determination unit 20 and the on-duty approximate value (duty approximate value) calculation unit 22. The difference compensation unit 24 includes a grouping unit 26 and an on-duty increase / decrease unit 28.

The rectangular wave generation unit 16 is provided to generate a rectangular wave according to a determined on-duty command value and repeatedly output the rectangular wave to the driver IC 6.

Hereinafter, a specific flow of arithmetic processing of the digital PWM control circuit 8 characteristic of the present invention will be described with reference to FIG. The series of arithmetic processing is started by the digital arithmetic unit 18 executing the program of the storage unit 18.

First, in the A / D conversion step (S10) of FIG. 2, the dimming signal (for example, 50.1%) of the analog voltage is converted into a digital value by the A / D conversion unit 12. Further, each detected value of the switching power supply circuit 4 is A / D converted as needed. For example, the converted dimming data may be appropriately corrected with the data of each detected value and treated as reference data. The reference data in this case is based on the dimming signal information, and the on-duty command value of the PWM signal to the switching element 5 is based on the reference data by the next on-duty digital calculation step (S20). Is calculated. Here, for the sake of simplicity, the procedure for determining the on-duty command value will be described using the converted dimming data as it is. When the signal from the outside is a digital signal, it is input to the digital PWM control circuit without A / D conversion.

In the on-duty digital calculation step (S20), the command value determination unit 20 in the digital calculation unit 18 calculates the on-duty command value based on the dimming data. For example, a 39.9% on-duty command value is calculated based on 50.1% dimming data. In this step, when the digital calculation unit 18 uses the data table stored in the storage unit 18 in advance, the dimming data is converted into a table to calculate the on-duty command value. Alternatively, when the digital arithmetic unit 18 uses the control formula incorporated in the program, the on-duty command value is calculated by performing a process of multiplying the dimming data by a predetermined coefficient. The on-duty command value may be calculated by using both the table conversion and the use of the control formula.

Further, in the digital calculation step (S20), the approximate value calculation unit 22 in the digital calculation unit 18 can generate on-duty with this resolution based on the on-duty resolution determined by the number of bits of the digital calculation unit 14. Calculate the approximate value. For example, assuming that the on-duty resolution determined by the number of bits of the digital arithmetic unit 14 is exactly 1%, the estimated value of the on-duty with respect to the command value of the on-duty of 39.9% is 39% or 40%. Here, a case where 40% close to the command value is used as an approximate value of on-duty will be described.

Next, a procedure for generating a rectangular wave corresponding to a digitally calculated on-duty command value will be described. In the square wave generation step (S30) of FIG. 2, the square wave generation unit 16 generates a square wave based on an estimated on-duty value (40%). By repeatedly outputting such a rectangular wave, a PWM signal to the switching element 5 is formed.

At the same time as the square wave generation step (S30), the difference compensation unit 24 in the digital calculation unit 18 sets the difference (0.1%) between the on-duty command value (39.9%) and the approximate value (40%). Perform the process for compensation. Specifically, the grouping unit 26 in the difference compensation unit 24 groups the sequence of square waves generated by the approximate value (40%) of the on-duty into, for example, 10 square waves. Here, since the on-duty resolution is 1% and the difference to be compensated is 0.1%, the number of square waves included in each group is 10, and 10 in each group. The on-duty of one of the square waves is changed from 40% to 39%, which is obtained by subtracting 1% of the resolution. The selection of the rectangular wave to be changed on the on-duty and the on-duty change processing of the square wave are executed by the on-duty increase / decrease unit 28 in the difference compensation unit 24. By executing such difference compensation, the average on-duty of each group becomes, for example, (40% × 9 + 39% × 1) ÷ 10 = 39.9%, which is the same as the on-duty command value.

When the on-duty command value is 39.7%, the difference to be compensated is 0.3%, and the on-duty resolution is reduced from 40% for 3 square waves in the group of 10 square waves. It may be changed to 39% by subtracting 1% of. Alternatively, for one of the 10 square wave groups, the on-duty may be changed to 36%, which is 40% minus 3%, which is 3 times the resolution of 1%. Both processes result in the average on-duty for each group being the same as the on-duty command value. In this process, when selecting a plurality of square waves from one group, it is preferable to select evenly from the entire column of square waves so that the square waves to be adjusted for duty are not biased as much as possible.

The setting of the number of square waves to be included in the group may be determined in relation to the magnitude of the on-duty resolution. For example, considering the case where the on-duty resolution is 0.39%, the estimated on-duty value for the command value (39.7%) is 39.78%, and the difference to be compensated is 0.08%. Become. As an example of the compensation procedure, the number of square waves included in the group is 20, and the on-duty for 3 of them is 39.78% minus 0.39% to 39.39%. do. As a result, the average on-duty for each group is about 39.72%, which can be closer to the command value of 39.7% than the estimated value of 39.78%. As described above, the number of square waves included in one group can be increased to more than 10 or less than 10. When using an 8-bit MCU for the convenience of timing continuous square waves, the maximum number of square waves in one group is 256. The effective on-duty resolution in this case is improved to 100% ÷ 256 ÷ 256 = about 0.0015%. Therefore, it may be determined according to the number of bits of the digital arithmetic unit that uses the maximum wave number of one group.

Further, when the on-duty command value becomes, for example, 39.2%, the estimated on-duty value is changed from 40% to 39%. Then, in the process of compensating for the difference (0.2%), the on-duty of two of the ten square waves in each group is changed from 39% to 40%, which is the sum of 1% of the resolution. do. As a result, the average on-duty of each group becomes the same as the on-duty command value.

As can be seen from the above various cases, the number of square waves whose on-duty should be changed from within the group is determined according to the magnitude of the difference to be compensated, and for one or more determined square waves. I decided to increase or decrease the on-duty in units of its resolution. By using a string of square waves whose on-duty has been increased or decreased in this way as a PWM signal, the average on-duty for each group becomes the same level as the on-duty command value, and even with the processing capacity of the conventional microcomputer, It is possible to digitally adjust the on-duty at the time of PWM signal generation with high resolution.

Actually, the PWM signal generation program executed by the digital PWM control circuit 8 is configured as follows. That is, the PWM signal generation program causes the command value determination unit 20 to determine the on-duty command value of the PWM signal based on the data such as the dimming signal after the A / D conversion, and the approximate value calculation unit 22. A step of calculating an approximate value of on-duty that can be generated based on the on-duty resolution determined by the number of bits, a step of causing the square wave generation unit 16 to repeatedly generate a rectangular wave based on the approximate value of on-duty, and this rectangle. At the same time as the wave is generated, the difference compensating unit 24 is configured to include a step of compensating for the difference between the on-duty command value and the approximate value. Then, in the step of difference compensation, the grouping unit 26 is made to group a row of rectangular waves for each of a plurality of rectangular waves, and the on-duty increase / decrease unit 28 is made to have at least one of the plurality of rectangular waves in each group. The on-duty of the wave is increased or decreased in units of the on-duty resolution. By executing such a program, the average on-duty of the PWM signal generated by the rectangular wave generation unit 16 can be brought close to the command value.

FIG. 3 shows a conventional control image. When the on-duty resolution is 1%, even if the on-duty command value changes from 50% to 49.9%, the on-duty of the output PWM signal remains 50% or is higher than the command value. You have the option of lowering it to 49%, which is significantly smaller. On the other hand, according to the control method of the present embodiment shown in FIG. 4, even if the on-duty resolution remains 1%, the average on-duty of a group of a plurality of square waves becomes 49.9%, which is the same as the command value. can do. As schematically shown in FIG. 5, in digital PWM control, the on-duty changes inevitably discontinuously, but if the control method of the present embodiment is used, the on-duty resolution determined by the number of bits of the CPU is used. For example, even if it remains at 1%, the on-duty can be changed stepwise with a higher resolution.

(Second embodiment)
The contents of the PWM control according to the second embodiment of the present invention will be described with reference to FIGS. 6 and 7. The configuration of the LED power supply for lighting is the same as the configuration of the above-described embodiment, but is characterized in that the lower limit of on-duty (dimming lower limit) can be made smaller than before.

Also in this embodiment, it is assumed that the on-duty resolution determined by the number of bits of the digital arithmetic unit 14 is 1%. FIG. 6 shows a pattern of the PWM signal output when the on-duty command value calculated in the digital calculation step (S20) changes from 1% to 0.9%.

First, as in the above-described embodiment, in the digital calculation step (S20), an approximate value of on-duty that can be generated with on-duty resolution is calculated. Here, it is an approximate value of 1%.
Next, in the rectangular wave generation step (S30), a rectangular wave based on the calculated on-duty estimated value (1%) is generated and repeatedly output.
Further, at the same time as the rectangular wave generation step (S30), a process for compensating for the difference (0.1%) between the on-duty command value (0.9%) and the approximate value (1%) is executed. Specifically, the sequence of square waves generated by the approximate value of on-duty (1%) is divided into groups, for example, by 10 square waves, and one of the 10 square waves in each group. Change the on-duty of each square wave to 0%, which is 1% minus 1% of the resolution. That is, one square wave is thinned out from the sequence of ten square waves. As shown in FIG. 7, the selection of one square wave to be the target of the thinning process may be arbitrarily selected from the sequence of ten square waves. By executing such a thinning process, the average on-duty of each group becomes (1% × 9 + 0% × 1) ÷ 10 = 0.9%, which is the same as the on-duty command value.

When the on-duty command value is 0.7%, the difference to be compensated is 0.3%, and the on-duty is 1% to 0 for 3 square waves in the group of 10 square waves. You can change it to% respectively.

When thinning out two or more square waves from the same group, it is preferable to select so that two consecutive square waves are not thinned out. Also, it is preferable to select so that both the front and last square waves of the group are not thinned out. This is because if the rectangular wave targeted for thinning continues to exist, the pause period of the load current becomes long, which may cause the LED element to flicker.

FIG. 8 graphically shows the relationship between the optical output (%) of the LED element and the on-duty (%) of switching. As shown in this graph, in the actual design, the relationship between the two companies is set so that an optical output with a rating of 100% can be obtained when switching is performed with, for example, 80% on-duty. To obtain 50% light output, set the on-duty to 50% x 0.8 = 40%.

Further, FIG. 9 graphically shows the relationship between the light output (%) of the LED element and the dimming signal. As shown in this graph, the optical output (%) and the dimming signal can be set to have a linear relationship, or the two companies can be set to have a non-linear relationship. In the latter case, as shown in FIG. 9, the dimming signal when obtaining a light output of 50% is about 20%. When converting to a table in the above embodiment, various data tables as shown in FIG. 9 can be applied.

In the above embodiment, the case where the digital arithmetic unit such as the CPU calculates the switching on-duty so that the dimming can be performed according to the dimming signal from the outside has been described.
There is a merit to apply the present invention to a switching power supply circuit that does not have a dimming function. For example, the present invention may be applied when the switching power supply circuit is controlled by a constant current by a microcomputer or the like.
Depending on the type of switching power supply circuit, the off-duty may be adjusted instead of the PWM control by adjusting the on-duty. INDUSTRIAL APPLICABILITY The present invention can be widely applied to PWM control duty adjustment regardless of the distinction between on-duty adjustment and off-duty adjustment.

2 LED element (illumination light source)
4 Switching power supply circuit 5 Switching element 8 PWM control circuit 10 Lighting power supply unit 14 Digital arithmetic unit (CPU)
16 Square wave generator

Claims (2)

A switching power supply circuit that supplies power to the illumination light source,
A PWM control circuit that oscillates a pulse width modulation (PWM) signal to a switching element provided in the switching power supply circuit to control the switching element by PWM.
A power supply for lighting that is configured with
The PWM control circuit includes a digital calculation unit for determining a duty command value of the PWM signal according to a dimming signal from the outside, and a square wave generation unit for generating a square wave corresponding to the duty command value. And have
The digital calculation unit is configured to calculate an approximate duty value that can be generated at the resolution according to the duty command value , based on the resolution of the duty determined by the number of bits of the digital calculation unit.
The square wave generation unit is configured to repeatedly generate a square wave based on the estimated duty value.
In order to compensate for the difference between the duty command value and the estimated duty value, the digital arithmetic unit further groups a sequence of rectangular waves generated by the estimated duty value into a plurality of square waves, and each group. The duty of at least one of the plurality of square waves in the square wave is configured to increase or decrease in units of the resolution of the duty .
In order to further lower the lower limit of the duty, the digital arithmetic unit further groups a sequence of square waves composed of the units of the resolution into a plurality of square waves, and at least one of the plurality of square waves in each group. It is configured to thin out two square waves,
A power supply for lighting that is characterized by that. A program for generating a pulse width modulation (PWM) signal to a switching power supply circuit for lighting.
For a computer configured with a digital arithmetic unit and a square wave generator
A command value determination step for determining a duty command value of the PWM signal according to a dimming signal from the outside, and a command value determination step.
An approximate value calculation step for calculating a duty approximate value that can be generated at the resolution according to the duty command value based on the duty resolution determined by the number of bits of the digital calculation unit.
A square wave generation step instructing the square wave generation unit to repeatedly generate a square wave based on the estimated duty value, and a square wave generation step.
At the same time as the square wave generation step, a difference compensation step that compensates for the difference between the duty command value and the estimated duty value, and
To execute,
In the difference compensation step, a sequence of square waves generated by the estimated duty value is grouped into a plurality of square waves, and at least among the plurality of square waves in each group for the square wave generation unit. Command the duty of one square wave to be increased or decreased by the unit of the resolution of the duty .
In the difference compensation step, in order to further lower the lower limit of the duty, a row of rectangular waves composed of the units of the resolution is grouped into a plurality of square waves, and each group is referred to the square wave generation unit. A program characterized in that at least one square wave is instructed to be thinned out from a plurality of square waves in the program.

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