JP2019050088A - Power supply device for illumination and program capable of executing pwm control by micro computer - Google Patents

Abstract

To provide a power supply device for illumination capable of performing digital adjustment of on-duty with high resolving-power at the PWM signal generation time, even with the processing capacity of a conventional micro computer.SOLUTION: A power supply device 10 for illumination includes a switching power supply circuit 4, and a PWM control circuit 8 oscillating a PWM signal to the switching elements 5 thereof. The PWM control circuit 8 has a digital arithmetic part 14 for determining the command value of on-duty, and a rectangular wave generation part 16 for generating a rectangular wave according to the command value. The digital arithmetic part 14 calculates the approximate value of on-duty that can be generated based on the resolving-power of on-duty determined by bit number. The rectangular wave generation part 16 generates a rectangular wave based on the approximate value of on-duty. The digital arithmetic part 14 is configured to group a train of rectangular waves, generated by the approximate values of on-duty, and to increase or decrease the on-duty of at least one rectangular wave in each group, in units of the resolving-power thereof.SELECTED DRAWING: Figure 1

Description

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

  A luminaire using a light emitter such as an LED element is widespread in the field of general luminaires. In particular, there are many LED elements that can keep their lighting even with a small current, and the actual lighting current is small, but they are not so dark by human vision, so a wide range from near zero to 100 percent There is a need for a luminaire that allows for continuous dimming of light.

  The power supply device of the lighting device basically requires constant current control because of the characteristics of the forward voltage and forward current of the LED elements. And in order to supply a stable continuous current to an illumination light source (LED element), the composition of the switching power supply circuit which consists of electrical storage elements, such as an inductance element, a switching element, and an electrolytic capacitor, is common as a power supply device.

  Also, as a control circuit that controls 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) whose ON period is variable, to turn on and off the switching element. Then, by changing the on-duty of the PWM signal in conjunction with the dimming signal from the outside, the light output of the luminaire according to the dimming signal can be obtained.

  Recently, the number of PWM control circuits having digital control configurations has increased. In the PWM signal based on the conventional analog control, variation in control characteristics occurs due to an error in characteristics of each element such as a capacitor or a resistor in the control circuit. On the other hand, in the case of the digital control configuration, since the characteristics of the control circuit are determined by the setting of the coefficients, variations in characteristics among the control circuits hardly occur.

  The digital PWM control circuit is usually composed of an A / D conversion unit, a digital operation unit (CPU), a PWM timer unit, a storage unit and the like, and the whole thereof is called a micro controller unit (MCU). In this document, it is abbreviated as microcomputer. For example, when the CPU executes a program, the A / D conversion unit reads a dimming signal from the outside, a feedback signal such as a load voltage of the power supply apparatus, or the like as a digital value. The digital calculation unit calculates the on-duty value of switching based on the read input value. Then, the PWM timer unit executes time measurement processing based on the on-duty value, repeatedly creates a rectangular wave of a desired on period, and outputs it as a PWM signal. The PWM signal is sent to a driver IC or the like of the switching element and used for on / off operation of the switching element. Patent Document 1 is given as an example of such a digital PWM control circuit. Patent Document 1 discloses an LED in which a microcomputer determines the on width of an on / off signal by numerical calculation of a program based on detection voltage values from a plurality of detection points on a switching power supply circuit, and executes constant current control of LED elements. A power supply is shown.

JP, 2014-032748, A (refer to Drawing 3)

  By the way, when executing PWM control using a microcomputer, any microcomputer having a CPU with a large number of bits and its peripheral devices may be used. However, for the purpose of simplifying system design and suppressing manufacturing costs, etc. In some cases, it may be desirable to actively use a suppressed 8-bit or 16-bit general-purpose microcomputer. Here, the “number of bits” is usually defined by the data width of the data bus of the CPU or the data width which can be processed by the CPU at one time.

  On the other hand, when using a general-purpose microcomputer as described above, it is difficult to maintain the on-duty resolution of the generated PWM signal in a high state while supporting a high switching frequency of around 100 KHz, for example. In some cases, the on-duty resolution may be reduced. For example, when executing a switching frequency of 100 KHz using an 8-bit microcomputer, if a clock number (0 to 255 clocks) for 8 bits is assigned to one switching cycle (10 μs cycle), 1 clock processing The time is 10 μsec ÷ 256 = about 39 nsec, which is an indication of the processing speed (clock frequency) required of the microcomputer. Further, with regard to the resolution of the on-duty in the rectangular wave of one cycle of the PWM signal, since the number of 8-bit clocks is 256, the width of the on-duty adjustable in one clock is 100% ÷ 256 = approximately 0. It will be 39%. Adjusting the on-duty in steps of about 0.39% is the limit of the on-duty resolution.

Thus, with regard to the resolution of the on-duty at the time of PWM signal generation, an increment (for example, about 0.39%) of one clock determined by the number of bits of the microcomputer is one unit, no matter how finely the on-duty is adjusted. It was the limit to adjust. Therefore, in order to adjust the on-duty of switching with higher resolution, it was necessary to select a microcomputer (clock frequency and number of bits) of high specification.
In PWM control, the on-duty is adjusted and the off-duty is adjusted. In either case, it is difficult to adjust the duty with higher resolution while the processing capability of the microcomputer remains the same.

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

That is, the lighting power supply device of the present invention is
A switching power supply circuit for supplying power to the illumination light source;
A PWM control circuit that generates a pulse width modulation (PWM) signal to a switching element provided in the switching power supply circuit to perform PWM control of the switching element;
Is configured with
The PWM control circuit includes a digital operation unit for determining a duty command value (for example, 39.9%) of the PWM signal, and a rectangular wave generation unit for generating a rectangular wave according to the duty command value. Have
The digital operation unit is configured to calculate an estimated duty value (for example, 40%) that can be generated with the resolution based on the resolution (for example, 1%) of the duty determined by the bit number of the digital operation unit.
The rectangular wave generation unit is configured to repeatedly generate a rectangular wave based on the estimated duty value (40%),
The digital operation unit further uses the estimated duty value (40%) to compensate for the difference (0.1%) between the duty command value (39.9%) and the estimated duty value (40%). The generated row of rectangular waves is grouped into a plurality of (for example, 10) rectangular waves, and the duty of at least one of the plurality of rectangular waves in each group is determined by the resolution (1%) of the duty (For example, the duty 40% of one rectangular wave in a group is reduced by 1%).

The numerical values in parentheses are an example. Here, the "switching power supply circuit" includes various chopper circuits including an inductance element, a switching element, and a storage element, a flyback power conversion circuit, and the like, but is not limited to them. It is assumed that a circuit capable of supplying desired power to the illumination light source by the on / off operation of the element is included.
Further, the present invention can be applied to the case of adjusting the on-duty of the PWM signal as well as the case of 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 to have a digital operation unit and a rectangular wave generation unit,
A command value determining step of determining a duty command value of the PWM signal;
An approximate value calculation step of calculating an approximate duty value that can be generated by the resolution based on the resolution of the duty determined by the number of bits of the digital operation unit;
A rectangular wave generation step of instructing the rectangular wave generation unit to repeatedly generate a rectangular wave based on the estimated duty value;
A difference compensation step of compensating for a difference between the duty command value and the estimated duty value simultaneously with the rectangular wave generation step;
To run
In the difference compensation step, a row of rectangular waves generated by the estimated duty value is grouped into a plurality of rectangular waves, and at least one of the plurality of rectangular waves in each group is The duty of one rectangular wave is commanded to be increased or decreased by the unit of the resolution of the duty.

  In the present invention, even if the duty command value (for example, 39.9%) when generating the PWM signal is a level that can not be generated with the duty resolution (for example, 1%) determined by the number of bits of the microcomputer, It was decided to generate a square wave by calculating an estimated duty value (for example, 40%) of 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%), grouping of rectangular wave columns and within a group are performed as follows: We decided to carry out the process of increasing and decreasing the duty of some square waves. That is, a row of rectangular waves generated with the estimated duty value (40%) is grouped into a plurality of rectangular waves, and the duty of at least one of the plurality of rectangular waves in each group is resolved ( Increase or decrease by 1%). For example, if ten rectangular waves are taken as one group and the duty of only one rectangular wave is 39%, then the average duty of the group is (40% × 9 + 39% × 1) ÷ 10 = 39.9% , Becomes equal to the duty command value. By using such a square wave train as a PWM signal, the average duty for each group becomes the same level as the duty command value, and the duty for generating the PWM signal can be obtained even with the processing capability of the conventional microcomputer. It is possible to perform digital adjustment with high resolution.

It is a schematic block diagram of the power supply device for illuminations which concerns on 1st embodiment of this invention. It is a processing flow figure of the embodiment. It is an image figure of conventional PWM control. It is an image figure of PWM control of the embodiment. It is a figure for demonstrating the improvement of the resolution of PWM control in the said embodiment. It is an image figure of light adjustment control concerning a second embodiment of the present invention. It is a figure for demonstrating the thinning-out process of the pulse (square wave) in the said embodiment. It is a graph which shows the relationship between the light output (%) in the said embodiment, and the on duty (%) of switching. The graph which shows the relationship between the light output (%) in the said embodiment, and a light control signal (%).

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

  FIG. 1 shows the configuration of a switching power supply circuit of a system in which the high side of the LED element 2 is switched. However, the present invention is not limited thereto, and a power supply circuit of a system in which the low side is switched may be used. In addition, as the switching power supply circuit, various chopper circuits including an inductance element, a switching element, and a storage element, a flyback power conversion circuit, or the like may be employed.

  The digital PWM control circuit 8 is configured of a one-chip microcomputer or the like, and receives a light control signal from an external light control controller or the like. Further, a voltage value of 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 converts a light control signal into a digital signal, a digital operation unit (CPU) 14 that carries out various digital operations, a rectangular wave generation unit (PWM timer etc.) 16 And a storage unit 18 that stores the

  The digital operation unit 14 is configured to realize each function such as determining an on-duty command value of a PWM signal by executing a 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, the on-duty approximate value (duty approximate value) calculation unit 22, and the like. 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 the determined on-duty command value and repeatedly output the rectangular wave to the driver IC 6.

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

  First, in the A / D conversion step (S10) of FIG. 2, the light adjustment signal (for example, 50.1%) of the analog voltage is converted into a digital value by the A / D conversion unit 12. Further, each detection value of the switching power supply circuit 4 is A / D converted as needed. For example, the converted light control data may be appropriately corrected with the data of each detection value and treated as reference data. The reference data in this case is based on the information of the light adjustment signal, and the on-duty command value of the PWM signal to the switching element 5 is based on the reference data in the next on-duty digital calculation step (S20). Calculated. Here, in order to simplify the description, a procedure for determining the on-duty command value using the converted light control data as it is will be described. Also, when the external signal 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 light adjustment data. For example, an on-duty command value of 39.9% is calculated based on 50.1% of dimming data. In this step, when the digital operation unit 18 uses a data table stored in advance in the storage unit 18, the light conversion data is converted to a table, and the on-duty command value is calculated. Alternatively, when the digital operation unit 18 uses a control equation incorporated in a program, the light adjustment data is multiplied by a predetermined coefficient to calculate the on-duty command value. Note that the on-duty command value may be calculated using both table conversion and use of a control equation.

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

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

  At the same time as the rectangular wave generation step (S30), the difference compensation unit 24 in the digital operation unit 18 calculates the difference (0.1%) between the on-duty command value (39.9%) and the estimated value (40%). Execute processing for compensation. Specifically, the grouping unit 26 in the difference compensation unit 24 groups the row of rectangular waves generated with the approximate value of on-duty (40%) into groups of, for example, ten rectangular waves. Here, since the resolution of on-duty is 1% and the difference to be compensated is 0.1%, the number of rectangular waves included in each group is 10, and the number of 10 in each group is 10 The on-duty of one of the square waves is changed from 40% to 39% minus 1% of the resolution. The selection of the rectangular wave whose on duty is to be changed and the process of changing the on duty of the rectangular 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 is, 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 is reduced from 40% for three of the ten rectangular wave groups. You can change it to 39% minus 1% of. Alternatively, the on-duty may be changed from 40% to 36% obtained by subtracting 3% which is three times 1% of resolution for one of the 10 groups of rectangular waves. Either process results in the average on-duty for each group being equal to the on-duty command value. In this process, when selecting a plurality of rectangular waves from one group, it is preferable to select evenly from the entire row of rectangular waves so that the rectangular waves whose duty is to be adjusted are not biased as much as possible.

  The setting of the number of rectangular waves included in the group may be determined in relation to the size of the on-duty resolution. For example, assuming that the on-duty resolution is 0.39%, the approximate 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, assuming that the number of rectangular waves included in the group is 20, the on-duty for three of the rectangular waves is 39.78% minus 39.39% to 39.39%. Do. As a result, the average on-duty for each group is about 39.72%, which can be closer to 39.7% of the command value than 39.78% of the estimated value. As described above, the number of rectangular waves included in one group may be more than ten, or less than ten. In the case of using 8-bit MCUs, the maximum number of rectangular waves in one group is 256, for the purpose of measuring continuous rectangular waves. The resolution of the substantial on-duty 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 operation unit using the maximum of the wave number of one group.

  When the on-duty command value is, for example, 39.2%, the approximate 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 rectangular waves in each group is changed from 39% to 40% obtained by adding 1% of the resolution. Do. As a result, the average on-duty of each group becomes equal to the on-duty command value.

  As can be seen from the above various cases, the number of rectangular waves whose on-duty from within the group is to be changed is determined according to the magnitude of the difference to be compensated, and for the determined one or more rectangular waves, It was decided to increase or decrease the on-duty by the unit of the resolution. By using the series of rectangular waves whose ON duty is thus increased or decreased as a PWM signal, the average ON duty for each group becomes the same level as the ON duty command value, and the processing capacity of the conventional microcomputer remains as it is. It is possible to digitally adjust the on-duty at the time of PWM signal generation with high resolution.

  In practice, 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 data such as the light adjustment signal after A / D conversion, and the approximate value calculation unit 22. Calculating an approximate on-duty value that can be generated based on the resolution of the on-duty determined by the number of bits; repeatedly generating a rectangular wave based on the approximate value of the on-duty by the rectangular wave generation unit 16; And at the same time as the generation of the wave, the difference compensation unit 24 compensates for the difference between the on-duty command value and the approximate value. Then, in the step of difference compensation, the grouping unit 26 groups the row of rectangular waves into groups of a plurality of rectangular waves, and the on-duty increase / decrease unit 28 generates at least one rectangle of the plurality of rectangular waves in each group. The on-duty of the wave is increased or decreased by the resolution of the on-duty. By executing such a program, the average on-duty of the PWM signal generated by the rectangular wave generation unit 16 can be made close to the command value.

  FIG. 3 shows a conventional control image. If the on-duty resolution is 1%, the on-duty of the output PWM signal remains at 50% or more than the command value even if the on-duty command value changes from 50% to 49.9%. It would be an option to reduce it to 49%, which is significantly smaller. On the other hand, according to the control method of this embodiment shown in FIG. 4, even if the resolution of the on-duty remains 1%, the average on-duty of the plurality of rectangular wave groups is made 49.9% the same as the command value. can do. As schematically shown in FIG. 5, in the digital PWM control, the on-duty changes by non-continuous change, but when the control method of this embodiment is used, the on-duty resolution determined by the number of bits of the CPU Even if, for example, 1% remains, it is possible to change the on-duty stepwise with 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 illumination LED power supply is the same as the configuration of the above-described embodiment, but is characterized in that the lower limit of the on duty (lower limit of dimming) can be made smaller than that of the related art.

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

First, as in the above embodiment, in the digital operation step (S20), an approximate value of on-duty that can be generated with the 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 approximate value (1%) is generated and repeatedly output.
Further, simultaneously with the rectangular wave generation step (S30), processing for compensating for the difference (0.1%) between the on-duty command value (0.9%) and the approximate value (1%) is executed. Specifically, a series of square waves generated with an approximate value of on-duty (1%) is grouped, for example, every 10 square waves, and one of 10 square waves in each group is grouped. Change the on-duty of this square wave to 0% minus 1% of resolution from 1%. That is, one rectangular wave is thinned out from the row of ten rectangular waves. In addition, what is necessary is just to select arbitrarily from the row | line | column of ten square waves as selection of one square wave used as the object of thinning-out processing, as shown in FIG. By executing such a thinning process, the average on-duty of each group is (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 three of the ten rectangular wave groups. You can change each to%.

  In the case of thinning out two or more rectangular waves from the same group, it is preferable to select such that two continuous rectangular waves are not thinned out. Also, it is preferable to select not to thin out both the first and last square waves of the group. This is because if the rectangular wave which is the target of thinning continues to be present, the quiescent period of the load current may be extended to cause flickering of the LED elements.

  FIG. 8 is a graph showing the relationship between the light 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 when the switching is performed at an on-duty of, for example, 80%, a light output of 100% rated can be obtained. In order to obtain 50% light output, the on duty is set to 50% × 0.8 = 40%.

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

In the above embodiment, the case has been described in which the on-duty of switching is calculated so that the digital operation unit such as the CPU can perform light adjustment according to the light adjustment signal from the outside.
The present invention can be advantageously applied to a switching power supply circuit that does not have a dimming function. For example, when the switching power supply circuit receives constant current control by a microcomputer or the like, the present invention may be applied.
Note that, depending on the type of the switching power supply circuit, not the PWM control by the adjustment of the on duty but the one adjusting the off duty. The present invention can be widely applied to duty adjustment of PWM control without distinction between these on-duty adjustment and off-duty adjustment.

2 LED element (illumination light source)
DESCRIPTION OF SYMBOLS 4 switching power supply circuit 5 switching element 8 PWM control circuit 10 illumination power supply device 14 digital operation part (CPU)
16 Square wave generator

Claims (2)

A switching power supply circuit for supplying power to the illumination light source;
A PWM control circuit that generates a pulse width modulation (PWM) signal to a switching element provided in the switching power supply circuit to perform PWM control of the switching element;
A power supply for lighting comprising:
The PWM control circuit has a digital operation unit for determining a duty command value of the PWM signal, and a rectangular wave generation unit for generating a rectangular wave according to the duty command value,
The digital operation unit is configured to calculate an estimated duty value that can be generated with the resolution based on the resolution of the duty determined by the number of bits of the digital operation unit.
The rectangular wave generation unit is configured to repeatedly generate a rectangular wave based on the estimated duty value,
The digital operation unit further groups a row of rectangular waves generated by the estimated duty value into groups of rectangular waves in order to compensate for the difference between the duty command value and the estimated duty value. Configured to increase or decrease the duty of at least one of the plurality of rectangular waves in the unit of the resolution of the duty,
A lighting power supply device characterized by A program for generating a pulse width modulation (PWM) signal to a switching power supply circuit for lighting, comprising:
For a computer configured to have a digital operation unit and a rectangular wave generation unit,
A command value determining step of determining a duty command value of the PWM signal;
An approximate value calculation step of calculating an approximate duty value that can be generated by the resolution based on the resolution of the duty determined by the number of bits of the digital operation unit;
A rectangular wave generation step of instructing the rectangular wave generation unit to repeatedly generate a rectangular wave based on the estimated duty value;
A difference compensation step of compensating for a difference between the duty command value and the estimated duty value simultaneously with the rectangular wave generation step;
To run
In the difference compensation step, a row of rectangular waves generated by the estimated duty value is grouped into a plurality of rectangular waves, and at least one of the plurality of rectangular waves in each group is Command to increase or decrease the duty of one rectangular wave by the unit of the resolution of the duty;
A program characterized by

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