JP2016207268A - Dimming control circuit for lighting power supply device, and dimming control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dimming control circuit for lighting power supply device which is capable of reducing calculation error of a duty ratio of a PWM signal for dimming and has excellent responsiveness with respect to a dimming knob.SOLUTION: A dimming control circuit 10 comprises a microcontroller (MCU) which receives a PWM signal for dimming and generates a command voltage V2 for controlling an LED current in accordance with the PWM signal. In the MCU, a rising edge interval of the PWM signal is counted, and its term t0 is obtained, and an interval between a rising edge and a falling edge is counted and a high level term t1 is obtained. Next, a digital signal of a ratio (t1/t0) thereof is normalized into a digital signal X having the number of bits of the MCU or the number of bits that is smaller than the number of bits of the MCU just by several bits. Further, the normalized digital signal X is digitally converted into the command voltage V2 of the LED current based on a conversion table of the MCU, and outputted as a voltage signal via a D/A converter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a dimming control circuit for an illumination power supply device.

  In recent years, the performance of LED elements has increased, and the life of luminaires using LED elements has increased, so that conventional light sources can be replaced with LED light sources. In the future, if the performance of LED elements is further improved, LED light sources will be adopted in the field of general-purpose lighting equipment, and the demand for lighting power supply devices such as LED power supply devices will increase. Some illumination power supply devices have a dimming function that can arbitrarily change the light output of a light source. In particular, the dimming range of the LED light source is wider than that of a conventional discharge lamp, and the user can finely set the brightness. Therefore, the utility value as a power-saving lighting fixture is high.

  In general, dimming methods in the field of LED illumination include a method involving blinking of light (such as PWM dimming and phase dimming) and a method not involving blinking of light (such as analog control). In any method, the dimming control circuit receives a PWM signal (Pulse Width Modulation) having a duty ratio corresponding to the dimming rate (dimming depth) from the outside, and is a controlled amount based on the PWM signal. The lamp current of the LED light source is controlled. For example, in the analog control method, a lamp current command voltage corresponding to a PWM signal from the outside is applied to a constant current circuit (such as a step-down conversion circuit or a flyback conversion circuit) that supplies current to an LED light source. The constant current circuit is driven based on the command voltage and performs analog control of the lamp current.

  In FIG. 1 of Patent Document 1, a first PWM signal for adjusting the amount of light is input, a dimming circuit 3 that generates a second PWM signal by the switching element Q1 in accordance with the first PWM signal, and a second PWM from the dimming circuit. A light source lighting device including a control circuit 4 that calculates a duty ratio of a signal is disclosed. The control circuit includes a storage unit 8, a measurement unit 9, and a calculation unit 10, and the measurement unit measures an on period and an off period of the second PWM signal. The calculation unit corrects the measured on period and off period using the correction value stored in the storage unit, and calculates the duty ratio. The control circuit outputs a control signal to the lighting control unit 5 according to the calculated duty ratio. Thus, although the light source lighting device of Patent Document 1 corrects the measured on-period and off-period, there are many attached circuits in the dimming circuit itself, which results from variations in circuit elements. There was still room for improvement with respect to the calculation error of the duty ratio.

  FIG. 1 of Patent Document 2 discloses an LED power supply circuit including a dimming circuit 6 including a dimming signal input circuit 61, a dimming signal normalization circuit 62, and an integration circuit 63. The dimming signal input circuit 61 generates a PWM signal based on the ground of the power supply circuit from an external PWM signal by an insulating circuit such as a photocoupler. The dimming signal normalization circuit 62 generates a PWM signal with the maximum on-width when a dimming signal indicating all light is input, and when a dimming signal indicating the lowest dimming rate is input. Then, normalization is performed to generate a PWM signal having the minimum on-width. The integrating circuit 63 integrates the normalized PWM signal and converts it into a direct current. The dimming signal converted into a direct current is sent to a control circuit 7 constituted by a microcomputer. As described above, in the LED power supply circuit of Patent Document 2, the dimming circuit 6 passes the PWM signal from the outside through the insulation circuit, normalizes the ON width by the normalization circuit, and converts it to DC by the integration circuit. Yes. The dimming signal converted to DC is input to the microcomputer (control circuit 7) via the A / D converter. As described above, the LED power supply device disclosed in Patent Document 2 has a method of integrating with an integration circuit and then reading with an A / D converter. Therefore, the response to the knob when adjusting the dimming rate is still much. There was room for improvement.

  In the above description, the case of the dimming control of the illumination power supply device including the constant current circuit is illustrated. However, in the dimming control by the PWM dimming method with the blinking of light, the constant power circuit and the constant voltage are also used. Similarly, there is room for improvement in the dimming control of the illumination power supply device constituted by a circuit or the like.

JP 2014-157784 A (FIG. 1) JP 2013-254606 A (FIG. 1)

  The present invention has been made in view of the above prior art, and the problem to be solved is that it is possible to reduce the calculation error of the duty ratio of the PWM signal which is an external dimming signal and to adjust the dimming rate An object of the present invention is to provide a dimming control circuit for an illumination power supply device excellent in responsiveness to a knob and a dimming control program thereof.

  In order to solve the above problems, the inventor adopts a method in which the microcontroller itself directly measures the period from the rising edge to the rising edge of the PWM signal, and the rising and falling periods, and further, the PWM obtained by direct measurement. By adding a process that normalizes the signal duty ratio to a value that is convenient for the calculation processing of the microcontroller, the calculation error of the duty ratio due to the simplification of the configuration of the dimming control circuit is reduced, and the dimming degree is adjusted. We paid attention to the fact that the responsiveness to the knob that performs the operation is greatly improved.

That is, the dimming control circuit for the illumination power supply device according to the present invention is:
A microcontroller that receives a PWM signal having a duty ratio according to the dimming rate and generates a control command value (V2) for controlling the light source current or the light source voltage of the illumination light source according to the PWM signal is provided. A dimming control circuit for a lighting power supply device,
The microcontroller is
The time between two rising edges or two falling edges of the received PWM signal is measured to obtain the period (t0) of the PWM signal, and the time between the rising edge and the falling edge is calculated. Counting means for measuring to obtain a high level period or a low level period (t1) and obtaining these ratios as digital signals of the duty ratio (t1 / t0);
The digital signal having the duty ratio (t1 / t0) obtained by the counting means is converted into a digital signal (the number of bits of digital processing of the microcontroller or a bit number smaller than the number of bits of digital processing by a few bits). X) normalization means for normalization,
Digital conversion means for digitally converting the digital signal (X) normalized by the normalization means to the control command value (V2) of the light source current or the light source voltage;
It is characterized by providing.
Here, the normalization process by the normalization means is performed by adding a bit number smaller than the number of bits of the digital processing of the microcontroller or the number of bits of the digital processing to the digital signal having the duty ratio (t1 / t0). A process of multiplying a coefficient (W) representing the magnitude of the number is preferable.

The digital conversion means performs digital conversion using a dimming characteristic conversion table representing the control command value (V2) associated with the normalized digital signal (X).
Here, the dimming characteristic conversion table is
The control command value (V2) changes slowly in the low dimming rate region,
The control command value (V2) is provided so as to change more rapidly than in a low dimming rate region in a high dimming rate region,
In a state where the temperature of the illumination light source is stable, it is preferable that the light amount of the illumination light source is linearly changed according to the dimming rate.
Alternatively, the dimming characteristic conversion table is
The control command value (V2) gradually changes with a slope close to zero in the low dimming rate region,
The control command value (V2) is provided so as to change more rapidly than in a low dimming rate region in a high dimming rate region,
It is preferable to linearly change the amount of light of the illumination light source recognized by the visual sense at the time of operation in accordance with an operation for increasing or decreasing the dimming rate at a constant rate.

Moreover, the dimming control program for the illumination power supply device according to the present invention is as follows:
For a lighting power supply apparatus that receives a PWM signal having a duty ratio corresponding to a dimming rate and generates a control command value (V2) for controlling a light source current or a light source voltage of an illumination light source according to the PWM signal A dimming control program,
The dimming control program is stored in the microcontroller.
The time between two rising edges of the input PWM signal or between two falling edges is measured to obtain the period (t0) of the PWM signal, and the time between the rising edge and the falling edge To obtain a high level period or a low level period (t1) and obtain these ratios as digital signals of the duty ratio (t1 / t0);
The digital signal having the duty ratio (t1 / t0) obtained by the counting function is converted into a digital signal (X of the bit number of the digital processing of the microcontroller or a bit number smaller than the number of bits of the digital processing) ) To normalize to normalize,
A digital conversion function for digitally converting the digital signal (X) normalized by the normalization means into the control command value (V2) of the light source current or the light source voltage;
It is a program for realizing.

  According to the configuration of the present invention, since the microcontroller (MCU) mounted on the dimming control circuit has the counting means and the digital conversion means, the duty ratio of the PWM signal from the outside is directly measured by the counting means. Then, a command voltage (V2) such as a lamp current corresponding to the duty ratio is generated by the digital conversion means. This command voltage is compared with the detection voltage of the lamp current by an operational amplifier, for example, and the comparison result is reflected in the switching operation of a constant current circuit or the like. In this way, dimming control is performed on the illumination light source based on the dimming rate.

  In the configuration of the present invention, the microcontroller is further provided with normalization means. The significance of this normalizing means will be described in detail.

  The frequency of the PWM signal is determined by the specifications of an external dimmer (such as a PWM oscillation device) connected to the dimming control circuit, and may be 1 kHz or 100 Hz. Also, the frequency of the PWM signal may be modulated according to the dimming rate. For such various PWM signal frequencies, the MCU uses a clock frequency of a certain speed in order to accurately count the PWM signals. However, this inevitably increases the count amount (bit number) data. Therefore, the MCU keeps the count number within a predetermined data capacity (for example, 16 bits) by appropriately changing the clock frequency. For example, when a 1 kHz PWM signal is counted with a 10 MHz clock, the number of counts in one cycle is 10,000. This count number fits in a 16-bit data capacity. On the other hand, if the PWM signal of 100 Hz is counted with the same clock, the number of counts in one cycle becomes 100,000, which does not fit in the 16-bit data capacity (upper limit is about 60,000). In such a case, the clock frequency is lowered to, for example, 1 MHz, and the number of counts in one cycle is set to about 10,000.

  In order to read the time (t0) between two rising edges (or between two falling edges) of the PWM signal with high accuracy, it is necessary to use a clock frequency of a certain level or higher. It becomes a certain size and cannot be made extremely small.

  The MCU reads the time (t1) between the rising edge and the falling edge simultaneously with the period (t0) of the PWM signal, and calculates the ratio (t1 / t0) between them as the duty ratio. The digital conversion means of the MCU digitally converts the duty ratio of the PWM signal into a control command value (V2) based on a predetermined rule. For example, if a conversion table with the horizontal axis representing the duty ratio and the vertical axis representing the control command value is used, the necessary control command value (V2) can be easily obtained simply by searching the horizontal axis using the duty ratio (t1 / t0). Can get to.

  Normally, regardless of the data capacity of the duty ratio (t1 / t0), the digital signal is used as it is and converted into the control command value (V2). If the data capacity of the duty ratio from the counting means is 16 bits, the conversion table is generally set so that the scale on the horizontal axis matches the data width of 16 bits.

  On the other hand, in the present invention, normalizing means is provided in the MCU so that the digital signal having the duty ratio (t1 / t0) matches the number of bits (for example, 16 bits) of the MCU digital processing in the arithmetic processing. Normalization to the number of bits (for example, 12 bits) was made. In this processing, when the duty ratio digital signal is larger than the MCU bit number, the duty ratio digital signal is converted into the MCU bit number digital signal, or the duty ratio digital signal is converted into the MCU bit number. This can be said to be a process of normalizing to a bit number smaller by several bits. When the digital signal with the duty ratio is the same as the number of bits of the MCU, it can also be said to be a process of normalizing the digital signal with the duty ratio to a number of bits smaller by several bits than the number of bits of the MCU. Then, the digital conversion means performs digital conversion to the control command value (V2) based on the normalized duty ratio (t1 / t0). If the duty ratio (t1 / t0) based on the measured count number is normalized to the number of bits of the digital processing of the MCU or a bit number slightly smaller than this, the digital conversion of the MCU is performed efficiently, and the processing time is increased. Will be shortened.

  As one aspect of the normalizing means, there is a process of multiplying a digital signal having a duty ratio (t1 / t0) from the counting means by a coefficient (W). This process includes a process of multiplying the count number (t1) between the rising edge and the falling edge by the coefficient (W) and then dividing by the cycle count number (t0). For example, in the case of a 16-bit MCU, 12 bits are easily used as the coefficient W. The coefficient W representing the size of 12 bits is 2 ^ 12-1 = 4095, and the coefficient W indicates a data width of 4096 levels from 0 to 4095. By multiplying the coefficient W by the count number t1 and dividing by the count number t0, the normalized duty ratio of the 12-bit signal is obtained.

Further, by executing such normalization processing, even if the conversion table in the digital conversion processing is set very complicated, the conversion processing is executed smoothly. Since there is no need to be restricted by the processing time of the microcomputer, the degree of freedom in setting the conversion table can be improved.
In particular, excellent responsiveness to a knob that adjusts the dimming degree is obtained, and this effect is remarkably exhibited during deep drawing (low dimming rate).

As described above, according to the configuration of the present invention, the duty ratio of the PWM signal is directly measured by the microcomputer by making the maximum use of the count function provided in the microcomputer. Many associated circuits can be greatly reduced, and the calculation error of the duty ratio can be reduced.
In addition, since the normalization means is provided in the microcomputer, the responsiveness to the knob when adjusting the dimming rate is greatly improved, and an illumination power supply apparatus having excellent responsiveness can be provided.

The block diagram of the illumination power supply device provided with the light control circuit which concerns on 1st embodiment of this invention. It is a flowchart which shows the signal processing in the said light control circuit. It is a figure which shows the time between the rising edges of a microcomputer input signal. It is a graph showing the conversion table from the duty ratio used in the said light control circuit to a current command value. It is a graph which shows the light quantity of the light source with respect to a duty ratio at the time of using the conversion table of FIG. The graph which is a conversion table of a 1st modification, and represents the conversion table set so that light quantity may show linearity with respect to a duty ratio in the state where the light source temperature was stabilized. 10 is a conversion table of a second modification, and is a graph representing a conversion table that is set so that the amount of light that is visually recognized when the duty ratio is changed exhibits linearity with respect to the duty ratio. The block diagram of the illumination power supply device provided with the light control circuit which concerns on 2nd embodiment of this invention.

  Hereinafter, with reference to the drawings, an overall configuration of an LED power supply device 1 including a dimming control circuit 10 according to an embodiment of the present invention will be described. Here, although the case where the dimming control circuit 10 of FIG. 1 is applied to the LED power supply device 1 mainly composed of the full-wave rectification circuit 2, the power factor correction circuit 3, and the flyback conversion circuit 4 will be described. Devices that do not include a power factor correction circuit and those that allow a flyback conversion circuit to perform a power factor correction function are also applicable. That is, the dimming control circuit 10 detects the lamp current from the switching conversion circuit exemplified by the flyback conversion circuit 4, and the voltage value indicating the detected voltage value and the target lamp current (hereinafter referred to as a command voltage value). ), And the comparison result is widely applied to an illumination power supply device configured to feed back the comparison result as a control signal to the switching conversion circuit.

  The flyback conversion circuit 4 includes a switching element S1, a flyback transformer T, a transformer secondary-side diode D1, a resistor R3 for detecting a lamp current as a controlled amount, a control circuit IC1 for driving the switching element S1, and The light control circuit 10 according to the present invention is included. In FIG. 1, the switching element (MOSFET) S <b> 1 is independent from the control circuit IC <b> 1, but a switch built-in control circuit may be connected to the subsequent stage of the power factor correction circuit 3.

  The flyback conversion circuit 4 further includes a control power supply 5 using a flyback transformer T and a photocoupler 6 that transmits a control signal from the dimming control circuit 10 to the control circuit IC1 as an auxiliary configuration. In this document, the commercial AC power supply AC side is called the primary side, and the LED light source side is called the secondary side. The flyback transformer T insulates the circuit current by the primary side transformer T1a and the secondary side transformer T1b. The control power supply 5 generates a primary control power supply (VCC1) to the control circuit IC1 and the phototransistor of the photocoupler 6 by the auxiliary transformer T1c for the auxiliary power supply. Further, the secondary-side transformer T1d for auxiliary power generates a secondary-side control power supply (VCC2) to the dimming control circuit 10 and the infrared LED of the photocoupler 6. The generated secondary control power supply VCC2 supplies a stable DC voltage to the secondary side via the three-terminal regulator IC2.

  Here, operation | movement of the LED power supply device 1 is demonstrated easily. The commercial AC voltage from the commercial AC power source AC is rectified by the full-wave rectifier circuit 2 to become direct current, is subjected to power factor improvement by the power factor correction circuit 3, and is supplied to the flyback conversion circuit 4. In the flyback conversion circuit 4, when the switching element S1 is turned on, a current from the high side of the capacitor C2 flows to the primary side T1a of the flyback transformer T, the switching element S1, and the low side of the capacitor C2, and the transformer T stores magnetic field energy. Next, when the switching element S1 is turned off, the energy of the magnetic field stored in the transformer T generates a damped oscillation voltage waveform in the primary side T1a of the transformer T, and at the same time, the voltage on the secondary side T1b of the transformer T. Is generated. This voltage is rectified by the diode D1 and charges the electrolytic capacitor C4. Then, a current from the high side of the electrolytic capacitor C4 flows to the LED light source, and the LED light source emits light.

<Dimming control circuit>
The dimming control circuit 10 includes an AC photocoupler 12 that receives a dimming signal from the outside, a microcontroller MCU, a D / A converter, and an operational amplifier 16. The external dimming signal may be a logic level signal that defines all light, dimming rate, or extinction depending on the logic level, or a pulse-like switching pulse that is input for each step when the dimming rate is switched stepwise. It may be a signal. Alternatively, it may be a PWM signal that specifies all light, dimming rate, or extinction by on-duty or frequency. In this embodiment, the PWM signal is used as the external dimming signal.

  The AC photocoupler 12 is a means for receiving PWM signals, and has a light emitting element composed of a parallel connection part of two infrared LEDs having opposite polarities, and a light receiving element composed of a phototransistor. When the PWM signal from the receiving terminal is applied to the series connection portion of the resistor R11 and the infrared LED, the infrared LED blinks according to the on-duty of the PWM signal. Further, an RC connection portion of a resistor R10 and a capacitor C8 is provided at the subsequent stage of the AC photocoupler 12. The capacitor C8 has a small capacity of about 1000 pF, and is provided to remove high-frequency noise riding on the signal waveform. Therefore, the capacity of C8 is about three orders of magnitude smaller than the capacity of capacitors normally used in the integration circuit. One end on the resistor R10 side of the RC connection portion receives the control power supply VCC2, and the other end on the capacitor C8 side is connected to the ground level. The collector of the phototransistor of the AC photocoupler 12 is connected to a connection point P1 between the resistor R10 and the capacitor C8, and the emitter of the phototransistor is connected to the ground level. The connection point P1 of this RC connection part is also connected to the input terminal of the MCU. As the infrared LED on the light emitting side of the AC photocoupler 12 blinks, the resistance between the CEs of the phototransistor on the light receiving side changes, and the potential at the connection point P1 that changes accordingly is input to the MCU. Thus, the light receiving means for the PWM signal serves to convert the input PWM signal into a microcomputer input signal.

  The microcontroller MCU converts the input signal from the AC photocoupler 12 into a microcomputer output signal by digital signal conversion based on the conversion table. The MCU is, for example, a 16-bit microcomputer, and may be an externally 16-bit microcomputer as well as an externally 16-bit microcomputer. This microcomputer output signal is converted into a command voltage V2 of the target lamp current by a D / A converter (or an fv converter is also possible) and output. Therefore, the MCU and the D / A converter can be said to be command voltage generating means. Here, the command voltage is a voltage signal representing a target value of the lamp current corresponding to the dimming rate of the PWM signal.

  The processing content of the input signal will be described based on the flowchart of FIG. First, in the frequency counting process S1, the MCU sets a pulse interval corresponding to one period of the microcomputer input signal (time t0 between rising edges in FIG. 3; time between falling edges) as compared to the PWM signal. Measure using high clock frequency and measure high / low level width of microcomputer input signal. In FIG. 3, the edge interval (high level width) from the rising edge to the falling edge is shown as time t1, and the edge interval (low level width) from the falling edge to the rising edge is shown as time t2. In the present invention, either of two types of count numbers (t1, t2) based on frequency count may be used for calculating the duty ratio. Here, a case where the count number (t1) is used will be described.

  The MCU is equipped with a 16-bit timer and a 12-bit interval timer with a maximum of 4 channels as timer functions. The frequency counting means measures the high / low level width of the input signal by the single channel operation function of the 16-bit timer. Starts counting at one edge (eg, rising edge) of the input signal and captures the count value at the other edge (eg, falling edge) to measure the high-level width and low-level width of the input signal it can.

  For example, assume that the frequency of the PWM signal is 1 kHz. The MCU keeps the count number within a predetermined data capacity (for example, 16 bits) by appropriately changing the clock frequency. When a 1 kHz PWM signal is counted with a 10 MHz clock, the number of counts in one cycle is 10,000. This count number fits in a 16-bit data capacity. If a 100 Hz PWM signal is input, the clock frequency is lowered to, for example, 1 MHz, and the number of counts in one cycle is set to about 10,000.

  Next, in normalization processing S2, the MCU performs normalization of the microcomputer input signal (also referred to as normalization of the external dimming signal) using the equation X = W × t1 / t0. The coefficient W is set to a value convenient for calculation processing. In the case of an 8-bit microcomputer, by setting W = (2 ^ 8) -1 = 255, the on-duty (t1 / t0) can be normalized to a digital value of 0 to 255 steps that are easy to digitally process. In the case of a 16-bit microcomputer, the coefficient W may be set between W = (2 ^ 10) -1 = 1023 and W = (2 ^ 15) -1 = 32767. That is, the coefficient W for the n-bit microcomputer can be set by the equation W = (2 ^ n) -1. Here, “2 ^ n” indicates 2 n-rows. Hereinafter, in this embodiment, the number of bits after normalization will be described as 12 bits (coefficient W = 4095), for example. In this way, the coefficient W is set to a digital value corresponding to the width (0 to 100%) of the horizontal axis of the characteristic graph of FIG. 4 described later.

  Thus, it is preferable to normalize to the number of bits of the digital processing of the MCU, or the number of bits smaller by several bits than the number of bits of the MCU. If the duty ratio (t1 / t0) based on the measured count number is normalized to the bit number of the digital processing of the MCU or a bit number slightly smaller than this, digital conversion of the MCU is efficiently performed.

  Further, in the digital conversion process S3, the MCU digitally converts the normalized on-duty X of the external dimming signal into a lamp current command voltage V2. However, the MCU only outputs a microcomputer output signal corresponding to the command voltage V2 by this digital conversion. For example, in the PWM oscillation process S4, a PWM signal corresponding to the microcomputer output signal is generated using an oscillator built in the MCU, and in the voltage signal generation process S5, the voltage of the command voltage V2 is generated using a low pass filter. You may convert into a signal. Alternatively, as shown in FIG. 1, a D / A converter is provided in the subsequent stage of the MCU, and a voltage signal generation process S6 for converting the microcomputer output signal output in the digital conversion process S3 into a voltage signal of the command voltage V2 is executed. May be. In any processing method, a voltage signal of the command voltage V2 is sent to the operational amplifier 16.

  In the flowchart shown in FIG. 2, for the frequency count process S1, the normalization process S2, and the digital conversion process S3, a dimming control program for causing the MCU to perform these functions may be executed. When executing the PWM oscillation process S4, the process S4 may be added to the dimming control program.

  In the MCU, a conversion table from the normalized on-duty X to the command voltage V2 is set and stored in advance. Alternatively, the MCU stores a program for calculating the command voltage V2 from the normalized on-duty X, and is configured to be able to execute the program. FIG. 4 shows the relationship between the normalized on-duty X and the command voltage V2. In this digital conversion, the horizontal axis is indexed by the normalized on-duty X value, and the V2 value on the vertical axis is obtained. Then, the MCU outputs a microcomputer output signal (for example, a 12-bit signal) corresponding to the V2 value to the D / A converter. The D / A converter D / A converts the microcomputer output signal to obtain the command voltage V2. The command voltage V2 output from the D / A converter is divided by a series connection circuit of resistors R8 and R9, and the voltage is applied to the plus terminal of the operational amplifier 16 via the resistor R6.

  The dimming characteristic conversion table 1 represented by the graph of FIG. 4 will be described. The horizontal axis represents a normalized on-duty X (for example, a 12-bit signal) obtained by normalizing the on-duty of the external dimming signal, but is indicated by 0 to 100% for convenience of explanation. The vertical axis represents the command voltage V2 indicating the target lamp current. When the control power supply VCC2 is, for example, 0-5V voltage, the lower end of the vertical axis is 0V and the upper end is 5V. In this embodiment, the conversion table is set so that the command voltage V2 indicating 100% of the rated lamp current (all light) is about 4.3V, which is slightly lower than 5V, for the microcomputer output voltage. In the range where the on-duty of the external dimming signal is 0% to “L”%, the command voltage V2 is set to a constant value (for example, 4.3V). That is, when the dimming rate is increased and the on-duty of the PWM signal reaches “L”%, for example, a rated lamp current of 100% flows.

  On the other hand, the command voltage V2 indicating 0% (light-off state) in the calculation of the rated lamp current is set to be, for example, about 0.3V, which is slightly higher than 0V. In the range where the on-duty of the external dimming signal is “U”% to 100%, the command voltage V2 is set to a constant value (for example, 0.6V). That is, the lamp current is set such that a lamp current of several percent of the rated value flows when the dimming rate is lowered and the on-duty of the PWM signal reaches “U”%. In the range where the on-duty is from “U”% to 100%, a constant lamp current of several percent of the rated value flows. In the figure, for example, the lamp current is 5% of the rated value. By setting the lower limit of the lamp current in this way, even when the dimming rate is lowered, the circuit efficiency does not decrease and noise that is difficult to reduce does not occur. Note that the slope of the characteristic graph is set so that the lamp current command voltage V2 is proportional to the on-duty when the on-duty of the PWM signal, which is an external dimming signal, is in the range from "L"% to "U"%. ing. The secondary control power supply VCC2 is supplied to both the microcomputer MCU and the D / A converter.

  Since the lamp current from the high side of the electrolytic capacitor C4 flows to the low side of C4 through the LED light source and the lamp current detection resistor R3, a voltage drop occurs in the resistor R3 due to the lamp current. A connection point P3 between the LED light source and the resistor R3 is connected to the negative terminal of the operational amplifier via the resistor R4. The resistor R4 corresponds to a lamp current detection voltage acquisition unit. The negative terminal and the output terminal of the operational amplifier 16 are connected by a resistor R5. The operational amplifier 16 corresponds to a comparison unit that compares the lamp current command voltage V2 and the lamp current detection voltage V1. In particular, in the present embodiment, the operational amplifier 16 causes the lamp current command voltage V2 and the lamp current detection voltage to be compared. A differential amplifier circuit that amplifies and outputs the difference of V1 is configured. The output voltage of the operational amplifier 16 is applied to the infrared LED of the photocoupler 6 via the resistor R7 as a control signal to the control circuit IC1.

  The infrared LED of the photocoupler 6 emits light according to the output voltage of the operational amplifier 16. That is, the current from the control power supply VCC2 enters the output terminal of the operational amplifier 16 through the infrared LED, and flows from the negative power supply terminal of the operational amplifier to the ground level. Therefore, the light output of the infrared LED changes according to the output voltage of the operational amplifier 16. Along with this, the resistance value between the CEs of the phototransistors connected to the primary side of the photocoupler 6 changes.

  The collector of the phototransistor is connected to the FB (feedback) terminal of the control circuit IC1. Further, since the FB terminal is also connected to the control power supply VCC1 by the resistor R1 (also referred to as pool-up), the change in the resistance value of the phototransistor is converted into the change in the voltage of the FB terminal, and the FB terminal The applied voltage changes. The amplified value of the difference between the detection voltage V1 and the command voltage V2 is sent to the constant current control circuit IC1 as the FB value. In this way, the control circuit IC1 changes the ON width or switching frequency of the switching element S1 so that the current flowing through the resistor R3 connected in series with the LED light source matches the current setting value set by the microcomputer MCU. . Since the current flowing through the resistor R3 is equal to the LED current, the LED current is controlled to a current setting value based on the dimming signal with high accuracy.

  According to the dimming control circuit 10 of the present embodiment, the on-duty of the PWM signal is directly measured by making maximum use of the frequency count function provided in the MCU. In addition, it is possible to significantly reduce the number of associated circuits, and it is possible to reduce the on-duty calculation error. In addition, even if the conversion table in the digital conversion process S3 is set very complicated by the MCU performing the normalization process, the conversion process is executed smoothly. Since there is no need to be restricted by the processing time of the MCU, the degree of freedom for setting the conversion table can be improved. Moreover, the responsiveness with respect to the knob at the time of adjusting a light control rate is improved significantly, and the illumination power supply device excellent in the responsiveness can be provided. In particular, this effect is prominent at the time of deep drawing (low light control rate).

  A modification of the conversion table in FIG. 4 will be described. FIG. 5 shows the output of the command voltage (indicated by “LED current”) and the light amount of the light source in the normalized on-duty X of the PWM signal when performing the dimming operation using the conversion table of FIG. As for the light amount of the light source, two types of light amount are shown: a light amount immediately after starting and a light amount in a stable state. The output (V2) of the LED current command voltage changes in proportion to the on-duty X in the on-duty range from “L”% to “U”%, and the slope of the LED current line is constant. First, immediately after the start of the LED light source, that is, before the temperature of the LED element rises, the light amount of the light source also changes in proportion to the on-duty X as shown by “light amount immediately after start” in FIG. The LED current and the amount of light have a linear relationship.

  On the other hand, in a state where the temperature of the LED element is stable, the LED element is at a high temperature. Therefore, the light amount is higher than that immediately after starting in an area where the on-duty X is approximately 50% or less (area where the dimming rate is high). Has fallen. This tendency is greater as the on-duty X is closer to “L”%. For example, when the on-duty X is changed from “L”% to “U”% by operating the dimming volume or knob in a stable state, the LED current decreases in proportion to the on-duty X. However, the curve indicating the change in the amount of light has a gentle slope near “L”%, gradually increases as it approaches 50%, and the slope becomes almost constant at about 50% or more. The slope of the light amount in the on-duty range from 50% to “U”% matches the slope of the light amount immediately after the start. As shown by “light quantity (when stable)” in FIG. 5, the change in the light quantity draws an upwardly bulging curve.

  Considering the characteristics of the LED light source as described above, the microcomputer is operated in accordance with the conversion table 2 shown in FIG. 6 instead of the conversion table 1 in FIG. On the other hand, it can be changed linearly. FIG. 6 is a conversion table of the first modification example. When the light source temperature reaches a stable state, the output of the command voltage of the LED current (in order that the light amount exhibits linearity with respect to the change of the on-duty X ( V2) is set. That is, as shown by “LED current (table 2)” in FIG. 6, the change in the LED current has a large slope in the vicinity of “L”%, and the slope gradually becomes gradually closer to the vicinity of 50%. Above%, the slope is almost constant. It is set so as to draw a curve in which the change in the LED current is slightly dented downward. As a result, the amount of swelling on the upper side in the curve of the change in light quantity at the time of stability in FIG. The amount of light decreases in proportion to the on-duty X when it is changed from “U”% to “U”%.

  Moreover, it may replace with the conversion table 1 of FIG. 4, and may operate a microcomputer according to the conversion table 3 shown in FIG. FIG. 7 is a conversion table of the second modified example. When the on-duty is changed, the change in the amount of light visually recognized during the change of the on-duty with a knob or the like is the change of the on-duty X. Is a conversion table set so as to show linearity. This dimming characteristic conversion table 3 shows that the control command value (V2) gradually changes in the on-duty X region (low dimming rate region) near “U”%, and the on-duty X near “L”%. The control command value (V2) is set so as to change more rapidly than the low light control rate region in the above region (high light control rate region). As shown by “LED current (table 3)” in FIG. 7, the change in the LED current is larger in the vicinity of “L”% than the curve in FIG. 6, and the inclination is suddenly changed in the vicinity of about 75%. It becomes gentle and the slope becomes almost constant in the region of approximately 50% or more. The slope near “U”% is almost zero. In this way, the LED current is set so as to draw a curve that is greatly depressed downward.

  By using the conversion table 3 of FIG. 7, the light amount of the illumination light source recognized by the vision at the time of operation is changed to the on-duty X according to the dimming operation that increases or decreases the on-duty X (dimming rate) at a constant rate. Can be changed linearly. For example, even if the dimming volume or knob is operated in a region with a high dimming rate, the user will not feel the stress that the amount of light is visually felt almost unchanged. Smooth light control can be realized with respect to a change in visual light quantity. In addition, when shifting to a stable state immediately after starting, the amount of light gradually decreases due to the temperature rise of the LED element. Change is not perceived.

  FIG. 8 shows an illumination power supply device 1a including a dimming control circuit 10a according to the second embodiment of the present invention. The main difference from the first embodiment is that the illumination power supply device 1a uses a step-down chopper circuit 4a as a switching conversion circuit and an illumination light source that is lit by voltage control of the lamp voltage V1. Further, the output signal of the operational amplifier 16, that is, the comparison result between the detection voltage V1 of the lamp voltage and the command voltage V2, is directly applied to the FB terminal of the control circuit IC1 without passing through the photocoupler. The dimming control circuit 10a includes an AC photocoupler 12, an MCU with a PWM signal transmission function, a low-pass filter including an inductor L2 and a capacitor C10, and an operational amplifier 16.

  In this embodiment, a microcomputer incorporating a PWM signal generator is used to output a PWM signal corresponding to the target lamp current from the microcomputer, and a PWM signal is commanded by a low-pass filter provided at the subsequent stage of the microcomputer. The voltage was converted to V2. The MCU is equipped with a 16-bit timer and a 12-bit interval timer with a maximum of 4 channels as timer functions. The PWM signal generator can arbitrarily set the PWM output pulse period (master-side timer) and duty (slave-side timer) by using a 2-channel 16-bit timer as a set. The MCU writes the value of the command voltage V2 in the register of the internal PWM signal generator, and a new PWM signal is output from the PWM signal generator to the low pass filter. The output voltage from the low pass filter is applied to the + terminal of the operational amplifier 16 as a current command value.

  Also in such an illumination power supply device 1a, the on-duty calculation error can be reduced by applying the dimming control circuit 10a. In addition, the responsiveness to the knob when adjusting the dimming rate is greatly improved, and an illumination power supply device with excellent responsiveness can be provided.

1 LED power supply (lighting power supply)
4 Flyback conversion circuit (switching conversion circuit)
5 Control power supply 6 Photocoupler 10 Dimming control circuit 12 AC photocoupler (light receiving means)
16 operational amplifier (comparison means)
D / A Digital-analog converter (command voltage generation means)
IC1 Switching element control circuit MCU Single chip microcontroller R3 Lamp current detection resistor (lamp current detector)
R4 resistance (Detection voltage acquisition means)

Claims (5)

A microcontroller that receives a PWM signal having a duty ratio according to the dimming rate and generates a control command value (V2) for controlling the light source current or the light source voltage of the illumination light source according to the PWM signal is provided. A dimming control circuit for a lighting power supply device,
The microcontroller is
The time between two rising edges or two falling edges of the received PWM signal is measured to obtain the period (t0) of the PWM signal, and the time between the rising edge and the falling edge is calculated. Counting means for measuring to obtain a high level period or a low level period (t1) and obtaining these ratios as digital signals of the duty ratio (t1 / t0);
The digital signal having the duty ratio (t1 / t0) obtained by the counting means is converted into a digital signal (the number of bits of digital processing of the microcontroller or a bit number smaller than the number of bits of digital processing by a few bits). X) normalization means for normalization,
Digital conversion means for digitally converting the digital signal (X) normalized by the normalization means to the control command value (V2) of the light source current or the light source voltage;
A dimming control circuit for an illumination power supply device, comprising: The dimming control circuit for the illumination power supply device according to claim 1,
The normalization processing by the normalizing means is such that the digital signal having the duty ratio (t1 / t0) has a bit number of digital processing of the microcontroller or a bit number smaller by a few bits than the bit number of the digital processing. A dimming control circuit for an illumination power supply apparatus, characterized in that the dimming control circuit is a process of multiplying a coefficient (W) representing the thickness. The dimming control circuit for an illumination power supply device according to claim 1 or 2,
The digital conversion means performs digital conversion using a dimming characteristic conversion table representing the control command value (V2) associated with the normalized digital signal (X),
The dimming characteristic conversion table is:
The control command value (V2) changes slowly in the low dimming rate region,
The control command value (V2) is provided so as to change more rapidly than in a low dimming rate region in a high dimming rate region,
A dimming control circuit for an illumination power supply apparatus, wherein the light amount of the illumination light source is linearly changed according to the dimming rate in a state where the temperature of the illumination light source is stable. The dimming control circuit for an illumination power supply device according to claim 1 or 2,
The digital conversion means performs digital conversion using a dimming characteristic conversion table representing the control command value (V2) associated with the normalized digital signal (X),
The dimming characteristic conversion table is:
The control command value (V2) gradually changes with a slope close to zero in the low dimming rate region,
The control command value (V2) is provided so as to change more rapidly than in a low dimming rate region in a high dimming rate region,
A dimming control for an illumination power supply device characterized by linearly changing the amount of light of the illumination light source recognized by the visual sense at the time of operation according to an operation for increasing or decreasing the dimming rate at a constant rate circuit. For a lighting power supply apparatus that receives a PWM signal having a duty ratio corresponding to a dimming rate and generates a control command value (V2) for controlling a light source current or a light source voltage of an illumination light source according to the PWM signal A dimming control program,
The dimming control program is stored in the microcontroller.
The time between two rising edges of the input PWM signal or between two falling edges is measured to obtain the period (t0) of the PWM signal, and the time between the rising edge and the falling edge To obtain a high level period or a low level period (t1) and obtain these ratios as digital signals of the duty ratio (t1 / t0);
The digital signal having the duty ratio (t1 / t0) obtained by the counting function is converted into a digital signal (X of the bit number of the digital processing of the microcontroller or a bit number smaller than the number of bits of the digital processing) ) To normalize to normalize,
A digital conversion function for digitally converting the digital signal (X) normalized by the normalization means into the control command value (V2) of the light source current or the light source voltage;
Is a program to realize
A dimming control program for an illumination power supply device.

Images