JP2014154493A - Lighting device for semiconductor light-emitting element, and illuminating fixture using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device for a semiconductor light-emitting element and an illuminating fixture using the same, capable of controlling a current flowing in a semiconductor element by means of a power conversion circuit operating in a critical mode, of having a simple configuration, of having a wide output adjustment width, and of performing output adjustment while suppressing a circuit loss.SOLUTION: A lighting device comprises a switching element, an inductance element, a regenerative diode, detection means, and control means, as a configuration for a critical mode operation. The detection means detects a current flowing in the switching element. A comparator included in the control device receives a detection value detected by the detection means at a first terminal and receives a threshold at a second terminal, and switches an output when the detection value reaches the threshold. The control means turns off the switching element depending on the output, and turns on the switching element when energy discharge of the inductance element is completed. The lighting device further comprises a variable resistive element that can change a voltage that determines the threshold.

Description

  The present invention relates to a lighting device for a semiconductor light-emitting element and a lighting fixture using the same.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2012-64431, a semiconductor light-emitting element lighting device that controls a current flowing in a semiconductor light-emitting element such as an LED by a power conversion circuit that operates in a critical mode, and the same There were known lighting fixtures.

  As a basic configuration for realizing the critical mode, a switching element connected in series to a DC power source and controlled to be turned on / off at a high frequency, an inductance element and a regenerative diode electrically connected to the switching element, and a flow through the switching element Current detection means for detecting current. A current flows from the DC power source to the inductance element when the switching element is turned on. The regenerative diode discharges energy stored in the inductance element when the switching element is turned on to the semiconductor light emitting element when the switching element is turned off. Furthermore, when the current value detected by the current detection means reaches a threshold value, there is provided control means for turning off the switching element and turning on the switching element when the energy emission of the inductance element is completed.

  Thus, the critical mode is a control mode in which the energy stored in the inductance element during the ON period of the switching element is released during the OFF period of the switching element, and the switching element is turned ON again at the timing when the energy release is completed. It is.

  In the above conventional lighting device, a variable resistance element for superimposing or subtracting a correction value for output adjustment is added to the current value detected by the current detecting means. By operating this variable resistance element, the detection value detected by the current detection means can be corrected. That is, the current detection sensitivity can be changed by changing the resistance value of the variable resistance element, and the peak value of the current flowing through the switching element can be increased or decreased. As a result, output adjustment is possible.

JP 2012-64431 A

  In the above conventional technique, it is assumed that a plurality of variable resistance elements, that is, a variable resistance element for superimposing a correction value for output adjustment and a variable resistance element for subtracting the correction value are used. Since each variable resistance element is assigned a correction superposition or a correction subtraction, the number of variable resistance elements inevitably increases, the circuit and the adjustment method are complicated, and the cost increases. It is expected that the harmful effect will be longer.

  Therefore, it is conceivable that one variable resistance element is also used for subtracting a correction value for output adjustment in addition to superimposing a correction value for output adjustment. However, in this case, if the superimposition width and the subtraction width of the correction value used for output adjustment are made as wide and uniform as possible, the resistance value of the detection resistor (current sense resistor) serving as the current detection means is It is necessary to enlarge it in advance. When the value of the detection resistor is increased, the circuit loss increases and the circuit efficiency decreases.

  As described above, in the above-described conventional technique of correcting the detected current value, it is difficult to satisfy the demands for simplifying the configuration, ensuring the output adjustment capability, and suppressing the reduction in circuit efficiency when performing output adjustment.

  The present invention has been made in order to solve the above-described problems. In a lighting device for a semiconductor light-emitting element that controls a current flowing in a semiconductor element by a power conversion circuit that operates in a critical mode, the circuit has a simple configuration, An object of the present invention is to provide a lighting device for a semiconductor light emitting element capable of adjusting output while suppressing loss, and a lighting fixture using the same.

1st invention is a lighting device of a semiconductor light emitting element,
A switching element connected in series to a DC power source and controlled to be turned on and off;
An inductance element connected in series with the switching element and through which a current flows from the DC power source when the switching element is on;
A regenerative diode that releases energy stored in the inductance element when the switching element is on to the semiconductor light emitting element when the switching element is off;
A detection unit including a detection resistor connected in series with the switching element, and detecting a current flowing through the switching element by detecting a voltage between terminals of the detection resistor;
A comparator having a first terminal receiving a detection value detected by the detection means and a second terminal receiving a threshold value and switching an output when the detection value reaches the threshold value; and turning off the switching element according to the output of the comparator Control means for turning on the switching element when the energy release of the inductance element is completed,
A variable resistance element capable of changing a voltage for determining the threshold;
It is characterized by providing.

The second invention is a lighting device,
A lighting device for a semiconductor light emitting element according to the first invention;
A semiconductor light emitting element supplied with a current from the lighting device;
It is characterized by providing.

  Advantageous Effects of Invention According to the present invention, in a lighting device for a semiconductor light-emitting element that controls a current flowing through a semiconductor element by a power conversion circuit that operates in a critical mode, output adjustment can be performed with a simple configuration while suppressing circuit loss. .

1 is a view showing a lighting device for a semiconductor light emitting element according to an embodiment of the present invention, and is also a view showing a lighting device including the lighting device and the semiconductor light emitting element. 1 is a circuit diagram of a step-down chopper circuit according to an embodiment of the present invention. It is a figure which shows the internal structure of the control integrated circuit concerning embodiment of this invention. In the control integrated circuit according to an embodiment of the present invention, showing a characteristic of the _{V THCS} (threshold voltage of the comparator CP1) for the voltage _{V MULT.} It is a circuit diagram of a step-down chopper circuit shown as a comparative example with respect to the embodiment. It is a figure which shows the characteristic of _Vthcs (threshold voltage of comparator CP1) with respect to voltage V _MULT in control integrated circuit IC1 concerning the comparative example with respect to embodiment.

Embodiment.
[Configuration and Operation of Apparatus of Embodiment]
(Lighting device and lighting device using the same)
FIG. 1 is a diagram showing a lighting device 100 for a semiconductor light emitting element according to an embodiment of the present invention, and also a diagram showing an illumination device according to an embodiment of the present invention. The lighting device according to the embodiment includes a lighting device 100 and a semiconductor light emitting element 16 that is lit by receiving current supplied thereby. The semiconductor light emitting element 16 is a light emitting diode (LED).

  An AC power supply Vac is input to the lighting device 100. The lighting device 100 lights the semiconductor light emitting element 16 by passing a constant current through the semiconductor light emitting element 16. The lighting device 100 includes an input terminal 10, a noise control circuit 11, a rectifier circuit 12, a step-up chopper circuit 13, a step-down chopper circuit 14, and an output terminal 15. The noise control circuit 11 is composed of an L-type or saddle-type noise filter. The rectifier circuit 12 includes a diode bridge that performs full-wave rectification of the AC power supply Vac.

  The step-up chopper circuit 13 is connected between the DC output terminals of the rectifier circuit 12 and converts the output voltage of the rectifier circuit 12 into a predetermined DC voltage. The step-down chopper circuit 14 converts the DC voltage output from the step-up chopper circuit 13 into a lower DC voltage. Further, current peak control is used to control the current flowing through the inductance element (inductor L1 described later) in a so-called “critical mode” operation, and further, high frequency ripple is suppressed by a smoothing capacitor (capacitor C1 described later). Thus, a constant current is passed through the semiconductor light emitting element 16.

  The “critical mode” is a control mode in which energy stored in the inductance element during the ON period of the switching element is released during the OFF period of the switching element, and the switching element is turned ON again at the timing when the energy release is completed. . Compared to the other control modes, the power conversion efficiency is higher, and since half of the peak value of the switching current is the effective value of the load current, constant current control can be easily realized.

  The noise control circuit 11, the rectifier circuit 12, and the step-up chopper circuit 13 need not be described in detail because various known configurations may be used as appropriate.

(Step-down chopper circuit configuration and critical mode operation)
FIG. 2 is a circuit diagram of the step-down chopper circuit 14 according to the embodiment of the present invention. FIG. 3 is a diagram showing an internal configuration of the control integrated circuit IC1 according to the embodiment of the present invention.

  2 and 3, the first pin (INV) is the inverting input terminal of the built-in error amplifier (error amplifier) EA, the second pin (COMP) is the output terminal of the error amplifier EA, and the third pin (MULTI) is the multiplication. The input terminal of the circuit 52, the 4th pin (CS) is a chopper current detection terminal, the 5th pin (ZCD) is a zero cross detection terminal, the 6th pin (GND) is a ground terminal, the 7th pin (GD) is a gate drive terminal, The eighth pin (VCC) is a power supply terminal.

  The switching element Q1 is driven on and off at a high frequency by the control integrated circuit IC1. The control integrated circuit IC1 is a control integrated circuit of a PFC circuit (a step-up chopper circuit for power factor correction control), and includes a multiplication circuit 52 therein. In the present embodiment, the multiplication circuit 52 is utilized as will be described later. Since the typical configuration of the control IC for the PFC circuit is already well known and not a new matter, further explanation is omitted.

As shown in FIG. 2, the voltage applied to the MULT terminal 3 of the multiplication circuit 52 is a voltage obtained by dividing the control power supply voltage by the resistor R8 and the variable resistance element R9. Hereinafter, this voltage is also referred to as voltage V _MULTI . That is, in the embodiment, the variable resistive element R9 forms a voltage dividing circuit together with the resistor R8, and generates the voltage V _MULTI from the DC power supply (control power supply voltage VCC). The variable resistance element R9 is a so-called volume resistance.

  When a control power supply voltage higher than a predetermined voltage is supplied between the power supply terminal (VCC) and the ground terminal GND, the control power supply 51 generates reference voltages Vref1 and Vref2, and each circuit in the control integrated circuit IC1 operates. It becomes possible. When the power is turned on by the starter 53, a start pulse is supplied to the set input terminal St of the flip-flop FF1, and the Q output of the flip-flop FF1 becomes High level. As a result, the 7th pin (gate drive terminal GD) becomes High level via the drive circuit 54.

Fourth pin of the control integrated circuit IC1 (CS) is a chopper current detection terminal, its voltage, via the formed noise filter IC internal _{R NF} and _{C NF,} is applied to the + input terminal of the comparator CP1 The A threshold voltage V _thcs is applied to the _negative input terminal of the comparator CP1.

  Next, the circuit configuration of the step-down chopper circuit 14, the on / off operation of the switching element Q1, and the critical mode operation associated therewith will be described.

  The DC voltage output from the step-up chopper circuit 13 is charged and smoothed by the capacitor C3 via the resistor R4, and is made constant by the Zener diode D3. This constant voltage is input as a control power supply voltage to the VCC terminal 8 of the control integrated circuit IC1. When the control power supply voltage is input to the control integrated circuit IC1, the gate drive terminal 7 becomes High level.

  When the gate drive terminal 7 of the control integrated circuit IC1 becomes High level, the gate drive voltage is applied between the gate and source of the switching element Q1 made of MOSFET via the resistor RG. As a result, the switching element Q1 is turned on.

  When the switching element Q1 is turned on, the negative side of the boost chopper circuit 13 is output from the output on the positive side a of the boost chopper circuit 13 via the semiconductor light emitting element 16, the smoothing capacitor C1, the inductor L1, the switching element Q1, and the resistor RCS. A current flows to the output of b. This current is detected by the resistor RCS and is input to the CS terminal 4 of the control integrated circuit IC1 through a low-pass filter for removing noise including the resistor R1 and the capacitor C2.

The CS terminal 4 of the control integrated circuit IC1 is an inductor current detection terminal. When the voltage Vcs of the CS terminal 4 exceeds the threshold voltage _Vthcs , the gate drive voltage from the gate drive terminal 7 becomes a low level, and the switching element Q1 Turn off.

Referring to the circuit diagram of FIG. 3, when the voltage Vcs of the chopper current detection terminal CS exceeds the threshold voltage _Vthcs , the output of the comparator CP1 becomes high level, and a reset signal is input to the reset input terminal Rst of the flip-flop FF1. . As a result, the Q output of the flip-flop FF1 becomes low level. As a result, the switching element Q1 is turned off.

  When the switching element Q1 is turned off, the electromagnetic energy accumulated in the inductor L1 when the switching element Q1 is turned on is released to the semiconductor light emitting element 16 and the smoothing capacitor C1 via the regenerative diode D1.

  The inductor L1 includes a primary winding P and a secondary winding S. The voltage of the secondary winding S of the inductor L1 is divided by resistors R2 and R3 and then input to the ZCD terminal 5 of the control integrated circuit IC1. A diode D2 is connected in parallel with the resistor R3.

  When the current of the inductor L1 disappears, no voltage is generated in the secondary winding S of the inductor L1. When the ZCD terminal 5 of the control integrated circuit IC1 detects that the voltage of the secondary winding S of the inductor L1 has fallen, the gate drive terminal 7 of the control integrated circuit IC1 is set to the high level, and the switching element Q1 is turned on again. Let

  Referring to the circuit diagram of FIG. 3, the fifth input pin (zero cross detection terminal ZCD) of the control integrated circuit IC1 is connected to the negative input terminal of the comparator CP2 for zero cross detection. A reference voltage Vref2 for zero cross detection is applied to the + input terminal of the comparator CP2. When the voltage of the secondary winding S applied to the 5th pin (zero cross detection terminal ZCD) disappears, the output of the comparator CP2 becomes High level, and the set pulse is applied to the set input terminal St of the flip-flop FF1 via the OR gate. Is supplied, and the Q output of the flip-flop FF1 becomes High level. As a result, the 7th pin (gate drive terminal GD) becomes High level via the drive circuit 54. As a result, the switching element Q1 is turned on again.

  Thereafter, the same operation is repeated.

  Thus, the peak value of the current flowing through the inductor L1 is detected to be constant, and the MOSFET Q1 is turned on / off. In so-called critical mode operation, the current of the inductor L1 is controlled, the high frequency ripple is suppressed by the smoothing capacitor C1, and a constant current is passed through the semiconductor light emitting element 16.

  In the step-down chopper circuit 14 according to the embodiment, the COMP terminal 2 voltage is used by saturating the internal error amplifier EA (ie, the clamp voltage) so as not to perform the feedback operation (in order to operate in an open loop). (See FIG. 4 described later). The INV terminal 1 is connected to the COMP terminal 2 via the resistor R5, and is given a voltage obtained by dividing the control power supply voltage VCC by the resistors R6 and R7. A capacitor C4 is connected in parallel with the resistor R7. The resistors R5, R6, and R7 are selected so that the voltage applied to the INV terminal 1 is equal to or lower than the feedback threshold voltage.

(Threshold voltage V _thcs and output adjustment)
FIG. 4 is a diagram showing a characteristic of V _thcs (threshold voltage of the comparator CP1) with respect to the voltage V _MULT in the control integrated circuit IC1 according to the embodiment of the present invention. The voltage V _MULT is a voltage input to the MULT terminal 3. Threshold voltage _{V THCS} is determined by applying a voltage _{V MULT} of the applied voltage and the third pin of the first pin (INV) (MULT). That is, the threshold voltage V _thcs can be varied by the voltage V _MULT of the control integrated circuit IC1.

As shown in FIG. 4, when the MULT terminal voltage (VMULT_PIN3) changes, the threshold voltage V _thcs changes. As described above, the voltage at the MULT terminal 3 is a voltage obtained by dividing the control power supply voltage using the resistor R8 and the variable resistance element R9. By changing the variable resistance element R9, the voltage of the MULT terminal 3 can be changed. By varying the voltage at the MULT terminal 3, for example, if Vcomp is a clamp voltage, the threshold voltage V _thcs can be raised or lowered according to the characteristic VV5 shown in FIG. Thus, the variable resistance element R9 can change the threshold voltage V _thcs by changing its own resistance value.

Since the on / off state of the switching element Q1 can be adjusted by increasing or decreasing the threshold voltage V _thcs , the peak value of the current flowing through the switching element Q1 can be increased or decreased. Thereby, output adjustment can be performed.

In the _embodiment, it is set to the operating point on the V _{MULT -V THCS} characteristics as follows. _V MULT _{-V THCS} characteristics shown in FIG. 4 may be changed according to the magnitude of the voltage Vcomp of COMP pin 2, further divided into a saturation region Astu linear region ALIN dashed X in FIG. 4 as a boundary . _V MULT _{-V THCS} characteristics shown in FIG. 4, the error amplifier EA in the internal control integrated circuit IC1, the multiplication circuit 52, and on the supply voltage of the comparator CP1.

In the embodiment, the central operating point P2 is set to VCS1 = 0.525V. This is exactly half of the saturation value (about 1.05 V) in the saturation region. With the operating point P2 as the center, the minimum operating point P1 is set on the side where V _thcs is decreased, and the maximum operating point P3 is set on the side where V _thcs is increased. Here, the width from P2 to P1 and the width from P2 to P3 are made uniform.

In order to arrange the operating points P1, P2, and P3 in the linear region, both ends (that is, the maximum value and the minimum value) of the resistance value variable width of the variable resistance element R9 are at least the voltage V _MULTI1 (about 0.15 V) and V _MULTI2. (About 0.67 V) is a value that can be generated by dividing the voltage from VCC (for example, 15 V).

In order to widen the adjustment range of the constant current to the semiconductor light emitting element 16, it is preferable that the width of the threshold voltage V _thcs to be increased and the width of the variable resistance element R9 to be as wide and the same as possible. In this respect, according to this embodiment, when a linear region ALIN and view Vcomp = characteristic of 6.0V VV5, maximum variable _{V THCS} with minimum _{V MULT} change width _{(V MULT1 ~V MULT2)} can do.

This is apparent when compared with each of the characteristics VV1 to VV4 (each of Vcomp = 3.0V to 5.0V). In the case of the characteristic VV5, the movement is from the minimum operating point P1 to the maximum operating point P3. Therefore, the change width of the voltage V _MULTI required for the purpose can be _minimized . Since the threshold voltage V _thcs can be sufficiently changed even if the change of the voltage V _MULT is small, the threshold voltage V _thcs can be adjusted quickly. In order to realize such an operation, in this embodiment, as shown in FIG. 4, the COMP terminal 2 voltage is set to a clamp voltage (6.0 V in this embodiment), and the linearity shown in FIG. The region ALIN is used, and the saturation region Astu shown in FIG. 4 is not used.

[Comparative example to the embodiment]
FIG. 5 is a circuit diagram of a step-down chopper circuit 114 shown as a comparative example with respect to the embodiment. The difference in configuration between the comparative example and the embodiment is only the circuit relating to output adjustment in the step-down chopper circuit 14.

(Difference 1)
As shown in FIG. 5, in the step-down chopper circuit 114 according to the comparative example, the voltage V _MULT that is the MULT terminal voltage is a voltage obtained by dividing the control power supply voltage by the resistor R8 and the resistor R19. The resistor R19 is not a variable resistance element. On the other hand, the voltage V _MULTI of the present embodiment is a voltage obtained by dividing the control power supply voltage by the resistor R8 and the variable resistance element R9, which are different from each other.

(Difference 2)
The step-down chopper circuit 114 according to the comparative example is different from the embodiment in that it includes a variable resistance element R10. The operation of the step-down chopper circuit 114 according to the comparative example will be described. First, when the switching element Q1 is turned on, the semiconductor light emitting element 16, the smoothing capacitor C1, the inductor L1, and the switching are output from the output on the positive side a of the step-up chopper circuit 13. A current flows to the output on the negative side b of the step-up chopper circuit 13 via the element Q1 and the resistor RCS.

  In the comparative example, this current is detected by the resistor RCS, and a voltage divided by the resistor R1 and the variable resistance element R10 is input to the CS terminal 4 of the control integrated circuit IC1. In the comparative example, the peak value of the current flowing through the switching element Q1 can be increased or decreased by changing the resistance value of the variable resistance element R10.

As described above, in the comparative example, output adjustment is performed by adjusting the resistance value of the variable resistance element R10, whereas in the embodiment, output adjustment is performed by changing the threshold voltage V _thcs by adjusting the resistance value of the variable resistance element R9. carry out. In this respect, the embodiment and the comparative example are essentially different. As can be seen by comparing FIG. 2 and FIG. 5, the step-down chopper circuit 14 according to the embodiment does not include the variable resistance element R10.

(Difference 3)
The CS terminal 4 of the control integrated circuit IC1 is an inductor current detection terminal. When the voltage Vcs of the CS terminal 4 exceeds a threshold value, the gate drive voltage from the gate drive terminal 7 becomes a low level, and the switching element Q1 is turned off. In the step-down chopper circuit 114 according to the comparative example, it is _assumed that the threshold voltage V _thcs is a fixed value because the voltage at the MULT terminal 3 cannot be changed, and this is different from the embodiment.

On the other hand, in the embodiment, when the switching element Q1 is turned on, the output from the positive side a of the boost chopper circuit 13 is passed through the semiconductor light emitting element 16, the smoothing capacitor C1, the inductor L1, the switching element Q1, and the resistor RCS. A current flows to the output on the negative side b of the boost chopper circuit 13. This current is detected by the resistor RCS and is input to the CS terminal 4 of the control integrated circuit IC1 through a low-pass filter for removing noise including the resistor R1 and the capacitor C2. The CS terminal 4 of the control integrated circuit IC1 is an inductor current detection terminal. When the voltage at the CS terminal 4 exceeds the threshold voltage V _thcs , the gate drive voltage from the gate drive terminal 7 becomes a low level, and the switching element Q1 is turned off. To do.

In the embodiment, the threshold voltage V _thcs can be varied by the voltage V _MULT input to the MULT terminal 3 of the control integrated circuit IC1. In the embodiment, as described above, by MULT pin voltage _(V MULT _PIN3), the threshold voltage _{V THCS} is determined.

In the embodiment, the voltage V _MULTI of the MULT terminal 3 is generated by _dividing the control power supply voltage by the resistor R8 and the variable resistance element R9, and is input to the MULT terminal 3 of the control integrated circuit IC1. Is done. By varying the variable resistance element R9, the voltage at the MULT terminal 3 can be varied to increase or decrease the threshold voltage V _thcs between the operating point P3 and the operating point P1, as shown in FIG. As a result, the peak value of the current flowing through the switching element Q1 can be increased or decreased, and the output can be adjusted.

(Difference 4)
As with the step-down chopper circuit 14 according to the embodiment, the step-down chopper circuit 114 according to the comparative example does not perform a feedback operation (in order to operate in an open loop). The amplifier is saturated and used (clamp voltage, see FIG. 6). The resistors R5, R6, and R7 are selected so that the INV terminal 1 voltage is equal to or lower than the feedback threshold voltage.

6, the control integrated circuit IC1 according to a comparative example for the embodiment, a diagram showing characteristics of _{V THCS} (threshold voltage of the comparator CP1) for the voltage _{V MULT.} As shown in FIG. 6, the COMP terminal 2 voltage is set to a clamp voltage, and the MULT terminal 3 voltage is a fixed voltage obtained by dividing the control power supply voltage by the resistors R8 and R19, and the operating point P4 in the saturation region shown in FIG. Is used. That is, in the comparative example, the linear region shown in FIG. 6 is not used, and this is different from the embodiment.

[Comparison with current value formula]
Next, the step-down chopper circuit 114 according to the comparative example and the step-down chopper circuit 14 according to the embodiment are compared using a calculation formula for the current value of the semiconductor light emitting element 16.

The following formula (1) is a formula for calculating the current value of the semiconductor light emitting element 16 in the present embodiment.

The following formula (2) is a formula for calculating the current value of the semiconductor light emitting element 16 in the comparative example.

Since the operation is in the critical mode, the current (output current) of the semiconductor light emitting element 16 is ½ of the inductor current. Note that td is the sum of the determination delay time and the off-delay time and turn-off time of the switching characteristics of the switching element Q1. The determination delay time is a delay time until the control integrated circuit IC1 determines that the voltage Vcs at the CS terminal 4 exceeds the threshold voltage _Vthcs by comparing the voltage Vcs at the CS terminal 4 with the threshold voltage _Vthcs .

Here, from FIG. 4 and FIG. 6, the relationship between Vcs1 and Vcs2 is as shown in the following formula (3).

Substituting equation (3) into equation (1) yields equation (4) below.

When formulas (2) and (4) are put together and arranged, formula (5) is obtained.

Here, for output adjustment, in order to obtain the same output adjustment capability in the comparative example and the embodiment, the condition of the following equation (6) is required. Here, the equivalent output adjustment capability means that the change width of the correction value in the case of the comparative example and the change width of the threshold voltage V _thcs in the present embodiment are set to the same extent. .

  In order to equalize the output adjustment capability, the resistance value of the detection resistor RCS (denoted as Rcs1 for distinction) included in the step-down chopper circuit 14 according to the embodiment is equal to the detection resistor RCS included in the step-down chopper circuit 114 of the comparative example. The resistance value may be half that of Rcs2 (for distinction). Since the resistance value of the detection resistor only needs to be small, circuit loss can be reduced, and output adjustment in the critical mode can be performed while avoiding a decrease in circuit efficiency.

  According to the lighting device 100 according to the embodiment described above, in the lighting device that controls the current flowing through the semiconductor light emitting element by the power conversion circuit operating in the critical mode, with a simple configuration, while suppressing a reduction in circuit efficiency, Output adjustment can be realized.

  That is, compared with the case where a variable resistance element for superimposing or subtracting a correction value is provided on the detection value detected by the detection resistor RCS, the present embodiment realizes an equivalent function with one variable resistance element. Even so, the resistance value of the detection resistor can be small and the output adjustment range can be widened. Since the resistance value of the detection resistor only needs to be small, circuit loss can be suppressed and a decrease in circuit efficiency can be suppressed.

  In the embodiment, a so-called volume resistor is used as the variable resistance element R9, but the present invention is not limited to this. A temperature-sensitive resistance element whose resistance value changes due to a temperature change such as a thermistor may be used as the variable resistance element R9. In addition, the temperature sensitive resistance element may be one that detects the ambient temperature of the semiconductor light emitting element 16 and varies the resistance value according to the detected temperature.

  In general, a semiconductor light emitting device has a characteristic that a voltage decreases when the ambient temperature increases, and conversely, a voltage increases when the ambient temperature decreases. That is, the luminous efficiency varies. For this reason, if the temperature is detected and the output is adjusted, the output can be made constant so as to cancel the ambient temperature change of the semiconductor light emitting element 16.

  In the embodiment, a so-called volume resistor is used as the variable resistance element R9, but the present invention is not limited to this. You may make it an output terminal of a microcomputer which mounts a circuit element, for example, a non-volatile memory. The microcomputer programs the data stored in advance in the nonvolatile memory so as to increase the output so that the semiconductor light emitting element 16 compensates for the decrease in light emission efficiency due to aging. As a result, even when a secular change appears in the semiconductor light emitting element 16, the output can be made constant to compensate for this.

DESCRIPTION OF SYMBOLS 11 Noise control circuit, 12 Rectifier circuit, 13 Step-up chopper circuit, 14 Step-down chopper circuit, 16 Semiconductor light emitting element, 51 Control power supply, 52 Multiplier circuit, 53 Starter, 54 Drive circuit, 100 Lighting device, 114 Step-down chopper circuit, D1 regeneration Diode, EA error amplifier (error amplifier), FF1 flip-flop, GD gate drive terminal, IC1 control integrated circuit, L1 inductor, Q1 switching element, R9 variable resistance element, RCS detection resistor

Claims (6)

A switching element connected in series to a DC power source and controlled to be turned on and off;
An inductance element connected in series with the switching element and through which a current flows from the DC power source when the switching element is on;
A regenerative diode that releases energy stored in the inductance element when the switching element is on to the semiconductor light emitting element when the switching element is off;
A detection unit including a detection resistor connected in series with the switching element, and detecting a current flowing through the switching element by detecting a voltage between terminals of the detection resistor;
A comparator having a first terminal receiving a detection value detected by the detection means and a second terminal receiving a threshold value and switching an output when the detection value reaches the threshold value; and turning off the switching element according to the output of the comparator Control means for turning on the switching element when the energy release of the inductance element is completed,
A variable resistance element capable of changing a voltage for determining the threshold;
A lighting device for a semiconductor light-emitting element, comprising:   The lighting device for a semiconductor light emitting element according to claim 1, wherein the variable resistance element includes a temperature sensitive resistance element whose resistance value is variable according to temperature.   The lighting device for a semiconductor light emitting element according to claim 1, wherein the variable resistance element includes a circuit element having a variable resistance value. The control means is
A third terminal for receiving an input voltage;
An error amplifier that receives a control power supply voltage as a first input and receives its output as a second input in a feedback manner;
A multiplication circuit that receives the input voltage and the output of the error amplifier to generate an output voltage, and applies the output voltage to the second terminal of the comparator as the threshold;
An input / output characteristic of the input voltage and the output voltage has a linear region and a saturation region,
The input voltage is a voltage that determines the threshold;
A voltage dividing resistor connected in series with the variable resistance element;
The variable resistance element generates the input voltage by dividing the control power supply voltage together with the voltage dividing resistor,
4. The semiconductor according to claim 1, wherein when the resistance value of the variable resistance element is changed, the input voltage changes so that the output voltage changes in the linear region. 5. Light-emitting element lighting device.   The lighting device for a semiconductor light emitting element according to claim 4, wherein the second input is a clamp voltage at which the error amplifier is saturated. A lighting device for a semiconductor light-emitting element according to any one of claims 1 to 5,
A semiconductor light emitting element supplied with a current from the lighting device of the semiconductor light emitting element;
A lighting device comprising:

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