JP6500657B2 - LED lighting device - Google Patents

Description

  The present invention relates to an LED lighting device.

  The LED has the characteristics of a diode, and the rate of change of the load current with respect to the load voltage is steep. Therefore, since the brightness is difficult to control at a constant voltage, the LED is generally driven by a constant current. FIG. 12 is a diagram showing the characteristics at the time of temperature change in the case of constant current control of the LED. When the load voltage of the LED rises at low temperature, the load current is constant but the power increases due to the increased load voltage. Although the light output is proportional to the load current, the change with temperature is larger, so the light output is bright at low temperatures and dark at high temperatures.

  When the LED is driven at a constant current as a light source of the emergency light, the battery capacity decreases at a low temperature, but the power consumption of the LED increases, so the battery duration is deteriorated. Because the light output is bright at low temperatures, it is wasting power consumption. On the other hand, although light output decreases at high temperature, it can not cope with constant current control.

  On the other hand, it is possible to drive LED by constant power (for example, refer patent documents 1-3). FIG. 13 is a diagram showing the characteristics at the time of temperature change when constant power control of the LED is performed. In the case of constant power control, since the load current is reduced and the power is made constant by the amount of increase in load voltage at low temperature, the duration of the battery can be increased. Although the light output decreases, the brightness is originally increased due to the temperature characteristics of the LED, so that the necessary brightness can be secured, and an increase in the useless light output can be suppressed. On the other hand, when the temperature is high, the load voltage decreases and the load current increases. Although this increases the light output, the brightness decreases due to the temperature characteristics of the LED, so this operation is compensated. However, since the temperature characteristic of the LED is generally larger, constant power control can not completely compensate.

JP, 2010-15887, A JP, 2009-231147, A JP, 2015-5410, A

  In the constant power control, when the load current changes due to the variation of the LED, the temperature characteristic, the failure or the disconnection, the load voltage changes accordingly. Similarly, when the load voltage changes, the load current changes accordingly. In particular, at the time of open circuit when the current becomes zero, the voltage and current become maximum at the short circuit when the voltage becomes zero. It is necessary to protect against over current and over voltage so that the maximum value at this time does not exceed the rating of the component.

  The lighting device described in JP2009-231147A includes a comparator and a diode-OR circuit as a circuit for performing voltage limit and current limit. However, the circuit described in this publication has a circuit operation in which the voltage limiter detection signal or the current limiter detection signal is interrupted by the diode OR circuit with respect to the normal LED voltage detection signal. Since only the maximum value among the three detection signals is input to the control circuit by the diode OR circuit, only one of the voltage limiter and the current limiter operates, and both of them can not operate simultaneously. Such alternative limiter operation still leaves room for improvement from the viewpoint of performing constant power control.

  The present invention has been made to solve the problems as described above, and an object thereof is to obtain an LED lighting device capable of performing constant power control and protecting against over current and over voltage.

  According to a first aspect of the present invention, there is provided an LED lighting device comprising: a power supply circuit for supplying a load current to an anode of an LED to light the LED; a first resistor serially connected between a cathode of the LED and a ground terminal; And a second resistor having one end and the other end connected to the connection point of the cathode of the LED and the first resistor, and one end and the other end according to the anode voltage of the LED at the one end A third resistor to which a voltage is applied, a voltage at a connection point connecting the other end of the second resistor and the other end of the third resistor, or a voltage of the other end of the second resistor and the An error amplifier for feeding back to the power supply circuit a difference between a voltage obtained by multiplying the voltage at the other end of the three resistors and a predetermined value determined in advance, and connected in parallel to the second resistor, the second resistor The voltage applied to the one end is predetermined A first limiter circuit that adjusts a voltage of the other end of the second resistor to set an upper limit to an output of the power supply circuit when the voltage is exceeded; and a second limiter circuit that sets an upper limit to a load voltage of the LED; And the power supply circuit controls the output to reduce the difference during lighting of the LED.

  According to a second aspect of the present invention, there is provided an LED lighting device comprising: a power supply circuit for supplying a load current to an anode of an LED to light the LED; a first resistor serially connected between a cathode of the LED and a ground terminal; And a second resistor having one end and the other end connected to the connection point of the cathode of the LED and the first resistor, and one end and the other end according to the anode voltage of the LED at the one end A third resistor to which a voltage is applied, a voltage at a connection point connecting the other end of the second resistor and the other end of the third resistor, or a voltage of the other end of the second resistor and the third An error amplifier for feeding back a difference between a voltage obtained by multiplying the voltage at the other end of the resistor and a predetermined value determined in advance to the power supply circuit and a voltage at the one end of the third resistor do not fall below the reference voltage. And the one of the third resistors And a fourth limiter circuit for setting an upper limit on the load voltage of the LED, wherein the power supply circuit is configured to reduce an output while the LED is lit. Control.

According to a third aspect of the present invention, there is provided an LED lighting device comprising: a power supply circuit for supplying a load current to an anode of an LED to light the LED; first detection means for detecting the load current; and a load voltage applied to the LED And a value detected by the second detection means when the value detected by the second detection means does not fall below a predetermined lower limit. A computing means for outputting a value obtained by adding or multiplying a low voltage limiter for outputting the lower limit value when the value is lower than the lower limit value, a value detected by the first detection means and a value output from the low voltage limiter And a high voltage limiter for providing an upper limit to the value output from the calculation means, and a difference between an output value from the calculation means limited by the high voltage limiter and a predetermined value determined in advance to the power supply circuit. The A comparison means for feedback, the power supply circuit controlling the output to reduce the difference during lighting of the LED.

According to the first to third invention, the LED lighting device that performs the constant power control, the calculated value of the value after the operation of the limiter is reflected is addition or multiplication can be fed back to the power supply circuit. Thereby, both the current limiter and the voltage limiter can be operated at the same time, and constant power control capable of setting the maximum power within the limited tolerance can be realized.

It is a figure which shows the LED lighting device which concerns on Embodiment 1 of this invention. It is a figure which shows the relationship of the addition and multiplication of load current and load voltage which flow into LED. It is the figure which expanded the use range of the load voltage in FIG. It is a figure which shows the LED lighting device which concerns on Embodiment 2 of this invention. It is a figure which shows the LED lighting device which concerns on Embodiment 3 of this invention. It is a figure for demonstrating the operation | movement of the low voltage limiter circuit which concerns on Embodiment 3 of this invention. It is a figure which shows the LED lighting device which concerns on Embodiment 4 of this invention. It is a figure for demonstrating the operation | movement of the low voltage limiter circuit which concerns on Embodiment 4 of this invention. It is a figure which shows the LED lighting device which concerns on Embodiment 5 of this invention. It is a figure which shows the LED lighting device which concerns on Embodiment 6 of this invention. It is the figure which deform | transformed the LED lighting device which concerns on Embodiment 1 as an example in the case of using a multiplier in embodiment of this invention. It is a figure which shows the characteristic at the time of the temperature change at the time of carrying out constant current control of LED. It is a figure which shows the characteristic at the time of the temperature change at the time of carrying out constant power control of LED. It is a functional block diagram of the microcomputer which the LED lighting device which concerns on Embodiment 6 of this invention has.

  An LED lighting device according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components may be assigned the same reference numerals and repetition of the description may be omitted.

Embodiment 1
FIG. 1 is a diagram showing an LED lighting device according to Embodiment 1 of the present invention. The power supply circuit 1 supplies a load current to the anode of the LED to light the LED. A resistor R1 is connected between the cathode of the LED and the ground terminal (GND).

  One end of the resistor R2 is connected to the connection point between the cathode of the LED and the resistor R1. One end of the resistor R3 is connected to the anode of the LED, and the other end of the resistor R3 is connected to the other end of the resistor R2.

  The error amplifier 2 feeds back the voltage Vin at the connection point between the resistors R2 and R3 to the power supply circuit 1. The error amplifier 2 is a differential amplifier circuit, which receives the voltage Vin from its negative input and receives the reference voltage Vref from its positive input. A capacitor C1 is connected between the negative input and the output of the error amplifier 2.

  The power supply circuit 1 is a chopper circuit including an inductor L1, a switching element Q1 such as a MOSFET, a diode D1, and a smoothing capacitor C2. One end of the inductor L 1 is connected to the battery 3. The switching element Q1 is connected between the other end of the inductor L1 and the ground terminal (GND). The anode of the diode D1 is connected to the other end of the inductor L1, and the connection point between the anode of the diode D1 and the other end of the inductor L1 is connected to the drain of the switching element Q1. The positive electrode of the smoothing capacitor C2 is connected to the cathode of the diode D1, and the negative electrode is connected to the ground terminal (GND).

  The switching element Q1 is controlled by the control circuit 4. When the switching element Q1 is turned on / off, energy stored in the inductor L1 during the on period of the switching element Q1 is released through the diode D1 during the off period of the switching element Q1. Then, the smoothing capacitor C2 is charged in such a manner that the energy released from the inductor L1 is superimposed on the output voltage of the battery 3, so that the voltage across the smoothing capacitor C2 can be boosted higher than the output voltage of the battery 3.

  The control circuit 4 controls the on / off frequency or duty ratio of the switching element Q1 according to the output of the error amplifier 2. Thus, the power supply circuit 1 controls the output such that the voltage Vin at the connection point between the resistor R2 and the resistor R3 becomes constant. The control circuit 4 is realized by a control IC, or a processing circuit such as a CPU or a system LSI. Further, a plurality of processing circuits may cooperate to execute the above function.

  The LED lighting device according to the first embodiment includes the current limiter circuit 10. The current limiter circuit 10 is connected in parallel to the resistor R2. Specifically, the positive input of the comparator 11 is connected to the connection point between the resistor R2 and the resistor R1. A predetermined voltage is applied to the negative input of the comparator 11. The output of the comparator 11 is connected to one end of the resistor R4, and the other end of the resistor R4 is connected to a connection point where the other end of the resistor R2 and the other end of the resistor R3 are connected.

  A series circuit of a Zener diode DZ2 and a resistor R5 is connected in parallel to R3. The series circuit of the Zener diode DZ2 and the resistor R5 corresponds to the "voltage limiter circuit" according to the present invention.

  The load current of the LED corresponds to the voltage applied to the resistor R1, and the load voltage of the LED corresponds to the voltage applied to the resistor R3. Therefore, the voltage Vin at the connection point between the resistor R2 and the resistor R3 corresponds to the addition of the load current and the load voltage of the LED. Therefore, the error amplifier 2 feeds back the addition of the load current and the load voltage of the LED to the power supply circuit 1. On the other hand, power is the multiplication of load current and load voltage. FIG. 2 is a diagram showing the relationship between addition and multiplication of LED load current and load voltage. As shown in FIG. 2, control to make the addition constant (addition constant control) and control to make the multiplication constant (multiplication constant control) are different.

  However, when an LED is used as a load, the change range of the load voltage is as small as several volts. FIG. 3 is an enlarged view of a use range of the load voltage in FIG. As shown in FIG. 3, constant multiplication control can be approximated by constant addition control within the use range of the load voltage. Further, although the addition constant control deviates from the curve of the multiplication constant control outside the use range of the load voltage, the addition constant control deviates in the direction in which the power becomes lower, which is safe.

  The current limiter circuit 10 realizes overcurrent protection by adding a voltage to the other end of the resistor R2 when the voltage applied to one end of the resistor R2 exceeds a predetermined voltage. Specifically, the comparator 11 goes high when the voltage applied to one end of the resistor R2 (ie, the voltage at the connection point of the resistor R1 and the cathode of the LED) exceeds a predetermined voltage. As the comparator 11 becomes high, the output voltage of the comparator 11 is added to the other end of the resistor R2. As a result, it is possible to obtain a circuit operation in which the voltage Vin is increased to lower the output of the power supply circuit 1. That is, constant power control is realized by the voltage Vin as an addition value (or a multiplication value as will be described later) being fed back to the power supply circuit 1 by the error amplifier 2. In order to keep the voltage Vin constant, the power supply circuit 1 reduces the output so as to reduce the increase when the voltage Vin is increased. Since the current limiter circuit 10 works to raise the voltage Vin when an overcurrent occurs, the voltage Vin is calculated as a larger value by the voltage addition amount by the current limiter circuit 10. Therefore, when an overcurrent occurs, feedback can be applied in the direction to lower the output of the power supply circuit 1 by the increased corrected voltage Vin. As a result, the load current of the current limiter circuit 10 can provide an upper limit to the load current. Preferably, when the load voltage is below a certain value, the current limiter circuit 10 preferably has an upper limit of the load current so that the load current is fixed at a certain upper limit regardless of the load voltage. . Specifically, the voltage Vin is corrected to be increased by the voltage addition of the current limiter circuit 10, and the output of the power supply circuit 1 is limited to stop the load current at a certain upper limit regardless of the load voltage as shown in FIG. preferable.

  The zener diode DZ2 is turned on when the load voltage of the LED exceeds a certain value in order to protect against an overvoltage. The operating point of the Zener diode DZ2 is provided outside the usable range, and the power is changed in the direction to reduce the power, thereby setting the operation to avoid a failure and to be a safe operation. As described in JP 2009-231147 A, since it is not necessary to form a voltage limiter circuit using a comparator, the voltage limiter circuit can be configured with a simple configuration.

  As described above, in the present embodiment, constant power control of the LED can be performed with a simple circuit configuration by feeding back the value obtained by adding the load current of the LED and the load voltage to the power supply circuit 1.

ここで、ＬＥＤの負荷電流と負荷電圧をそれぞれＩＦ，ＶＦ、抵抗Ｒ１，Ｒ２，Ｒ３の抵抗値をそれぞれｒ１，ｒ２，ｒ３とする。 Further, the voltage Vin input to the error amplifier 2 can be obtained by the following equation 1.

Here, let the load current and load voltage of the LED be IF and VF, and the resistances of the resistors R1, R2 and R3 be r1, r2 and r3, respectively.

If the resistance values r2 and r3 of the resistors R2 and R3 are determined by the following equation 2 in these parameters, P ′ = 0 in the vicinity of the load voltage VF, and the power P becomes constant. Therefore, constant power control can be performed regardless of the power P and the resistance value r1 of the resistor R1. Also, constant design can be simplified.

  Further, a Zener diode DZ2 is connected in parallel with a resistor R3 for obtaining a load voltage, and the Zener diode DZ2 is turned on when the load voltage exceeds a predetermined value. Thus, the LED, the resistor R1, and the elements in the power supply circuit 1 can be protected from overvoltage.

Second Embodiment
FIG. 4 is a diagram showing an LED lighting device according to Embodiment 2 of the present invention. In the LED lighting device according to the second embodiment, the current limiter circuit 10 is replaced with the Zener diode DZ1, and in FIG. 1, the resistor R5 is connected in series to the Zener diode DZ2, but this is omitted in FIG. The circuit configuration is the same as that of the LED lighting device according to the first embodiment shown in FIG. 1 except that the voltage limiter circuit is formed by a single modification of the Zener diode DZ2. Therefore, in the following description, the same or corresponding components as or to those of the first embodiment will be denoted by the same reference numerals, and differences from the first embodiment will be mainly described. Or omitted.

  In the second embodiment, the Zener diode DZ1 is connected in parallel to the resistor R2. In order to protect against an overcurrent, the Zener diode DZ1 is turned on when the load current exceeds a certain value. The operating point of the Zener diode DZ1 is provided outside the use range, and by changing the power in the direction of reduction, the failure is avoided and the safe operation is set. When the Zener diode DZ1 is turned on, the voltage across the resistor R2 is kept constant, so the voltage at the other end of the resistor R2 can be limited to a constant value, and the voltage Vin can be limited. Since the output of the power supply circuit 1 is limited by limiting the voltage Vin, an upper limit can be provided so that the power supply circuit 1 does not increase the output when an overcurrent occurs.

  As described above, in the second embodiment, the Zener diodes DZ1 and DZ2 are connected in parallel to the resistors R2 and R3 for obtaining the load current and the load voltage, respectively, and the load current and the load voltage each exceed a predetermined value. In this case, the Zener diodes DZ1 and DZ2 are turned on. This makes it possible to protect the LED, the resistor R1, and the elements in the power supply circuit 1 from overcurrent and overvoltage with a simple circuit configuration. In addition, since it is not necessary to form a complicated circuit in which three comparators are connected in parallel as described in the diagram of JP 2009-231147 A, the limiter circuit of current and voltage is configured with a simple configuration. be able to.

Third Embodiment
FIG. 5 is a diagram showing an LED lighting device according to Embodiment 3 of the present invention. In the present embodiment, a high voltage limiter circuit 5 and a low voltage limiter circuit 6 are provided instead of the Zener diodes DZ1 and DZ2 of the second embodiment shown in FIG. Further, a resistor R4 is connected between a connection point between the resistor R2 and the resistor R3 and the error amplifier 2. The other configuration is the same as that of the second embodiment.

  The high voltage limiter circuit 5 is connected between the connection point of the resistors R2 and R3 and the anode of the LED. The high voltage limiter circuit 5 has a Zener diode DZ3 and a resistor R5 connected in series. The low voltage limiter circuit 6 is connected to one end of the resistor R 3, and the low voltage limiter circuit 6 has a comparator 7 and a switching circuit 8. The comparator 7 compares the anode voltage of the LED with the reference voltage Vth. The switching circuit 8 applies the anode voltage to one end of the resistor R3 when the anode voltage is equal to or higher than the reference voltage Vth, and applies the reference voltage Vth to one end of the resistor R3 when the anode voltage is lower than the reference voltage Vth. Switch the connection to Thus, the low voltage limiter circuit 6 limits the voltage at one end of the resistor R3 so as not to fall below the reference voltage Vth.

  Also, in order to protect from an overvoltage, when the load voltage exceeds a certain value, the Zener diode DZ3 of the high voltage limiter circuit 5 is turned on to set the upper limit of the load voltage of the LED. The operating point of the Zener diode DZ3 is provided outside the use range, and by changing the power in the direction of reduction, the failure is avoided and the safe operation is set.

  In addition, the low voltage limiter circuit 6 limits the voltage at one end of the resistor R3 so as not to fall below the reference voltage Vth. FIG. 6 is a diagram for explaining the operation of the low voltage limiter circuit according to the third embodiment of the present invention. Here, the resistance value of the resistor R1 is 1Ω, the resistance value of the resistor R2 is 4.0367 KΩ, the resistance value of the resistor R3 is 440 KΩ, the reference voltage Vth is 34 V, the reference voltage Vref is 0.8 V, and the constant power value is 17.7 W And

  When the load voltage of the LED decreases from 48 V to 30 V, the comparator 7 outputs “H” until the reference voltage Vth = 34 V. In response to this, the switching circuit 8 applies the anode voltage of the LED to one end of the resistor R3.

  Thereafter, when the load voltage of the LED falls below the reference voltage Vth = 34 V, the comparator 7 outputs “L”, and the switching circuit 8 applies the reference voltage Vth to one end of the resistor R3. As a result, even if the load voltage of the LED falls below 34 V, 34 V is input to one end of the resistor R3.

  Since the load voltage decreases as the LED load current increases, the constant power control alone can not prevent the overcurrent. Therefore, the load current of the LED does not exceed the fixed value (0.495 A) by limiting the low voltage limiter circuit 6 so that the voltage at one end of the resistor R3 does not fall below the reference voltage. As a result, it is possible to protect against overcurrent.

  As described above, in the present embodiment, constant power control of the LED can be performed with a simple circuit configuration by feeding back the value obtained by adding the load current of the LED and the load voltage to the power supply circuit 1.

  Further, the high voltage limiter circuit 5 can protect against overvoltage by setting the upper limit of the load voltage of the LED. Furthermore, the low voltage limiter circuit 6 limits the voltage at one end of the resistor R3 so as not to fall below the reference voltage Vth. This can protect against over current.

Fourth Embodiment
FIG. 7 is a diagram showing an LED lighting device according to Embodiment 4 of the present invention. A low voltage limiter circuit 9 is provided instead of the low voltage limiter circuit 6 of the third embodiment shown in FIG. The other configuration is the same as that of the third embodiment.

  The low voltage limiter circuit 9 has resistors R6, R7, R8, a transistor Q2 such as a MOSFET, a shunt regulator 21, and a bias resistor R21. The resistor R6 is connected between the anode of the LED and one end of the resistor R3. The emitter of the transistor Q2 is connected to the connection point of the resistors R3 and R6, and the collector is connected to the anode of the LED. One end of the bias resistor R21 is connected to the collector of the transistor Q2, and the other end of the bias resistor R21 is connected to the connection point between the base of the transistor Q2 and the cathode of the shunt regulator 21. The shunt regulator 21 inputs a voltage obtained by dividing the voltage at the connection point of the resistors R3 and R6 by the resistors R7 and R8 as a reference voltage, and the current supplied from the bias resistor R21 outputs the output voltage to the base of the transistor Q2. Apply.

  FIG. 8 is a diagram for explaining the operation of the low voltage limiter circuit according to the fourth embodiment of the present invention. Here, the resistance value of the resistor R1 is 1Ω, the resistance value of the resistor R2 is 4.0367 KΩ, the resistance value of the resistor R3 is 22 KΩ, the resistance value of the resistor R6 is 418 KΩ, the reference voltage of the shunt regulator 21 is 3.06 V, the reference voltage The Vref is 0.8 V, and the constant power value is 17.8 W.

  When the load voltage of the LED drops from 48 V, the voltage at the connection point of the resistors R3 and R6 also drops, but when it is higher than the output voltage of the shunt regulator 21, it is sent to the error amplifier 2 as it is. At this time, since the reference voltage is higher than the threshold, the shunt regulator 21 operates to lower the output voltage. Therefore, the output voltage of the shunt regulator 21 is not generated at the emitter of the transistor Q2 because the base voltage of the transistor Q2 is lowered and the base-emitter is reversely biased. For example, the base voltage of the transistor Q2 is about 1 V, and the emitter voltage is 2 to 3 V.

  Thereafter, when the load voltage of the LED drops to about 30 V and the voltage at the connection point between the resistors R3 and R6 falls below the output voltage of the shunt regulator 21, the base and emitter of the transistor Q2 conduct and the resistors R3 and R6 The output voltage of the shunt regulator 21 is generated at the connection point of. Therefore, even if the load voltage of the LED is lower than the reference voltage, the low voltage limiter circuit 9 receives the output voltage of the shunt regulator 21 at one end of the resistor R3. As a result, the low voltage limiter circuit 9 limits the voltage at one end of the resistor R3 so as not to fall below the reference voltage. Thereby, the same effects as in the first to third embodiments can be obtained.

  Further, in the fourth embodiment, the switching circuit 8 of the third embodiment is substituted by a diode or by the base-emitter diode of the transistor Q2, and the comparator 7 of the third embodiment and the reference voltage source are substituted by the shunt regulator 21. ing. Therefore, since the comparator is not used, the comparator itself and the power supply circuit can be omitted. Further, since there is no power supply circuit, there is no restriction due to increase or decrease of the power supply voltage. Then, since the transistor Q2 takes charge of the voltage, the reference voltage can be set low, and a low voltage shunt regulator can be used. Furthermore, since the output buffer and the switching circuit are shared by the transistor Q2, the circuit is simplified.

Embodiment 5
FIG. 9 is a diagram showing an LED lighting device according to Embodiment 5 of the present invention. A low voltage limiter circuit 22 is provided instead of the low voltage limiter circuit 6 of the third embodiment shown in FIG. The other configuration is the same as that of the third embodiment.

  The low voltage limiter circuit 22 includes resistors R6 and R9, a diode D5, and a zener diode DZ4. The resistor R6 is connected in series between the anode of the LED and one end of the resistor R3. The cathode of the diode D5 is connected to the connection point of the resistors R3 and R6, and the anode of the diode D5 is connected to the cathode of the zener diode DZ4. The anode of the Zener diode DZ4 is connected to the ground terminal.

To describe an example of a circuit design method of the fifth embodiment, where, by selecting the Zener diode DZ 4 breakdown voltage is 5.1V, the cathode connection point of the resistor R9 and a Zener diode DZ 4 is at 5.1V Configure to be maintained. The resistors R3 and R6 are selected so that the voltage at the connection point between the resistors R3 and R6 is, for example, about 7 V, for example. When 5.1 V is applied to the anode of the diode D5 and a voltage of about 7 V is applied to the cathode of the diode D5, the diode D5 is reverse biased. After that, it is assumed that the load voltage of the LED decreases and, for example, the voltage at the connection point of the resistor R3 and the resistor R6 drops to 7V to less than 4.5V. In this case, 4.5 V obtained by subtracting the voltage drop of 0.6 V from the voltage of 5.1 V at the anode of the diode D5 continues to be supplied to the connection point of the resistors R3 and R6, so the voltage applied to one end of the resistor R3 Can have a lower limit. Thus, the low voltage limiter circuit 9 limits the voltage at one end of the resistor R3 so as not to fall below the reference voltage. Thereby, the same effect as in the first to fourth embodiments can be obtained.

  Further, as compared with the third embodiment and the like, there is also an advantage that the circuit configuration is simplified since circuit components such as transistors or shunt regulators are not included.

Sixth Embodiment
FIG. 10 is a diagram showing an LED lighting device according to a sixth embodiment of the present invention, and a diagram showing an LED lighting device using the microcomputer 34. As shown in FIG. The sixth embodiment provides an LED lighting device in which the circuits according to the first to fifth embodiments are integrated. The microcomputer 34 has the voltage detecting function by the resistors R1 to R3, the function of the error amplifier 2, the function of the control circuit 4, the function of the low voltage limiter circuits 6, 9, 22 and the high voltage limiter circuit 5 in the first to fifth embodiments. The functions of the above are incorporated internally, and programs for executing these functions are stored in advance in the internal memory. The power supply circuit 101 of the sixth embodiment is a step-up chopper circuit portion (a portion formed of the inductor L1, the switching element Q1, the diode D1, and the capacitor C2 of the power supply circuit 1) in the first to fifth embodiments. , Is provided outside the microcomputer 34. The control circuit 4 included in the power supply circuit 1 is mounted on the microcomputer 34 side. The resistors R1 and R3 are provided outside the microcomputer 34.

  The microcomputer 34 is realized in the form of a memory and a CPU that executes a program stored in the memory, or in the form of a processing circuit such as a system LSI. Further, the microcomputer 34 may be configured by combining a plurality of at least one of a memory, a CPU, and a processing circuit, and a plurality of processing circuits or the like may cooperate to execute the above function. The microcomputer 34 includes the same configuration as that of a well-known microcomputer for digital control power supply, and includes an input / output interface, an A / D converter, a processor for performing digital operation, various volatile and non-volatile memories, It includes an oscillator, a pulse width modulator for generating a PWM signal used for on / off control of switching elements, and various peripheral circuits.

  FIG. 14 is a functional block diagram of the microcomputer 34 included in the LED lighting device according to the sixth embodiment. As an example, the microcomputer 34 includes an A / D conversion unit, a high voltage limiter function unit, a low voltage limiter function unit, a feedback function unit (hereinafter, an FB function unit), and a PWM signal generation function unit. The FB function unit includes an arithmetic function unit and a comparison function unit. The functions of the microcomputer 34 may be realized by storing a program in which the processing of each functional unit is modularized in the built-in non-volatile memory and executing the program by a processor. Hereinafter, for convenience of explanation, an example of the processing content of the microcomputer 34 will be described while the functional units are divided for each function.

  (Process S1) First, the microcomputer 34 acquires the voltage Vin1 corresponding to the load current of the LED by acquiring the voltage from one end of the resistor R1 through the interface. Further, the microcomputer 34 acquires the voltage Vin2 corresponding to the load voltage of the LED by acquiring the voltage divided by the voltage dividing circuit of the resistors R3 and R102 through the interface.

  (Process S2) Next, the voltages Vin1 and Vin2 are converted into digital values Vin1 ′ and Vin2 ′ by the A / D conversion unit in the microcomputer 34.

  (Processing S3) Next, a digital value Vin1 'obtained by A / D converting the voltage Vin1 corresponding to the LED load current is input to the low voltage limiter function unit of the microcomputer 34. The operation of the low voltage limiter function unit is the same as the input / output operation of the low voltage limiter circuits 6, 9 and 22 described in the third to fifth embodiments. That is, the low voltage limiter function unit compares Vin1 'with the lower limit value, outputs Vin1' itself when Vin1 'is equal to or greater than the lower limit, and outputs the lower limit itself when Vin1' falls below the lower limit.

  (Processing S4) Further, a digital value Vin2 'obtained by A / D converting the voltage Vin2 corresponding to the LED load voltage is input to the high voltage limiter function unit. The high voltage limiter function unit is the same as the input / output operation of the high voltage limiter circuits 5, 9, 22 described in the first to fifth embodiments. The high voltage limiter function unit compares the digital value Vin2 ′ with a predetermined breakdown voltage value VDZ ′. The breakdown voltage value VDZ 'is a value set from the same viewpoint as the breakdown voltage in the Zener diode DZ2 according to Embodiments 1 and 2 and the high voltage limiter circuit 5 used in Embodiments 3 to 5.

  The high voltage limiter function unit performs the same function as the Zener diode DZ2 according to the first and second embodiments and the high voltage limiter circuit 5 used in the third to fifth embodiments. First, the circuit operation of the first to fifth embodiments will be described with respect to this point. The breakdown voltage value VDZ 'plays the same role as the breakdown voltage of the Zener diode DZ3 of the high voltage limiter circuit 5 shown in FIG. When the LED voltage rises and the Zener diode DZ3 conducts, the resistor R5 and the Zener diode DZ3 constituting the high voltage limiter circuit 5 are connected in parallel to the resistors R6 and R3 used for detecting the LED voltage. As a result of the parallel connection, the impedance of this path is lower than when the zener diode DZ3 is not conducting. As the impedance decreases, the current of the parallel circuit including the resistors R6, R3 and R5 and the Zener diode DZ3 increases even with the same LED voltage, and thus the negative input voltage of the error amplifier 2 increases. As a result, feedback is applied to reduce the increase in the negative electrode input voltage, and the power supply circuit 1 reduces the output. Thus, in the first to fifth embodiments, a high voltage limiter is applied as the operation of the entire circuit.

  In order to exhibit the same function as that of the high voltage limiter function unit according to the sixth embodiment, Vin2 'and VDZ' are compared, and either of the following operations are performed according to the comparison result. First, when Vin2 'is lower than VDZ' (Vin2 '<VDZ'), the input Vin2 'is output as Vhi as it is. If the LED is normal, VDZ 'is set so that the LED voltage is lower than VDZ'. Therefore, while the LED indicates normal characteristics, the high voltage limiter function unit outputs Vin2 'as it is. On the other hand, when Vin2 'becomes equal to or greater than VDZ' (Vin'ZVDZ '), a value larger than the input Vin2' is output as the output value Vhi. At this time, the value output by the high voltage limiter functional unit may be a predetermined value stored in advance, or may be calculated by multiplying the current Vin2 ′ by a coefficient. In any case, when the output value Vhi is calculated to be larger than Vin2 ', "For example, the impedance is lowered by the conduction of the Zener diode DZ3 in FIG. 7, and even with the same LED voltage, the resistors R6, R3, R5 and the Zener diode It is possible to perform control similar to the circuit operation in which the current of the parallel circuit configured by DZ3 increases and the negative electrode input voltage of the error amplifier 2 increases. When the output value Vhi is calculated to be large, a process to reduce the output of the power supply circuit 101 is performed in the feedback function unit described later.

  (Process S5) Next, the output value Vlo of the low voltage limiter function unit and the output value Vhi of the high voltage limiter function unit are input to the arithmetic function unit in the feedback function unit. The arithmetic function unit outputs a calculated value Vinc ′ as an added value of Vlo and Vhi. A value obtained by integration (multiplication) instead of addition may be used as the calculated value Vinc '.

  (Processing S6) Next, the calculated value Vinc 'and the predetermined reference voltage digital value Vref' are compared by the comparison function unit, and the difference ΔVin 'is calculated. The difference ΔVin 'is an output of the feedback function unit and is input to the PWM signal generation function unit.

  (Process S7) If the difference ΔVin ′ is positive, the PWM signal generation function unit reduces the frequency or duty ratio of the on / off signal to be supplied to the switching element Q1 to reduce the power supplied to the LED. Conversely, if the difference ΔVin ′ is negative, the PWM signal generation function unit raises the frequency or duty ratio of the on / off signal to be supplied to the switching element Q1 to increase the power supplied to the LED. The PWM signal Vout adjusted in a feedback manner based on the difference ΔVin ′ is supplied to the control terminal of the switching element Q1 through the interface.

  Thus, the microcomputer 34 capable of performing constant current control while protecting against over current and over voltage is provided.

Modified example.
In the first embodiment, by connecting the resistors R1, R2 and R3, a load voltage and a load current are added to generate a voltage Vin, which is fed back to the power supply circuit 1 by the error amplifier 2. This enables constant power control of the LED with a simple circuit configuration. However, the present invention is not limited to this, and as shown in FIG. 11, a multiplier 30 (specifically, a dedicated IC or a microcomputer) of a load voltage and a load current may be used. FIG. 11 is a diagram in which the LED lighting device according to the first embodiment is modified as an example of using a multiplier in the embodiment of the present invention. The circuit is the same as that of FIG. 1 except that a multiplier 30 connected to the other end of the resistor R2 and the other end of the resistor R3 is provided. The output of the multiplier 30 is input to the error amplifier 2. In the second to fifth embodiments, the multiplier 30 may be provided similarly.

  The LED lighting device according to the first and second embodiments described above corresponds to a specific embodiment of the LED lighting device according to the first invention, and the LED according to the third to fifth embodiments described above. The lighting device corresponds to a specific embodiment of the LED lighting device according to the second invention. The lighting device according to the sixth embodiment described above corresponds to a specific embodiment of the LED lighting device according to the third aspect of the present invention.

  According to the LED lighting device according to the first and second embodiments, the voltage Vin used for constant power control can be corrected by adjusting the voltage by the current limiter circuit 10 at the time of over current, and over current protection can be reliably performed. The circuit can be reliably protected from overvoltage by the zener diode DZ2 (voltage limiter circuit). In constant power control, the power supply circuit 1 changes its output so as to keep the output power constant. The output of the power supply circuit 1 can be limited by the first limiter circuit adjusting the voltage when an overcurrent occurs. Thus, in the constant power control, an operation of limiting the output of the power supply circuit 1 can be realized such that the upper limit of the load current is provided when the overcurrent occurs.

  According to the LED lighting device according to the third to fifth embodiments, when the low voltage limiter circuits 6, 9 and 22 limit the voltage at the time of an overcurrent, the reduction of the voltage value Vin used for constant power control can be suppressed. In addition to reliably protecting the over current, the high voltage limiter circuit 5 can reliably protect the circuit from over voltage. The low voltage limiter circuits 6, 9 and 22 impose a limit on the voltage drop at one end of the third resistor R3 when the anode voltage drops at which the occurrence of an overcurrent is estimated. By setting the lower limit of the voltage at one end of the third resistor R3, it is possible to prevent the voltage Vin at the time of occurrence of the overcurrent from becoming too small. Therefore, it is possible to suppress the feedback control that increases the output of the power supply circuit 1 despite the occurrence of the overcurrent. Thus, in the constant power control, an operation of limiting the output of the power supply circuit 1 can be realized such that the upper limit of the load current is provided when the overcurrent occurs.

1 power supply circuit, 2 error amplifier, 3 batteries, 4 control circuits, 5 high voltage limiter circuits, 6, 9, 22 low voltage limiter circuits, 7 comparators, 8 switching circuits, 10 current limiter circuits, 21 shunt regulators, 11 comparators, 30 multiplier, 34 microcomputer, C1 capacitor, C2 smoothing capacitor, D1 diode, D5 diode, DZ1, DZ2, DZ3, DZ4 Zener diode, L1 inductor, Q1 switching element, Q2 transistor, R21 bias resistor

Claims (11)

A power supply circuit that supplies load current to the anode of the LED to light the LED;
A first resistor connected in series between the cathode of the LED and the ground terminal;
A second resistor having one end and the other end, the one end connected to a connection point between the cathode of the LED and the first resistor;
A third resistor having one end and the other end to which a voltage corresponding to the anode voltage of the LED is applied at the one end;
A voltage at a connection point connecting the other end of the second resistor and the other end of the third resistor, or a voltage of the other end of the second resistor and a voltage of the other end of the third resistor An error amplifier for feeding back to the power supply circuit the difference between the multiplied voltage and a predetermined value determined in advance;
The other end of the second resistor is connected in parallel with the second resistor, and when the voltage applied to the one end of the second resistor exceeds a predetermined voltage, the output of the power supply circuit has an upper limit. A first limiter circuit that adjusts the voltage of
A second limiter circuit for providing an upper limit to the load voltage of the LEDs;
Equipped with
An LED lighting device, wherein the power supply circuit controls an output to reduce the difference while the LED is lit.   The LED according to claim 1, wherein the first limiter circuit adds a voltage to the other end of the second resistor when a voltage applied to the one end of the second resistor exceeds a predetermined voltage. Lighting device.   The LED lighting device according to claim 1, wherein the first limiter circuit includes a first Zener diode connected in parallel to the second resistor.   The LED lighting device according to claim 2 or 3, wherein the second limiter circuit includes a Zener diode having an anode connected to the other end of the third resistor, and a cathode receiving a voltage according to the anode of the LED. A power supply circuit that supplies load current to the anode of the LED to light the LED;
A first resistor connected in series between the cathode of the LED and the ground terminal;
A second resistor having one end and the other end, the one end connected to a connection point between the cathode of the LED and the first resistor;
A third resistor having one end and the other end to which a voltage corresponding to the anode voltage of the LED is applied at the one end;
A voltage at a connection point connecting the other end of the second resistor and the other end of the third resistor, or a voltage of the other end of the second resistor and a voltage of the other end of the third resistor An error amplifier for feeding back to the power supply circuit the difference between the multiplied voltage and a predetermined value determined in advance;
A third limiter circuit providing a lower limit to the voltage at the one end of the third resistor so that the voltage at the one end of the third resistor does not fall below the reference voltage;
A fourth limiter circuit that imposes an upper limit on the load voltage of the LEDs;
Equipped with
An LED lighting device, wherein the power supply circuit controls an output to reduce the difference while the LED is lit. The third limiter circuit is
A comparator comparing the anode voltage of the LED with a reference voltage;
When the anode voltage is higher than the reference voltage, the anode voltage is applied to the one end of the third resistor, and when the anode voltage is lower than the reference voltage, the reference voltage is applied to the one end of the third resistor Switching circuit to switch the connection to apply
The LED lighting device according to claim 5, comprising The third limiter circuit is
A limiter resistor having one end connected to the anode of the LED and the other end connected to the one end of the third resistor;
A transistor whose emitter is connected to the connection point of the third resistor and the limiter resistor, and whose collector is connected to the anode of the LED ;
A shunt regulator that receives a voltage corresponding to the voltage at the connection point at a reference terminal and applies an output voltage to the base of the transistor;
The LED lighting device according to claim 5, comprising The third limiter circuit is
A first limiter resistor having one end connected to the anode of the LED and the other end connected to one end of the third resistor;
A diode whose cathode is connected to a first connection point where the third resistor and the first limiter resistor are connected;
A second limiter resistor connected at one end to the anode of the LED and at the other end to the anode of the diode;
Cathode connected to the second connection point and the other end anode and the second limiter resistance of the diode is connected, a Zener diode having an anode connected to ground terminal,
The LED lighting device according to claim 5, comprising The fourth limiter circuit according to any one of claims 6 to 8, wherein the fourth limiter circuit includes a zener diode receiving a voltage corresponding to the voltage of the other end of the third resistor at its anode and receiving a voltage corresponding to the anode of the LED at the cathode. The LED lighting device according to claim 1 or 2.   A power supply circuit that supplies load current to the anode of the LED to light the LED;
  First detection means for detecting the load current;
  Second detection means for detecting a load voltage applied to the LED;
  The value detected by the second detection means is output when the value detected by the second detection means does not fall below a predetermined lower limit value, and the value detected by the second detection means is less than the lower limit value A low voltage limiter that outputs a value,
  Computing means for outputting a value obtained by adding or multiplying the value detected by the first detection means and the value output from the low voltage limiter;
  A high voltage limiter for providing an upper limit to the value output from the computing means;
  Comparing means for feeding back, to the power supply circuit, the difference between the output value from the calculating means limited by the high voltage limiter and a predetermined value determined in advance;
  Equipped with
  An LED lighting device, wherein the power supply circuit controls an output to reduce the difference while the LED is lit. The LED lighting device according to claim 10 , wherein the comparison means , the low voltage limiter, and the high voltage limiter are incorporated in a microcomputer.

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