JP2014096576A - LED Drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the following problem: A varistor used as surge measures may be incapable of sufficiently lowering a surge voltage, which may then fracture a load circuit.SOLUTION: The LED drive circuit includes: a bridge rectifier circuit that converts an AC voltage into a pulsating current for output; an LED row connected with the output side of the bridge rectifier circuit; a first constant current circuit connected in series to the LED row; and a second constant current circuit connected in series between the bridge rectifier circuit and the LED row and has a current setting value set to be not less than an ordinary current value running through the first constant current circuit.

Description

  The present invention relates to an LED driving circuit, and more particularly to an LED driving circuit including a plurality of constant current circuits.

  There is known an illumination device that uses a commercial AC power source to rectify an AC voltage into a pulsating flow to emit light from a light emitting diode (hereinafter referred to as “LED”) (for example, Patent Document 1). FIG. 1 shows a configuration of a conventional LED driving circuit. A conventional LED drive circuit 1001 includes a bridge rectifier circuit 105 using a diode that converts an AC voltage input from an AC power supply 107 into a pulsating current, a fuse 106, and an LED circuit 10a. The LED circuit 10a The pulsating current output from the bridge rectifier circuit 105 is input to.

  The LED circuit 10a includes an LED array 1011 in which a plurality of LEDs are connected in series and a constant current circuit 100a. The LED array 1011 has a configuration in which, for example, 80 LEDs are connected in series. Each LED has a threshold value called a forward voltage Vf, and when a voltage equal to or higher than the threshold voltage Vf is applied, a current flows through the LED to emit light. The threshold voltage Vf is about 3 [V].

  The constant current circuit 100 a includes a depletion type n-type MOS field effect transistor (hereinafter simply referred to as “FET”) 1021, a gate protection resistor 1031, and a current detection resistor 1041. The gate protection resistor 1031 is a protection resistor for protecting the gate of the FET 1021 from a surge. The current detection resistor 1041 is a resistor for detecting a current, and feedback is applied to the FET 1021 so that the current flowing through the current detection resistor 1041 is constant.

  Assuming that lighting devices using LEDs are used in homes and offices, there is a test (IEC 61000-4-5) to determine the effects when power lines are subjected to lightning disturbances (lightning surges). Has been done. Then, the influence of a lightning surge is examined about the illuminating device using conventional LED.

  When a 230 [V] AC power supply is used as the commercial AC power supply 107 and the surge voltage is 1 [kV], 1.3 [kV] including the maximum value of about 300 [V] of the pulsating current is LED. Applied to the circuit 10a. When the threshold voltage of the LED is 3 [V], the voltage drop in the 80 LED rows 1011 is 240 [V]. In this case, a voltage of about 1 [kV] is applied to the FET 1021. When an FET having a withstand voltage of 600 [V] is used as the FET 1021, a voltage exceeding the withstand voltage is applied to the FET 1021 to cause breakdown, and as a result, a number [A] instantaneously flows in the LED array 1011. Individual LEDs constituting the LED array 1011 are destroyed.

  On the other hand, a varistor is known as a component for protecting an electronic device from a high voltage. Therefore, the effect of surge voltage when using a varistor is examined. FIG. 2 shows a conventional LED driving circuit including a varistor. The varistor 208 is connected in parallel with the bridge rectifier circuit 205. Under the same conditions as described above, the voltage applied to the LED circuit 20a is relaxed by using the varistor 208 having a surge withstand voltage of 1 [kV], so that the destruction of the LED array 2011 and the FET 2021 can be avoided. However, when a certain voltage or higher is applied to the varistor 208, a large current of 100 [A] or more may flow.

JP 2010-178571 A

  However, it is desirable that the fuse 206 provided in the LED drive circuit 1002 be blown when the average value of the current flowing in the period until it blows is several [A] to several tens [A]. However, in order to make the varistor 208 function, there is a problem that it is difficult to set the fuse 206 so that the fuse 206 is not blown even if a current of 100 [A] or more flows instantaneously through the fuse 206.

  The voltage at which the varistor is turned on increases with the current flowing through the varistor. For this reason, when the surge current is large, the varistor may not be able to sufficiently reduce the surge voltage. At this time, there is a problem that the LED circuit 20a that is the load circuit is destroyed.

  Furthermore, the varistor has an impulse life of several to 10 times. Overcurrent protection is indispensable for varistors, and there is a problem that heating protection is required on the power supply side to prevent temperature rise when a large voltage is applied halfway.

  An LED driving circuit according to an embodiment of the present invention includes a bridge rectifier circuit that converts an AC voltage into a pulsating current and outputs the LED, an LED string connected to the output side of the bridge rectifier circuit, and a first LED connected in series to the LED string. A second constant current circuit, a current setting value that is connected in series between the bridge rectifier circuit and the LED string, and has a current setting value that is set to be equal to or higher than a normal current value that flows through the first constant current circuit; And a constant current circuit.

  In the LED drive circuit according to the embodiment of the present invention, the second constant current circuit preferably includes a depletion type FET.

  The LED driving circuit according to another embodiment of the present invention preferably further includes a varistor at the input terminal of the AC voltage of the bridge rectifier circuit.

  In the LED driving circuit according to still another embodiment of the present invention, the LED array and the first constant current circuit are configured in a multi-stage configuration in which a plurality of LED arrays and a plurality of first constant current circuits are connected in parallel. Also good.

  In the LED drive circuit according to another embodiment of the present invention, the second constant current circuit may be connected to the ground side of the bridge rectifier circuit.

  In the LED drive circuit according to still another embodiment of the present invention, the second constant current circuit preferably includes a plurality of constant current circuits connected in series.

  In the LED drive circuit according to still another embodiment of the present invention, it is preferable that the second constant current circuit is provided on the same substrate as at least one of the LED array and the first constant current circuit.

  In an LED drive circuit according to still another embodiment of the present invention, it is preferable that the first constant current circuit includes a depletion type FET and includes a FET gate protection resistor.

  A surge voltage is applied to the LED drive circuit, and the other constant current circuit limits the current at the very early stage of the breakdown of one constant current circuit. Can be suppressed. As a result, the FET does not break down due to breakdown until the sum of the withstand voltage of the two constant current circuits and the forward voltage drop amount of the LED string, and it is possible to prevent a large current from flowing through the entire LED driving circuit. it can.

  In addition, when the LED array and its driving circuit are mounted on the same surface on the circuit board, the constant current circuit to be added is the same as or similar to the components included in the driving circuit, so the constant current circuit can also be mounted on the circuit board. . As a result, an LED module with a circuit that is easy to handle can be obtained.

It is a block diagram of the conventional LED drive circuit. It is a block diagram of the conventional LED drive circuit which has a varistor. It is a block diagram of the LED drive circuit which concerns on Example 1 of this invention. It is a block diagram of the LED drive circuit which concerns on Example 2 of this invention. It is a block diagram of the LED drive circuit which concerns on Example 3 of this invention. It is a block diagram of the LED drive circuit which concerns on Example 4 of this invention. It is a block diagram of the LED drive circuit which concerns on Example 5 of this invention. It is a block diagram of the LED drive circuit which concerns on Example 6 of this invention. It is a figure which shows the 1st mounting example of the LED drive circuit of this invention. It is a figure which shows the 2nd mounting example of the LED drive circuit of this invention. It is a figure which shows the 3rd mounting example of the LED drive circuit of this invention.

  Hereinafter, an LED drive circuit according to the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

[Example 1]
First, an LED drive circuit according to Example 1 of the present invention will be described with reference to the drawings. FIG. 3 is a configuration diagram of the LED drive circuit according to the first embodiment of the present invention. The LED drive circuit 101 according to the first embodiment of the present invention includes a bridge rectifier circuit 15 that converts an alternating voltage into a pulsating current and outputs the LED, an LED array 11 connected to the output side of the bridge rectifier circuit 15, And a second constant current circuit 10x connected in series between the bridge rectifier circuit 15 and the LED array 11.

  The LED drive circuit 101 is connected to a commercial AC power supply 17, and an AC voltage is input to the bridge rectifier circuit 15 via the fuse 16.

  The bridge rectifier circuit 15 constitutes a diode bridge composed of four diodes. A commercial AC power supply 17 is connected to the AC input side of the diode bridge to convert the AC voltage into a pulsating current and output it. The terminal A on the current outflow side of the bridge rectifier circuit 15 is connected to the FET 10 of the second constant current circuit 10 x, and the terminal B on the current inflow side is a gate protection resistor 13 and a current detection resistor of the first constant current circuit 19. 14.

  The LED string 11 is connected to the output side of the bridge rectifier circuit 15. In the LED array 11, for example, 80 LEDs are connected in series. Since the threshold voltage Vf of each LED constituting the LED array 11 is about 3 [V], when a voltage of 240 [V] is applied to the entire LED array 11 to which 80 LEDs are connected, the LED Row 11 emits light.

  The first constant current circuit 19 is connected in series to the LED array 11. The first constant current circuit 19 includes a depletion type n-type MOS field effect transistor (hereinafter simply referred to as “FET”) 12, a gate protection resistor 13, and a current detection resistor 14. The gate protection resistor 13 is a protection resistor for protecting the gate of the FET 12 from a surge. The current detection resistor 14 is a resistor for detecting a current, and feedback is applied to the FET 12 so that the current flowing through the current detection resistor 14 becomes constant. As the FET 12, for example, an FET having a breakdown voltage of 600 [V] between the drain and the source can be used.

  The second constant current circuit 10 x is connected in series between the bridge rectifier circuit 15 and the LED string 11. The second constant current circuit 10x includes an FET 10. For example, an FET having a withstand voltage of 600 [V] can be used as the FET 10. The current setting value of the second constant current circuit 10x is preferably set in a range that is equal to or higher than the normal current value flowing through the first constant current circuit 19 and that does not destroy the FET 12 due to overcurrent. Here, the “normal current value” refers to a current value at which the FET 12 can operate without causing breakdown. The second constant current circuit 10x preferably includes a depletion type FET.

  According to the LED driving circuit 101 according to the first embodiment of the present invention, when a surge voltage is input, even if the first constant current circuit 19 breaks down and an overcurrent is likely to flow, the second constant current Circuit 10x limits the current. For this reason, the FET breakdown accompanying the breakdown of the first constant current circuit 19 can be suppressed. As a result, FET breakdown due to breakdown does not occur until the breakdown voltage of the first constant current circuit 19 and the second constant current circuit 10x and the forward voltage drop amount of the LED array 11 are reached, and a large current is generated in the entire circuit. Can be prevented from flowing. As an example, the voltage 240 [V] applied to the LED string 11, the withstand voltage 600 [V] of the FET 12 of the first constant current circuit 19, and the withstand voltage 600 [V] of the FET 10 of the second constant current circuit 10 x A total withstand voltage of 1440 [V] can be obtained. Therefore, when an AC voltage of 230 [V] is used as the AC power supply 17, even if the surge voltage 1 [kV] is applied to the peak voltage 300 [V] of the pulsating current, the FET breakdown accompanying the breakdown is suppressed. it can.

  Further, as a countermeasure against surges, by using an FET instead of a conventional varistor, it is possible to embed a bare chip FET in a coating resin in a COB (Chip On Board) structure, thereby realizing space saving. it can.

  In addition, since the varistor current does not flow through the fuse, it is easy to set the fuse, and a fast-acting type fuse can be used.

[Example 2]
Next, an LED drive circuit according to Embodiment 2 of the present invention will be described with reference to the drawings. FIG. 4 is a configuration diagram of an LED drive circuit according to the second embodiment of the present invention. The LED driving circuit 102 according to the second embodiment of the present invention is different from the LED driving circuit 101 according to the first embodiment in that a varistor 28 is further provided at the input terminal of the AC voltage of the bridge rectifier circuit 25. is there. Other configurations are the same as the configuration of the LED drive circuit 101 according to the first embodiment, and thus detailed description thereof is omitted.

  The LED drive circuit 102 according to the second embodiment of the present invention includes a bridge rectifier circuit 25 that converts an alternating voltage into a pulsating current and outputs the LED, an LED array 21 connected to the output side of the bridge rectifier circuit 25, and an LED array 21. A second constant current circuit 20x connected in series between the bridge rectifier circuit 25 and the LED array 21, and in addition to this, a varistor 28 is further provided. The current setting value of the second constant current circuit 20x is preferably set in a range not less than the normal current value flowing through the first constant current circuit 29 and not destroying the FET 22 due to overcurrent.

  According to the LED drive circuit according to the second embodiment of the present invention, by adding a varistor in addition to the second constant current circuit 20x, a larger surge voltage is applied compared to the LED drive circuit according to the first embodiment. However, the breakdown of the FETs 10 and 20 can be suppressed, and the operation can be further stabilized.

[Example 3]
Next, an LED drive circuit according to Embodiment 3 of the present invention will be described with reference to the drawings. FIG. 5 is a configuration diagram of an LED drive circuit according to Embodiment 3 of the present invention. The LED drive circuit 103 according to the third embodiment of the present invention is different from the LED drive circuit 101 according to the first embodiment in that the LED array and the first constant current circuit include a plurality of LED arrays 311 to 314 and a plurality of LED arrays. The first constant current circuits 30a to 30d are multi-stage connected in parallel.

  As shown in FIG. 3, the LED circuit 1 of the LED drive circuit 101 according to the first embodiment has a single-stage configuration, whereas the LED circuit of the LED drive circuit 103 according to the third embodiment has 3a to 3d. It has a four-stage configuration consisting of The operation of this multi-stage LED driving circuit will be briefly described.

  When a pulsating current is used as a voltage for driving the LED array, the voltage applied to the LED array periodically varies from 0 [V] to the peak voltage. When an AC power supply of 230 [V] is used, the peak voltage is about 320 [V]. The voltage applied to the LED string is set to a voltage lower than the peak voltage. Since the threshold voltage of the LED is about 3 [V], for example, the LED array can be configured by connecting 80 LEDs in series. In this case, when the voltage applied to the LED array is equal to or lower than the total threshold voltage 240 [V] of the LED array, the LED array does not emit light. In view of this, it is conceivable that the LED circuit for driving the LED array has a multi-stage configuration.

  In the LED drive circuit 103 shown in FIG. 5, the LED circuit has a four-stage configuration of 3a to 3d. For example, when a one-stage LED circuit for driving an LED array in which 80 LEDs are connected in series has a four-stage configuration, the LED arrays 311 to 314 can have a configuration in which 20 LEDs are connected in series. In this case, none of the LED strings is lit until the pulsating voltage exceeds 60 [V]. However, when the pulsating voltage exceeds about 60 [V], only the FET 321 of the first constant current circuit 30a is turned on, and the FET 322 is turned on. Since ˜324 is in a non-conductive state, 60 [V] is applied only to the LED array 311 to emit light. When the pulsating voltage further increases and exceeds about 120 [V], the voltage drop of the current detection resistor 341 of the first constant current circuit 30a constituting the first stage LED circuit 3a becomes large, and the FET 321 is cut off. Only the FET 322 of the second constant current circuit 30b constituting the second-stage LED circuit 3b is turned on, and the FETs 323 and 324 remain in a non-conductive state. As a result, a pulsating voltage is applied to the LED rows 311 and 312 and these emit light. Similarly, since the LED strings 313 and 314 additionally emit light as the pulsating voltage increases, the LED strings 311 to 314 start to emit light when the pulsating voltage is about 60 [V] or more. The efficiency can be increased.

  When the LED circuit has a multi-stage configuration as described above, the number of LEDs in the LED array included in each LED circuit is smaller than that in the single-stage configuration. For example, when a single-stage LED circuit having an LED array in which 80 LEDs are connected in series as described above has a four-stage configuration, the number of LEDs in the LED array included in each LED circuit is equally divided into four equal parts. In this case, the number of LEDs included in the LED array is 20. In this case, considering the case where only the first-stage LED circuit 3a is conducting, the voltage drop in the LED array 311 is about 60 [V], and the multi-stage configuration is compared with the single-stage configuration. The voltage applied to the first constant current circuit 30a increases, and a greater breakdown voltage is required.

  In the LED drive circuit 103 according to the third embodiment of the present invention, the LED circuit has a multi-stage configuration, and further includes a second constant current circuit 30x connected in series between the bridge rectifier circuit 35 and the LED rows 311 to 314. doing. As a result, as in the case of the first embodiment, the withstand voltage of the LED drive circuit 103 can be improved by the amount of withstand voltage of the FET 30 of the second constant current circuit 30x. For example, if the withstand voltage of the FET 321 of the first constant current circuit 30a is 600 [V] and the withstand voltage of the FET 30 of the second constant current circuit 30x is 600 [V], the LED string 311 is lit only under the most severe conditions. In addition, a breakdown voltage of 1260 [V] can be obtained. The current setting value of the second constant current circuit 30x is set to be equal to or larger than a normal current value flowing through the first constant current circuits 30a to 30d and within a range in which the FETs 321 to 324 are not destroyed by an overcurrent. preferable.

  Therefore, according to the LED drive circuit according to the third embodiment of the present invention, the second constant current circuit can be realized even if the voltage drop of the LED array included in each LED circuit is reduced by configuring the LED circuit in a multistage configuration. A large breakdown voltage can be obtained by adding.

[Example 4]
Next, an LED drive circuit according to Embodiment 4 of the present invention will be described with reference to the drawings. FIG. 6 is a configuration diagram of an LED drive circuit according to Embodiment 4 of the present invention. The LED drive circuit 104 according to the fourth embodiment of the present invention is different from the LED drive circuit 103 according to the third embodiment in that a varistor 48 is further provided at the input terminal of the AC voltage of the bridge rectifier circuit 45. is there. Other configurations are the same as those of the LED drive circuit 103 according to the third embodiment, and thus detailed description thereof is omitted.

  The LED drive circuit 104 according to the fourth embodiment of the present invention includes a bridge rectifier circuit 45 that converts an alternating voltage into a pulsating current and outputs the LED, an LED array 411 to 414 connected to the output side of the bridge rectifier circuit 45, an LED First constant current circuits 40a to 40d connected in series to the columns 411 to 414, respectively, and further includes a second constant current circuit 40x connected in series between the bridge rectifier circuit 45 and the LED column 411. In addition, a varistor 48 is further provided. The current setting value of the second constant current circuit 40x is set to be equal to or higher than the normal current value flowing through the first constant current circuits 40a to 40d and within a range in which the FETs 421 to 424 are not destroyed by overcurrent. preferable.

  According to the LED drive circuit according to the fourth embodiment of the present invention, by adding a varistor in addition to the second constant current circuit 40x, a larger surge voltage is applied compared to the LED drive circuit according to the third embodiment. However, the breakdown of the FETs 421 to 424 and 40 can be suppressed, and the operation can be further stabilized.

[Example 5]
Next, an LED drive circuit according to Embodiment 5 of the present invention will be described with reference to the drawings. FIG. 7 is a configuration diagram of an LED drive circuit according to the fifth embodiment of the present invention. The LED driving circuit 105 according to the fifth embodiment of the present invention is different from the LED driving circuit 103 according to the third embodiment in that the second constant current circuit 50x is connected to the ground side of the bridge rectifier circuit 55. It is a point. Other configurations are the same as the configuration of the LED drive circuit 103 according to the third embodiment, and thus detailed description thereof is omitted.

  The LED drive circuit 105 according to the fifth embodiment of the present invention includes a bridge rectifier circuit 55 that converts an alternating voltage into a pulsating current and outputs the LED, LED rows 511 to 514 connected to the output side of the bridge rectifier circuit 55, and LEDs The first constant current circuits 50 a to 50 d connected in series to the columns 511 to 514, respectively, and further includes a second constant current circuit 50 x connected to the ground side of the bridge rectifier circuit 55. When the second constant current circuit 50x is connected to the ground side of the bridge rectifier circuit 55, a gate protection resistor 59 is provided to protect the gate of the FET 50. The current setting value of the second constant current circuit 50x is set to be equal to or larger than the normal current value flowing through the first constant current circuits 50a to 50d and within a range in which the FETs 521 to 524 are not destroyed by an overcurrent. preferable.

  In the LED drive circuit 105 according to the fifth embodiment of the present invention, the second constant current circuit having a multi-stage LED circuit and connected in series between the bridge rectifier circuit 55 and the first constant current circuits 50a to 50d. 50x is further included. As a result, the breakdown voltage of the LED drive circuit 105 can be improved by the breakdown voltage of the FET 50 of the second constant current circuit 50x as in the case of the third embodiment. For example, if the withstand voltage of the FET 521 of the first constant current circuit 50a is 600 [V] and the withstand voltage of the FET 50 of the second constant current circuit 50x is 600 [V], the LED string 511 is lit only under the most severe conditions. In addition, a breakdown voltage of 1260 [V] can be obtained.

  Therefore, according to the LED drive circuit according to the fifth embodiment of the present invention, the second constant current circuit can be provided even if the voltage drop of the LED array included in each LED circuit is reduced by using the multi-stage LED circuit. A large breakdown voltage can be obtained by adding.

[Example 6]
Next, an LED drive circuit according to Embodiment 6 of the present invention will be described with reference to the drawings. FIG. 8 is a configuration diagram of an LED drive circuit according to Embodiment 6 of the present invention. The LED driving circuit 106 according to the sixth embodiment of the present invention is different from the LED driving circuit 103 according to the third embodiment in that the second constant current circuit includes a plurality of constant current circuits 60x and 60y connected in series. Is a point. Other configurations are the same as the configuration of the LED drive circuit 103 according to the third embodiment, and thus detailed description thereof is omitted.

  The LED driving circuit 106 according to the sixth embodiment of the present invention includes a bridge rectifier circuit 65 that converts an alternating voltage into a pulsating current and outputs the LED, an LED array 611 to 614 connected to the output side of the bridge rectifier circuit 65, an LED First constant current circuits 60 a to 60 d connected in series to the columns 611 to 614, respectively, and a plurality of constant current circuits 60 x and 60 y connected in series between the bridge rectifier circuit 65 and the LED columns 611 are further provided. I have. The current setting values of the plurality of constant current circuits 60x and 60y are set to be equal to or larger than the normal current value flowing through the first constant current circuits 60a to 60d and within a range in which the FETs 621 to 624 are not destroyed by overcurrent. Is preferred.

  In the LED drive circuit 106 according to the sixth embodiment of the present invention, the LED circuit has a multi-stage configuration, and two second constant current circuits 60x connected in series between the bridge rectifier circuit 65 and the LED rows 611 to 614, and 60y is further included. As a result, the breakdown voltage of the LED drive circuit 106 can be improved by the breakdown voltage of the FETs 601 and 602 of the second constant current circuits 60x and 60y, as in the third embodiment. For example, if the withstand voltage of the FET 621 of the first constant current circuit 60a is 600 [V], the withstand voltage of the FET 601 of the second constant current circuit 60x and the FET 602 of the second constant current circuit 60y is 600 [V], the LED A withstand voltage of 1860 [V] can be obtained even under the most severe conditions where only the column 611 is lit.

  In general, the number of second constant current circuits to be added can be calculated as follows. First, the desired total withstand voltage is calculated from the surge voltage and the peak voltage of the pulsating current. Next, the second constant current is determined by determining the series number of LEDs included in the LED string and comparing the result obtained by subtracting the value obtained by multiplying the series number of LEDs by the voltage drop of the LED from the total breakdown voltage with the breakdown voltage of the FET. The number of circuits is determined.

  As described above, according to the LED drive circuit according to the sixth embodiment of the present invention, even if the LED circuit includes a multi-stage configuration, even when the voltage drop amount of the LED array included in each LED circuit is reduced, a plurality of LED circuits are provided. A large breakdown voltage can be obtained by adding the second constant current circuit. In this embodiment, an example in which two constant current circuits are connected in series as the second constant current circuit is shown, but the present invention is not limited to this, and three or more constant current circuits may be connected in series.

  As described above, the LED drive circuit of the present invention is provided with the second constant current circuit including the FET instead of the varistor or in addition to the varistor as a countermeasure against the surge. Since the second constant current circuit includes an FET as a constituent element, it can be provided on the same substrate as at least one of the LED array and the first constant current circuit. Hereinafter, an example in which the second constant current circuit is mounted on the COB will be described.

(First implementation example)
First, FIG. 9 shows a first mounting example in which the LED driving circuit of the present invention is mounted on a COB. FIG. 9A shows a circuit configuration including a second constant current circuit 70x as the LED driving circuit of the present invention, and FIG. 9B is a plan view of a COB having the circuit configuration of FIG. 9A. .

  In FIG. 9B, reference numeral 107 denotes a substrate. On the substrate 107, LED rows 711 and 712, FETs 721 and 722 constituting the first constant current circuits 70a and 70b, gate protection resistors 731 and 732, current The detection resistors 741 and 742 are mounted, and the FET 70 constituting the second constant current circuit 70x of the present invention is mounted on the same substrate. Reference numerals 79 a and 79 b denote connection terminals for the bridge rectifier circuit 75. The current setting value of the second constant current circuit 70x is set to be equal to or larger than the normal current value flowing through the first constant current circuits 70a and 70b and within a range in which the FETs 721 and 722 are not destroyed by an overcurrent. preferable.

  As described above, in the first mounting example of the LED driving circuit according to the present invention, the second constant current circuit provided for surge countermeasures can be packaged in a conventional COB, so that the chip is increased in size. Surge countermeasures can be taken without any problems.

(Second implementation example)
Next, FIG. 10 shows a second mounting example in which the LED driving circuit of the present invention is mounted on the COB. FIG. 10A shows a circuit configuration including a plurality of second constant current circuits 80x and 80y as the LED drive circuit of the present invention, and FIG. 10B shows a COB having the circuit configuration of FIG. It is a top view.

  In FIG. 10B, reference numeral 108 denotes a substrate. On the substrate 108, LED strings 811 to 814, FETs 821 to 825 constituting the first constant current circuits 80a to 80e, gate protection resistors 831 to 835, current Detection resistors 841 to 845 are mounted, and further, FETs 801 and 802 constituting a plurality of second constant current circuits 80x and 80y of the present invention are mounted on the same substrate. Reference numerals 89 a and 89 b denote connection terminals for the bridge rectifier circuit 85. The current setting values of the plurality of constant current circuits 80x and 80y are set to be equal to or larger than the normal current values flowing through the first constant current circuits 80a to 80e and within a range in which the FETs 821 to 825 are not destroyed by overcurrent. Is preferred.

  As described above, in the second mounting example of the LED drive circuit of the present invention, since a plurality of second constant current circuits provided for surge countermeasures can be packaged in a conventional COB, the chip is large-sized. Surge countermeasures can be taken without becoming

(Third implementation example)
Next, FIG. 11 shows a third mounting example in which the LED driving circuit of the present invention is mounted on a COB. FIG. 11A shows a circuit configuration including a second constant current circuit 90x as an LED drive circuit of the present invention, and FIG. 11B is a plan view of a COB having the circuit configuration of FIG. 11A. . The varistor 98 can be omitted when the target value of the surge withstand voltage is low or when the withstand voltage of the second constant current circuit 90x is high. At this time, since an element to be prepared other than the LED drive circuit 109 can be only a fuse, the external circuit can be simplified.

  In FIG. 11B, reference numeral 109 denotes a substrate. On the substrate 109, LED rows 911 and 912, FETs 921 and 922 constituting the first constant current circuits 90a and 90b, gate protection resistors 931 and 932, current The detection resistors 941 and 942 are mounted, and the FET 90 constituting the second constant current circuit 90x of the present invention is mounted on the same substrate. In the third mounting example, the bridge rectifier circuit 95 is also mounted on the same substrate. Reference numerals 99 a and 99 b denote connection terminals for the AC power source 97. The current setting value of the second constant current circuit 90x is set to be equal to or larger than a normal current value flowing through the first constant current circuits 90a and 90b and within a range in which the FETs 921 and 922 are not destroyed by an overcurrent. preferable.

  As described above, in the third mounting example of the LED driving circuit according to the present invention, the second constant current circuit and the bridge rectifier circuit provided for surge countermeasures are packaged in the conventional COB. Surge countermeasures can be taken without increasing the size.

  In the above description, an example in which the LED circuit has a multi-stage configuration of two stages, four stages, or five stages is shown, but the present invention is not limited to these cases, and may be three stages or six stages or more.

10 FET
10x second constant current circuit 11 LED string 12 FET
DESCRIPTION OF SYMBOLS 13 Gate protection resistor 14 Current detection resistor 15 Bridge rectifier circuit 16 Fuse 17 AC power supply 19 First constant current circuit 101 LED drive circuit 28 Varistor

Claims (8)

A bridge rectifier circuit that converts an alternating voltage into a pulsating current and outputs it;
LED strings connected to the output side of the bridge rectifier circuit;
A first constant current circuit connected in series to the LED string;
A second constant current circuit connected in series between the bridge rectifier circuit and the LED string, and having a current setting value set to be equal to or higher than a normal current value flowing through the first constant current circuit; ,
An LED driving circuit comprising:   The LED driving circuit according to claim 1, wherein the second constant current circuit includes a depletion type FET.   The LED drive circuit according to claim 1, further comprising a varistor at an AC voltage input terminal of the bridge rectifier circuit.   4. The LED array and the first constant current circuit have a multi-stage configuration in which a plurality of LED arrays and a plurality of first constant current circuits are connected in parallel. 5. LED drive circuit.   The LED driving circuit according to claim 1, wherein the second constant current circuit is connected to a ground side of the bridge rectifier circuit.   The LED driving circuit according to claim 1, wherein the second constant current circuit includes a plurality of constant current circuits connected in series.   The LED driving circuit according to any one of claims 1 to 6, wherein the second constant current circuit is provided on the same substrate as at least one of the LED row and the first constant current circuit. .   The LED driving circuit according to claim 1, wherein the first constant current circuit includes a depletion type FET, and includes a gate protection resistor of the FET.

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