JP2010021332A - Led drive circuit, led mount substrate, and method of driving led - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED drive circuit which can effectively prevent LED destruction with time. <P>SOLUTION: The LED drive circuit 1 comprises a circuit board 23 having a mount surface and a non-mount surface on the back of the mount surface; a series LED group 27 mounted on the mount surface of the circuit board via a circuit pattern 25; a rectifier circuit 5 for causing a forward DC current to flow from the anode to the cathode side of the series LED group; and a hot-side input terminal 3H and a cold-side input terminal 3C for supplying an AC voltage to the rectifier circuit. In the LED drive circuit 1, a ground coupling suppression and prevention means 11 and 11' is provided for suppressing and preventing ground coupling via a ground stray capacitance C of the circuit pattern. By preventing the inflow of a current into the ground stray capacitance by the working of the ground coupling suppression and prevention means, a backward voltage is never applied to the LED and thereby LED destruction with time which is caused by application of a backward voltage can be effectively prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an LED driving circuit, an LED mounting board, and an LED driving method using an LED (Light Emitting Diode).

There is known an LED drive circuit that drives a plurality of LEDs to be turned on simultaneously using a commercial power supply (for example, AC 100 V). As such, there is an LED drive circuit (hereinafter referred to as “conventional drive circuit” as appropriate) shown in FIG. The conventional drive circuit 101 is generally composed of an AC input terminal 103, a bridge rectifier circuit 105, a smoothing capacitor 107, a DC output terminal 109, and an LED mounting substrate 111. The AC voltage input to the AC input terminal 103 is supplied from, for example, a 100V commercial power source. The AC voltage input to the AC input terminal is full-wave rectified by the bridge rectifier circuit 105, and then the pulsation is reduced by the smoothing capacitor 107 to be applied as a DC voltage to the LED mounting substrate 111 via the DC output terminal 109. Is done. The LED mounting substrate 111 includes a plurality of LEDs (series LED group 113) connected in series via a circuit pattern 115 (see FIG. 12), and these are applied to a DC voltage applied via a DC output terminal 109. Is driven to light. For example, Patent Documents 1 to 6 disclose a drive circuit having the same operation principle as that of a conventional drive circuit. The AC input terminal 103 includes a hot line side input terminal 103H and a cold line side input terminal 103C. Reference numeral 103Hs denotes a switch provided between the input terminal 103H and the bridge rectifier circuit 105, and reference numeral 103Cs denotes a switch provided between the input terminal 103C and the bridge rectifier circuit 105. The DC output terminal 109 includes a positive electrode output terminal 109P on the positive electrode side and a negative electrode output terminal 109N on the negative electrode side.
JP 54-152987 A (see FIG. 3) Japanese Patent Laid-Open No. 7-27331 (see FIG. 1) Japanese Patent Laying-Open No. 2005-142137 (see FIG. 1) JP 2007-287617 A (see FIG. 1) JP 2008-130438 A (see FIG. 1) International publication WO 01/045470 (see FIG. 1)

  However, none of the above-described conventional driving circuits and circuits described in each patent document can solve the following problems. The problem is that the LED located on the anode side end or the LED located on the cathode side end of the series LED group mounted on the LED mounting substrate is deteriorated or damaged over time. is there. The problem to be solved by the present invention is to provide an LED driving circuit capable of solving the above-mentioned LED destruction problem.

  In order to find a solution, it is necessary to know the cause of the LED destruction problem. The inventors speculated that the destruction of the LED over time is that a reverse voltage (a voltage at which the anode is lower than the cathode) is repeatedly applied between the anode and cathode of the LED, and a reverse minute current flows repeatedly. If there is no ground stray capacitance in each part of the circuit, the current in each part is determined by the potential difference between the parts in the circuit and does not depend on the (ground) potential of each part in the circuit. However, since the ground stray capacitance always exists, we studied in detail the behavior of the potential of the output terminal of the rectifier circuit, which is not usually a problem with this in mind. Description will be made with reference to FIGS. 8 and 9 in addition to FIG. The analysis performed by the inventors was that the potential difference (measurement point) between (1) measurement point P1 (equipotential with output terminal 109P) and ground (equipotential with input terminal 103C) of the conventional drive circuit shown in FIG. (Ground potential of P1) (2) Similarly, the potential difference between the measurement point P2 (equipotential with the output terminal 109N) and the ground (ground potential of the measurement point P2), and (3) between the measurement point P1 and the measurement point P2. The potential difference between them was measured. As a premise of the measurement, the closing timing of the switch 103Hs and the switch 103Cs was slightly shifted. The analysis was performed with the DC output terminal 109 unloaded (with the LED mounting substrate 111 removed).

  FIG. 7 shows a potential difference when the switch 103Cs is closed and then the switch 103Hs that has been opened is closed. FIG. 8A shows the same (b) to (d) in an overlapping manner. The switch 103Cs was closed at the time “0 (zero, origin)” on the x-axis, and the switch 103Hs was closed 55 ms later. The reason why it is set to 55 ms is that the timing at which the potential that was 0 (zero) V when the switch 103Cs is closed in the 50 Hz commercial power supply becomes the maximum negative potential is 55 ms. That is, since the time required for 1 Hz is 20 ms (1000 ms / 50), the third time (15 ms) is the timing at which the negative potential maximum value is reached. 55 ms is a time equal to the sum (40 + 15 ms) of the time of 2 Hz (20 ms × 2) and the time of 3/4 of 1 Hz (15 ms). The reason for selecting the timing of the negative potential maximum value is that it is considered that the above-described reverse minute current is maximized at the same timing. As shown in FIGS. 8A and 8B, when 1 ms elapses after the switch 103Hs is closed (that is, when 56 ms elapses from the origin), the potential difference between the measurement point P1 and the measurement point P2 is around + 140V. To rise. Similarly, as shown in FIGS. 8A and 8D, the potential at the measurement point P2 drops to around −140V. There is no problem with these points. However, as shown in FIG. 8C, a negative potential spike that suddenly drops from ± 0 V and peaks at −70.7 V is generated at the measurement point P1, that is, the output terminal 109P on the positive electrode side. I understood. This −70.7 V is a potential divided by two diodes (two vertically aligned in FIG. 7) of the bridge rectifier circuit 105 and the resistor R3. As will be described later, if this negative potential spike is connected to the LED mounting substrate 111, it is applied to the anode of the LED 113p closest to the output terminal 109P in the series LED group 113, and this LED 113p is destroyed over time. Can be.

  Reference is now made to FIGS. FIG. 9 shows a potential difference when the switch 103Cs is closed and then the switch 103Hs that has been opened is closed. 8 is different from the case in FIG. 8 in that the time difference of switch closing is 55 ms in FIG. 8 and is 65 ms in FIG. The reason why it is set to 65 ms is that the potential that was 0 (zero) V when the switch 103Cs is closed in the commercial power supply of 50 Hz becomes the maximum positive potential, but is 65 ms. That is, since the time required for 1 Hz is 20 ms (1000 ms / 50) as described above, a quarter of the time (5 ms) is the timing when the positive potential becomes the maximum value. 65 ms is a time equal to the sum (60 + 5 ms) of the time of 3 Hz (20 ms × 3) and the time of 1/4 of 1 Hz (5 ms). The reason why the timing of the maximum positive potential is selected is that the above-described reverse minute current is maximized at the same timing. FIG. 9A shows the same (b) to (d) in an overlapping manner. The switch 103Cs was closed at a “0 (zero, origin)” point on the x-axis, and the switch 103Hs was closed 65 ms later. As shown in FIGS. 9A and 9B, the potential difference between the measurement point P1 and the measurement point P2 is around +140 V when 1 ms elapses after the switch 103Hs is closed (that is, when 66 ms elapses from the origin). To rise. Similarly, as shown in FIGS. 9A and 9C, the potential at the measurement point P1 rises to around + 140V. There is no problem with these points. However, as shown in FIG. 9 (d), it can be seen that a positive potential spike that suddenly rises from ± 0V and peaks at + 70.7V is generated at the measurement point P2, that is, the output terminal 109N on the negative electrode side. It was. This +70.7 V is a potential divided by two diodes (two vertically aligned in FIG. 7) of the bridge rectifier circuit 105 and a resistor R4 (the same constant as R3). This positive potential spike of 70.7 V is applied to the LED 113n closest to the output terminal 109N in the series LED group 113 if the LED mounting substrate 111 is connected. It can cause destruction.

  Further, refer to FIG. 7 and FIG. FIG. 10 shows the potential difference when the switch 103Hs is closed and then the switch 103Cs that has been opened is closed. The order of closing the switches is reversed from that shown in FIG. FIG. 10A shows the same (b) to (d) in an overlapping manner. The switch 103Hs was closed at a “0 (zero, origin)” point on the x-axis, and the switch 103Cs was closed 55 ms later. The reason for setting to 55 ms is as described above. As shown in FIGS. 10A and 10B, the potential difference between the measurement point P1 and the measurement point P2 is around +140 V when 1 ms elapses after the switch 103Cs is closed (that is, when 56 ms elapses from the origin). To rise. There is no problem with this point. On the other hand, as shown in FIGS. 10A and 10D, it was found that the potential at the measurement point P2 rapidly increased from −140 V to −70.7 V, but decreased to about −140 V with the peak. This −70.7 V is a potential divided by two diodes (two vertically aligned in FIG. 7) of the bridge rectifier circuit 105 and the resistor R4. If the LED mounting substrate 111 is connected, this sudden increase in potential at the measurement point P2 is applied to the LED 113n closest to the output terminal 109N in the series LED group 113, and this LED may be destroyed over time. Furthermore, the situation shown in FIG. That is, after closing the switch 103Hs, before closing the previously opened switch 103Cs, a negative potential of −140 V is applied to the output terminal 109P. This negative potential is applied to the LED 113p that is closest to the output terminal 109P in the series LED group 113, and may cause the LED 113p to break down with time, as will be described later.

  Finally, refer to FIG. 7 and FIG. FIG. 11 shows a potential difference when the switch 103Hs is closed and then the switch 103Cs that has been opened is closed. The order of closing the switches is reversed from that shown in FIG. 10 is different from the case in FIG. 10 in that the time difference of switch closing is 55 ms in FIG. 10 and is 65 ms in FIG. FIG. 11A shows the same (b) to (d) in an overlapping manner. The switch 103Hs was closed at a “0 (zero, origin)” point on the x-axis, and the switch 103Cs was closed 65 ms later. The reason for setting to 65 ms is as described above. As shown in FIGS. 11A and 11B, the potential difference between the measurement point P1 and the measurement point P2 is around +140 V when 1 ms elapses after the switch 103Cs is closed (ie, 66 ms elapses from the origin). To rise. There is no problem with this point. On the other hand, as shown in FIGS. 11A and 11C, it was found that the potential at the measurement point P1 suddenly dropped from + 140V to + 70.7V, but increased to around + 140V with the peak. This +70.7 V is a potential divided by two diodes (two vertically aligned in FIG. 7) of the bridge rectifier circuit 105 and the resistor R1. If the LED mounting substrate 111 is connected, this sudden drop in potential at the measurement point P1 is applied to the LED closest to the output terminal 109P in the series LED group 113, and this LED 113p may be destroyed over time. Further, the situation shown in FIG. That is, after the switch 103Hs is closed, a positive potential of +140 V is applied to the output terminal 109N before the previously opened switch 103Cs is closed. This positive potential is applied to the LED 113n closest to the output terminal 109N in the series LED group 113, and may cause the LED 113n to break down over time.

  When the potentials or changes thereof described with reference to FIGS. 7 to 11 are arranged, the potential difference between the measurement point P1 and the measurement point P2 (between the output terminal 109P and the output terminal 109N) is the switch on the hot line side. Even if there was a delay in the closing timing between Hs and the switch Cs on the cold line side, no problem could be found. This was common sense until now. However, the potential of the output terminal 109P viewed from the cold line, that is, viewed from the ground side is applied with a negative potential when the circuit is not lit, that is, when either the switch 103Hs or the switch 103Cs is open, It has been found that a spike in the negative potential direction may be applied during the lighting transition, that is, at the moment when the two switches 103Hs and 103Cs are finally closed. The potential of the output terminal 109N is applied when the circuit is not lit, that is, when either the switch 103Hs or the switch 103Cs is open, or when the lighting is in transition, that is, finally, the two switches 103Hs. It was also found that a spike in the positive potential direction may be applied at the moment when the switch 103Cs is closed.

  So why does the application of the reverse polarity potential described above cause destruction of the LED over time? If each part of the LED drive circuit 101 does not have any ground stray capacitance, the current of each part of the LED drive circuit 101 is determined only by the potential difference in the circuit, and the (ground) potential of each part is not related at all. However, in reality, there is always ground coupling due to so-called stray capacitance (parasitic capacitance, stray capacitance, stray capacitance). The stray capacitance, which is also referred to as a capacitor that does not appear in the circuit diagram, includes inter-component capacitance and line-to-line capacitance on the circuit board. However, the LED group 113 is mounted on the LED destruction. This is a pattern stray capacitance (pattern-to-ground stray capacitance) that the circuit pattern 115 of the LED mounting substrate 111 has with respect to the ground (C shown in FIG. 12). The circuit pattern 115 has a role of electrically connecting adjacent LED groups (series LED groups, a plurality of LEDs connected in series) 113 by soldering or the like, but at the same time, it is important to release heat generated by the series LED groups 113 to the substrate. In general, a certain size is necessary because of its role. For example, if the circuit pattern is a conductor disk having a radius of 1 cm, the ground capacitance is 0.71 pF. Commonly speaking, the capacitance is extremely small, and the presence of this pattern-to-ground floating capacitance does not cause any problem in a state where the LED drive circuit is lighting and driving the series LED group, that is, in the series LED group conduction state. However, there is a problem that the impedance of the pattern-to-ground stray capacitance is sufficiently smaller than the reverse impedance of the LED when the LED driving circuit is not lit or during lighting transient. That is, when the LED is reverse-biased, the LED terminal is grounded through the pattern-to-ground floating capacitance. Therefore, the negative potential applied to the LED group anode end (or negative direction potential spike application) or the positive potential application (or positive direction potential spike application) to the LED group cathode end, which occurs at the time of non-lighting or lighting transition described above. In this case, a reverse voltage is applied between the anode-end LED terminals and the cathode-end LED terminals, respectively, which is considered to cause LED destruction over time.

  Based on the analysis results described above, the inventors have effectively applied repeated reverse voltage to the LED repeatedly by taking measures to prevent or prevent ground coupling that suppresses or prevents ground coupling through the ground stray capacitance of the circuit pattern. In this way, the LED destruction problem was solved. The details will be explained anew in the section. It should be noted that the definitions of terms used to describe the invention described in any claim are not limited to other claims as far as possible, regardless of the description order, differences in expression, and differences in invention category. It is assumed that the invention described is also applicable.

(Characteristics of the invention of claim 1)
An LED drive circuit according to the invention described in claim 1 (hereinafter, appropriately referred to as “drive circuit of claim 1”) includes a mounting surface, a circuit board having an anti-mounting surface on the back side of the mounting surface, and mounting of the circuit board. A series LED group mounted on the surface via a circuit pattern, and a rectifier circuit (a voltage control circuit, a current control circuit, a switching power source, etc.) for flowing a forward direct current from the anode side to the cathode side of the series LED group ) And a hot-side input terminal and a cold-side input terminal for supplying an AC voltage to the rectifier circuit. Here, ground coupling suppression preventing means for suppressing or preventing ground coupling through the ground stray capacitance of the circuit pattern is provided.

  A circuit pattern including a pad group and various wiring pattern groups is formed on the circuit board, and the LED group is soldered to the circuit pattern (the pad group). The LED group composed of a plurality of LEDs is connected in series, and a forward voltage is applied to the LED group connected in series. The applied voltage is obtained through rectification of the AC voltage input from the hot side input terminal and the cold side input terminal, and possibly through an appropriate control circuit. Here, normally, a reverse voltage is repeatedly applied between the anode terminal and the cathode terminal of some LEDs at the time of non-lighting or lighting transient due to the presence of the pattern-to-ground stray capacitance, However, according to the driving circuit of the first aspect, it is possible to eliminate such fear by suppressing or preventing the ground coupling through the pattern-to-ground floating capacitance by the action of the ground coupling suppression preventing means. it can. Therefore, according to the drive circuit of claim 1, LED destruction is effectively prevented.

(Characteristics of the invention described in claim 2)
The LED drive circuit according to the invention of claim 2 (hereinafter referred to as “drive circuit of claim 2” as appropriate) is provided with the basic configuration of the drive circuit of claim 1 and the ground coupling suppression preventing means. Includes a shield layer that at least partially covers the non-mounting surface of the circuit board, and a connection member for connecting the shield layer and the anode side or the cathode side of the series LED group in a direct current manner. It is configured. The shield layer is simple and low-cost to be configured with a shield plate installed on the non-mounting surface, but a mesh plate or other form may be used instead of the shield plate if the effect is not inferior. . Furthermore, what has a three-dimensional form like a shield case is also contained in a shield layer. If it is a range which does not impair a function as a shield layer, there will be no restriction | limiting in the shape and thickness of a shield layer.

  According to the drive circuit of claim 2, the function and effect of the drive circuit of claim 1 are achieved by the shield layer connected to the anode side end or the cathode side end of the series LED group. That is, the reverse voltage is repeatedly applied between some LED terminals at the time of non-lighting or lighting transient, and the main factor that causes LED destruction over time is the pattern-to-ground stray capacitance. It was stated in the description of the invention. One method for suppressing or preventing ground coupling through the pattern ground stray capacitance is to prevent current from flowing through the pattern ground stray capacitance. Although the shield layer is interposed between the circuit pattern and the ground, it seems that the coupling between the circuit pattern and the ground is interrupted at first glance, but the circuit pattern and the shield layer are on the other hand. In addition, a capacitor structure is formed between the shield layer and the ground. Since both capacitor structures are connected in series, the circuit pattern and the ground are still coupled. If there is a potential difference between the circuit pattern and the ground, a current can flow. Here, if the anode side or cathode side of the series LED group and the shield layer are at least equipotential during non-lighting or excessive lighting when a reverse voltage is applied, the current in one of the capacitor structures connected in series Can be cut off, thereby suppressing or preventing ground coupling. Note that the connecting member plays the role of equipotentiality.

(Characteristics of Claim 3)
The LED drive circuit according to the invention of claim 3 (hereinafter referred to as “drive circuit of claim 3” as appropriate) is provided with the basic configuration of the drive circuit of claim 2 and then from the side opposite to the mounting surface. The shield layer is formed so that almost all of the circuit pattern is hidden underneath when the circuit board is seen through.

  According to the drive circuit of claim 3, in addition to the operation and effect of the drive circuit of claim 2, the shield layer hides almost all of the circuit pattern, so that the shield layer is sufficiently interposed between the circuit pattern and the ground. It becomes. This effectively suppresses or prevents the connection between the exposed portion and the ground that would have occurred if there was an exposed portion that was not hidden by the shield layer among the portions constituting the circuit pattern.

(Feature of the invention of claim 4)
The LED drive circuit according to the invention of claim 4 (hereinafter referred to as “drive circuit of claim 4” as appropriate) is provided with the basic configuration of the drive circuit of any of claims 1 to 3, and then the AC The voltage source is a commercial power source.

  According to the drive circuit of claim 4, in addition to the operation and effect of the drive circuit of any of claims 1 to 3, the LED group can be driven to be lit using a commercial power supply as a direct power supply. Can do. Although not intended to deny the use of a transformer, if you do not use a transformer, it will greatly contribute to weight reduction and cost reduction.

(Feature of the invention of claim 5)
An LED mounting board according to the invention described in claim 5 (hereinafter referred to as “the board of claim 5”) includes a mounting surface, a circuit board having an anti-mounting surface on the back side of the mounting surface, and a mounting surface of the circuit board. A series LED group mounted on a circuit pattern on the top and formed on the side opposite to the mounting surface so that at least almost all of the circuit pattern is hidden underneath when the circuit board is seen through from the side opposite to the mounting surface. The shield layer is configured to include a connection member for connecting the conductor layer and the anode side or the cathode side of the series LED group in a direct current manner. Further, the substrate according to claim 5 is configured to allow a forward direct current to flow from the anode side to the cathode side of the series LED group.

  According to the substrate of the fifth aspect, the series LED group can be driven to light by passing a direct current from the anode side to the cathode side. At that time, the conductor layer having the same potential as the anode side end or the cathode side end shields the floating capacitance of the circuit pattern to the ground, so that the LED destruction based on the ground coupling can be effectively prevented.

(Characteristics of the invention described in claim 6)
The LED driving method according to the invention of claim 6 (hereinafter referred to as “the driving method of claim 6” as appropriate) is the AC voltage received by the series LED group mounted on the mounting surface of the circuit board via the circuit pattern. LED driving method in which lighting is driven by flowing forward direct current obtained by rectifying. Here, by suppressing or preventing ground coupling through the ground stray capacitance of the circuit pattern, application of reverse voltage to the LED is suppressed or prevented.

  According to the driving method of the sixth aspect, since the reverse voltage is suppressed or prevented from being applied to the LED, it is possible to effectively prevent the destruction of the LED mainly caused by such application.

(Feature of the invention of claim 7)
The LED driving method according to the seventh aspect of the invention (hereinafter referred to as “the driving method of the seventh aspect” as appropriate) is the driving method according to the sixth aspect, wherein the stray capacitance of the circuit pattern is changed to the series LED group. Is shielded by a shield layer that is connected to the anode side or the cathode side in a direct current manner.

  According to the drive method of Claim 7, the effect of the drive method of Claim 6 is specifically show | played by the shield layer connected with the anode side end or cathode side end of series LED group. That is, the reverse voltage is repeatedly applied between some LED terminals at the time of non-lighting or lighting transient, and the main factor that causes LED destruction over time is the pattern-to-ground stray capacitance. It was stated in the description of the invention. One method for suppressing or preventing ground coupling through the pattern ground stray capacitance is to prevent current from flowing through the pattern ground stray capacitance. Although the shield layer is interposed between the circuit pattern and the ground, it seems that the coupling between the circuit pattern and the ground is interrupted at first glance, but the circuit pattern and the shield layer are on the other hand. In addition, a capacitor structure is formed between the shield layer and the ground. Since both capacitor structures are connected in series, the circuit pattern and the ground are still coupled. If there is a potential difference between the circuit pattern and the ground, a current can flow. Here, if the anode side or cathode side of the series LED group and the shield layer are at least equipotential during non-lighting or excessive lighting when a reverse voltage is applied, the current in one of the capacitor structures connected in series Can be cut off, thereby suppressing or preventing ground coupling. Note that the equipotential is because the anode side or cathode side of the series LED group and the shield layer are connected in a direct current manner.

  ADVANTAGE OF THE INVENTION According to this invention, the destruction problem of LED can be solved in the LED drive circuit, LED mounting board, and LED drive method which rectify | straighten alternating current and drive a series LED group to light.

  Next, the best mode for carrying out the present invention (hereinafter referred to as “this embodiment” as appropriate) will be described with reference to the drawings. FIG. 1 is a circuit diagram of an LED drive circuit according to the present embodiment. FIG. 2 is a perspective view of an LED mounting substrate included in the LED driving circuit. 3 is a cross-sectional view taken along the line AA of the LED mounting substrate shown in FIG. FIG. 4 is a modified circuit diagram of the LED drive circuit according to the present embodiment. 5 and 6 are diagrams showing analysis results of the circuit diagram shown in FIG.

(Schematic structure of LED drive circuit)
The LED drive circuit 1 shown in FIG. 1 includes an AC input terminal 3 (hot side input terminal 3H, cold side input terminal 3C), a bridge rectifier circuit 5, a smoothing capacitor 7, a constant current circuit 8, and a DC output terminal 9. The main components are (the positive electrode output terminal 9P and the negative electrode output terminal 9N) and the LED mounting substrate 21 surrounded by a two-dot chain line. Reference numeral 3Hs denotes a switch inserted between the hot-side input terminal 3H and the bridge rectifier circuit 5, and reference numeral 3Cs denotes a switch inserted between the cold-side input terminal 3C and the bridge rectifier circuit 5. The bridge rectifier circuit 5 is a full-wave rectifier circuit, but may be a half-wave rectifier circuit. Moreover, if it is a rectifier circuit which can send a forward direct current to the series LED group (after-mentioned) which LED mounting board | substrate 21 contains like a switching power supply etc., it will not interfere with employ | adopting suitably. The smoothing capacitor 7 may be omitted if unnecessary. The constant current circuit 8 is a circuit for keeping the load current constant. The resistors R1 and R2 are resistors for protecting the rectifier diode by limiting the inrush current to the smoothing capacitor during the lighting transition. Either one of the resistor R1 and the resistor R2 can be omitted, but both are inserted in order to make the measurement state at the measurement point P1 and the measurement point P2 the same.

(Structure of LED mounting substrate)
As shown in FIGS. 1 to 3, the LED mounting board 21 is generally composed of a circuit board 23, a circuit pattern 25, a series LED group 27, a shield layer 29, a connection member 31, and a DC input terminal 33. The circuit board 23 is a rectangular synthetic resin board provided with a mounting surface 23a on one side and an anti-mounting surface 23b on the other side, and a circuit pattern 25 may be provided on the mounting surface 23a, inside the laminate, or both. it can. As shown in FIG. 3, the circuit pattern 25 in the present embodiment is inside the circuit board 23. The circuit pattern 25 includes a pad group for soldering each LED constituting the series LED group 27, a wiring pattern group, and a conductive paste filled in an interlayer connection hole (via hole) (applied to the inner wall). Hole plating) is also included in the circuit pattern. The series LED group 27 includes a plurality (20 in this embodiment) connected in series via the circuit pattern 25, and among the LEDs connected in series, the anode terminal 11A of the LED 27p closest to the positive input terminal 9P is the positive electrode. The cathode terminal 11C of the farthest LED 27n is connected to the input terminal 33P and to the negative input terminal 33N, respectively. The positive input terminal 33P and the negative input terminal 33N constitute the direct-current input terminal 33 described above. The positive output terminal 9P and the positive input terminal 33P were connected by a connection line 30p, and the negative output terminal 9N and the negative input terminal 33N were connected by a connection line 30n. The shield layer 29 and the connection member 31 will be described in the next section.

(Shield layer structure)
As shown in FIGS. 2 and 3, the shield layer 29 is formed on the non-mounting surface 23 b of the circuit board 23. The shield layer 29 is, for example, a metal foil such as a copper foil attached to the anti-mounting surface 23b, a conductive resin applied to the anti-mounting surface 23b, or a metal plate or metal fixed on the anti-mounting surface using a fixing member. Can be configured by case. In the present embodiment, the shield layer 29 is formed of the copper foil attached to the non-mounting surface 23b. The shield layer 29 may be formed in a size that covers the entire surface of the anti-mounting surface 23b. However, as shown in FIG. 2, when the circuit board 23 is seen through from the anti-mounting surface 23b side, the shape is not limited. However, it is preferable that at least almost all of the circuit pattern 25 be formed in such a size as to be hidden underneath. Since the shield layer 29 hides almost all of the circuit pattern 25, the shield layer 29 is sufficiently interposed between the circuit pattern 25 and the ground. Thereby, it is possible to effectively suppress or prevent the coupling between the exposed portion and the ground that would have occurred if there was an exposed portion that was not hidden by the shield layer 29 among the respective portions constituting the circuit pattern 25. . The connection member 31 is a conductive member for connecting the shield layer 29 and the anode terminal 11A, which is the anode side of the series LED group 27, in a DC manner so that the shield layer 29 has the same potential as the anode side or the cathode side. In the present embodiment, the other end of the covered wire (not shown) whose one end is soldered to the shield layer 29 is soldered to the anode terminal 11 </ b> A, thereby connecting them in a DC manner. This covered wire corresponds to the connecting member 31 in the present embodiment. Although not shown in addition to the covered wire, for example, a portion for connecting the two included in the circuit pattern, conductive resin filled in the through hole, inner wall plating, or other conductive members may be employed as the connecting member 31. it can. The shield layer 29 and the connecting member 31 constitute the ground coupling suppression preventing means 11 in the present embodiment (see FIG. 1). In this embodiment, the shield layer 29 is connected to the anode side. However, as shown in FIG. 4, the connection member 31 is removed to open the anode terminal 11A, and the connection member 31 ′ is used to connect the cathode terminal 11C. You may connect to. There is no difference between the circuit diagram shown in FIG. 4 and the circuit diagram shown in FIG. 1 except for the point relating to the connection member 31 ′. The shield layer 29 and the connection member 31 ′ provide the ground coupling suppression prevention means 11 ′. Constitute.

(Operational effect of the LED drive circuit according to the present embodiment)
The operation and effect of the LED drive circuit 1 will be described with reference to FIGS. The AC voltage input to the AC input terminal 3 of the LED drive circuit 1 is a commercial power supply of 50 Hz. The hot line is connected to the input terminal 3H, and the cold line is connected to the input terminal 3C. By closing both the switch 3Hs and the switch 3Cs, the DC voltage rectified by the bridge rectifier circuit 5 and smoothed by the smoothing capacitor 7 appears at the DC output terminal 9 (positive output terminal 9P, negative output terminal 9N). The appearing DC voltage is applied to the series LED group 27 via the DC input terminal 33 (positive input terminal 33P, negative input terminal 33N), whereby forward DC current flows from the anode terminal 11A to the cathode terminal 11C in series. The LED group 27 is turned on. On the other hand, the shield layer 29 that is kept at the same potential as the anode terminal 11A by the connection of the connection member 31 is interposed between the circuit pattern 25 of the circuit board 23 and the ground, and the ground stray capacitance (pattern stray capacitance between them). ) To suppress or prevent the coupling between the circuit pattern 25 and the ground (ground coupling) to such an extent that a current that causes LED breakdown does not flow.

(Control or prevention of ground connection)
In order to solve the above-mentioned problem, the reverse voltage is repeatedly applied between some LED terminals during non-lighting or lighting transition, and the main factor causing LED destruction over time is the pattern-to-ground floating capacitance. This has already been described in the column of means with reference to FIGS. In this embodiment, in order to suppress or prevent the ground coupling through the pattern ground floating capacitance, a method of preventing current from flowing through the pattern ground floating capacitance is employed. Although the shield layer 29 shown in FIG. 1 is interposed between the circuit pattern and the ground, it seems that the coupling between the circuit pattern 25 and the ground E is cut off at first glance. Actually, the capacitance C1 related to the capacitor structure formed between the circuit pattern 25 and the shield layer 29 connected in series and the capacitance C2 related to the capacitor structure formed between the shield layer 29 and the ground E are Connected through. A combined capacity of the capacity C1 and the capacity C2 is defined as a capacity C. This capacitance C becomes a pattern stray capacitance. The circuit pattern 25 and the ground E are still connected. If there is a potential difference between the circuit pattern 25 and the ground E, a current can flow. Here, in the present embodiment, the 27 anode side (anode terminal 11A) of the series LED group and the shield layer 29 are connected in a DC manner by the connecting member 31, so that at least a reverse voltage is applied or not lit. It is configured to be equipotential when it is excessive. By doing this, the impedance of the pattern-to-ground stray capacitance is sufficiently large at that time as compared with the reverse impedance of the LED, and thereby the current flow in one of the capacitors C1 or C2 connected in series can be cut off. As a result, it is possible to suppress or prevent ground coupling through the capacitance C which is a pattern stray capacitance. Such a shield layer 29 and the anode terminal 11A are driven to light while maintaining the equipotential during non-lighting or excessive lighting, so that the series LED group 27 is not lighted or is in a lighting transient. When applying a negative potential to the anode end (anode terminal 11A) of the LED group, application of a reverse voltage between the anode end LED terminals and between the cathode end LED terminals can be prevented. Prevention of reverse voltage application effectively prevents LED destruction over time caused by severe application of the reverse voltage. In the case of the circuit shown in FIG. 4 as well, there is no difference in the principle of effectively preventing LED destruction only by reversing the positive and negative cases.

  Please refer to FIGS. 5 and 6 in addition to FIGS. FIG. 5 shows a change in potentials at both ends of the LED 27p and the LED 27n when the hot line side switch 3Hs is closed at 0 (zero) s and the cold line side switch 3Cs is closed 55 ms later and vice versa. Show. Regardless of which of the switch 3Hs and the switch 3Cs precedes (the graph lines overlap), no potential is applied to the LED 27p until the switch 3Cs is closed. The potential is rising. No reverse voltage is applied. No reverse spike voltage is applied. The potential change shown in FIG. 6 is the same as that shown in FIG. 5 even if any switch is preceded by closing except that the closing timing of the switches 3Hs and 3Cs is 65 ms. Again, the graph lines overlap. No reverse voltage is applied. No reverse spike voltage is applied. Although not shown, the same result was obtained in the analysis performed using the LED drive circuit shown in FIG. From the above, according to the LED lighting driving method by the LED drive circuit 1 including the ground coupling suppression prevention means 11 (ground coupling suppression prevention means 11 ′), the reverse voltage application and the reverse spike potential application are effectively prevented. As a result, the LED destruction problem can be solved.

It is a circuit diagram of the LED drive circuit which concerns on this embodiment. It is a perspective view of the LED mounting board | substrate with which an LED drive circuit is provided. It is AA sectional drawing of the LED mounting board shown in FIG. It is a modification circuit diagram of the LED drive circuit which concerns on this embodiment. It is a figure which shows the analysis result of the circuit diagram shown in FIG. It is a figure which shows the analysis result of the circuit diagram shown in FIG. It is a conventional LED drive circuit diagram. It is a figure which shows the analysis result of the conventional LED circuit diagram. It is a figure which shows the analysis result of the conventional LED circuit diagram. It is a figure which shows the analysis result of the conventional LED circuit diagram. It is a figure which shows the analysis result of the conventional LED circuit diagram. It is a longitudinal cross-sectional view of the conventional LED mounting substrate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 LED drive circuit 3 AC input terminal 3H Hot side input terminal 3C Cold side input terminal 5 Bridge rectifier circuit 7 Smoothing capacitor 8 Constant voltage circuit 9 DC output terminal 9P Positive output terminal 9N Negative output terminal 11 Ground floating capacity suppression prevention means 11 ' Floating capacitance suppression prevention means 21 LED mounting board 23 Circuit board 25 Circuit pattern 27 Series LED group 29 Shield layer 30p Connection line 30n Connection line 31 Connection member 31 'Connection member 33 DC input terminal 33P Positive input terminal 33N Negative input terminal 101 ( Conventional LED drive circuit 103 AC input terminal 105 Bridge rectifier circuit 107 Smoothing capacitor 109 DC output terminal 109P Positive output terminal 109N Negative output terminal 111 LED mounting board 113 Series LED group 115 Circuit pattern

Claims (7)

A circuit board having a mounting surface and an anti-mounting surface on the back side of the mounting surface;
A series LED group mounted on the mounting surface of the circuit board via a circuit pattern;
A rectifier circuit for flowing a forward direct current from the anode side to the cathode side of the series LED group;
A hot-side input terminal and a cold-side input terminal for supplying an AC voltage to the rectifier circuit;
In the LED driving circuit configured to include:
An LED driving circuit, characterized in that ground coupling suppression preventing means for suppressing or preventing ground coupling through the ground stray capacitance of the circuit pattern is provided. The ground coupling suppression preventing means is
A shield layer for at least partially covering the non-mounting surface of the circuit board;
The LED driving circuit according to claim 1, further comprising a connecting member for connecting the shield layer and the anode side or the cathode side of the series LED group in a direct current manner. The LED driving circuit according to claim 2, wherein the shield layer is formed so that substantially all of the circuit pattern is hidden underneath when the circuit board is seen through from the side opposite to the mounting surface. The LED drive circuit according to claim 1, wherein the AC voltage power supply is a commercial power supply. A circuit board having a mounting surface and an anti-mounting surface on the back side of the mounting surface;
A series LED group mounted on the mounting surface of the circuit board via a circuit pattern;
When the circuit board is seen through from the non-mounting surface side, at least a shield layer formed on the non-mounting surface side so that almost all of the circuit pattern is hidden below,
A connection member for connecting the conductor layer and the anode side or the cathode side of the series LED group in a direct current manner,
An LED mounting substrate used for an LED drive circuit, wherein a forward direct current is passed from the anode side to the cathode side of the series LED group. In the LED driving method for lighting and driving by flowing a forward direct current obtained by rectifying the received alternating voltage to the series LED group mounted on the circuit board mounting surface via the circuit pattern,
An LED driving method comprising suppressing or preventing ground coupling through a ground stray capacitance of a circuit pattern. The LED driving method according to claim 6, wherein the stray capacitance of the circuit pattern is shielded by a shield layer that is DC-connected to the anode side or the cathode side of the series LED group.

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