JP2014013865A - Led driver circuit and lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driver circuit and a lighting system which can prevent beforehand an electric shock in replacement work of LED lamps and destruction of a circuit element.SOLUTION: The LED driver circuit includes: a DC power supply 10; a pair of positive and negative terminals 15a, 15b which attachably/detachably hold an LED array 14 where a plurality of LEDs are connected in series; an LED drive circuit 16 which turns on the LED array 14 using the DC power supply 10; a voltage control circuit 11 which controls so as to supply a constant voltage to the LED drive circuit 16; and overvoltage prevention means 30 which controls open voltage between a pair of terminals to be a predetermined voltage or lower when the LED array is removed from the terminal.

Description

  The present invention relates to an LED drive circuit and an illumination device, and more particularly to an LED drive circuit and an illumination device having an overvoltage prevention function.

In recent years, LED lamps having long life and power saving characteristics are becoming popular as light sources for various lighting devices.
In particular, straight tube type LED lamps having an LED array in which a plurality of LEDs are connected in series are being applied to lighting for vehicles such as indoor lighting and trains in place of conventional fluorescent lamps.

  In the prior art, there are a technique related to an illumination device using a straight tube type LED lamp and a technique related to a drive circuit of the LED array (see, for example, Patent Documents 1 and 2).

JP 2011-90852 A JP 2010-110157 A

  By the way, although the LED lamp has a long life, it needs to be periodically replaced, and it is necessary to temporarily remove the LED lamp from the socket (terminal) at the time of replacement. Also, the LED lamp may be removed when performing maintenance such as cleaning.

  Here, when removing the LED lamp from the socket (terminal) of the lighting device, when the main power supply of the lighting device is turned off, problems such as electric shock during work do not occur.

  On the other hand, when exchanging a large number of LED lamps or performing maintenance in an office or train, etc., if the main power is turned off, the lighting device that is not working is turned off and darkened. There is a desire to perform replacement work with the main power turned on.

  However, there is a risk of an electric shock when the LED lamp is replaced with the main power turned on.

  In particular, when the LED lamp is removed from the socket (terminal) of the lighting device, a relatively high open-circuit voltage (for example, 35 V or more) is applied between the terminals, which may cause an electric shock to workers or the like.

  Further, the open circuit voltage may exceed the breakdown voltage of the elements constituting the circuit and be destroyed.

  An object of the present invention is to provide an LED driver circuit and an illuminating device capable of preventing an electric shock accident and a circuit element destruction in an LED lamp replacement operation or the like.

  According to one aspect of the present invention for achieving the above object, a DC power source, a pair of positive and negative terminals that removably hold an LED array in which a plurality of LEDs are connected in series, and the DC power source are used to An LED driving circuit for lighting the LED array, a voltage control circuit for controlling to supply a constant voltage to the LED driving circuit, and an open voltage between the pair of terminals when the LED array is removed from the terminals. There is provided an LED driver circuit comprising overvoltage prevention means for reducing the voltage to a predetermined voltage or lower.

  Moreover, according to the other aspect of this invention, the illuminating device provided with the LED driver circuit of any one of Claims 1-8, and lighting an LED array is provided.

  ADVANTAGE OF THE INVENTION According to this invention, the LED driver circuit and illuminating device which can prevent the electric shock accident and destruction of a circuit element in replacement | exchange work etc. of an LED lamp can be provided.

1 is a block diagram showing a schematic configuration of an LED driver circuit according to a first embodiment. 1 is a circuit diagram showing a circuit configuration example of an LED driver circuit according to a first embodiment. The graph which shows the open circuit voltage when not providing an overvoltage protection circuit. When an overvoltage protection circuit is provided, (a) a graph showing an open circuit voltage, (b) a graph showing a gate voltage of the MOSFET Q2. The graph which shows the short circuit current when not providing an overcurrent protection circuit. The graph which shows the short circuit current at the time of providing an overcurrent protection circuit. The block diagram which shows schematic structure of the LED driver circuit which concerns on 2nd Embodiment. The circuit diagram which shows the circuit structural example of the LED driver circuit which concerns on 2nd Embodiment. FIG. 5 shows waveforms during dimming when no bleeder circuit is provided; (a) a waveform of the gate of the transistor Q1, (b) a waveform of the voltage VCC supplied to the current control circuit, and (c) a waveform of the current I _LED of the LED array. Graph showing. FIG. 6 shows waveforms during dimming when a bleeder circuit is provided; (a) a waveform of the gate of the transistor Q1, (b) a waveform of the voltage VCC supplied to the current control circuit, and (c) a waveform of the current I _LED of the LED array. Graph showing. (A) Waveforms of reference voltage V _ref and input voltage V _b for all lamps when no bleeder circuit is provided, (b) Reference voltage V _ref and input voltage V _b for all lamps when a bleeder circuit is provided The graph which shows a waveform. The top view which shows the surface side of the example of a layout pattern of the LED driver circuit which concerns on 2nd Embodiment. The top view which shows the back surface side of the example of a layout pattern of the LED driver circuit which concerns on 2nd Embodiment. The typical sectional view of a straight tube type LED lamp. The partial see-through | perspective view of a straight tube | pipe type LED lamp.

  Next, embodiments will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the embodiments of the present invention include the material, shape, structure, The layout is not specified as follows. Various modifications can be made to the embodiment of the present invention within the scope of the claims.

[First embodiment]
(Configuration example of LED driver circuit)
A configuration example of the LED driver circuit 1 according to the first embodiment will be described with reference to the block diagram of FIG. 1 and the circuit diagram of FIG.

  As shown in the block diagram of FIG. 1, the LED driver circuit 1 according to the present embodiment includes a pair of positive and negative terminals 15a that detachably hold a DC power source 10 and an LED array 14 in which a plurality of LEDs are connected in series. 15b, an LED drive circuit 16 that lights the LED array 14 using the DC power supply 10, a voltage control circuit 11 that controls the LED drive circuit 16 to supply a constant voltage, and the LED array 14 with terminals 15a and 15b. And an overvoltage prevention means 30 that lowers the open voltage between the pair of terminals 15a and 15b to a predetermined voltage or less when removed from the terminal.

  More specifically, the overvoltage prevention unit 30 includes a monitoring unit that monitors the voltage between the pair of terminals 15a and 15b, a switching unit that turns on / off a part of the supply voltage to the LED array 14, and a monitoring unit. And an overvoltage protection circuit 13 that turns off the switching means when the detected voltage exceeds a preset threshold value.

  As shown in the circuit diagram of FIG. 2, the monitoring means is composed of resistance elements R1 and R2 for voltage detection, and the switching means is turned on / off based on the voltage detected by the monitoring means (resistance elements R1 and R2). Transistors Q2 and Q4, and a constant voltage diode (Zener diode) ZD4 for securing a constant voltage.

Further, in FIG. 2, the resistance element for voltage detection, the resistance value R ₁ · 2 single resistor element R ₂ R1 · R2 is configured by serially connecting, transistor Q4, operating voltage V _BE is at voltages V ₁ consists of certain bipolar transistor reduced, when a constant voltage supplied by a constant voltage diode (Zener diode) ZD4 is a voltage V _Z, when removal of the LED array 14 from the terminal 15a · 15b, the overvoltage protection circuit 13 An open circuit voltage V _OPEN between the pair of terminals is expressed by equation (1). That is,

V _OPEN = ((R ₁ + R ₂ ) / R ₁ ) × (V _Z + V ₁₀ ) (1)

As shown in FIGS. 1 and 2, the overvoltage prevention means 30 may include an overcurrent protection circuit 12 that reduces the current between the terminals of the pair of terminals 15a and 15b.

  The overcurrent protection circuit 12 is composed of, for example, a bipolar transistor Q3 that is turned on / off based on a voltage detected by the monitoring means, and a current adjustment resistor element R3 connected to the emitter terminal side of the bipolar transistor Q3. May be.

The resistance value of the resistance element R3 for current regulation is R _3, if the operating voltage V _BE of the bipolar transistor Q3 is a voltage V _10, a current value V _short, which is reduced by the overcurrent protection circuit 12, It is represented by the formula (2). That is,

V _short = V ₁₀ / R ₃ (2)

The LED array 14 can be a straight tube type LED lamp, for example. A specific example of the straight tube type LED lamp will be described later.

(Circuit configuration)
Here, the circuit configuration of the LED driver circuit 1 according to the first embodiment will be described with reference to the circuit diagram of FIG.

  The DC power supply 10 in the LED driver circuit 1 includes, for example, a 100 V AC power supply 41 and a bridge-type full-wave rectification circuit 42 that is connected to the AC power supply 41 and rectifies an AC current.

  One terminal of the bridge-type full-wave rectifier circuit 42 is set to the ground potential, and a capacitor C20 of about 330 μF, for example, is connected to the output terminal side from which a direct current of 64 V, for example, is output, via the node N1.

  The cathode terminal of the diode D7 (D8) is connected via the node N2 on the output end side of the bridge-type full-wave rectifier circuit 42. The diode D7 (D8) corresponds to a case where two diodes are provided in a pattern layout (FIGS. 12 and 13) described later.

  A resistance element R3 for adjusting current is connected between the node N3 and the node N4. The emitter terminal and the base terminal of the transistor Q3 are connected to the node N3 and the node N4. In addition, the resistance value of the resistance element R3 for current adjustment is, for example, about 0.33Ω.

A cathode terminal of a Zener diode ZD4 is connected to a node N5 adjacent to the node N4.

  The emitter terminal of the transistor Q4 is connected to the anode terminal of the Zener diode ZD4.

  For example, a resistance element R1 of about 39 kΩ and a resistance element R2 of about 83.5 kΩ are connected in series to the node N6 adjacent to the node N5.

  The resistance elements R1 and R2 monitor the voltage between the pair of terminals 15a and 15b.

  The base terminal of the transistor Q4 is connected to the connection node N7 between the resistance elements R1 and R2.

  Further, the collector terminal of transistor Q4 and the collector terminal of transistor Q3 are connected via node N8.

  For example, an inductance L1 (L2) of about 200 μH is connected via the node N9. The inductance L1 (L2) corresponds to the case where two inductances are provided in a pattern layout (FIGS. 12 and 13) described later.

  The other end of the inductance L1 (L2) is connected to the anode terminal of the diode D7 (D8) via the node N10.

  A terminal 15a for the LED array 14 is connected to the node N6, and a terminal 15b is connected to the node N9.

  For example, a straight tube type LED lamp provided with the LED array 14 is detachably mounted between the pair of terminals 15a and 15b.

  The node N10 is connected to the drain terminal of a switching transistor (MOSFET) Q2.

  The gate terminal of the transistor (MOSFET) Q5 and the resistance element R11 are connected to the source terminal of the transistor (MOSFET) Q2. The resistance element R11 is configured by connecting, for example, three resistance elements of about 1.8Ω, about 1.8Ω, and about 1.6Ω in parallel.

  The source terminal of the transistor (MOSFET) Q5 is set to the ground potential, and the drain terminal is connected to the gate terminal of the transistor (MOSFET) Q2 via the node N12.

  The node N12 is connected to the voltage control circuit 11 via a resistance element R10 having a resistance value, for example, about 51Ω. Note that the voltage control circuit 11 is constituted by, for example, a power supply IC provided with a latch circuit.

  Further, a resistance element R31 having a resistance value, for example, about 10 kΩ is connected to the node N8, and connected to a resistance value, for example, a resistance element R28 having a resistance value, for example, about 2 kΩ, through the node N13. The other end of the resistance element R28 is set to the ground potential.

  The overvoltage protection circuit 13 and the overcurrent protection circuit 12 are represented by a broken line and an alternate long and short dash line in FIG.

(Overvoltage protection circuit operation)
First, when the LED array 14 is connected to the terminals 15a and 15b and the transistor Q4 is turned on, a current flows through the inductance L1 (L2) and the LED array 14. Thereby, a predetermined voltage (for example, 35 V) controlled by the voltage control circuit 11 is supplied to the LED array 14, and the LED array 14 is turned on.

  On the other hand, when the LED array 14 is removed from the terminals 15a and 15b, the transistor Q4 is turned off with a change in the divided voltage in the resistance elements R1 and R2 that monitor the voltage between the terminals 15a and 15b. As a result, a back electromotive force is generated in the inductance coil L1 (L2), and a current flows through the diode D7 (D8), the inductance coil L1 (L2), and the resistance elements R1, R2, and R3.

When the Zener voltage V _Z of the Zener diode ZD4 is determined by the operation of the overvoltage protection circuit 13, the output voltage is determined by the ratio of the resistance values of the resistance elements R1 and R2. Therefore, when the preset output voltage is reached, the transistor Q4 is turned on and the MOSFET Q5 is turned on. As a result, the gate potential of the MOSFET Q2 is lowered, and the MOSFET Q2 is turned off. As a result, an open circuit voltage V _{O that} is equal to or higher than the set voltage is prevented between the terminals 15a and 15b.

  Here, the effect of the overvoltage protection circuit 13 will be described with reference to the graphs of FIGS. 3 and 4.

FIG. 3 is a graph showing the open voltage V _O when the overvoltage protection circuit 13 is not provided. FIGS. 4A and 4B show the open voltage V _O and the gate voltage when the overvoltage protection circuit 13 is provided. It is a graph which shows.

As can be seen from FIG. 3, when the overvoltage protection circuit 13 is not provided, the open-circuit voltage V _O increases from the time when the output is opened (time t _O ) when the LED array 14 is removed, and reaches the maximum voltage V1.

  In this case, there is a risk of electric shock during the effect work of the straight tube type LED lamp, or destruction due to the breakdown voltage of the elements constituting the circuit being exceeded.

On the other hand, in the case where the overvoltage protection circuit 13 is provided, as shown in FIG. 4B, the gate voltage of the MOSFET Q2 is repeatedly changed from the high state to the low state after the output is opened when the LED array 14 is removed. It will be in a state of repeating on and off. More specifically, until a predetermined time elapses from when the output is opened (time t _O ), for example, a state in which fine switching of about 100 kHz is continued, and then, for example, a pulse wave of about 10 Hz to about 1000 Hz. It becomes.

As a result, as shown in FIG. 4A, the open circuit voltage V _O has a sawtooth waveform, remains at the predetermined open circuit voltage V _OPEN , and is prevented from becoming a high voltage as shown in FIG.

Here, the open circuit voltage V _OPEN is expressed by the equation (1) as described above, and R ₁ = 39 kΩ, R ₂ = 83.5Ω, V _Z = 10 V, and V ₁₀ = 0.7 V are substituted as numerical examples. Then, the open circuit voltage V _OPEN becomes about 33.6V.

(Operation of overcurrent protection circuit)
When a current flows through the resistance element R3 included in the overcurrent protection circuit 12, a voltage difference is generated. When the voltage V _BE between the base and the emitter of the transistor Q3 becomes about 0.7 V, for example, the transistor Q3 is turned on. As a result, as in the case of the overvoltage protection circuit 13, the MOSFET Q2 is turned off, so that an open voltage V _O higher than the set voltage is not output between the terminals 15a and 15b.

  Here, the effect of the overcurrent protection circuit 12 will be described with reference to the graphs of FIGS. 5 and 6.

Figure 5 is a graph showing a short-circuit current I _LED of the case without the overcurrent protection circuit 12, FIG. 6 is a graph showing the short-circuit current I _LED obtained when a overcurrent protection circuit 12. t _s indicates the time at which a short circuit occurs.

As can be seen from FIG. 5, in the case where the overcurrent protection circuit 12 is not provided, when a short circuit (time t _s ) occurs in the circuit, the short circuit current I _LED rapidly rises, and an electric shock or an element is destroyed. Etc.

On the other hand, when the overcurrent protection circuit 12 is provided, as shown in FIG. 6, even if a short circuit (time t _s ) occurs in the circuit, the short circuit current I _LED has a sawtooth waveform and a predetermined short circuit. The situation where the current I _short remains and the current increases rapidly as shown in FIG. 5 is prevented.

Here, as described above, the short-circuit current I _short is expressed by the equation (2). As a numerical example, when V ₁₀ = 0.7 V and R ₃ = 0.33Ω are substituted, the short-circuit current I _short is about 2.12A.

  According to the first embodiment, it is possible to provide an LED driver circuit and an illuminating device capable of preventing an electric shock accident and a circuit element destruction in an LED lamp replacement operation or the like.

[Second Embodiment]
(Configuration example of LED driver circuit)
A configuration example of the LED driver circuit 2 according to the second embodiment will be described with reference to the block diagram of FIG. 7 and the circuit diagram of FIG.

  As shown in the block diagram of FIG. 7, the LED driver circuit 2 according to the second embodiment includes a pair of positive and negative electrodes that detachably hold a DC power supply 10 and an LED array 14 in which a plurality of LEDs are connected in series. When the output load on the LED array 14 decreases, the terminals 15a and 15b, the LED drive circuit 16 that lights the LED array 14 using the DC power supply 10, the current control circuit 23 that controls the current to the LED drive circuit 16, and In addition, a bleeder circuit 22 that secures power supplied to the current control circuit 23 and a voltage control circuit 21 that controls the voltage to the LED drive circuit 16, the current control circuit 23, and the bleeder circuit 22 are provided.

  The bleeder circuit 22 is a resistance element R46 that monitors the voltage supplied between the pair of terminals 15a and 15b, and switching means that adjusts the power supplied to the current control circuit 23 according to the monitoring result of the resistance element R46. A transistor Q6, an operational amplifier 130, and a capacitor C7 are provided.

  Further, as shown in FIG. 8, the LED driver circuit 2 according to the second embodiment includes a transformer 50 having a primary side 50 a connected to the DC power supply 10, and the voltage control circuit 21 includes a primary side of the transformer 50. The output of 50a is turned on / off.

  The voltage control circuit 21 is connected to the constant voltage circuit 40 through the photocoupler 150, and the constant voltage circuit 40 is connected to the first winding 50b and the second winding 50b on the secondary side of the transformer 50.

  Further, the bleeder circuit 22 is connected to the first winding 50 a and the second winding 50 b on the secondary side of the transformer 50.

  Note that the reduction in the output load on the LED array 14 includes a reduction in the output load based on the dimming of the LED array 14. Further, the reduction in the output load on the LED array 14 may include a case where the LED array 14 is removed from the terminals 15a and 15b.

  The LED array 14 may be a straight tube type LED lamp, for example. A specific example of the straight tube type LED lamp will be described later.

(Circuit configuration)
Here, the circuit configuration of the LED driver circuit 2 according to the second embodiment will be described with reference to the circuit diagram of FIG.

  The DC power source 10 in the LED driver circuit 2 includes, for example, a 100V AC power source 41 and a bridge-type full-wave rectifier circuit 42 that is connected to the AC power source 41 and rectifies an AC current.

  One terminal of the bridge-type full-wave rectifier circuit 42 is set to the ground potential. For example, a capacitor C20 of about 330 μF, for example, is connected to the output end side from which a direct current of about 64 V is output via the node N1.

  Further, the positive electrode of the primary side 50a of the transformer 50 is connected via the node N1.

  The transformer 50 includes, for example, a primary side 50a having 52 turns, a secondary side first winding 50b having 15 turns, and a second winding 50b having 4 turns. Voltages V1 and V2 corresponding to the number of windings are induced at the terminals of the second winding 50b.

  The other end (negative electrode) of the primary side 50a of the transformer 50 is connected to the drain terminal of the MOSFET Q1.

  Further, the source terminal of the MOSFET Q 1 is set to the ground potential, and the gate terminal is connected to the voltage control circuit 21.

  The other end of the voltage control circuit 21 is coupled to the constant voltage circuit 40 via the photocoupler 150.

  A diode D10 is connected to the negative electrode of the first winding 50b on the secondary side of the transformer 50, and is connected to the capacitor C10 via the node N20. The other end of the capacitor C10 is connected to the positive electrode of the first winding 50b on the secondary side of the transformer 50 via the node N21.

  A diode D11 is connected to the negative electrode of the first winding 50c on the secondary side of the transformer 50, and is connected to the capacitor C11 via the node N23. The other end of the capacitor C11 is connected to the positive electrode of the second winding 50c on the secondary side of the transformer 50 via the node N24.

  The negative side of the first winding 50b on the secondary side of the transformer 50 is connected to the constant voltage circuit 40 via the node N22, and the negative side of the second winding 50c on the secondary side of the transformer 50 is current controlled. Connected to the circuit 23.

  The negative side of the first winding 50b on the secondary side of the transformer 50 is connected to the resistance element R52 of the bleeder circuit 22 via nodes N22 and N29. The resistance element R52 has a resistance value, for example, about 3 kΩ.

On the other hand, the positive side of the second winding 50c on the secondary side of the transformer 50 is connected to the resistance element R46 of the bleeder circuit 22 via the node N26. The resistance element R46 has a resistance value, for example, about 0.5Ω. The other end of the resistor element R46 is grounded and functions as a detection resistor for the input voltage _Vb .

  In the bleeder circuit 22, a capacitor C7 is connected between the node N28 and the ground potential. The node N28 is connected to the positive input terminal of the operational amplifier 130 as a comparator.

For example, about −100 mV is supplied as a reference voltage V _ref to the input terminal on the negative electrode side of the operational amplifier 130.

  The output terminal of the operational amplifier 130 is connected to the base terminal of the transistor Q6 via a resistance element R43 having a resistance value, for example, about 2.4 kΩ.

  Transistor Q6 has an emitter terminal connected to the ground potential and a collector terminal connected to resistance element R52.

  The cathode terminals of the diodes D7 (D8) are connected to the nodes N29 and N2. The diode D7 (D8) corresponds to a case where two diodes are provided in a pattern layout (FIGS. 12 and 13) described later.

  A resistance element R3 for current adjustment is connected between the node N3 and the node N4. Further, between the node N3 and the node N4, an emitter terminal and a gate terminal of the transistor Q3 are connected. In addition, the resistance value of the resistance element R3 for current adjustment is, for example, about 0.33Ω.

  The cathode terminal of the Zener diode ZD4 is connected to the node N5.

  The emitter terminal of the transistor Q4 is connected to the anode terminal of the Zener diode ZD4.

  For example, a resistance element R1 of about 39 kΩ and a resistance element R2 of about 83.5 kΩ are connected in series to the node N6.

  The voltage between terminals of a pair of terminals 15a and 15b described later is monitored by the resistance elements R1 and R2.

  The base terminal of the transistor Q4 is connected to the connection node N7 between the resistance elements R1 and R2.

  Further, the collector terminal of transistor Q4 and the collector terminal of transistor Q3 are connected via node N8.

  For example, an inductance L1 (L2) of about 200 μH is connected between the node N9 and the node N10. The inductance L1 (L2) corresponds to the case where two inductances are provided in a pattern layout (FIGS. 12 and 13) described later.

  The other end of the inductance L1 (L2) is connected to the anode terminal of the diode D7 (D8) via the node N10.

  A node 15a for the LED array 14 is connected to the node N6, and a terminal 15b is connected to the node N9.

  For example, a straight tube type LED lamp including the LED array 14 is detachably mounted between the pair of terminals 15a and 15b.

  The node N10 is connected to the drain terminal of a switching transistor (MOSFET) Q2.

  A resistor R11 is connected between the source terminal of the transistor (MOSFET) Q2 and the ground potential. The resistance element R11 is configured by connecting, for example, three resistance elements of about 1.8Ω, about 1.8Ω, and about 1.6Ω in parallel.

  A transistor (MOSFET) Q5 is connected between the gate terminal of the transistor (MOSFET) Q2 and the ground potential. That is, the source terminal of the transistor (MOSFET) Q5 is set to the ground potential, and the drain terminal is connected to the gate terminal of the transistor (MOSFET) Q2 via the node N12.

  The node N12 is connected to the current control circuit 23 via a resistance element R10 having a resistance value, for example, about 51Ω. Note that the current control circuit 23 is configured by, for example, a power supply IC provided with a latch circuit.

  Further, a resistance element R31 having a resistance value, for example, about 10 kΩ is connected to the node N8, and connected to a resistance value, for example, a resistance element R28 having a resistance value, for example, about 2 kΩ, through the node N13. The other end of the resistance element R28 is set to the ground potential.

(Bleeder circuit operation)
In the LED driver circuit 2 according to the second embodiment, the LED array 14 emits light by the voltage induced in the first winding 50b on the secondary side of the transformer 50.

  The LED array 14 is dimmed by an external signal (not shown).

  When the load on the secondary side of the transformer 50 becomes small, intermittent operation occurs in the voltage control circuit 21. In a state where the intermittent operation occurs, the power source of the current control circuit 23 is secured by the voltage induced in the secondary winding 50c on the secondary side of the transformer 50.

  Here, in the second winding 50c, a phenomenon in which the voltage increases or decreases due to the intermittent operation of the primary side 50a occurs.

  When the voltage of the second winding 50c decreases, the power supply voltage of the secondary side current control circuit 23 is insufficient, and the secondary side circuit stops, so the LED array 14 blinks and flickers occur. End up.

  Therefore, a bleeder circuit 22 is added to the LED driver circuit 2 according to the second embodiment.

  The bleeder circuit 22 can eliminate the intermittent operation by applying a pseudo load. As a result, even when the output load decreases due to dimming, the LED array 14 does not blink, and flicker does not occur.

The bleeder circuit 22 detects the load (current) on the secondary side with the resistance element R46, and compares it with the reference voltage (negative voltage) _Vref with the operational amplifier (comparator) 130.

  Only when the current on the secondary side decreases, the transistor Q6 is turned on and a current flows through the bleeder circuit 22.

  As a result, the intermittent operation of the primary side 50a is eliminated, so that the voltage drop of the second winding 50c on the secondary side of the transformer 50 can be prevented, and the power supply voltage of the current control circuit 23 can be prevented from decreasing. .

  The intermittent operation described above refers to a phenomenon in which switching stops intermittently.

Such intermittent operation is effective for energy saving because it is not necessary to perform continuous switching when the load (current) is small. However, since the same current is always supplied to the power supply of the current control circuit 23 on the secondary side, when intermittent operation occurs, the voltage is supplied to the secondary side when it is turned on, but the switching is constant. When the period is stopped, the secondary voltage drops.

  In the LED driver circuit 2 according to the second embodiment, the above-described problems are solved.

  Here, effects of the bleeder circuit 22 will be described with reference to the graphs of FIGS.

9 shows a waveform at the time of dimming when the bleeder circuit 22 is not provided, FIG. 9A shows the gate waveform of the transistor Q1, and FIG. 9B shows the waveform of the voltage VCC supplied to the current control circuit 23. FIG. 9C is a graph showing the waveform of the current I _LED of the LED array 14.

  In FIG. 9A, the pulse waves P1 to P3 are in a state where fine switching of about 50 kHz to about 500 kHz is continued, for example. Moreover, the period of P1-P3 is about 10 Hz-about 1000 Hz, for example.

  In FIG. 9B, the section of T1 is about 10 Hz, for example, and the pulse waves P1 to P3 in FIG.

As can be seen from FIG. 9, in the case where the bleeder circuit is not provided, the transistor Q1 is turned off when a state in which the gate input of the transistor Q1 is absent occurs, and the voltage VCC (that is, supplied to the current control circuit 23 during this period) The output waveform V ₂ of the secondary winding 50c on the secondary side of the transformer 50 is reduced (see FIGS. 9A and 9B).

As a result, the current I _LED supplied to the LED array 14 also repeats the high state and the low state (see FIG. 9C), and appears as flickering of the LED array 14.

On the other hand, FIG. 10 shows the waveform at the time of dimming when the bleeder circuit 22 is provided, FIG. 10 (a) shows the gate waveform of the transistor Q1, and FIG. 10 (b) shows the voltage VCC supplied to the current control circuit 23. FIG. 10C is a graph showing the waveform of the current I _LED of the LED array 14.

As can be seen from FIG. 10, in the case where the bleeder circuit 22 is provided, the state where the gate input of the transistor Q1 does not occur does not occur, and the voltage VCC supplied to the current control circuit 23 (that is, the secondary of the transformer 50). The state in which the output waveform V ₂ ) of the second winding 50c on the side is lowered does not occur (see FIGS. 10A and 10B).

As a result, the current I _LED supplied to the LED array 14 is also stably supplied (see FIG. 10C), and flickering of light emission of the LED array 14 is prevented.

11A shows the waveforms of the reference voltage V _ref and the input voltage V _b when all lamps are provided when the bleeder circuit 22 is not provided, and FIG. 11B shows the waveforms when all the lamps are provided when the bleeder circuit 22 is provided. It is a graph which shows the waveform of reference voltage _Vref and input voltage _Vb .

As shown in FIG. 11A, when no bleeder circuit is provided, the reference voltage V _ref for all lamps input to the operational amplifier 130 becomes a pulsating current, which is lower than the input voltage V _b appearing at the resistance element R46. This causes flickering of light emission of the LED array 14.

On the other hand, as shown in FIG. 11B, when the bleeder circuit 22 is provided, the voltage Vb appearing in the resistance element R46 becomes a triangular wave, and the reference voltage V _ref for all lamps input to the operational amplifier 130 is obtained. Is stabilized, and flickering of light emission of the LED array 14 is prevented.

(LED driver circuit layout pattern)
An example of the layout pattern of the LED driver circuit 2 according to the second embodiment will be described with reference to FIGS.

  FIG. 12 is a plan view showing the front side of the layout pattern example of the LED driver circuit 2, and FIG. 13 is a plan view showing the back side thereof.

  12 and 13, region A indicates the primary side, and region B indicates the secondary side.

  On the boundary between the region A and the region B, as shown in FIG. 12, a transformer circuit unit 103 is disposed on the surface side. Further, a photocoupler 150 is disposed on the back surface side, and the primary region A and the secondary region B are electrically insulated by connecting via the photocoupler 150.

  As shown in FIG. 12, for example, the control circuit IC 201 constituting the voltage control circuit 21 and the like, the MOSFET Q1 for switching the control circuit IC 201, and the transformer 50 in FIG. A filter transformer FL1, a fuse F1, an input terminal 100 connected to an AC power supply, a GND terminal 101, and the like are disposed.

  Further, as shown in FIG. 13, for example, a diode bridge DB configuring the bridge-type full-wave rectifier circuit 42 is disposed on the back side of the primary region A.

  On the other hand, on the surface side of the region B on the secondary side, as shown in FIG. 12, for example, a control circuit IC200 constituting the current control circuit 23, coils L1 and L2 as inductances, and resistance elements R52, 57, 59˜ 66, a bleeder circuit 22 including a switching transistor Q6, an output terminal 104, a dimming terminal 105 for dimming the LED array 14, and the like are arranged.

  Further, as shown in FIG. 13, for example, an overcurrent protection circuit 12, an overvoltage protection circuit 13, and a resistance element R <b> 43 of the bleeder circuit 22 are disposed on the back side of the secondary region B.

(Straight tube type LED lamp)
Referring to FIGS. 14 and 15, a configuration of straight tube type LED lamp 500 using LED array 14 to which LED driver circuits 1 and 2 according to the first embodiment and the second embodiment can be applied. An example will be described.

  FIG. 14 is a schematic sectional view of a straight tube type LED lamp, and FIG. 15 is a partially transparent perspective view thereof.

  The LED lamp 500 according to this configuration example includes the LED array 14, a power supply module 520, a heat sink 530, and a straight tubular case 540.

  The heat radiating plate 530 is a metal member that radiates heat generated from the LED array 14.

  The LED array 14 and the power supply module 520 are respectively installed on different surfaces of the heat sink 530.

  The LED array 14 and the power supply module 520 are electrically connected by a cable (not shown) at the end of the heat sink 530.

  The heat sink 530 may also have a function as a support portion that fixes the LED array 14 and the power supply module 520 in the case 540.

  The case 540 is a straight tube fluorescent lamp type (cylindrical) hollow member that houses the LED array 14, the power supply module 520, and the heat radiating plate 530 and that diffuses and transmits the light emitted from the LED array 14.

  As the color of the case 540, a milky white case from which soft and more expansive light is obtained, or a translucent case from which light with higher illuminance is obtained can be used. Note that the case 540 can be a waterproof type assuming that the LED lamp 1 is used outdoors.

  As shown in FIG. 14, since the light from the LED array 14 is scattered by the case 540 as the height H1 from the heat sink 530 to the lower end of the case 540 is larger, the LED having a wide light distribution. The lamp 500 can be used.

  Further, the straight tube fluorescent lamp type LED lamp 500 includes a terminal 533 having the same shape as the straight tube fluorescent lamp, as shown in FIG. Therefore, the straight tube fluorescent lamp type LED lamp 500 having such a configuration can be attached to an existing lighting device instead of the straight tube fluorescent lamp tube.

  Then, by mounting the LED driver circuits 1 and 2 according to the first embodiment and the second embodiment on the lighting device, an electric shock accident or circuit in the replacement work of the straight tube fluorescent lamp type LED lamp 500 or the like It is possible to provide an illuminating device that can prevent element destruction.

  Further, when the LED driver circuit 2 provided with the bleeder circuit 22 is mounted as shown in the second embodiment, flicker during dimming of the straight tube fluorescent lamp type LED lamp 500 can be prevented. it can.

[Other embodiments]
As described above, the embodiments have been described. However, it should be understood that the descriptions and drawings constituting a part of this disclosure are illustrative and do not limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  The LED driver circuit and the lighting device of the present invention can be applied to a lighting fixture or the like using a straight tube type LED lamp or the like.

A ... Primary side region B ... Secondary side region C7, C10, C11, C20 ... Capacitor D7, D10, D11 ... Diode DB ... Diode bridge F1 ... Fuse L1, L2 ... Inductance (coil)
N1 to N29 ... Nodes Q1 to Q9 ... Transistors R1 to R57 ... Resistance values 1, 2 ... LED driver circuit 11 ... Voltage control circuit 12 ... Overcurrent protection circuit 13 ... Overvoltage protection circuit 14 ... LED arrays 15a, 15b ... Terminal 16 ... LED drive circuit 21 ... Voltage control circuit 22 ... bleeder circuit 23 ... current control circuit 30 ... overvoltage prevention means 40 ... constant voltage circuit 41 ... AC power supply 42 ... bridge-type full-wave rectifier circuit 50 ... transformer 50a ... primary side 50b ... secondary Side first winding 50c ... secondary side second winding 100 ... input terminal 101 ... GND terminal 103 ... transformer circuit section 104 ... output terminal 105 ... dimming terminal 130 ... operational amplifier 150 ... photocoupler 500 ... LED lamp 520 ... Power supply module 530 ... Heat sink 533 ... Terminal 540 ... Case

Claims (16)

DC power supply,
A pair of positive and negative terminals that detachably hold an LED array in which a plurality of LEDs are connected in series;
An LED drive circuit for lighting the LED array using the DC power supply;
A voltage control circuit for controlling the LED drive circuit to supply a constant voltage;
An LED driver circuit comprising: an overvoltage preventing unit that sets an open voltage between the pair of terminals to a predetermined voltage or less when the LED array is detached from the terminals. The overvoltage prevention means includes
Monitoring means for monitoring the voltage between the terminals of the pair of terminals;
Switching means for turning on and off a part of the supply voltage to the LED array;
The LED driver circuit according to claim 1, further comprising: an overvoltage protection circuit that turns off the switching unit when a voltage detected by the monitoring unit exceeds a preset threshold value. The monitoring means includes a resistance element for voltage detection,
The switching means includes a transistor that is turned on / off based on a voltage detected by the monitoring means,
The LED driver circuit according to claim 2, further comprising a constant voltage diode connected to the transistor to ensure a constant voltage. The resistance element for voltage detection is configured by connecting two resistance elements having resistance values R ₁ and R ₂ in series,
The transistor is a bipolar transistor having an operating voltage V _BE of a voltage V ₁₀ ,
When the constant voltage supplied by the constant voltage diode is the voltage V _z ,
When the LED array is removed from the terminal, the open voltage V _OPEN between the pair of terminals reduced by the overvoltage protection circuit is:
V _OPEN = ((R ₁ + R ₂ ) / R ₁ ) × (V _Z + V ₁₀ )
The LED driver circuit according to claim 3, wherein:   The LED driver circuit according to claim 1, wherein the overvoltage prevention unit includes an overcurrent protection circuit that reduces a current between the terminals of the pair of terminals. The overcurrent protection circuit is
A bipolar transistor that is turned on and off based on a voltage detected by the monitoring means;
The LED driver circuit according to claim 5, further comprising: a current adjusting resistance element connected to an emitter terminal side of the bipolar transistor. The resistance value of the resistance element for current adjustment is R ₃ ,
If the operating voltage V _BE of the bipolar transistor is a voltage V _10,
The current value V _short reduced by the overcurrent protection circuit is
V _short = V ₁₀ / R ₃
The LED driver circuit according to claim 6, wherein:   The LED driver circuit according to claim 1, wherein the LED array is a straight tube type LED lamp. A bleeder circuit that secures power to be supplied to a current control circuit that controls current supplied to the LED array when an output load on the LED array decreases;
The LED driver circuit according to claim 1, wherein the voltage control circuit controls a voltage to the LED drive circuit, the current control circuit, and the bleeder circuit. The bleeder circuit is
A resistance element for monitoring a voltage supplied between the pair of terminals;
The LED driver circuit according to claim 9, further comprising: a transistor, an operational amplifier, and a capacitor as a switching unit that adjusts power supplied to the voltage control circuit according to a monitoring result of the resistance element. A transformer having a primary side connected to the DC power supply;
The LED driver circuit according to claim 9, wherein the voltage control circuit performs on / off control of an output on a primary side of the transformer. The voltage control circuit is coupled to a constant voltage circuit through a photocoupler,
The LED driver circuit according to any one of claims 9 to 11, wherein the constant voltage circuit is connected to a first winding and a second winding on a secondary side of the transformer.   The LED driver circuit according to claim 12, wherein the bleeder circuit is connected to a first winding and a second winding on the secondary side of the transformer.   The LED driver circuit according to any one of claims 9 to 13, wherein the reduction in output load on the LED array includes a reduction in output load based on dimming of the LED array.   An illumination device comprising the LED driver circuit according to claim 1, wherein the LED array is turned on.   The lighting device according to claim 15, wherein the LED array is a straight tube type LED lamp.

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