JP2012043735A - Led drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED drive circuit capable of appropriately changing over between LED blocks by changing over between current paths without the provision of a switching circuit for performing digital control, while preventing power loss.SOLUTION: An LED drive circuit (1) comprises: a rectifier (12); a first LED group (21) connected to the rectifier; a second LED group (31) connected to the rectifier; a third LED group (41) connected to the rectifier; a detection unit (36) which detects a current flowing through two consecutive LED groups among the first LED group, the second LED group, and the third LED group when the two consecutive LED groups are connected in series; and a current limiting unit (44) which limits a current flowing from the rectifier to the remaining one of the first LED group, the second LED group, and the third LED group, based on a result of detection by the detection unit.

Description

  The present invention relates to an LED drive circuit, and more particularly to an LED drive circuit for performing efficient LED light emission using an AC power supply.

  When applying a rectified voltage output from a bridge diode for full-wave rectification of AC power supplied from a commercial power source to a plurality of LED blocks, the connection forms of the plurality of LED blocks are connected in parallel and in series according to the power supply voltage. There is known a method of switching between (see, for example, Patent Document 1).

  The LED has a non-linear characteristic in which a current starts to flow suddenly when a voltage equal to or higher than the forward drop voltage is applied to the LED. A predetermined forward current (If) is applied to emit light with a predetermined luminous intensity by a method of forming a constant current circuit by inserting a current limiting resistor or another active element. At this time, the forward voltage drop is the forward voltage (Vf). Therefore, when n LEDs are connected in series, the LEDs emit light when a voltage of n × Vf or higher is applied to the LEDs. In addition, the rectified voltage output from the bridge diode that full-wave rectifies the alternating current supplied from the commercial power supply repeats a change from 0 (v) to the maximum output voltage at a period twice the commercial power supply frequency. Accordingly, the plurality of LEDs emit light only when the rectified voltage becomes n × Vf (v) or more, but the plurality of LEDs do not emit light when less than n × Vf (v).

  Therefore, for example, two LED blocks including n LEDs are prepared, and when the power supply voltage is 2 × n × Vf (v) or more, the two LED blocks are connected in series, When the LED included in the LED block is caused to emit light and the power supply voltage is less than 2 × n × Vf (v), the two LED blocks are connected in parallel, and the LEDs included in both LED blocks are caused to emit light. Thus, by switching the plurality of LED blocks between parallel connection and series connection according to the power supply voltage, it becomes possible to lengthen the light emission period of the LED with respect to changes in the commercial power supply voltage.

  However, when LED blocks having different impedances are connected in parallel to the power supply voltage, the LEDs included in each group should be driven with a constant current, but the impedances are different. There is a problem that current adjustment must be performed in the current adjustment unit, which causes power loss.

  In addition, a switch circuit for switching the connection method of a plurality of LED blocks is required, which increases the space and cost of the entire LED drive circuit, and increases the power consumption for driving the switch circuit. there were. In particular, in order to make the light emission period of the LED longer, it is necessary to provide a large number of LED blocks. However, if a large number of LED blocks are set, more switch circuits are required.

  Furthermore, the switching timing of the switch circuit is set based on the expected n × Vf (v), but since Vf is not constant for each LED, the actual n × Vf (v) of each LED block is preliminarily determined. There is a difference from the set n × Vf (v). For this reason, even if the switch circuit operates according to the power supply voltage, the LEDs included in both LED blocks do not emit light, or conversely, there is a possibility that they will emit light even if they are switched earlier. In addition, there is a problem that it is difficult to optimize power consumption.

JP2009-283775 (FIG. 1)

  Therefore, an object of the present invention is to provide an LED drive circuit that aims to solve the above-mentioned problems.

  It is another object of the present invention to provide an LED drive circuit in which each LED block is appropriately switched by switching a current path without providing a digitally controlled switch circuit while preventing power loss. And

  An LED driving circuit according to the present invention includes a rectifier, a first LED group connected to the rectifier, a second LED group connected to the rectifier, a third LED group connected to the rectifier, a first LED group, a second LED group, and A detection unit that detects a current flowing through the two consecutive LED groups when the two consecutive LED groups of the third LED group are connected in series, and the first LED group, the first LED from the rectifier based on the detection result of the detection unit; It has the current limiting part which restrict | limits the electric current which flows into the remaining LED group of 2LED group and 3rd LED group, It is characterized by the above-mentioned.

  In the LED drive circuit according to the present invention, since the LED group having different impedance with respect to the full-wave rectifier circuit 12 is provided in parallel, a limiting mechanism for limiting the flow of current to the predetermined LED group is provided. It is possible to suppress power loss and increase the conversion efficiency of the LED drive circuit.

  Further, the LED drive circuit according to the present invention is configured such that the current path is switched in accordance with the output voltage of the full-wave rectifier circuit 12, so that it is not necessary to provide a large number of switch circuits.

  Furthermore, in the LED driving circuit according to the present invention, the switching of the current path is automatically determined according to the output voltage of the full-wave rectifier circuit 12 and the total of the actual Vf of all LEDs included in each LED block. Therefore, there is no need to predict and control the timing of switching each LED block from the number of LEDs included in the LED block in advance, and switching between the LED blocks in series and parallel is performed at the most efficient timing. Became possible.

It is a schematic block diagram of the LED drive circuit 1 which concerns on this invention. It is a figure which shows the circuit example 100 of the LED drive circuit 1 shown in FIG. It is a figure which shows the output voltage waveform example of the full wave rectifier circuit 12. FIG. It is a figure which shows the example of a switching sequence of the LED block of the LED drive circuit 1 shown in FIG. It is a figure which shows the example of an electric current of each part of the period of the time T0-T7 of FIG. It is a figure which shows the input electric power of LED drive circuit 1 and LED drive circuit 8, power consumption, and power loss. It is a schematic block diagram of the other LED drive circuit 2 which concerns on this invention. It is a schematic block diagram of the further another LED drive circuit 3 which concerns on this invention. It is a schematic block diagram of the further another LED drive circuit 4 which concerns on this invention. It is a figure which shows the example of a switching sequence of the LED block of the LED drive circuit 4 shown in FIG. It is a figure which shows the input electric power of LED drive circuit 4, power consumption, and power loss. It is a schematic block diagram of the further another LED drive circuit 5 which concerns on this invention. It is a figure which shows the example of a switching sequence of the LED block of the LED drive circuit 5 shown in FIG. It is a figure which shows the input electric power of LED drive circuit 5, power consumption, and power loss. It is a schematic block diagram of the further another LED drive circuit 6 which concerns on this invention. It is a figure which shows the example of a switching sequence of the LED block of the LED drive circuit 6 shown in FIG. It is a figure which shows the input electric power of LED drive circuit 6, power consumption, and power loss. It is a schematic block diagram of the further another LED drive circuit 7 which concerns on this invention. It is a figure which shows the example of a switching sequence of the LED block of the LED drive circuit 7 shown in FIG. It is a figure which shows the input electric power of LED drive circuit 7, power consumption, and power loss. 2 is a schematic configuration diagram of an LED drive circuit 8. FIG. It is a figure which shows the example of a switching sequence of the LED block in the LED drive circuit 8 shown in FIG.

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

  FIG. 1 is a schematic explanatory diagram of an LED drive circuit according to the present invention.

  The LED drive circuit 1 includes a connection terminal 11 connected to a commercial AC power supply (AC 100 V) 10, a full-wave rectifier circuit 12, a start circuit 20, an intermediate circuit 30, a termination circuit 40, reverse current prevention diodes 15 and 16, It comprises a current diode 17 and the like. The start end circuit 20, the intermediate circuit 30, and the end circuit 40 are connected in parallel between the plus power output 13 and the minus power output 14 of the full-wave rectifier circuit 12. The start circuit 20 and the intermediate circuit 30 are connected via a diode 15, and the intermediate circuit 30 and the termination circuit 40 are connected via a diode 16 and a constant current diode 17.

The start circuit 20 includes a first LED block (LED group) 21 including one to a plurality of LEDs, a first current monitor 22 for detecting a current I ₁ flowing through the first LED block 21, a first current control unit 23, and the like. Contains. The first current monitor 22 operates to limit the current flowing through the first current control unit 23 according to the current I ₁ flowing through the first LED block 21.

The intermediate circuit 30 includes a second LED block (LED group) 31 including one to a plurality of LEDs, a 2-1 current monitor 32 and a 2-2 current monitor 34 for detecting a current flowing through the second LED block 31, A 2-1 current control unit 33, a 2-2 current control unit 35, a 2-3 current monitor 36, and the like are included. The 2-1 current monitor 32 controls to adjust the current I ₄ flowing through the 2-1 current control unit 33 according to the current I ₅ flowing through the second LED block 31, and the 2-2 current monitor 34 is The current I ₆ flowing through the second-second current control unit 35 is limited in accordance with the current I ₅ flowing through the second LED block 31. Also, 2-3 current monitor 36, 3-2 current controller 44 and the 1LED block 21 and the 2LED block 31 will be described later in response to the current I ₅ flowing through the two LED blocks when connected in series It operates so as to limit the current I ₈ flowing therethrough.

The termination circuit 40 includes a third LED block (LED group) 41 including one to a plurality of LEDs, a third current monitor 42 for detecting a current I ₉ flowing through the third LED block 41, and a 3-1 current control unit 43. The 3-2 current control unit 44 and the like are included. The third current monitor 42 operates to limit the current I ₈ flowing through the third-first current control unit 43 according to the current I ₉ flowing through the third LED block 41. In addition, the 3-2 current control unit 44 operates to limit a current I ₈ flowing in a later-described 3-2 current control unit 44 according to a current I ₅ flowing in the second LED block 31.

  FIG. 2 is a diagram showing a specific circuit example 100 of the LED drive circuit 1 shown in FIG. In the circuit example 100, the same components as those in FIG. 1 are denoted by the same reference numerals, and portions corresponding to the components in FIG. 1 are indicated by dotted lines.

  The connection terminal 11 of the circuit example 100 is for connecting to the commercial AC power supply 10 and is formed as a base of the LED bulb when the LED drive circuit 1 is used for an LED bulb.

  The full-wave rectifier circuit 12 is a diode bridge type composed of four rectifier elements D1 to D4, and has a positive power output 13 and a negative power output 14. The full-wave rectifier circuit 12 may be a full-wave rectifier circuit including a transformer circuit using a transformer, or may be a two-phase full-wave rectifier circuit using a transformer with a center tap.

  The first LED block 21 of the starting circuit 20 includes 12 LEDs connected in series. The first current monitor 22 includes two resistors R1 and R2 and a transistor Q1, and the first current control unit 23 includes M1 which is a P-type MOSFET. The base voltage of the transistor Q1 is changed using the voltage drop generated in the resistor R1 due to the current flowing through the first LED block 21. The change in the base voltage of the transistor Q1 causes a change in the emitter-collector current of the transistor Q1 flowing through the resistor R2, thereby adjusting the gate voltage of the MOSFET M1 and the current between the source and drain of the MOSFET M1. The configuration is limited.

  The second LED block 31 of the intermediate circuit 30 is configured to include 12 LEDs connected in series. The 2-1 current monitor 32 includes two resistors R3 and R4 and a transistor Q2, and the 2-1 current control unit 33 includes M2 that is an N-type MOSFET. The base voltage of the transistor Q2 is changed using the voltage drop generated in the resistor R3 due to the current flowing through the second LED block 31. The change in the base voltage of the transistor Q2 causes a change in the collector-emitter current of the transistor Q2 flowing through the resistor R4, thereby adjusting the gate voltage of the MOSFET M2, and the current between the source and drain of the MOSFET M2 is changed. The configuration is limited.

  The 2-2 current monitor 34 includes two resistors R5 and R6 and a transistor Q3, and the 2-2 current control unit 35 includes M3 that is a P-type MOSFET. The operations of the 2-2 current monitor 34 and the 2-2 current control unit 35 are the same as those of the first current monitor 22 and the first current control unit 23. The 2-3 current monitor 36 includes two resistors R7 and R8 and a transistor Q4.

  The third LED block 41 of the termination circuit 40 includes twelve LEDs connected in series. The third current monitor 42 includes two resistors R9 and R10 and a transistor Q5, and the 3-1 current controller 43 includes an M4 that is an N-type MOSFET. The operations of the third current monitor 42 and the 3-1 current control unit 43 are the same as those of the 2-1 current monitor 32 and the 2-1 current control unit 33.

The 3-2 current controller 44 is configured to include M5 which is an N-type MOSFET. In the 2-3 current monitor 36, by using a voltage drop caused by the resistor R7 by the current I ₅ changing the base voltage of the transistor Q4. As the base voltage of the transistor Q4 changes, a change occurs in the collector-emitter current of the transistor Q4 flowing through the resistor R8, thereby adjusting the gate voltage of the MOSFET M5, and the current between the source and drain of the MOSFET M5 is changed. The configuration is limited.

  In the circuit example 100, each of the first LED block 21, the second LED block 31, and the third LED block 41 has 12 LEDs connected in series, so the first forward voltage V1 (12 × Vf = 12 × 3). .2 = 38.4 (v)) is applied to each of the first LED block 21, the second LED block 31, and the third LED block 41, the first LED block 21, the second LED block 31, and the third LED block 41 The included LED lights up.

  When a voltage of about the second forward voltage V2 ((12 + 12) × 3.2 = 76.8 (v)) is applied to the first LED block 21 and the second LED block 31 connected in series, The LEDs included in the first LED block 21 and the second LED block 31 are lit. In addition, the voltage of the third forward voltage V3 ((12 + 12 + 12) × 3.2 = 15.2 (v)) is about the first LED block 21, the second LED block 31, and the third LED block 41 connected in series. When applied, the LEDs included in the first LED block 21, the second LED block 31, and the third LED block 41 are turned on.

  When the commercial power supply voltage is used at 100 (V), the maximum voltage is about 141 (V). The stability of this voltage should take into account fluctuations of about ± 10%. The forward voltage of the rectifying elements D1 to D4 of the full-wave rectifier circuit 12 is 1.0 (V). In the circuit example 100, when the commercial power supply voltage is 100 (V), the maximum output voltage of the bridge full-wave rectifier circuit 12 is It becomes about 139 (V). The total number (n) × Vf when all the LEDs included in the first LED block 21, the second LED block 31, and the third LED block 41 are connected in series does not exceed the maximum output voltage of the full-wave rectifier circuit 12. The total number was 36 (36 × 3.2 = 15.2). As described above, the forward voltage Vf of all LEDs is 3.2 (v), but there are individual differences and actual values vary somewhat.

  Note that the circuit configuration of the circuit example 100 shown in FIG. 2 is an example, and is not limited thereto, including the number of LEDs included in the first LED block 21, the second LED block 31, and the third LED block 41. It should be noted that various changes can be made.

Hereinafter, the operation of the circuit example 100 will be described with reference to FIGS. 3 is a diagram illustrating an output voltage waveform example 50 of the full-wave rectifier circuit 12, FIG. 4 is a diagram illustrating an example of a switching sequence of LED blocks in the circuit example 100, and FIG. 5 is a diagram at times T0 to T7 in FIG. It is a figure which shows the example of an electric current of each part of a period. 5A shows the current I ₁ , FIG. 5B shows the current I ₂ , FIG. 5C shows the current I ₄ , FIG. 5D shows the current I ₆ , FIG. 5 (e) shows the current I ₈ and FIG. 5 (f) shows the current I ₉ .

Further, the set current of the current I ₂ set by the first current monitor 22 is S2, the set current of the current I ₄ set by the 2-1 current monitor 32 is S4, and the 2-2 current monitor 34 is set. the set current of the current I ₆ which is set S6, the set current of the third current monitor 42 to set current of the current I ₈ which is set in S8, a current I ₈ which is set at the 2-3 current monitor 36 Is S10, and the set current of the current I ₇ set by the constant current diode 17 is S7. In the LED drive circuit 1 shown in FIG. 1, for example, S2 = S4 = S8 <S10 <S6 <S7 is set. The magnitude relationship of the set current is not limited to the above, and may be set to other relationships.

  At time T0 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 is 0 (v), the voltage for lighting any one of the first LED block 21, the second LED block 31, and the third LED block 41 Therefore, the LEDs included in all the LED blocks are not lit.

  At time T1 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 becomes the first forward voltage V1, and the voltages are sufficient to turn on the first LED block 21, the second LED block 31, and the third LED block 41, respectively. Then, current paths are formed through the first LED block 21, the second LED block 31, and the third LED block 41, and the LEDs included in the first LED block 21, the second LED block 31, and the third LED block 41 are lit (FIG. 4). (See (a)). As described above, since there is a difference in the Vf of each LED included in each LED block, is the first forward voltage V1 (38.4 (v)) that actually starts lighting? Whether or not depends on the actual circuit. However, the first LED block 21, the second LED block 31, and the third LED block are applied when a voltage obtained by adding Vf of 12 LEDs included in the first LED block 21, the second LED block 31, and the third LED block 41 is applied. Twelve LEDs included in each of 41 start lighting.

In the state of FIG. 4A, since I ₁ = I ₂ , I ₄ = I ₅ = I ₆ , and I ₈ = I ₉ , and a reverse voltage is applied to the diodes 15 and 16, I ₃ And the current of I ₇ is not flowing. Here, the first current limiting unit 23, the 2-1 current control unit 33, and the 3-1 current limiting unit 43 control the currents of the first block 20 to the third block 40, respectively. At that time, the impedances of the 2-2 current control unit 35 and the 3-2 current limiting unit 44 are in a very low state, that is, in the ON state, from the relationship of the set current described above.

Since the first LED block 21, the second LED block 31, and the third LED block 41 are driven at a constant current, currents I ₁ , I ₂ , I ₄ , I ₆ , I ₈ and I ₉ shows a substantially constant value (see FIGS. 5A to 5F).

  Next, at time T2 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 becomes the second forward voltage V2, and is included even when the first LED block 21 and the second LED block 31 are connected in series. When the voltage is sufficient to turn on all the LEDs, the current path is switched so that the first LED block 21 and the second LED block 31 are connected in series to the full-wave rectifier circuit 12 (FIG. 4). (See (b)).

Hereinafter, the transition from FIG. 4A to FIG. 4B will be described.
When the output voltage of the full-wave rectifier circuit 12 rises from the first forward voltage V1 to the second forward voltage V2, the first current monitor 22 controls the first current controller 23 to limit the current I _3. is doing. As described above, in the state of FIG. 4A, the first current limiting unit 23, the 2-1 current control unit 33, and the 3-1 current limiting unit 43 are connected to the currents of the first block 20 to the third block 40. Control each. However, when the output voltage of the full-wave rectifier circuit 12 increases, the forward voltage of the first LED block 21 remains constant V1, and the voltage drop in the first current control unit 23 increases, that is, the first current control. Control is performed so that the impedance of the unit 23 becomes high.

Thus, in the transition state from FIG. 4A to FIG. 4B, the voltage drop of the first current control unit 23 and the voltage drop of the 2-1 current control unit 33 are large. Here, although the reverse bias is applied to the diode 15 until then, the forward bias is applied and the current I ₃ starts to flow. Then, the first current monitor 22 operates so as to increase the impedance of the first current control unit 23 and reduce the current I ₂ .

Further, since the 2-1 current monitor 32 adds the current I ₃ to the current I ₄ that has been monitored so far, the 2-1 current control unit 33 reduces the current I ₄ in the direction, that is, Control is performed to increase the impedance of the 2-1 current controller 33. Therefore, the currents I ₂ and I ₄ gradually decrease, and finally the currents I ₂ and I ₄ become almost zero, so that I ₁ = I ₃ = I ₅ = I ₆ (in FIG. 4B) (See FIG. 5 (b) and FIG. 5 (c)). At this time, the 1st current control part 23 and the 2nd-1 current control part 33 are high impedance, ie, an OFF state. Then, the 2-2 current monitor 34 controls the impedance of the 2-2 current control unit 35, and a current flows in the set current S6 in current I _6.

Thus, by the impedance control of the 2-2 current control unit 35 by the 2-2 current monitor 34, the currents I ₁ , I ₃ , I ₅ and I ₆ are changed from the time T1 to T2 during the time T2 to T3. The constant current drive is performed at a higher value (see FIGS. 5A and 5D). At this time, when the first LED block 21 and the second LED block 31 are connected in series, the second-3 current monitor 36 detects an increase in the value of the current I ₅ flowing through both the LED blocks, The current controller 44 is controlled so that the current I ₈ does not flow, and the third LED block 41 is controlled not to be lit (see FIGS. 5E and 5F). Therefore, only a current path as shown in FIG. 4B is formed. Note that the reason why the third LED block 41 is controlled not to be lit in FIG. 4B will be described later.

As described above, since the setting current is S2 = S4 = S8 <S6, in the state of FIG. 4B, the first current limiting unit 23 and the 2-1 current limiting unit 33 have high impedance. It is in the OFF state. Further, since it is set as S10 <S6, the 2-3 current monitor 36, which is the first 3-2 current limiting unit 44 a high impedance OFF state, i.e. the state current I ₈ is that blocked . Therefore, in the state of FIG. 4B, the 3-2 current limiting unit 35 controls the current flowing through the first LED block 21 and the second LED block 31. By the way, when the output voltage of the full-wave rectifier circuit 12 is equal to or higher than the second forward voltage V2, the current limitation by the third-second current limiting unit 44 is not always released by the second-third current monitor 36. The current I ₈ is always cut off.

  Next, even at the time T3 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 becomes the third forward voltage V3, and the first LED block 21, the second LED block 31, and the third LED block 41 are connected in series. The first LED block 21, the second LED block 31, and the third LED block 41 are connected in series to the full-wave rectifier circuit 12 when the voltage is sufficient to light all the LEDs included in them. Then, the current path is switched (see FIG. 4C).

Hereinafter, the transition from FIG. 4B to FIG. 4C will be described.
When the output voltage of the full-wave rectifier circuit 12 approaches the third forward voltage V3, the diode 16 has been reverse-biased so far, but is now forward-biased, and the current I ₇ becomes the termination circuit. 40 begins to flow.

When the output voltage of the full-wave rectifier circuit 12 rises from the second forward voltage V2 to the third forward voltage V3, the 2-2 current monitor 34 adjusts the impedance of the 2-2 current control unit 35. The current I ₆ is controlled to be limited. At this time, the voltage drop of the 2-2 current control unit 35 gradually increases. Since the current setting S10 of the 2-3 current monitor 36 is set lower than the current setting S6 of the 2-2 current monitor 34, when the output voltage of the full-wave rectifier circuit 12 is equal to or higher than the second forward voltage V2, The impedance of the third-second current limiting unit 44 is high, and the current I ₈ does not flow. In addition, the 2-2 current monitor 34 performs control to increase the impedance of the 2-2 current control unit 35 and reduce the current I ₆ . Accordingly, the current I ₆ gradually decreases and finally the current I ₆ becomes almost zero, and the state of I ₁ = I ₃ = I ₅ = I ₇ = I ₉ (the state of FIG. 4C) Become.

In the state of FIG. 4C, if I ₁ = I ₃ = I ₅ = I ₇ = I ₉ and the set current of the constant current diode 17 is S7, the current in this state is S7 (FIG. 5 (a) and FIG. 5 (f)). In this state, the currents I ₂ , I ₄ , I ₆ and I ₈ hardly flow (see FIGS. 5B to 5E). As described above, since S2 = S4 = S8 <S10 <S6 <S7 is set, in the state of FIG. 4 (c), the constant current diode 17 has a current flowing through the first block 20 to the third block 40. I have control.

Next, at time T4 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 drops below the third forward voltage V3, the 2-2 current monitor 34 Control is performed so that the limit of the current I ₆ is relaxed. Then, the current I ₆ begins to flow gradually, and the current I ₇ decreases. At this time, the current setting S10 of the second-3 current monitor 36 is set lower than the current setting S6 of the 2-2 current monitor 34. Has a high impedance, and the current I ₈ does not flow. When the power supply voltage drops below V3, the third LED block 41 is turned off and the state shown in FIG. 4C is shifted to the state shown in FIG. In this state, current I ₁ = I ₃ = I ₅ = I ₆ (see FIGS. 5A and 5D).

  As described above, the set voltage S2 of 22 similar to the first current and the set voltage S6 of the 2-2 current monitor 34 are set in advance so that the relationship of S2 <S6 is satisfied. From the serial relationship between the 1LED block 21 and the second LED block 31, the serial relationship between the second LED block 31 and the third LED block 41 is cut first.

Next, when the output voltage of the full-wave rectifier circuit 12 becomes less than the second forward voltage V2 at time T5 (see FIG. 3), the LEDs included in the first LED block 21 and the second LED block 31 connected in series. Therefore, current paths are formed through the first LED block 21, the second LED block 31, and the third LED block 41, respectively, and the first LED block 21, the second LED block 31, and the third LED block 41 are formed. The LED included in is turned on (see FIG. 4E). In addition, since the output voltage of the full-wave rectifier circuit 12 becomes less than the second forward voltage V2, the 2-3 current monitor 36 turns on the 3-2 current control unit 44. The interruption is released. Therefore, since I ₁ = I ₂ , I ₄ = I ₅ = I ₆ , and I ₈ = I ₉ and the reverse voltage is applied to the diodes 15 and 16, the currents I ₃ and I ₇ flow. (See FIG. 5 (a) to FIG. 5 (f)).

Next, at time T6 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 becomes less than the first forward voltage V1, all of the first LED block 21, the second LED block 31, and the third LED block 41 are included. Since the voltage is less than a voltage sufficient to light the LED, all currents I _{1 to} I ₉ do not flow (see FIGS. 5A to 5F). Thereafter, the LEDs of the first LED block 21, the second LED block 31, and the third LED block 41 are lit while repeating the state from time T0 to time T7 (which corresponds to the time T0 of the cycle next).

  The reverse current preventing diode 15 prevents the current included in the first circuit block 21 from being damaged due to an erroneous flow of current from the intermediate circuit 30 to the start circuit 20 side. Further, the reverse current prevention diode 16 prevents the current included in the second circuit block 31 from being damaged due to an erroneous flow of current from the termination circuit 40 to the intermediate circuit 30 side. Note that the current control units included in the start circuit 20, the intermediate circuit 30, and the termination circuit 40 adjust the impedance and perform current control. At this time, the voltage drop of the current control unit also changes. When a forward bias is applied to the reverse current prevention diodes 15 and 16, the current begins to flow gradually and the current path is switched as described above.

  The constant current diode 17 prevents an overcurrent from flowing through the first LED block 21, the second LED block 31, and the third LED block 41, particularly in the situation of FIG. As can be understood from FIGS. 4A to 4E, any current control unit is present in the current path except for the state of FIG. Can be prevented from flowing. However, in the state of FIG. 4C, since the current control unit does not exist in the current path, the constant current diode 17 is inserted. The insertion location of the constant current diode 17 is not limited between the intermediate circuit 30 and the termination circuit 40, and may be another location as long as it is in the current path in the state of FIG.

  Also, constant current diodes may be arranged at a plurality of locations in the current path in the state of FIG. In addition, if it can prevent that overcurrent flows into the 1st LED block 21, the 2nd LED block 31, and the 3rd LED block 41 in the condition of FIG.4 (c), a current adjustment circuit, such as a constant current circuit or high resistance, or An element may be used instead of the constant current diode 17.

  As described above, the circuit example 100 is configured such that the current path is switched according to the output voltage of the full-wave rectifier circuit 12, so that it is not necessary to provide a large number of switch circuits. The switching of the current path is automatically determined according to the total output voltage of the full-wave rectifier circuit 12 and the actual Vf of all LEDs included in each LED block. Therefore, it is not necessary to predict and control the switching timing of each LED block, and it is possible to switch between the LED blocks in series and in parallel at the most efficient timing.

  Hereinafter, the functions of the second-3 current monitor 36 and the third-2 current control unit 44 in the LED drive circuit 1 will be further described with reference to FIGS. 21 and 22.

  FIG. 21 shows an LED drive circuit 8 in which the 2-3 current monitor 36 and the 3-2 current control unit 44 are omitted from the LED drive circuit 1 shown in FIG. FIG. 22 is a diagram showing an example of a switching sequence of LED blocks when the output voltage of the full-wave rectifier circuit 12 changes as in the waveform example 50 shown in FIG. 3 in the LED drive circuit 8 shown in FIG. .

  In the LED drive circuit 8 shown in FIG. 21, since the second-3 current monitor 36 and the third-2 current control unit 44 are not present, the output voltage of the full-wave rectifier circuit 12 is changed from the first voltage V1 to the second voltage. When the voltage V2 is reached, the state shown in FIG. 22A is shifted to the state shown in FIG.

  In the state of FIG. 22B, a voltage for lighting the LEDs included in both LED blocks with the first LED block 21 and the second LED block 31 connected in series is applied only to the third LED block 41. It becomes. Since the impedance of the third LED block 41 is about ½ of the total impedance of the first LED block 21 and the second LED block 31, a larger amount of current normally flows. However, the third LED block 41 41 is driven by a constant current by the third current control unit 43. That is, the current limit in the third current control unit 43 is a loss of the circuit shown in FIG. The above power loss also occurs when the state shown in FIG. 22C is changed to the state shown in FIG.

  As described above, the second-3 current monitor 36 and the third-2 current control unit 44 have two LED blocks connected in series as shown in FIGS. 22B and 22D. LED blocks having different impedances such that one LED block is connected in parallel to the full-wave rectifier circuit 12 are prevented from being connected in parallel to the full-wave rectifier circuit 12. That is, as shown in FIGS. 4B and 4D, the third LED block 41 is controlled not to be lit in order to prevent the occurrence of a non-uniform state. It prevents power loss.

  6A is a diagram showing the input power, power consumption, and power loss of the LED drive circuit 1, and FIG. 6B is a diagram showing the input power, power consumption, and power loss of the LED drive circuit 8.

  In FIG. 6A, the solid line 70 indicates the input power in the LED drive circuit 1, the dotted line 71 indicates the power consumption in the LED drive circuit 1, and the alternate long and short dash line 72 indicates the power loss in the LED drive circuit 1. Similarly, in FIG. 6B, the solid line 73 indicates the input power in the LED drive circuit 8, the dotted line 74 indicates the power consumption in the LED drive circuit 8, and the alternate long and short dash line 75 indicates the power loss in the LED drive circuit 8. Yes.

  If conversion efficiency (%) = power consumption / input power × 100 is defined, from FIG. 6A and FIG. 6B, the conversion efficiency in the LED drive circuit 1 shown in FIG. 1 is 80.3 (%). On the other hand, the conversion efficiency of the LED drive circuit 8 shown in FIG. 21 is as low as 72.9 (%). As described above, this is because, in the state of FIG. 22B or FIG. 22D, two LED blocks including the same number of LEDs are connected in series and one LED block is connected in parallel. This is presumably because a non-uniform state of impedance that is connected to the wave rectifier circuit 12 occurs. As described above, in the LED drive circuit 1, the third LED block 41 is turned off at a predetermined timing by the second-3 current monitor 36 and the third-2 current control unit 44. It became possible to increase the conversion efficiency of the circuit.

  FIG. 7 is a schematic explanatory diagram of another LED driving circuit according to the present invention.

  The LED drive circuit 2 shown in FIG. 7 is different from the LED drive circuit 1 shown in FIG. 1 only in that the LED drive circuit 2 has an electrolytic capacitor 60 between the output terminals of the full-wave rectifier circuit 12. is there.

  The output voltage waveform of the full-wave rectifier circuit 12 is smoothed by the electrolytic capacitor 60 (see the voltage waveform 51 in FIG. 3). In the voltage waveform example 50 of the LED drive circuit 1 shown in FIG. 1, since the time T0 to the time T1 and the time T6 to the time T7 are less than the first forward voltage V1, none of the LEDs is lit. Therefore, in the LED drive circuit 1 shown in FIG. 1, the period in which the LED is not lit and the period in which the LED is lit are alternately repeated, that is, the LED blinks at 100 Hz when the commercial frequency is 50 Hz and 120 Hz when the commercial frequency is 60 Hz. Become.

  On the other hand, in the LED drive circuit 2 shown in FIG. 7, since the output voltage waveform of the full-wave rectifier circuit 12 is smoothed, the output voltage of the full-wave rectifier circuit 12 is always the first forward voltage V1. Thus, all the LED blocks are turned on (see dotted line 51 in FIG. 3). Note that the output voltage of the full-wave rectifier circuit 12 may always be equal to or higher than the second forward voltage V2. Thus, the LED drive circuit 2 shown in FIG. 7 can prevent the LED from blinking.

  In the example of FIG. 7, the electrolytic capacitor 60 is added, but instead of the electrolytic capacitor 60, a ceramic capacitor for smoothing the output voltage waveform of the full-wave rectifier circuit 12, another element or circuit is used. Also good. Further, in order to suppress the harmonic current and improve the power factor, the coil may be placed on the AC input side before the diode bridge of the full-wave rectifier circuit 12 or the rectified output side after the diode bridge.

  FIG. 8 is a schematic configuration diagram of still another LED driving circuit according to the present invention.

  In the LED drive circuit 3 shown in FIG. 8, the commercial AC power supply (AC 100V) 10 shown in FIG. 1, the connection terminal 11 connected to the commercial AC power supply 10, and the full-wave rectifier circuit 12 are omitted. A power output 13 and a negative power output 14 are connected to a full wave rectifier circuit 12 (not shown). The difference between the LED drive circuit 3 shown in FIG. 8 and the LED drive circuit 1 shown in FIG. 1 is that in the LED drive circuit 3, the second-3 current monitor 36 is different from the second LED block 31 and the second-2 current monitor 34. It is not disposed between them, but only between the reverse current prevention diode 15 and the 2-1 current monitor 32. The current path switching sequence in the LED drive circuit 3 is the same as that in the LED drive circuit 1 shown in FIG.

  In the LED drive circuit 1 shown in FIG. 1, as described above, the current setting S10 of the second-3 current monitor 36 is the same as the current setting S4 of the 2-1 current monitor 32 and the current of the 2-2 current monitor 34. It is necessary to set in the middle of the setting S6. This is because the 3-2 current limiting unit 44 needs to be in the ON state in the state of FIG. 4A, and the 3-2 current limiting unit 44 needs to be in the OFF state in the state of FIG. 4B. is there.

  On the other hand, in the LED drive circuit 3 shown in FIG. 8, the current setting S10 of the 2-3 current monitor 36 only needs to be lower than the current setting S6 of the 2-2 current monitor 34, and the degree of freedom of current setting is high. There is an advantage of increasing. Further, as the difference between the current setting S10 of the second-3 current monitor 36 and the current setting S6 of the 2-2 current monitor 34 is larger, the operation of the third-2 current limiting unit 44 in the state of FIG. There is also an advantage that becomes stable.

  FIG. 9 is a schematic configuration diagram of still another LED driving circuit according to the present invention.

  In the LED drive circuit 4 shown in FIG. 9, the commercial AC power supply (AC 100 V) 10, the connection terminal 11 connected to the commercial AC power supply 10 and the full-wave rectifier circuit 12 shown in FIG. A power output 13 and a negative power output 14 are connected to a full wave rectifier circuit 12 (not shown). The LED drive circuit 4 includes a start circuit 101, four intermediate circuits 102 to 105, and a termination circuit 106, and includes reverse current prevention diodes 181 to 185 and a constant current diode 190 between the circuits. .

  As with the start circuit 20 shown in FIG. 1, the start circuit 101 includes a first LED block 110 including a plurality of LEDs, a first current monitor 111 that detects a current flowing through the first LED block 110, a first current control unit 112, and the like. Contains. The first current monitor 111 operates to limit the current flowing through the first current control unit 112 according to the current flowing through the first LED block 110.

  As with the termination circuit 40 shown in FIG. 1, the termination circuit 106 includes a sixth LED block 160 including a plurality of LEDs, a sixth current monitor 161 for detecting a current flowing through the sixth LED block 160, and a sixth current control unit 162. Etc. The sixth current monitor 161 operates to limit the current flowing through the sixth current control unit 162 according to the current flowing through the sixth LED block 160.

  Similar to the intermediate circuit 30 shown in FIG. 1, the intermediate circuit 102 includes a second LED block 120 including a plurality of LEDs, a 2-1 current monitor 121 and a 2-2 for detecting a current flowing through the second LED block 120. A current monitor 123, a 2-1 current control unit 122, a 2-2 current control unit 124, and the like are included. The 2-1 current monitor 121 controls to adjust the current flowing through the 2-1 current control unit 122 according to the current flowing through the second LED block 120, and the 2-2 current monitor 123 is controlled by the second LED block 120. The operation is performed so as to limit the current flowing through the second-second current control unit 124 according to the current flowing through 120. Similarly to the intermediate circuit 103, the intermediate circuits 103 to 105 also include an LED block including a plurality of LEDs, a current monitor for detecting current flowing through the LED block, and two currents limited by the current monitor. It has a current controller.

  Further, the LED drive circuit 4 has the same functions as the 2-3 current monitor 36 and the 3-2 current control unit 44 of the LED drive circuit 1 shown in FIG. 1, and the LED blocks are connected in series and / or in parallel. When the switching is performed, the current flowing through the current monitor 171 and the current monitor to prevent the occurrence of a power loss due to an uneven state (when the third LED block 130 and the fourth LED block 140 are connected in series) A current control unit 172 that restricts the current flowing through both LED blocks.

  FIG. 10 is a diagram showing an example of the LED block switching sequence of the LED drive circuit 4 shown in FIG.

  In FIG. 9, in the start circuit 101, the termination circuit 106, and the intermediate circuits 102 to 105, the LED block is switched in series and / or in parallel according to the output voltage of the full-wave rectifier circuit 12. Since it is the same as that described in the circuit 1, a switching sequence of each LED block will be described according to the output voltage of the full-wave rectifier circuit 12 with reference to FIG. Each of the LED blocks of the start circuit 101, the termination circuit 106, and the four intermediate circuits 102 to 105 has all six LEDs connected in series, and the total number of LEDs included in the LED drive circuit 4 is There are 36 pieces.

  For example, when the output voltage of the full-wave rectifier circuit 12 is 0 (zero) at time T0, none of the LEDs included in the first LED block 110 to the sixth LED block 160 is lit.

  Since six LEDs are connected in series to each of the first LED block 110 to the sixth LED block 160, for example, at time T1, the first forward voltage V1 (6 × When a voltage of about Vf = 6 × 3.2 = 19.2 (v) is applied to each of the first LED block 110 to the sixth LED block 160, the LEDs included in each of the first LED block 110 to the sixth LED block 160 are Lights up (see FIG. 10A). At this time, the current controller 172 is ON, the current flowing through the fifth LED block 150 is controlled by the 5-2 current controller 154, and the current flowing through the sixth LED block 160 is controlled by the sixth current controller 162. Yes.

  Next, for example, at time T2, a voltage of about the second forward voltage V2 ((6 + 6) × 3.2 = 38.4 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 110 and Applied to the second LED block 120 connected in series, the third LED block 130 and the fourth LED block 140 connected in series, and the fifth LED block 150 and the sixth LED block 160 connected in series. Then, the LEDs included in the respective LED blocks are turned on (see FIG. 10B). At this time, the current control unit 172 is in the ON state, and the current flowing through the fifth LED block 150 and the sixth LED block 160 is controlled by the 5-1 current control unit 152.

  Next, for example, at time T <b> 3, a voltage of about the third forward voltage V <b> 3 ((6 + 6 + 6 + 6) × 3.2 = 76.8 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 110, When applied to the second LED block 120, the third LED block 130, and the fourth LED block 140 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 10C). Here, even if the third forward voltage V3 is applied from the full-wave rectifier circuit 12 to the fifth LED block 150 and the sixth LED block 160 connected in series, the LEDs included therein can be turned on. It is. However, when the LEDs included in the fifth LED block 150 and the sixth LED block 160 are turned on with the third forward voltage V3, as described with reference to FIGS. 4B and 4D, the 5-1 current A power loss in the limiting unit 152 occurs. Therefore, in the LED drive circuit 4, the current controller 172 is turned off by the current monitor 171, and control is performed so that no current flows through the fifth LED block 150 and the sixth LED block 160. At the third forward voltage V3 or higher, the current monitor 171 turns off the current control unit 172 and cuts off the current passing through the current control unit 172.

  Next, for example, at time T <b> 4, a voltage of about the fourth forward voltage V <b> 4 ((6 + 6 + 6 + 6 + 6) × 3.2 = 96.0 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 110, When applied to the second LED block 120, the third LED block 130, the fourth LED block 140, and the fifth LED block 150 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 10D). ). When the fourth forward voltage V4 is approached, the diode 184 has been reverse-biased so far, but the forward bias is applied and current starts to flow through the fifth LED block 150. However, since the output voltage of the output full-wave rectifier circuit 12 is not sufficiently high, no current flows to the sixth LED block 160. At this time, the current controller 172 is in an OFF state by the current monitor 171.

  Here, even if the fourth forward voltage V4 is applied from the full-wave rectifier circuit 12 to the sixth LED block 160, the LEDs included therein can be turned on. However, when the LEDs included in the sixth LED block 160 are turned on with the fourth forward voltage V4, as described with reference to FIGS. 4B and 4D, the power loss in the sixth current limiting unit 162 is reduced. Will occur. Therefore, in the LED drive circuit 4, the current monitor 171 and the current control unit 172 operate as described above, and control is performed so that no current flows through the sixth LED block 160.

  Next, for example, at time T <b> 5, a voltage of about the fifth forward voltage V <b> 5 ((6 + 6 + 6 + 6 + 6 + 6) × 3.2 = 15.2 (v)) from the full-wave rectifier circuit 12 is the first LED block 110 to the first LED When 6 LED blocks 160 are applied to those connected in series, the LEDs included in the respective LED blocks are turned on (see FIG. 10E). When the fifth forward voltage V5 is approached, the diode 185 has been reverse-biased until then, but the forward-bias is applied and current starts to flow through the sixth LED block 160. At this time, the current controller 172 is in an OFF state by the current monitor 171.

  In the LED drive circuit 4 shown in FIG. 9, each LED block is turned on while repeating the states of FIGS. 10A to 10E according to the output voltage of the full-wave rectifier circuit 12. As described above, in the LED drive circuit 4, the current monitor 171 and the current control unit 172 prevent the occurrence of power loss due to the occurrence of an uneven state.

  FIG. 11 is a diagram illustrating input power, power consumption, and power loss of the LED drive circuit 4.

  In FIG. 11, the solid line 191 indicates the input power in the LED drive circuit 4, the dotted line 192 indicates the power consumption in the LED drive circuit 4, and the alternate long and short dash line 193 indicates the power loss in the LED drive circuit 4. From FIG. 11, the conversion efficiency in the LED drive circuit 4 shown in FIG. 9 is 81.5 (%). As described above, in the LED drive circuit 4, the fifth LED block 150 and / or the sixth LED block 160 are extinguished at a predetermined timing by the current monitor 171 and the current control unit 172. It became possible to increase the conversion efficiency.

  FIG. 12 is a schematic configuration diagram of still another LED driving circuit according to the present invention.

  In the LED drive circuit 5 shown in FIG. 12, the commercial AC power supply (AC 100V) 10 shown in FIG. 1, the connection terminal 11 connected to the commercial AC power supply 10, and the full-wave rectifier circuit 12 are omitted. A power output 13 and a negative power output 14 are connected to a full wave rectifier circuit 12 (not shown). The LED drive circuit 5 includes a start circuit 201, two intermediate circuits 202 and 203, and a termination circuit 204, and includes reverse current prevention diodes 281 to 283 and a constant current diode 290 between the circuits. .

  As with the start circuit 20 shown in FIG. 1, the start circuit 201 includes a first LED block 210 including a plurality of LEDs, a first current monitor 211 that detects a current flowing through the first LED block 210, a first current control unit 212, and the like. Contains. The first current monitor 211 operates to limit the current flowing through the first current control unit 212 according to the current flowing through the first LED block 210.

  Similarly to the termination circuit 40 shown in FIG. 1, the termination circuit 204 includes a fourth LED block 240 including a plurality of LEDs, a fourth current monitor 241 for detecting a current flowing through the fourth LED block 240, and a fourth current control unit 242. Etc. The fourth current monitor 241 operates to limit the current flowing through the fourth current control unit 242 according to the current flowing through the fourth LED block 240.

  Similar to the intermediate circuit 30 shown in FIG. 1, the intermediate circuit 202 includes a second LED block 220 including a plurality of LEDs, a 2-1 current monitor 221 and a 2-2 for detecting a current flowing through the second LED block 220. A current monitor 223, a 2-1 current controller 222, a 2-2 current controller 224, and the like are included. The 2-1 current monitor 221 controls to adjust the current flowing through the 2-1 current control unit 222 according to the current flowing through the second LED block 220, and the 2-2 current monitor 223 controls the second LED block 220. According to the current flowing through 220, the current flowing through the second-second current control unit 224 is limited. The intermediate circuit 203, like the intermediate circuit 202, includes an LED block including a plurality of LEDs, two current monitors that detect current flowing through the LED block, and two current controls in which the current is limited by the current monitor. Has a part.

  Further, the LED drive circuit 5 has the same functions as the 2-3 current monitor 36 and the 3-2 current control unit 44 of the LED drive circuit 1 shown in FIG. 1, and the LED blocks are connected in series and / or in parallel. Current flowing through the current monitor 271 and the current monitor 271 to prevent a non-uniform state from occurring and causing power loss when switched (when the first LED block 210 and the second LED block 220 are connected in series) Current control section 272 that restricts the current flowing through both LED blocks.

  FIG. 13 is a diagram showing an example of the LED block switching sequence of the LED drive circuit 5 shown in FIG.

  In FIG. 12, in the start circuit 201, the termination circuit 204, and the intermediate circuits 202 and 203, the LED block is switched in series and / or in parallel in accordance with the output voltage of the full-wave rectifier circuit 12. Since it is the same as that described in the circuit 1, a switching sequence of each LED block will be described using FIG. 13 according to the output voltage of the full-wave rectifier circuit 12. The first LED block 210 of the start circuit 201 has six, the second LED block 220 of the intermediate circuit 202 has six, the third LED block of the intermediate circuit 203 has twelve, and the fourth LED block 240 of the termination circuit 204 has a fourth. Twelve LEDs are connected in series, and the total number of LEDs included in the LED drive circuit 5 is 36.

  For example, when the output voltage of the full-wave rectifier circuit 12 is 0 (zero) at time T0, none of the LEDs included in the first LED block 210 to the fourth LED block 240 is lit.

  Since six LEDs are connected in series to each of the first LED block 210 and the second LED block 220, for example, at time T1, the first forward voltage V1 (6 × When a voltage of about Vf = 6 × 3.2 = 19.2 (v) is applied to each of the first LED block 210 and the second LED block 220, the LEDs included in each of the first LED block 210 and the second LED block 220 are Lights up (see FIG. 13A).

  Next, for example, at time T2, a voltage of about the second forward voltage V2 ((6 + 6) × 3.2 = 38.4 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 210 and When applied to the second LED block 220 connected in series, the third LED block 230, and the fourth LED block 240, the LEDs included in the respective LED blocks are lit (see FIG. 13B).

  Next, for example, at time T3, a voltage of about the third forward voltage V3 ((6 + 6 + 12) × 3.2 = 76.8 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 210, When applied to the second LED block 220 and the third LED block 230 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 13C). Here, even if the third forward voltage V3 is applied from the full-wave rectifier circuit 12 to the fourth LED block 240, it is possible to light the LED included therein. However, when the LEDs included in the fourth LED block 240 are turned on with the third forward voltage V3, as described with reference to FIGS. 4B and 4D, power loss in the fourth current limiting unit 242 occurs. Will occur. Therefore, in the LED drive circuit 5, the current monitor 271 and the current control unit 272 operate to control the current not to flow through the fourth LED block 240.

  Next, for example, at time T <b> 4, a voltage of about the fourth forward voltage V <b> 4 ((6 + 6 + 12 + 12) × 3.2 = 115.2 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 210, When applied to the second LED block 220, the third LED block 230, and the fourth LED block 240 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 13D).

  In the LED drive circuit 5 shown in FIG. 12, each LED block is lit while repeating the states of FIGS. 13A to 13D in accordance with the output voltage of the full-wave rectifier circuit 12. As described above, in the LED drive circuit 5, the current monitor 271 and the current control unit 272 prevent the occurrence of power loss due to an uneven state.

  FIG. 14 is a diagram illustrating input power, power consumption, and power loss of the LED drive circuit 4.

  In FIG. 14, the solid line 291 indicates the input power in the LED drive circuit 5, the dotted line 292 indicates the power consumption in the LED drive circuit 5, and the alternate long and short dash line 293 indicates the power loss in the LED drive circuit 5. From FIG. 14, the conversion efficiency in the LED drive circuit 5 shown in FIG. 12 is 80.0 (%). As described above, in the LED drive circuit 5, the fourth LED block 240 is turned off at a predetermined timing by the current monitor 271 and the current control unit 272. Therefore, it is possible to suppress power loss and increase the conversion efficiency of the LED drive circuit. It has become possible.

  FIG. 15 is a schematic configuration diagram of still another LED driving circuit 6 according to the present invention.

  In the LED drive circuit 6 shown in FIG. 15, the commercial AC power supply (AC 100 V) 10, the connection terminal 11 connected to the commercial AC power supply 10 and the full-wave rectifier circuit 12 shown in FIG. A power output 13 and a negative power output 14 are connected to a full wave rectifier circuit 12 (not shown). The LED drive circuit 6 includes a start circuit 301, two intermediate circuits 302 and 303, and a termination circuit 304, and includes reverse current prevention diodes 381 to 383 and a constant current diode 390 between the circuits. .

  Like the start circuit 20 shown in FIG. 1, the start circuit 301 includes a first LED block 310 including a plurality of LEDs, a first current monitor 311 that detects a current flowing through the first LED block 310, a first current control unit 312 and the like. Contains. The first current monitor 311 operates to limit the current flowing through the first current control unit 312 according to the current flowing through the first LED block 310.

  As with the termination circuit 40 shown in FIG. 1, the termination circuit 304 includes a fourth LED block 340 including a plurality of LEDs, a fourth current monitor 341 for detecting a current flowing through the fourth LED block 340, and a fourth current control unit 342. Etc. The fourth current monitor 341 operates to limit the current flowing through the fourth current control unit 342 according to the current flowing through the fourth LED block 340.

  Similar to the intermediate circuit 30 shown in FIG. 1, the intermediate circuit 302 includes a second LED block 320 including a plurality of LEDs, a 2-1 current monitor 321 and a 2-2 for detecting a current flowing through the second LED block 320. A current monitor 323, a 2-1 current control unit 322, a 2-2 current control unit 324, and the like are included. The 2-1 current monitor 321 controls to adjust the current flowing through the 2-1 current control unit 322 according to the current flowing through the second LED block 320, and the 2-2 current monitor 323 controls the second LED block. The operation is performed so as to limit the current flowing through the second-second current control unit 324 according to the current flowing through 320. The intermediate circuit 303, like the intermediate circuit 302, has an LED block including a plurality of LEDs, two current monitors that detect current flowing through the LED block, and two current controls in which the current is limited by the current monitor. Has a part.

  Moreover, the LED drive circuit 6 has the same function as the 2-3 current monitor 36 and the 3-2 current control unit 44 of the LED drive circuit 1 shown in FIG. 1, and the LED blocks are connected in series and / or in parallel. Current flowing through the current monitor 371 and the current monitor 371 to prevent the occurrence of power loss due to non-uniform state when switched (when the first LED block 310 and the second LED block 320 are connected in series) Current control section 372 for limiting the current flowing in both LED blocks.

  FIG. 16 is a diagram showing an example of the LED block switching sequence of the LED drive circuit 6 shown in FIG.

  In FIG. 15, in the start circuit 301, the termination circuit 304, and the intermediate circuits 302 and 303, each LED block is switched in series and / or in parallel according to the output voltage of the full-wave rectifier circuit 12. Since it is the same as that described in the circuit 1, a switching sequence of each LED block will be described with reference to FIG. The first LED block 310 of the start circuit 301 has 12 pieces, the second LED block 320 of the intermediate circuit 302 has 12 pieces, the third LED block 330 of the intermediate circuit 303 has 6 pieces, and the fourth LED block 340 of the termination circuit 304 has pieces. Six LEDs are connected in series, and the total number of LEDs included in the LED drive circuit 6 is 36.

  For example, when the output voltage of the full-wave rectifier circuit 12 is 0 (zero) at time T0, none of the LEDs included in the first LED block 310 to the fourth LED block 340 is lit.

  Since six LEDs are connected in series to each of the third LED block 330 and the fourth LED block 340, for example, at time T1, the first forward voltage V1 (6 × When a voltage of about Vf = 6 × 3.2 = 19.2 (v) is applied to each of the third LED block 330 and the fourth LED block 340, the LEDs included in each of the third LED block 330 and the fourth LED block 340 are displayed. Lights up (see FIG. 16A).

  Next, for example, at time T2, a voltage of about the second forward voltage V2 ((6 + 6) × 3.2 = 38.4 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 310, When applied to the second LED block 320, the third LED block 330, and the fourth LED block 340 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 16B).

  Next, for example, at time T <b> 3, a voltage of about the third forward voltage V <b> 3 ((12 + 12) × 3.2 = 76.8 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 310 and When the second LED block 320 is applied to one connected in series, the LED included in each LED block is turned on (see FIG. 16C). At the third forward voltage V3 or higher, the current monitor 371 turns off the current control unit 372 and cuts off the current passing through the current control unit 372.

  Here, even if the third forward voltage V3 is applied from the full-wave rectifier circuit 12 to the third LED block 330 and the fourth LED block 340 connected in series, the LEDs included therein can be turned on. It is. However, when the LEDs included in the third LED block 330 and the fourth LED block 340 are turned on with the third forward voltage V3, as described in FIGS. 4B and 4D, the current limiting unit 332 Power loss will occur. Therefore, in the LED drive circuit 6, the current monitor 371 and the current control unit 372 operate to perform control so that no current flows through the third LED block 330 and the fourth LED block 340.

  Next, for example, at time T4, a voltage of about the fourth forward voltage V4 ((12 + 12 + 6) × 3.2 = 96.0 (v)) is output from the full-wave rectifier circuit 12 to the first LED block 310, When applied to the second LED block 320 and the third LED block 330 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 16D). When approaching the fourth forward voltage V 4, the diode 382 has been reversely biased until then, but the forward bias is applied and current starts to flow through the third LED block 330. However, since the output voltage of the output full-wave rectifier circuit 12 is not sufficiently high, no current flows to the fourth LED block 340.

  Here, even if the fourth forward voltage V4 is applied from the full-wave rectifier circuit 12 to the fourth LED block 340, it is possible to light the LED included therein. When the LEDs included in the fourth LED block 340 are turned on with the fourth forward voltage V4, as described with reference to FIGS. 4B and 4D, power loss occurs in the current limiting unit 342. . Therefore, in the LED drive circuit 6, the current monitor 371 and the current control unit 372 operate to control the current not to flow through the fourth LED block 340.

  Next, for example, at time T <b> 5, a voltage of about the fifth forward voltage V <b> 5 ((12 + 12 + 6 + 6) × 3.2 = 15.2 (v)) from the full-wave rectifier circuit 12 is the first LED block 310 to the second LED. When the 4LED block 340 is applied to one connected in series, the LED included in each LED block is turned on (see FIG. 16 (e)). When approaching the fifth forward voltage V <b> 5, the diode 383 has been reversely biased so far, but is now forward-biased and current begins to flow through the fourth LED block 340. However, at the third forward voltage V3 or higher, the current monitor 371 turns off the current control unit 372 and blocks the current passing through the current control unit 372.

  In the LED drive circuit 6 shown in FIG. 15, each LED block is turned on while repeating the states of FIGS. 5A to 16E in accordance with the output voltage of the full-wave rectifier circuit 12. As described above, in the LED drive circuit 6, the current monitor 371 and the current control unit 372 prevent the occurrence of a non-uniform state and the occurrence of power loss.

  FIG. 17 is a diagram illustrating input power, power consumption, and power loss of the LED drive circuit 6.

  In FIG. 17, the solid line 391 indicates the input power in the LED drive circuit 6, the dotted line 392 indicates the power consumption in the LED drive circuit 6, and the alternate long and short dash line 393 indicates the power loss in the LED drive circuit 6. From FIG. 17, the conversion efficiency in the LED drive circuit 6 shown in FIG. 15 is 82.3 (%). As described above, in the LED drive circuit 6, the third LED block 330 and / or the fourth LED block 340 are extinguished at a predetermined timing by the current monitor 371 and the current control unit 372. It became possible to increase the conversion efficiency.

  FIG. 18 is a schematic configuration diagram of still another LED driving circuit according to the present invention.

  In the LED drive circuit 7 shown in FIG. 18, the commercial AC power supply (AC 100 V) 10, the connection terminal 11 connected to the commercial AC power supply 10 and the full-wave rectifier circuit 12 shown in FIG. A power output 13 and a negative power output 14 are connected to a full wave rectifier circuit 12 (not shown). The LED drive circuit 7 includes a start circuit 401, three intermediate circuits 402 to 404, and a termination circuit 405, and includes reverse current prevention diodes 481 to 484 and a constant current diode 490 between the circuits. .

  As with the start circuit 20 shown in FIG. 1, the start circuit 401 includes a first LED block 410 including a plurality of LEDs, a first current monitor 411 that detects a current flowing through the first LED block 410, a first current control unit 412, and the like. Contains. The first current monitor 411 operates to limit the current flowing through the first current control unit 412 according to the current flowing through the first LED block 410.

  Similar to the termination circuit 40 shown in FIG. 1, the termination circuit 405 includes a fifth LED block 450 including a plurality of LEDs, a fifth current monitor 451 for detecting a current flowing through the fifth LED block 450, and a fifth current control unit 452. Etc. The fifth current monitor 451 operates to limit the current flowing through the fifth current control unit 452 according to the current flowing through the fifth LED block 450.

  Similar to the intermediate circuit 30 shown in FIG. 1, the intermediate circuit 402 includes a second LED block 420 including a plurality of LEDs, a 2-1 current monitor 421 and a 2-2 for detecting a current flowing through the second LED block 420. A current monitor 423, a 2-1 current control unit 422, a 2-2 current control unit 424, and the like are included. The 2-1 current monitor 421 controls to adjust the current flowing through the 2-1 current control unit 422 according to the current flowing through the second LED block 420, and the 2-2 current monitor 423 controls the second LED block 422. It operates so as to limit the current flowing through the second-second current control unit 424 in accordance with the current flowing through 420. Similarly to the intermediate circuit 402, the intermediate circuits 403 and 404 also have an LED block including a plurality of LEDs, a current monitor for detecting current flowing through the LED block, and two currents limited by the current monitor. It has a current controller.

  Further, the LED drive circuit 7 has the same functions as the 2-3 current monitor 36 and the 3-2 current control unit 44 of the LED drive circuit 1 shown in FIG. 1, and the LED blocks are connected in series and / or in parallel. The current monitor 471 and the current flowing through the current monitor 471 (a first LED block 410, a second LED block 420, and a third LED block 430 are connected in series) to prevent a non-uniform state from occurring and causing power loss when switched. A current control unit 472 that restricts a current flowing through the LED block when connected to.

  FIG. 19 is a diagram showing an example of the LED block switching sequence of the LED drive circuit 7 shown in FIG.

  In FIG. 18, in the start circuit 401, the termination circuit 405, and the intermediate circuits 402 to 404, each LED block is switched in series and / or in parallel according to the output voltage of the full-wave rectifier circuit 12. Since it is the same as that described in the circuit 1, the switching sequence of each LED block will be described using FIG. 19 according to the output voltage of the full-wave rectifier circuit 12. FIG. The first LED block 410 of the start circuit 401 has six, the second LED block 420 of the intermediate circuit 402 has six, the third LED block 430 of the intermediate circuit 403 has twelve, and the fourth LED block 440 of the intermediate circuit 404 has four. The fifth LED block 450 of the termination circuit 405 includes six LEDs, which are connected in series, and the total number of LEDs included in the LED drive circuit 7 is 36.

  For example, when the output voltage of the full-wave rectifier circuit 12 is 0 (zero) at time T0, none of the LEDs included in the first LED block 410 to the fifth LED block 450 is lit.

  Since six LEDs are connected in series to each of the first LED block 410, the second LED block 420, the fourth LED block 440, and the fifth LED block 450, for example, at time T1, the full-wave rectifier circuit 12 A voltage of about the first forward voltage V1 (6 × Vf = 6 × 3.2 = 19.2 (v)) is applied to each of the first LED block 410, the second LED block 420, the fourth LED block 440, and the fifth LED block 450. When applied, the LEDs included in each of the first LED block 410, the second LED block 420, the fourth LED block 440, and the fifth LED block 450 are turned on (see FIG. 19A).

  Next, for example, at time T <b> 2, a voltage of about the second forward voltage V <b> 2 ((6 + 6) × 3.2 = 38.4 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 410. When applied to the second LED block 420 connected in series, the third LED block 430, and the fourth LED block 440 and the fifth LED block 450 connected in series, the LEDs included in each LED block Lights up (see FIG. 19B).

  Next, for example, at time T <b> 3, a voltage of about the third forward voltage V <b> 3 ((6 + 6 + 12) × 3.2 = 76.8 (v)) from the full-wave rectifier circuit 12 is applied to the first LED block 410, When applied to the second LED block 420 and the third LED block 430 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 19C). At the third forward voltage V3 or higher, the current monitor 471 turns off the current control unit 472 and cuts off the current passing through the current control unit 472.

  Here, even if the third forward voltage V3 is applied from the full-wave rectifier circuit 12 to the fourth LED block 440 and the fifth LED block 450 connected in series, the LEDs included therein can be turned on. It is. However, when the third forward voltage V3 turns on the LEDs included in the fourth LED block 440 and the fifth LED block 450, as described in FIGS. 4B and 4D, the 4-1 current A power loss in the limiting unit 442 occurs. Therefore, in the LED drive circuit 7, the current monitor 471 and the current control unit 472 operate to control the current not to flow through the fourth LED block 440 and the fifth LED block 450.

  Next, for example, at time T <b> 4, a voltage of about the fourth forward voltage V <b> 4 ((6 + 6 + 12 + 6) × 3.2 = 96.0 (v)) is output from the full-wave rectifier circuit 12 to the first LED block 410, When applied to the second LED block 420, the third LED block 430, and the fourth LED block 440 connected in series, the LEDs included in the respective LED blocks are lit (see FIG. 19D). When the fourth forward voltage V4 is approached, the diode 483 has been reversely biased until then, but the forward bias is applied and current starts to flow through the fourth LED block 440. However, since the output voltage of the output full wave rectifier circuit 12 is not sufficiently high, no current flows to the fifth LED block 450.

  Here, even if the fourth forward voltage V4 is applied from the full-wave rectifier circuit 12 to the fifth LED block 450, it is possible to light the LED included therein. However, when the fourth forward voltage V4 turns on the LEDs included in the fifth LED block 450, a power loss occurs in the current limiting unit 452, as described with reference to FIGS. 4B and 4D. End up. Therefore, in the LED drive circuit 7, the current monitor 471 and the current control unit 472 operate to control the current not to flow through the fifth LED block 450.

  Next, for example, at time T <b> 5, a voltage of about the fifth forward voltage V <b> 5 ((6 + 6 + 12 + 6 + 6) × 3.2 = 15.2 (v)) from the full-wave rectifier circuit 12 is the first LED block 410 to the second LED. When the 5 LED blocks 450 are applied to the ones connected in series, the LEDs included in the respective LED blocks are turned on (see FIG. 19E). When the fifth forward voltage V5 is approached, the diode 484 has been reversely biased so far, but the forward bias is applied and current starts to flow through the fifth LED block 450. However, at the third forward voltage V3 or higher, the current monitor 471 turns off the current control unit 472 and cuts off the current passing through the current control unit 472.

  In the LED drive circuit 7 shown in FIG. 18, each LED block is lit while repeating the states of FIGS. 19A to 19E in accordance with the output voltage of the full-wave rectifier circuit 12. As described above, in the LED drive circuit 7, the current monitor 471 and the current control unit 472 prevent the occurrence of a non-uniform state and power loss.

  FIG. 20 is a diagram illustrating the input power, power consumption, and power loss of the LED drive circuit 7.

  In FIG. 20, the solid line 491 indicates the input power in the LED drive circuit 7, the dotted line 492 indicates the power consumption in the LED drive circuit 7, and the alternate long and short dash line 493 indicates the power loss in the LED drive circuit 7. From FIG. 20, the conversion efficiency in the LED drive circuit 7 shown in FIG. 18 is 81.9 (%). Thus, in the LED drive circuit 7, the third LED block 430 and / or the fifth LED block 450 are extinguished at a predetermined timing by the current monitor 471 and the current control unit 472, so that power loss is suppressed, and the LED drive circuit It became possible to increase the conversion efficiency.

  In the above description, the LED driving circuits 1 to 6 having the start end circuit and the end circuit, and a plurality of intermediate circuits, and LED blocks including different numbers of LEDs in each circuit have been described. However, the number of intermediate circuits and the number of LEDs included in each circuit are merely examples, and are not limited to the LED driving circuits 1 to 6 described above.

  The LED drive circuits 1 to 6 described above can be used for LED lighting fixtures such as LED bulbs, liquid crystal televisions using LEDs as backlights, lighting fixtures for backlights of PC screens, and the like.

1, 2, 3, 4, 5, 6, 7 LED drive circuit 11 Connection terminal 12 Full-wave rectifier circuit 13 Positive power supply 14 Negative power supply 15, 16, 18 Reverse current prevention diode 17, 70 Constant current diode 20 Start circuit 21 1st LED block 22 1st current monitor 23 1st current control part 30 intermediate circuit 31 2nd LED block 32 2nd-1 current monitor 33 2nd-1 current control part 34 2nd-2 current monitor 35 2nd-2 current control Unit 36 Second-3 Current Monitor 40 Termination Circuit 41 Third LED Block 42 Third Current Monitor 43 Third-1 Current Control Unit 44 Third 3-2 Current Control Unit

Claims (8)

A rectifier,
A first LED group connected to the rectifier;
A second LED group connected to the rectifier;
A third LED group connected to the rectifier;
A detection unit for detecting a current flowing through the two consecutive LED groups when the two consecutive LED groups of the first LED group, the second LED group, and the third LED group are connected in series;
Based on the detection result of the detection unit, a current limiting unit that limits current flowing from the rectifier to the remaining LED groups of the first LED group, the second LED group, and the third LED group;
An LED driving circuit comprising:   The current limiting unit is configured to reduce a current flowing to the remaining LED groups of the first LED group, the second LED group, and the third LED group so that LED groups having different impedances are not connected in parallel to the rectifier. The LED driving circuit according to claim 1, wherein the LED driving circuit is limited.   Depending on the output voltage of the rectifier, the first LED group, the second LED group, and the third LED group are respectively connected in parallel to the rectifier, and the first LED group, The LED drive circuit according to claim 1 or 2, wherein a current path is formed in which two consecutive LED groups of the second LED group and the third LED group are connected in series. The rectifier has a positive power output and a negative power output,
A first current detecting unit for detecting a current flowing through the first LED group; and a first current for controlling a current flowing from the first LED group to the negative power source output according to the current detected by the first current detecting unit. A first circuit having a control unit;
The second LED group, a second current detection unit that detects a current flowing through the second LED group, and a current that flows from the positive power output to the second LED group according to the current detected by the second current detection unit. A second circuit having a second current control unit and a third current control unit for controlling a current flowing from the second LED group to the negative power source according to the current detected by the second current detection unit;
The third LED group, a third current detection unit for detecting a current flowing through the third LED group, and a current flowing from the positive power supply output to the third LED group according to the current detected by the third current detection unit A third circuit having a fourth current control unit,
The LED drive circuit according to claim 1, further comprising:   The LED drive circuit according to any one of claims 1 to 4, further comprising a current adjustment unit disposed between the first LED group, the second LED group, and the third LED group.   The LED driving circuit according to claim 5, wherein the current adjustment unit is a constant current diode, a high resistance, or a constant current circuit.   The LED drive circuit according to any one of claims 1 to 6, further comprising a reverse current prevention diode disposed between the first LED group, the second LED group, and the third LED group.   The LED drive circuit according to any one of claims 1 to 7, further comprising a smoothing unit disposed between power supply outputs of the rectifiers.

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