JP5441745B2 - LED drive circuit - Google Patents

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, 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.

  In addition, the switching timing of the switch circuit is set based on an expected n × Vf (v), but since Vf is not constant for each LED, the actual n × Vf (v) of each LED block is preset. 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.

  Another object of the present invention is 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.

  An LED driving circuit according to the present invention includes a rectifier having a positive power output and a negative power output, a first LED group, a first current detection unit and a first current detection unit that are connected to the rectifier and detect a current flowing through the first LED group. A first circuit having a first current control unit for controlling a current flowing from the first LED group to the negative power source output according to the current detected in step, and a current flowing through the second LED group and the second LED group connected to the rectifier. And a second circuit having a second current control unit for controlling a current flowing from the positive power supply output to the second LED group in accordance with the current detected by the second current detection unit and the output of the rectifier Depending on the voltage, the first LED group and the second LED group are connected in parallel to the rectifier, and the first LED group and the second LED group are connected in series to the rectifier. Characterized in that a current path is formed to be.

In the LED drive circuit according to the present invention, since the current path is switched according to the output voltage of the full-wave rectifier circuit 12, it is not necessary to provide a large number of switch circuits.
Further, in the LED drive 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 the 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 which concerns on this invention. It is a figure which shows the circuit example 100 of the LED drive circuit shown in FIG. It is a figure which shows the output voltage waveform example of the full wave rectifier circuit 12. FIG. 6 is a diagram showing an example of a switching sequence of LED blocks in a circuit example 100. FIG. It is a figure for demonstrating the operation | movement shown in FIG. It is a schematic block diagram of the other LED drive circuit which concerns on this invention. It is a schematic block diagram of the further another LED drive circuit which concerns on this invention. It is a figure which shows the output voltage waveform example of the full wave rectifier circuit 12. FIG. FIG. 3A is a diagram (1) illustrating an example of a switching sequence of LED blocks of an LED drive circuit 3; FIG. 6B is a diagram (2) illustrating an example of a switching sequence of LED blocks of the LED drive circuit 3; It is a figure for demonstrating the development form of this invention. It is a schematic block diagram of the further another LED drive circuit which concerns on this invention.

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

  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 21 including a plurality of LEDs, a first current monitor 22 for detecting a current flowing through the first LED block 21, a first current control unit 23, and the like. The first current monitor 22 operates to limit the current flowing through the first current control unit 23 according to the current flowing through the first LED block 21.

  The intermediate circuit 30 includes a second LED block 31 including 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, and a 2-1 current control unit. 33 and the 2-2 current control part 35 etc. are included. The 2-1 current monitor 32 performs control so as to adjust the current flowing through the 2-1 current control unit 33 in accordance with the current flowing through the second LED block 31, and the 2-2 current monitor 34 is controlled by the second LED block. It operates so as to limit the current flowing through the second-second current control unit 35 according to the current flowing through 31.

  The termination circuit 40 includes a third LED block 41 including a plurality of LEDs, a third current monitor 42 for detecting a current flowing through the third LED block 41, a third current control unit 43, and the like. The third current monitor 42 operates to limit the current flowing through the third current control unit 43 according to the current flowing through the third LED block 41.

  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 end circuit 20 is configured to include ten 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 third LED block 41 of the termination circuit 40 includes 14 LEDs connected in series. The third current monitor 42 includes two resistors R7 and R8 and a transistor Q4, and the third current control unit 43 includes M4 that is an N-type MOSFET. The operations of the third current monitor 42 and the third current control unit 43 are the same as those of the 2-1 current monitor 32 and the 2-1 current control unit 33.

  In the circuit example 100, since ten LEDs are connected in series in the first LED block 21, the voltage is about the first forward voltage V1 (10 × Vf = 10 × 3.2 = 32.0 (v)). Is applied to the first LED block 21, the LEDs included in the first LED block 21 are turned on. Further, since 12 LEDs are connected in series in the second LED block 31, a voltage of about the second forward voltage V2 (12 × Vf = 12 × 3.2 = 38.4 (v)) is applied to the second LED. When applied to the block 31, the LEDs included in the second LED block 31 are lit. Furthermore, since 14 LEDs are connected in series in the third LED block 41, a voltage of about the third forward voltage V3 (14 × Vf = 14 × 3.2 = 44.8 (v)) is applied to the third LED. When applied to the block 41, the LEDs included in the third LED block 41 are lit.

  Similarly, when a voltage of about the fourth forward voltage V4 ((10 + 12) × 3.2 = 70.4 (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, a voltage of about the fifth forward voltage V6 ((10 + 12 + 14) × 3.2 = 15.2 (v)) is obtained by connecting the first LED block 21, the second LED block 31, and the third LED block 41 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 showing an output voltage waveform example 50 of the full-wave rectifier circuit 12, FIG. 4 is a diagram showing an example of a switching sequence of LED blocks in the circuit example 100, and FIG. 5 is a partial extract of FIG. FIG.

  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), when the output voltage of the full-wave rectifier circuit 12 becomes the first forward voltage V1 and becomes a voltage sufficient to light the first LED block 21, the current path through the first LED block 21 is The formed LED included in the first LED block 21 is turned on (see FIG. 4A). As described above, since there is a solid difference in Vf of each LED included in the first LED block 21, the first forward voltage V1 (32.0 (v)) is actually started to light. Whether or not depends on the actual circuit. However, when the voltage obtained by adding Vf of the 10 LEDs included in the first LED block is applied, the 10 LEDs included in the first LED block start lighting. Even if the output voltage of the full-wave rectifier circuit 12 further increases, the first LED block 21 is driven with a constant current. Therefore, the forward voltage of the first LED block 21 is the sum of Vf of LEDs (ie, V1). It remains. The same applies to the second forward voltage V2 to the fifth forward voltage V5.

  At time T2 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 becomes the second forward voltage V2 and becomes a voltage sufficient to turn on the second LED block 31, the first LED block 21 and the second LED block 31. However, a current path connected in parallel to the output of the full-wave rectifier circuit 12 is formed, and the LEDs included in the first LED block 21 and the second LED block 31 are lit (see FIG. 4B).

Next, the transition from FIG. 4A to FIG. 4B will be described.
The first LED block 21, the second LED block 31, and the third LED block 41 are respectively connected in parallel to the full-wave rectifier circuit 12, and the first LED block 21, the second LED block 31, and the third LED block 41 are mutually connected. Also connected between the diodes 15 and 16 for preventing reverse current.

  At time T1 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 is the first forward voltage V1, and a voltage for lighting the LEDs included in the first LED block 21 is applied. The forward voltages V2 and V3 for lighting the 2LED block 31 and the third LED block 41 are not applied. Therefore, the current I1 flows from the positive power supply output of the full-wave rectifier circuit 12 to the first LED block 21 as the current I2, and flows into the negative power supply output of the full-wave rectifier circuit 12 as the current I2. However, the current I4 and the current I8 are not flowing. In this case, since the diode 15 is reverse-biased, the current I3 does not flow.

  Here, the first current monitor 22 detects the current I1 flowing through the first LED block 21, and controls the first current control unit 23 so that I2 becomes a predetermined current. Here, the set current of the current I2 set by the first current monitor 22 is S2. When the power supply current is supplied, a voltage is applied to the gate of the MOSFET M1 by the bias resistor R2 of the first current monitor 22, and the MOSFET M1 is turned on. The same current I1 also flows through the monitor resistor R1 of the first current monitor 22.

  At this time, when the current I1 flowing through the monitor resistor R1 increases from a predetermined current, the base voltage of the transistor Q1 exceeds the threshold voltage, and the transistor Q1 is turned on. Then, the gate voltage of the MOSFET M1 of the current control unit 23 is pulled to a high potential, the impedance of the MOSFET M1 is increased, and the current flowing through the first LED block 21 is reduced.

  On the contrary, when the current I1 flowing through the first LED block 21 decreases, the impedance of the MOSFET M1 decreases, and the current I1 flowing through the first LED block 21 increases. By repeating this, the current I1 flowing through the first LED block 21 is controlled to be a constant current. In other words, the first current monitor 22 adjusts the impedance of the first current control unit 23 to adjust the current so that the current flowing through the first LED block 21 does not exceed a predetermined value. In this state, I1 = I2.

  From time T1 to time T2 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 becomes the second forward voltage V2, and the voltage for lighting the LEDs included in the first LED block 21 and the second LED block 31 is The applied voltage is less than the voltage for lighting the third LED block 41. Therefore, the current I1 flows through the first LED block 21 and the current I4 flows through the second LED block 31, but the current I8 does not flow. In addition, since the diodes 15 and 16 are reversely biased, the current I2 and the current I7 do not flow.

  Here, the 2-1 current monitor 32 detects the current flowing through the second LED block 31 and controls the 2-1 current control unit 33 to control the current I4 to be a predetermined current. The 2-2 current monitor 34 has a circuit configuration capable of detecting the current flowing through the second LED block 31 and controlling the 2-2 current control unit 35 so that the current I6 becomes a predetermined current. In this state, I4 = I5 = I6.

  In this way, the state of FIG. 4A is shifted to the state of FIG. When the output voltage of the full-wave rectifier circuit 12 becomes the third forward voltage V3 at time T3 (see FIG. 3) (time T3), the state shown in FIG. The transition to the state is the same as above.

Next, the transition from FIG. 4C to FIG. 4D will be described.
At time T4 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 becomes the fourth forward voltage V4, and even when the first LED block 21 and the second LED block 31 are connected in series, all the LEDs included in them. When the voltage is sufficient to light the LED, 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. 4D). reference).

  In the state of FIG. 4C, I1 = I2, I4 = I5 = I6, and I8 = I9, and a reverse voltage is applied to the diodes 15 and 16, so the currents I3 and I7 do not flow. . Here, if the set current of the current I4 set by the 2-1 current monitor 32 is S4 and the set current of the current I6 set by the 2-2 current monitor 34 is S6, S4 <S6 is set. It is. Therefore, it is the 2-1 current control unit 33 that controls the flowing current, and the impedance of the 2-2 current control unit 35 is in a very low state.

  When the output voltage of the full-wave rectifier circuit 12 rises from the third forward voltage V3 to the fourth forward voltage V4, the first current monitor 22 controls the first current control unit 23 to limit the current I3. Yes. At this time, 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 is performed so that the impedance of the control unit 23 is high.

  As described above, in the transition state from FIG. 4C to FIG. 4D, 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 was applied to the diode 15 until then, the forward bias is applied and the current I3 starts to flow. Then, the impedance of the first current control unit 23 is increased so that the current I2 is reduced.

  The 2-1 current monitor 32 adds the current I3 to the current I4 that has been monitored so far, so that the 2-1 current control unit 33 reduces the current I4, that is, the 2-1 The impedance of the current control unit 33 is limited to be high. Accordingly, the currents I2 and I4 gradually decrease, and finally the currents I2 and I4 become almost zero, resulting in a state of I1 = I3 = I5 = I6 (the state of FIG. 4D). At this time, the first current control unit 23 and the 2-1 current control unit 33 have high impedance. Then, the 2-2 current monitor 34 controls the impedance of the 2-2 current control unit 35 and causes the current to flow at the set current S6 of the current I6.

Next, the transition from FIG. 4D to FIG. 4E will be described.
At time T5 (see FIG. 3), the output voltage of the full-wave rectifier circuit 12 becomes the fifth forward voltage V5, and even when the first LED block 21, the second LED block 31, and the third LED block 41 are connected in series, When the voltage is sufficient to light all the included LEDs, the first LED block 21, the second LED block 31, and the third LED block 41 are connected to the full-wave rectifier circuit 12 in series. The route is switched (see FIG. 4E).

  The third current monitor 42 controls the impedance of the third current control unit 43. And the voltage drop of the 3rd current control part 43 is also increasing gradually. The diode 16 has been reversely biased until then, but is now forward-biased and the current I7 begins to flow to the termination circuit 40.

  When the output voltage of the full-wave rectifier circuit 12 rises from the fourth forward voltage V4 to the fifth forward voltage V5, the 2-2 current monitor 34 adjusts the impedance of the 2-2 current control unit 35, Control is performed to limit the current I6. At this time, the voltage drop of the 2-2 current control unit 35 gradually increases. Since the current I7 is added to the current I8 that has been monitored so far, the third current monitor 42 increases the impedance of the third current control unit 43 and controls the current I8 to decrease. 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 I6. Therefore, the currents I6 and I8 gradually decrease, and finally the currents I6 and I8 become almost zero, resulting in a state of I1 = I3 = I5 = I7 = I9 (the state of FIG. 4E).

  In the state of FIG. 4E, if I1 = I3 = I5 = I7 = I9 and the set current of the constant current diode 17 is S7, the current in this state is S7. In this state, the currents I2, I4, I6 and I8 hardly flow. As described above, in order to prevent almost any current from flowing, the set current S7 of the constant current diode 17 is set in advance so as to be larger than the other set currents S2, S4, S6 and S8.

Next, the transition from FIG. 4E to FIG. 4F will be described.
When the output voltage of the full-wave rectifier circuit 12 drops below the fifth forward voltage V5 at time T6 (see FIG. 3), the 2-2 current monitor 34 Control to loosen the limit. Then, the current I6 begins to flow gradually, and the current I7 decreases. Since the current I9 decreases when the current I7 decreases, the third current monitor 42 controls the third current control unit 43 to loosen the limit of the current I8. Then, the current I8 begins to flow gradually, and the state shown in FIG. 4 (e) is shifted to the state shown in FIG. 4 (f). Here, as described above, since the relationship of S6 <S2 is set in advance, the second LED block 31 and the third LED block 41 are connected by the series relationship of the first LED block 21 and the second LED block 31. Will be cut first.

Next, the transition from FIG. 4 (f) to FIG. 4 (g) will be described.
At time T7 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 is less than the fourth forward voltage V4, all of them included in the first LED block 21 and the second LED block 31 connected in series. Since the voltage is less than a voltage sufficient to light the LED, currents I2 and I4 start to flow, and the state shifts to the state shown in FIG.

Next, the transition from FIG. 4G to FIG. 4H will be described.
At time T8 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 becomes equal to or lower than the third forward voltage V3, it becomes equal to or lower than a voltage sufficient to light all the LEDs included in the third LED block 41. , Currents I7, I8 and I9 stop flowing, and the state shifts to the state shown in FIG.

Next, the transition from FIG. 4 (h) to FIG. 4 (i) will be described.
At time T9 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 becomes less than the second forward voltage V2, it becomes less than a voltage sufficient to light all the LEDs included in the second LED block 31. Further, the currents I3 to I9 no longer flow, and the state shifts to the state of FIG.

  At time T10 (see FIG. 3), when the output voltage of the full-wave rectifier circuit 12 becomes less than the first forward voltage V1, it becomes less than a voltage sufficient to light all the LEDs included in the first LED block 21. All the currents I1 to I9 do not flow. Thereafter, the LEDs of the first LED block 21, the second LED block 31, and the third LED block 41 are turned on while repeating the state from time T0 to time T11 (which corresponds to the time T0 of the next cycle).

  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. In addition, the reverse current prevention diode 14 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.

  In particular, 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 in the situation of FIG. As can be understood from FIGS. 4A to 4I, since any current control unit exists in the current path except for the state of FIG. 4E, each LED block has an overcurrent. Can be prevented from flowing. However, in the state of FIG. 4 (e), the current control unit does not exist in the current path, and therefore the constant current diode 17 is inserted. The place where the constant current diode 17 is inserted is not limited between the start circuit 20 and the intermediate circuit 30, and may be another place as long as it is in the current path in the state of FIG. Further, constant current diodes may be arranged at a plurality of locations in the current path in the state of FIG. In the situation of FIG. 4 (e), if it is possible to prevent an overcurrent from flowing through the first LED block 21, the second LED block 31, and the third LED block 41, a constant current circuit or a current adjustment circuit such as a 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.

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

  The difference between the LED drive circuit 2 shown in FIG. 6 and the LED drive circuit 1 shown in FIG. 1 is 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 output voltage waveform 50 of the LED drive circuit 1 shown in FIG. 1, since the time between time T0 to time T1 and time T10 to time T11 is 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. Become.

  On the other hand, in the LED drive circuit 2 shown in FIG. 6, 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 third forward voltage V3. 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 first forward voltage V1. Thus, the LED drive circuit 2 shown in FIG. 6 can prevent the LED from blinking.

  In the example of FIG. 6, the electrolytic capacitor 60 is added. However, 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. 7 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. 7, the same components as those of the LED drive circuit 1 shown in FIG. The difference between the LED drive circuit 3 shown in FIG. 7 and the LED drive circuit 1 shown in FIG. 1 is that the second intermediate between the intermediate circuit 30 (hereinafter referred to as “first intermediate circuit 30”) and the termination circuit 40. Only the point where the circuit 50 is inserted and the reverse current preventing diode 18 and the constant current diode 19 are arranged between the first intermediate circuit 30 and the second intermediate circuit 50.

  The second intermediate circuit 50 includes a fourth LED block 51 including a plurality of LEDs, a 4-1 current monitor 52 and a 4-2 current monitor 54 for detecting a current flowing through the fourth LED block 51, and a 4-1 A current control unit 53, a 2-2 current control unit 55, and the like are included. The 4-1 current monitor 52 operates to limit the current flowing through the 4-1 current control unit 53 according to the current flowing through the fourth LED block 51, and the 4-2 current monitor 54 is connected to the fourth LED block 51. It operates so as to limit the current flowing through the 5-2 current controller 35 in accordance with the current flowing through 51. Note that the specific circuit configuration of the second intermediate circuit 50 can be the same as that of the first intermediate circuit 30 shown in FIG.

  Also in the LED driving circuit 3, the total number (n) × Vf when all the LEDs included in the first LED block 21 to the fourth LED block 51 are connected in series is higher than 80% of the instantaneous maximum voltage. The total number of LEDs connected in series was 39 (39 × 3.2 = 12.8). In the following, the number of LEDs included in the first LED block 21 is 8, the number of LEDs included in the second LED block 31 is 12, the number of LEDs included in the third LED block 41 is 12, and the fourth LED block is included. The operation of the LED drive circuit 3 will be described based on a circuit example in which the number of LEDs included in 51 is 10.

  In this case, since eight LEDs are connected in series to the first LED block 21, a voltage of about the first forward voltage V1 (8 × 3.2 = 25.6 (v)) is applied to the first LED block 21. When applied, the LEDs included in the first LED block 21 are lit. Since the second LED block 21 has nine LEDs connected in series, a voltage of the second forward voltage V2 (9 × 3.2 = 28.8 (v)) is applied to the second LED block 31. Then, the LEDs included in the second LED block 31 are turned on. Furthermore, since ten LEDs are connected in series in the fourth LED block 51, a voltage of about the third forward voltage V3 (10 × 3.2 = 32.0 (v)) is applied to the fourth LED block 51. Then, the LEDs included in the fourth LED block 51 are turned on. Furthermore, since 12 LEDs are connected in series to the third LED block 41, a voltage of about the fourth forward voltage V4 (12 × 3.2 = 38.4 (v)) is applied to the third LED block 41. Then, the LEDs included in the third LED block 41 are turned on.

  Similarly, when a voltage of about the fifth forward voltage V5 ((8 + 9) × 3.2 = 54.4 (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. When a voltage of about the sixth forward voltage V6 ((10 + 12) × 3.2 = 70.4 (v)) is applied to the third LED block 41 and the fourth LED block 51 connected in series, The LEDs included in the third LED block 41 and the fourth LED block 51 are lit. Furthermore, when a voltage of about the seventh forward voltage V7 ((8 + 9 + 10 + 12) × 3.2 = 12.8 (v)) is applied to the first LED block 21 to the fourth LED block 51 connected in series, The LEDs included in the first LED block 21 to the fourth LED block 51 are lit.

  Hereinafter, the operation of the LED drive circuit 3 will be described with reference to FIGS. FIG. 8 is a diagram showing an output voltage waveform example 50 of the full-wave rectifier circuit 12, and FIGS.

  At time T0 (see FIG. 8), when the output voltage of the full-wave rectifier circuit 12 is 0 (v), the voltage for turning on any LED block of the first LED block 21 to the fourth LED block 51 has not been reached. The LEDs included in all the LED blocks are not lit.

  At time T1 (see FIG. 8), when the output voltage of the full-wave rectifier circuit 12 becomes the first forward voltage V1 and becomes a voltage sufficient to light the first LED block 21, the LEDs included in the first LED block 21 are Lights up (see FIG. 9A). As described above, since there is a solid difference in Vf of each LED included in the first LED block 21, it is the first forward voltage V1 (25.6 (v)) that actually starts lighting. Whether or not depends on the actual circuit. However, when the voltage obtained by adding up Vf of the eight LEDs included in the first LED block is applied, the eight LEDs included in the first LED block start to light. The same applies to the second forward voltage V2 to the seventh forward voltage V7.

  At time T2 (see FIG. 8), when the output voltage of the full-wave rectifier circuit 12 becomes the second forward voltage V2 and becomes a voltage sufficient to turn on the second LED block 31, the first LED block 21 and the second LED block 31. The LED included in is turned on (see FIG. 9B). At this time, a current path in which the first LED block 21 and the second LED block 31 are connected in parallel to the full-wave rectifier circuit 12 is formed.

  At time T3, when the output voltage of the full-wave rectifier circuit 12 becomes the third forward voltage V3 and becomes a voltage sufficient to turn on the fourth LED block 51, the first LED block 21, the second LED block 31, and the fourth LED block 51. The LED included in is turned on (see FIG. 9C). At this time, a current path is formed in which the first LED block 21, the second LED block 31, and the fourth LED block 51 are connected in parallel to the full-wave rectifier circuit 12.

  At time T4, when the output voltage of the full-wave rectifier circuit 12 becomes the fourth forward voltage V4 and becomes a voltage sufficient to light the third LED block 41, the LEDs included in the first LED block 21 to the fourth LED block 51 are displayed. The lighting is continued by changing the current path (see FIG. 9D). At this time, a current path in which the first LED block 21 to the fourth LED block 51 are connected in parallel to the full-wave rectifier circuit 12 is formed.

  At time T5, when the output voltage of the full-wave rectifier circuit 12 becomes the fifth forward voltage V5 and becomes a voltage sufficient to light up the first LED block 21 and the second LED block 31 connected in series, the first LED block The LEDs included in the 21st to 4th LED blocks 51 change the current path and continue to light (see FIG. 9E). At this time, the first LED block 21 and the second LED block 31 are connected in series to the full-wave rectifier circuit 12, and the current path, and the fourth LED block 51 and the third LED block 41 are connected in parallel to the full-wave rectifier circuit 12. Current paths are formed.

  At time T6, when the output voltage of the full-wave rectifier circuit 12 becomes the sixth forward voltage V6 and becomes a voltage sufficient to turn on the third LED block 41 and the fourth LED block 51 connected in series, the first LED block The LEDs included in the 21st to 4th LED blocks 51 change the current path and continue to light (see FIG. 9F). At this time, the first LED block 21 and the second LED block 31 are connected in series to the full-wave rectifier circuit 12, and the current path, and the third LED block 41 and the fourth LED block 51 are connected in series to the full-wave rectifier circuit 12. Current paths are formed.

  At time T7, when the output voltage of the full-wave rectifier circuit 12 becomes equal to or higher than the seventh forward voltage V7 and becomes a voltage sufficient to turn on the first LED block 21 to the fourth LED block 51 connected in series, the first LED The LEDs included in the block 21 to the fourth LED block 51 change the current path and continue to light (see FIG. 9G). At this time, a current path in which the first LED block 21 to the fourth LED block 51 are connected in series to the full-wave rectifier circuit 12 is formed.

  When the output voltage of the full-wave rectifier circuit 12 becomes less than the seventh forward voltage V7 at time T8, the LEDs included in the first LED block 21 to the fourth LED block 51 change their current paths and continue to light (FIG. 10 ( a)). At this time, the first LED block 21 and the second LED block 31 are connected in series to the full-wave rectifier circuit 12, and the current path, and the third LED block 41 and the fourth LED block 51 are connected in series to the full-wave rectifier circuit 12. Current paths are formed.

  When the output voltage of the full-wave rectifier circuit 12 becomes less than the sixth forward voltage V6 at time T9, the LEDs included in the first LED block 21 to the fourth LED block 51 change their current paths and continue to light (FIG. 10 ( b)). At this time, a current path in which the first LED block 21 and the second LED block 31 are connected in series, the fourth LED block 51, and the third LED block 41 are connected in parallel to the full-wave rectifier circuit 12. Is formed.

  When the output voltage of the full-wave rectifier circuit 12 becomes less than the fifth forward voltage V5 at time T10, the LEDs included in the first LED block 21 to the fourth LED block 51 change their current paths and continue to light (FIG. 10 ( c)). At this time, a current path in which the first LED block 21 to the fourth LED block 51 are connected in parallel to the full-wave rectifier circuit 12 is formed.

  At time T11, when the output voltage of the full-wave rectifier circuit 12 becomes less than the fourth forward voltage V4, the third LED block 41 is turned off, and the first LED block 21, the second LED block 31, and the fourth LED block 51 are continuously turned on. (See FIG. 10D). At this time, a current path is formed in which the first LED block 21, the second LED block 31, and the fourth LED block 51 are connected in parallel to the full-wave rectifier circuit 12.

  At time T12 (see FIG. 8), when the output voltage of the full-wave rectifier circuit 12 becomes less than the third forward voltage V3, the fourth LED block 51 is turned off, and the first LED block 21 and the second LED block 31 are kept on. (See FIG. 10E). At this time, a current path in which the first LED block 21 and the second LED block 31 are connected in parallel to the full-wave rectifier circuit 12 is formed.

  When the output voltage of the full-wave rectifier circuit 12 becomes less than the second forward voltage V2 at time T13, the second LED block 31 is turned off and the first LED block 21 is continuously turned on (see FIG. 10 (f)). At this time, a current path is formed so that the first LED block is connected to the full-wave rectifier circuit 12. Further, at time T14, when the output voltage of the full-wave rectifier circuit 12 becomes less than the first forward voltage V1, all the LEDs are not turned on.

  The reverse current prevention diode 15 prevents the current included in the first LED block 21 from being damaged due to an accidental flow of current from the first intermediate circuit 30 to the start circuit 20 side. Further, the reverse current prevention diode 18 prevents a current from flowing from the second intermediate circuit 50 to the first intermediate circuit 30 side accidentally, thereby preventing the LED included in the second LED block 31 from being damaged. . Further, the reverse current preventing diode 16 prevents the current included in the fourth LED block 51 from being damaged due to the accidental flow of current from the termination circuit 40 to the second intermediate circuit 50 side. The current control units included in the start circuit 20, the first intermediate circuit 30, the second intermediate circuit 50, 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, 16 and 18, the current starts to flow gradually and the current path is switched as described above.

  The constant current diode 19 prevents an overcurrent from flowing through the first LED block 21 to the fourth LED block 51 particularly in the situation of FIG. As can be understood by looking at FIGS. 9A to 9G and FIGS. 10A to 10F, any current control unit is in the current path except for the state of FIG. 9G. Therefore, it is possible to prevent an overcurrent from flowing through each LED block. However, in the state of FIG. 9 (g), since the current control unit does not exist in the current path, the constant current diode 19 is inserted. The place where the constant current diode 19 is inserted is not limited between the first intermediate circuit 20 and the second intermediate circuit 50, and if it is in the current path in the state of FIG. Other locations may be used. Further, constant current diodes may be arranged at a plurality of locations in the current path in the state of FIG. In addition, as long as it can prevent an overcurrent flowing into the 1st LED block 21-the 4th LED block 51 in the condition of FIG.9 (g), you may comprise with another electric current adjustment element, for example, junction type FET. . In addition, a current control circuit including a resistor and a bipolar transistor using a start circuit 20, a first intermediate circuit 30, a second intermediate circuit 50, and a termination circuit 40, and a current control circuit including a MOSFET are used as current adjustment elements. It can also be used.

  As described above, the LED drive circuit 3 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. Even if the power supply voltage of the commercial power supply is different, the number of LEDs in each LED block may be adjusted accordingly, and the circuit itself does not need to be changed.

  Also in the LED drive circuit 3 shown in FIG. 7, as shown in FIG. 6, an element or a circuit for smoothing the output of the electrolytic capacitor 60 or the like may be arranged between the output terminals of the full-wave rectifier circuit 12. good. Further, for convenience of explanation, in the above example, the number of LEDs in each LED block in series is changed for each LED block, but the number of LEDs in all LED blocks or some LED blocks may be the same. . If the number of LEDs in all LED blocks or some of the LED blocks is set to the same number, it is convenient for manufacturing and may lead to cost reduction. Further, in the above example, in each LED block, all LEDs are connected in series, but in the block, a plurality of LEDs connected in series are connected in parallel in two circuits, three circuits, and a plurality of circuits. Also good.

  FIG. 11 is a diagram for explaining a development of the present invention.

  The case where there is one intermediate circuit (the LED drive circuit 1 shown in FIG. 1) and the case where there are two intermediate circuits (the LED drive circuit 3 shown in FIG. 7) have been described above. However, the LED drive circuit according to the present invention is also applicable when there are N intermediate circuits. That is, as shown in FIG. 11, a plurality of intermediate circuits can be provided as appropriate between the start circuit 20 and the termination circuit 40. It should be noted that FIG. 11 does not show all circuit configurations for convenience of explanation.

  In the example of FIG. 11, one constant current diode 70 is arranged on the terminal circuit 40 side of the second intermediate circuit 50. However, the arrangement location and the number of the constant current diodes 70 are not limited to this, and there is a current path in which LED blocks included in all circuits are connected in series to the full-wave rectifier circuit 12. When formed (for example, see FIG. 9G), the constant current diodes 70 may be arranged at any one or a plurality of locations in such a path so that no overcurrent flows through each LED block. .

  As can be understood by comparing FIG. 3 and FIG. 8, the time from the time T0 to the time T1 (the time when the LED starts to light first) is shortened by reducing the number of LEDs included in the LED block. Can do. Therefore, by increasing the number of intermediate circuits and reducing the number of LEDs included in one intermediate circuit, it is possible to further increase the LED driving efficiency. In particular, in the LED drive 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, even if there are many intermediate circuits, there is an advantage that switching between the LED blocks can be performed efficiently. Furthermore, when the number of LED blocks is increased and the forward voltage of the LEDs in the LED blocks is lowered, the power loss of the current control unit including the MOSFET can be reduced.

In addition, the drive efficiency of LED means the time ratio which all the LEDs drive with a rated current. In the case of the LED drive circuit 1 shown in FIG. 1, the LED drive efficiency (K (%)) can be expressed as follows with reference to FIG.
K = 100 * {V1 * (T10-T1) + V2 * (T9-T2) + V3} / {(V1 + V2 + V3) * (T11-T0)}

  For example, in the case of the LED driving circuit 1 shown in FIG. 1 including three LED blocks (the number of LEDs in the first LED block is 10, the number of LEDs in the second LED block is 12, and the number of LEDs in the third LED block is 14). In the case of the LED drive circuit 3 shown in FIG. 7 including four LED blocks (the number of LEDs in the first LED block is eight, the number of LEDs in the second LED block is 80.5%). The drive efficiency is 93.9% when the number of LEDs is 9, the number of LEDs of the fourth LED block is 10, and the number of LEDs of the third LED block is 12. The driving efficiency can also be increased by adjusting the number of LEDs and adjusting the distribution to each block. For example, the number of LEDs in the first LED block is nine and the number of LEDs in the second LED block is nine. When the number of LEDs in the fourth LED block is nine and the number of LEDs in the third LED block is nine, the driving efficiency is 86.0%.

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

  The LED driving circuit 4 shown in FIG. 12 includes only the start-end circuit 20, the termination circuit 40, and the reverse current prevention diode 15 that connects the start-end circuit 20 and the termination circuit 40, which are the minimum elements of the LED drive circuit according to the present invention. Is included. The feature of the LED drive circuit according to the present invention is that the first LED block 21 included in the start circuit 20 and the third LED block 41 included in the termination circuit 40 are arranged in a full-wave rectifier circuit according to the output voltage of the full-wave rectifier circuit 12. The current path (Ix and Iy) connected in parallel to 12 and the current path (Iz) connected in series to the full-wave rectifier circuit 12 are formed by automatically switching. . In addition, in this specification, when it is said that it is connected in parallel, it means that the main current path is formed so as to be connected in parallel, and the current path that is connected in series is very small. Including the case where current flows. Similarly, in this specification, when it is said that it is connected in series, it means that the main current path is formed to be connected in series, and the current path that is connected in parallel is very small. Including the case where a large current flows.

  The switching of the current path from parallel to serial is performed when the output voltage of the full-wave rectifier circuit 12 increases and the current Ia passing through the first LED block 21 increases, so that the impedance of the first current control unit 23 is high. The current Ib is limited by being controlled so that the forward bias is applied to the diode 15 which has been reversely biased until then, the current Ic which has not flowed until then starts to flow, and the current Ic flows. When started, the current Ie flowing through the third LED block 41 is increased, whereby the impedance of the third current control unit 43 is controlled to be high, and the current Id is limited.

  In the above description, the switching of the current path from parallel to series has been described using the LED driving circuit 4 including the start circuit 20 and the termination circuit 40. However, one or more intermediate points are provided between the start circuit 20 and the termination circuit 40. Even in an LED drive circuit including a circuit, switching of a current path between the circuits is performed based on the same principle as described above.

  The LED driving circuit described above can be used for LED lighting devices such as LED bulbs, liquid crystal televisions using LEDs as backlights, lighting devices for backlights of PC screens, and the like.

1, 2, 3, 4 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 First LED block 22 First Current Monitor 23 First Current Control Unit 30 (First) Intermediate Circuit 31 Second LED Block 32 2-1 Current Monitor 33 2-1 Current Control Unit 34 2-2 Current Monitor 35 2-2 Current Control Unit 40 Termination Circuit 41 Third LED Block 42 Third Current Monitor 43 Third Current Control Unit 50 Second Intermediate Circuit 51 Fourth LED Block 52 4-1 Current Monitor 53 4-1 Current Control Unit 54 4-2 Current Monitor 55 4-2 Current Control Unit

Claims (7)

A rectifier having a positive power output and a negative power output;
A first LED group connected to the rectifier, a first current detection unit for detecting a current flowing through the first LED group, and the negative power source from the first LED group according to a current detected by the first current detection unit; A first circuit having a first current control unit for controlling a current flowing to the output;
A second LED group connected to the rectifier, a second current detection unit for detecting a current flowing through the second LED group, and the second LED from the positive power output according to the current detected by the second current detection unit A second circuit having a second current control unit for controlling a current flowing through the group,
A current path in which the first LED group and the second LED group are connected in parallel to the rectifier according to an output voltage of the rectifier, and the first LED group and the second LED group are connected in series to the rectifier. A connected current path is formed,
An LED drive circuit characterized by that.   In accordance with the current detected by the third LED group, the third current detection unit, which is disposed between the first circuit and the second circuit, detects a current flowing into the third LED group, and the third current detection unit. The current detected by the fourth current detection unit, the third current control unit for controlling the current flowing from the positive power supply output to the third LED group, the fourth current detection unit for detecting the current flowing out from the third LED group, The LED drive circuit according to claim 1, further comprising an intermediate circuit having a fourth current control unit that controls a current flowing from the third LED group to the negative power supply output in response.   The LED driving circuit according to claim 2, wherein a plurality of the intermediate circuits are provided between the first circuit and the second circuit.   The LED drive circuit according to claim 1, further comprising a current adjustment unit disposed between the first circuit and the second circuit.   The LED drive circuit according to claim 4, 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 5, further comprising a diode for preventing reverse current to the LED group disposed between the first circuit and the second circuit.   The LED drive circuit according to claim 1, further comprising a smoothing unit disposed between the positive power supply output and the negative power supply output.

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