JP2012084668A - Led driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an LED driver configured so that a control unit performing the switching control of an LED block can be driven at low voltage and thereby the LED driver can be implemented easily on an IC.SOLUTION: The LED driver (2) comprises a rectifier (12) having a high side power supply output (13) and a low side power supply output (14), a voltage division unit (20) which divides the voltage between the high side power supply output and the low side power supply output, a first LED group (210) including a plurality of LEDs, a second LED group (220) including a plurality of LEDs, a connection which connects the first and second LED groups in series or parallel with the rectifier, comparison units (34, 44) which compare the voltage division output from the voltage division unit with a threshold, and control units (33, 43) which switch the first and second LED groups from parallel connection to series connection with the rectifier by controlling the connection according to the outputs from the comparison units.

Description

  The present invention relates to an LED driving device, and more particularly to an LED driving device for performing efficient LED light emission using a commercial power source.

  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. When a predetermined forward current (If) is passed through the LED to emit light with a predetermined luminous intensity, 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).

  When applying the rectified voltage output from the bridge diode that full-wave rectifies the AC power supplied from the commercial power source to the LED array 1 and the LED array 2, the first to third analog switches are controlled according to the power supply voltage. A method of switching the connection form of the LED array 1 and the LED array 2 between parallel connection and series connection is known (see, for example, Patent Document 1).

  In the apparatus described in Patent Document 1, the intermediate potential determination circuit 2 controls the first to third analog switches in order to switch the LED array 1 and the LED array 2 between parallel connection and series connection. ing. However, since the intermediate potential determination circuit 2 is driven with the power supply voltage as it is, particularly when used in an area where the power supply voltage is as high as 220 V, it must be driven with a high voltage, and it is difficult to make an IC. was there.

  Further, in the apparatus described in Patent Document 1, when the LED array 1 and the LED array 2 are connected in parallel, the LED array 1 and the first analog switch are connected in series with respect to the power supply voltage, and the LED array 2 and the second analog switch are connected in series to the power supply voltage, and the LED array 1 and the LED array 2 are connected in series, the LED array 1, the third analog switch, and the LED array 2 are the power supplies. It is connected in series with the voltage. Switching between parallel connection and series connection changes the impedance of the element connected to the power supply voltage. Therefore, the current flowing through the circuit changes as a result of switching between parallel connection and series connection, resulting in total harmonic distortion (THD). : Total harmonic distortion) worsened.

JP2009-283775 (FIG. 1)

  Therefore, an object of the present invention is to provide an LED driving device aimed at solving the above-mentioned problems.

  It is another object of the present invention to provide an LED driving device configured to be easily integrated into an IC by enabling a control unit for performing LED block switching control to be driven at a low voltage.

  Furthermore, an object of the present invention is to provide an LED driving device capable of suppressing the total harmonic distortion to a low level irrespective of the LED block switching control.

  An LED driving device according to the present invention includes a rectifier having a high-side power output and a low-side power output, a voltage dividing unit that divides a voltage between the high-side power output and the low-side power output, and a plurality of LEDs. A first LED group, a second LED group including a plurality of LEDs, and a connecting portion for connecting the first and second LED groups in series to the rectifier or connecting the first and second LED groups in parallel to the rectifier; The comparison unit that compares the partial pressure output of the pressure unit and the threshold value, and the connection unit is controlled according to the output from the comparison unit to switch the first and second LED groups from parallel connection to series connection with respect to the rectifier. And a control unit.

  In the LED drive device according to the present invention, the connecting portion is disposed at least between the first LED group and the high-side power output, and between the first LED group and the low-side power output. Second current control circuit, a third current control circuit disposed between the second LED group and the high-side power output, and a fourth current control disposed between the second LED group and the low-side power output. It is preferable to include a circuit.

  In the LED driving device according to the present invention, the control unit controls the second current control circuit and the third current control circuit to cut off the current, thereby connecting the first and second LED groups in parallel to the rectifier. It is preferable to switch from serial connection to serial connection.

  In the LED driving apparatus according to the present invention, the control unit controls the first and second LED groups from the serial connection to the rectifier by controlling the second current control circuit and the third current control circuit to pass the current. It is preferable to switch to parallel connection.

  In the LED driving device according to the present invention, the maximum current passing amount in the first current control circuit and the fourth current control circuit is larger than the maximum current passing amount in the second current control circuit and the third current control circuit. It is preferable to set as follows.

  In the LED drive device according to the present invention, the number of current control transistors constituting the first current control circuit and the fourth current control circuit is equal to the number of current control transistors constituting the second current control circuit and the third current control circuit. It is preferable to set the number to be larger than the number.

  In the LED drive device according to the present invention, the control unit generates a high-side control signal based on the high-side power supply output according to the output from the comparison unit, and controls the first and third current control circuits. A first control circuit; and a second control circuit that generates a low-side control signal based on the low-side power supply output and controls the second and fourth current control circuits according to an output from the comparison unit. preferable.

  In the LED driving device according to the present invention, the comparison unit preferably includes a first comparison circuit that outputs a comparison signal to the first control circuit and a second comparison circuit that outputs a comparison signal to the second control circuit.

  In the LED driving device according to the present invention, it is preferable that the first control circuit, the first comparison circuit, the second control circuit, and the second comparison circuit are integrated into an IC.

  In the LED driving device according to the present invention, it is preferable that the LED driving device further includes a reverse current prevention diode disposed between the first LED group and the second LED group.

  In the LED driving device according to the present invention, it is preferable that the saturation current is controlled by varying a control voltage of a current control transistor constituting the first current control circuit and the fourth current control circuit.

  In the LED driving device according to the present invention, the control circuit for switching control of the LED block is driven using the low voltage obtained by resistance-dividing the power supply voltage, so that the high breakdown voltage control circuit is not used, and It became possible to easily make IC.

  In the LED driving device according to the present invention, since the amount of current flowing through the LED block is controlled when the LED block is switched, it is possible to suppress the total harmonic distortion to a low level regardless of the switching control of the LED block.

It is a schematic explanatory drawing of the LED drive device which concerns on this invention. 2 is a circuit diagram showing details of an LED drive circuit 100. FIG. It is a figure which shows the output voltage waveform example 50 of the full wave rectifier circuit 12. FIG. It is a figure which shows the example of a switching sequence of LED block. FIG. 4 is a diagram illustrating a control signal from a first control unit 33. FIG. 6 is a diagram illustrating a control signal from a second control unit 43. FIG. 3 is a diagram illustrating voltages and currents supplied from a full-wave rectifier circuit 12 in the LED drive circuit 1. It is a schematic explanatory drawing of the other LED drive device which concerns on this invention. It is a schematic explanatory drawing of the further another LED drive device which concerns on this invention. 2 is a circuit diagram showing details of an LED drive circuit 200. FIG. It is a figure which shows the other example of a switching sequence of an LED block.

  Hereinafter, an LED driving device 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 driving device according to the present invention.

  As shown in FIG. 1, the LED driving device 1 includes a connection terminal 11 connected to a commercial power source (for example, AC 100 V) 10, a full-wave rectifier circuit 12, a resistance voltage dividing unit 20, a high-side control circuit 30, and a low-side side. The control circuit 40 and the LED drive circuit 100 are configured.

  The connection terminal 11 is for connecting to a commercial AC power source, and is formed as a base of an LED bulb when the LED driving device 1 is configured as an LED bulb. The full-wave rectifier circuit 12 is a diode bridge type composed of four diodes D1 to D4, and has a high-side power output 13 and a low-side 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 trap.

  The resistance voltage dividing unit 20 includes three resistors 21, 22, and 23, and divides the full-wave rectified output from the full-wave rectifier circuit 12 so that the maximum voltage is about 3 V, thereby controlling the high side. The circuit 30 and the low-side control circuit 40 can be supplied respectively. Since the voltage applied to the high-side control circuit 30 and the low-side control circuit 40 is reduced by the resistance voltage dividing unit 20, it is easy to make an IC using a CMOS or the like without using a high-voltage control element. It became possible.

  The high-side control circuit 30 includes a Zener diode 31 and a resistor 32, a 1-1 comparator 34, a 1-2 comparator 35, and a first controller 33. The Zener diode 31 and the resistor 32 generate a reference voltage and supply it to the first control unit 33 as a drive voltage for the high-side control circuit 30. The first-first comparator 34 detects whether the output from the divided full-wave rectifier circuit 12 has exceeded a first threshold voltage described later, and supplies a detection signal to the first control unit 33. To do. Further, the first-second comparator 35 detects whether the output from the divided full-wave rectifier circuit 12 exceeds a second threshold voltage described later, and supplies a detection signal to the first control unit 33. To do. Here, the portion surrounded by the dotted line 38, that is, the first-first comparator 34, the first-second comparator 35, and the first control unit 33 can be integrated with a CMOS or the like.

  The low-side control circuit 40 includes a Zener diode 41 and a resistor 42, a 2-1 comparator 44, a 2-2 comparator 45, and a second controller 43. The Zener diode 41 and the resistor 42 generate a reference voltage and supply it to the second control unit 43 as a drive voltage for the low-side control circuit 40. The 2-1 comparator 44 detects whether the output from the divided full-wave rectifier circuit 12 has exceeded a first threshold voltage described later, and supplies a detection signal to the second control unit 43. To do. Further, the 2-2 comparator 45 detects whether or not the output from the divided full-wave rectifier circuit 12 exceeds a second threshold voltage described later, and supplies the detection signal to the second controller 43. To do. Here, the portion surrounded by the dotted line 48, that is, the 2-1 comparator 44, the 2-2 comparator 45, and the second control unit 43 can be made into an IC by CMOS or the like.

  The LED driving circuit 100 includes a first LED block 110 including a plurality of LEDs, a second LED block 120 including a plurality of LEDs, a third LED block 130 including a plurality of LEDs, a fourth LED block 140 including a plurality of LEDs, and a plurality of LEDs. The fifth LED block 150 includes a sixth LED block 160 including a plurality of LEDs. The first LED block 110 to the sixth LED block 160 are obtained by connecting six white LEDs of Vf = 3.2 V in series. Accordingly, in each LED block alone, when the applied voltage becomes equal to or higher than the first forward voltage (V1: 3.2 V × 6 = 19.2 V), the LEDs included in each block start to emit light. When two of the first LED block 110 to the sixth LED block 160 are connected in series, the applied voltage is equal to or higher than the second forward voltage (V2: 3.2 V × 6 × 2 = 38.4 V). In this case, the LEDs included in the two blocks connected in series start to emit light. Furthermore, when three of the first LED block 110 to the sixth LED block 160 are connected in series, the applied voltage is equal to or higher than the third forward voltage (V3: 3.2 V × 6 × 3 = 57.6 V). In this case, the LEDs included in the three blocks connected in series start to emit light.

  In the LED drive circuit 100, the first LED block 110 is connected to the high-side power output 13 of the full-wave rectifier circuit 12 via the first-first current control unit 111, and the low-side power supply of the full-wave rectifier circuit 12 is connected. The output 14 is connected to the first-second current control unit 112. Similarly, the second LED block 120 is connected to the high-side power output 13 via the 2-1 current control unit 121 and connected to the low-side power output 14 via the 2-2 current control unit 122. Yes. Similarly, the third LED block 130 is connected to the high-side power output 13 through the 3-1 current controller 131, and is connected to the low-side power output 14 through the 3-2 current controller 132. Yes. Similarly, the fourth LED block 140 is connected to the high-side power output 13 through the 4-1 current control unit 141 and connected to the low-side power output 14 through the 4-2 current control unit 142. Yes. Similarly, the fifth LED block 150 is connected to the high-side power supply output 13 via the 5-1 current control unit 151 and connected to the low-side power supply output 14 via the 5-2 current control unit 152. Yes. Similarly, the sixth LED block 160 is connected to the high-side power output 13 through the 6-1 current controller 161, and is connected to the low-side power output 14 through the 6-2 current controller 162. Yes.

  Further, in the LED drive circuit 100, the first reverse current prevention diode 171 is disposed between the first LED block 110 and the second LED block 120. Similarly, a second reverse current prevention diode 172 is disposed between the second LED block 120 and the third LED block 130, and a third reverse current prevention diode is provided between the third LED block 130 and the fourth LED block 140. 173 is disposed, the fourth reverse current prevention diode 174 is disposed between the fourth LED block 140 and the fifth LED block 150, and the fifth reverse current prevention is performed between the fifth LED block 150 and the sixth LED block 160. A diode 175 is disposed.

  FIG. 2 is a circuit diagram showing details of the LED drive circuit 100.

  The first-first current control unit 111 includes four P-type MOSFETs M1 to M4. In each of M1 to M4, the source is connected to the high-side power supply output 13 of the full-wave rectifier circuit 12, the drain is connected to the first LED block 110, and the control signal P1 from the first control unit 33 is applied to the gate. It is comprised so that. The first-first current control unit 111 sets the M1 and M2 to the ON state and M3 and M4 when only the M1 is turned on and the M2 to M4 are turned off by the control signal P1 from the first control unit 33. Is set to the OFF state, the three states are controlled when all of M1 to M4 are set to the ON state.

  The 2-1 current control unit 121 includes one P-type MOSFET M5. M5 has a source connected to the high-side power output 13 of the full-wave rectifier circuit 12, a drain connected to the second LED block 120, and a gate to which the control signal P2 from the first controller 33 is applied. It is configured. The 2-1 current control unit 121 is controlled by the control signal P2 from the first control unit 33 into two states when M5 is turned on and when M5 is turned off.

  The 3-1 current control unit 131 includes two P-type MOSFETs M6 and M7. Each M6 and M7 has a source connected to the high-side power supply output 13 of the full-wave rectifier circuit 12, a drain connected to the third LED block 130, and a control signal P3 from the first control unit 33 applied to the gate. It is comprised so that. The 3-1 current control unit 131 uses the control signal P3 from the first control unit 33 to turn on only M6 and turn off M7, turn on M6 and M7, and turn on M6 and M7. Are controlled in three states.

  The 4-1 current control unit 141 is composed of four P-type MOSFETs M8 to M11. In each of M8 to M11, the source is connected to the high-side power supply output 13 of the full-wave rectifier circuit 12, the drain is connected to the fourth LED block 140, and the control signal P4 from the first control unit 33 is applied to the gate. It is comprised so that. In the case where only M8 is turned on and M9 to M11 are turned off by the control signal P4 from the first control unit 33, the fourth-first current control unit 141 turns M8 and M9 on and M10 and M11. Is set to the OFF state, the three states are controlled when all of M8 to M11 are set to the ON state.

  The 5-1 current control unit 151 is composed of one P-type MOSFET M12. M12 has a source connected to the high-side power output 13 of the full-wave rectifier circuit 12, a drain connected to the second LED block 150, and a gate to which the control signal P5 from the first control unit 33 is applied. It is configured. The 5-1 current control unit 151 is controlled by the control signal P5 from the first control unit 33 in two states when M12 is turned on and M12 is turned off.

  The 6-1 current controller 161 includes two P-type MOSFETs M13 and M14. In each of M13 and M14, the source is connected to the high-side power output 13 of the full-wave rectifier circuit 12, the drain is connected to the sixth LED block 160, and the control signal P6 from the first control unit 33 is applied to the gate. It is comprised so that. The 6-1 current control unit 161 uses the control signal P6 from the first control unit 33 to turn on only M13 and turn off M14, to turn on M13 and M14, and to turn on M13 and M14. Are controlled in three states.

  The P-type MOSFETs M1 to M14 are turned on when a voltage equal to or lower than a predetermined threshold voltage (−Vth) is applied to the gate with reference to the source potential, and the high-side power supply output 13 and each LED block are electrically connected. When the voltage having the same potential as that of the source is applied to the gate, the transistor is turned off and the conduction between the high-side power supply output 13 and each LED block is cut off.

  As described above, the voltage (L) for the first control unit 33 of the high-side control circuit 30 to turn on M1 to M14 is the threshold voltage (−Vth) from the voltage of the high-side power supply output 13. The voltage value (H) for subtracting more than or equal to the minute and causing M1 to M14 to be in the OFF state is the same voltage as the high-side power supply output 13. Since the high-side control circuit 30 operates with the potential of the high-side power supply output 13 as a reference, a control signal for supplying the first-1 current control unit 111 to the 6-1 current control unit 161 When generating P1 to P6, it is not necessary to perform voltage level shift or the like.

  The first-second current control unit 112 includes one N-type MOSFET M20. The M20 is configured such that the source is connected to the low-side power output 14 of the full-wave rectifier circuit 12, the drain is connected to the first LED block 110, and the control signal N1 from the second control unit 43 is applied to the gate. Has been. The first-second current control unit 112 is controlled by the control signal N1 from the second control unit 43 into two states when M20 is turned on and when M20 is turned off.

  The 2-2 current controller 122 includes two N-type MOSFETs M21 and M22. In each of M21 and M22, the source is connected to the low-side power output 14 of the full-wave rectifier circuit 12, the drain is connected to the second LED block 120, and the control signal N2 from the second control unit 43 is applied to the gate. It is configured as follows. The second-second current control unit 122 uses the control signal N2 from the second control unit 43 to turn on only M21 and turn off M22, turn on M21 and M22, and turn on M21 and M22. Are controlled in three states.

  The 3-2 current controller 132 is composed of four N-type MOSFETs M23 to M26. In each of M23 to M26, the source is connected to the low-side power output 14 of the full-wave rectifier circuit 12, the drain is connected to the third LED block 130, and the control signal N3 from the second control unit 43 is applied to the gate. It is configured as follows. In the case where only the M23 is turned on and the M24 to M26 are turned off by the control signal N3 from the second control unit 43, the 3-2 current controller 132 turns the M23 and M24 on and M25 and M26. Is set to the OFF state, the three states are controlled when all of M23 to M26 are set to the ON state.

  The 4-2 current control unit 142 includes one N-type MOSFET M27. The M27 is configured such that the source is connected to the low-side power output 14 of the full-wave rectifier circuit 12, the drain is connected to the fourth LED block 140, and the control signal N4 from the second control unit 43 is applied to the gate. Has been. The 4-2 current control unit 142 is controlled by the control signal N4 from the second control unit 43 into two states when M27 is turned on and when M27 is turned off.

  The 5-2 current control unit 152 includes two N-type MOSFETs M28 and M29. In each M28 and M29, the source is connected to the low-side power supply output 14 of the full-wave rectifier circuit 12, the drain is connected to the fifth LED block 150, and the control signal N5 from the second control unit 43 is applied to the gate. It is configured as follows. The 5-2 current control unit 152 sets the M28 and the M29 in the ON state when the M28 is turned on and the M29 is turned off by the control signal N5 from the second control unit 43. Control is made to three states in the OFF state.

  The 6-2 current control unit 162 includes four N-type MOSFETs M30 to M34. In each of M30 to M34, the source is connected to the low-side power output 14 of the full-wave rectifier circuit 12, the drain is connected to the sixth LED block 160, and the control signal N6 from the second control unit 43 is applied to the gate. It is configured as follows. The 6-2 current control unit 162 sets the M30 and M31 to the ON state and M32 and M33 when only the M30 is turned on and the M31 to M34 are turned off by the control signal N6 from the second control unit 43. Is set to the OFF state, the three states are controlled when all of M30 to M34 are set to the ON state.

  The N-type MOSFETs M20 to M34 are turned on when a voltage higher than a predetermined threshold voltage (+ Vth) is applied to the gate with reference to the source potential, and the low-side power supply output 14 and each LED block are made conductive. When a voltage having the same potential as that of the source is applied, the power supply output 14 is turned off and the conduction between the low-side power output 14 and each LED block is cut off.

  As described above, the voltage (L) for causing the second control unit 43 of the low-side control circuit 40 to turn off M20 to M34 is the same voltage as the low-side power supply output 14, and turns on M20 to M34. The voltage (H) for setting the state becomes a voltage value higher than the voltage of the low-side power supply output 14 by a threshold voltage (+ Vth) or more. Since the low-side control circuit 40 operates based on the potential of the low-side power output 14, the control signals N <b> 1 to N <b> 1 for supplying the first-second current control unit 121 to the 6-2 current control unit 162 are used. When N6 is generated, there is no need to perform voltage level shift or the like.

  As described above, the current control circuit of the LED drive circuit 100 includes the P-type MOSFETs M1 to M14 and the N-type MOSFETs M20 to M34. Since the above-mentioned MOSFETs all have the same W / L size, it is possible to control the maximum amount of current passing through each current control unit by changing the number of MOSFETs that pass through the MOSFETs. .

  Hereinafter, operation | movement of the LED drive device 1 is demonstrated using FIGS. FIG. 3 is a diagram illustrating an output voltage waveform example 50 of the full-wave rectifier circuit 12, and FIG. 4 is a diagram illustrating an example of a switching sequence of LED blocks. In FIG. 4, the reverse current preventing diodes 171 to 175 are omitted for convenience. 5A to 5F are diagrams showing control signals P1 to P6 from the first control unit 33, and FIGS. 6A to 6F are the second control unit 43. FIG. It is the figure which showed the control signals N1-N6 from.

  From time T0 (see FIG. 3) when the output voltage of the full-wave rectifier circuit 12 is 0 (v) to time T2 (see FIG. 3) when the output voltage of the full-wave rectifier circuit 12 reaches V2 (v). The first-first comparator 34 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V2. Accordingly, the control signals P1 to P6 (see FIG. 5) supplied from the first control unit 33 are set so that the first-1 current control unit 111 to the 6-1 current control unit 161 are all turned on. All become LOW level. Similarly, the 2-1 comparator 44 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V2. Accordingly, the control signals N1 to N6 (see FIG. 6) supplied from the second control unit 43 so that all of the first-2 current control unit 112 to the 6-2 current control unit 162 are turned on. All become HIGH level.

  As described above, at time T0 to T2, a current path as shown in FIG. 4A is formed. That is, a current path in which the first LED block 110 to the sixth LED block 160 are connected in parallel is formed between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12.

  Furthermore, at time T0 to T2, the control signal P1 from the first control unit 33 turns on only M1 of the 1-1 current control unit 111, and the control signal P3 is only M6 of the 3-1 current control unit 131. Is set to ON state, the control signal P4 is set to turn on only M8 of the 1-1 current control unit 141, and the control signal P6 is set to turn on only M13 of the 6-1 current control unit 161. . Similarly, the control signal N2 from the second control unit 43 turns on only M21 of the 2-2 current control unit 122, and the control signal N3 turns on only M23 of the third-2 current control unit 132, The control signal N5 is set to turn on only M28 of the 5-2 current control unit 152, and the control signal N6 is set to turn on only M30 of the 6-2 current control unit 162. That is, in this state, all the current control units respectively turn on one MOSFET, so that each LED block and the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12 are connected in parallel. Current path is formed.

  Since the 2-1 current control unit 121 has only one MOSFET, the control signal P2 turns M5 on. Similarly, the control signal P5 also turns M12 on, the control signal N1 also turns M20 on, and the control signal N4 also turns M27 on. By the way, in the current control unit including only one MOSFET (the 1-2 current control unit 121, the 5-1 current control unit 151, the 1-2 current control unit 112, and the 4-2 current control unit 142). Since the control of the current control unit and the control of the MOSFET are the same, the description is omitted below.

[Operation at time T0]
At time T0, the output voltage of the full-wave rectifier circuit 12 is 0 (v), and since the voltage for lighting the LED blocks included in the first LED block 110 to the sixth LED block 160 has not been reached, the LEDs do not light up. .

[Operation at time T1]
At time T1, the output voltage of the full-wave rectifier circuit 12 becomes the first forward voltage V1, which is a voltage sufficient to light each LED block of the first LED block 110 to the sixth LED block 160 alone. Therefore, each LED of the 1st LED block 110-the 6th LED block 160 lights (refer Fig.4 (a)).

[Operation from Time T2 to Time T3]
From time T2 (see FIG. 3) to time T3 (see FIG. 3), the 1-1 comparator 34 detects that the output voltage of the full-wave rectifier circuit 12 is equal to or higher than the second forward voltage V2. To do. Accordingly, the first control unit 33 controls the control signals P1, P3 so that only the first-1 current control unit 111, the 3-1 current control unit 131, and the 5-1 current control unit 151 are turned on. And P5 only are set to the LOW level (see FIGS. 5A, 5C and 5E), and the control signals P2, P4 and P6 are set to the HIGH level (FIG. 5B, FIG. 5). (See (d) and FIG. 5 (f)).

  Similarly, at times T2 to T3, the 2-1 comparator 44 detects that the output voltage of the full-wave rectifier circuit 12 is equal to or higher than the second forward voltage V2. Accordingly, the second control unit 43 controls the control signals N2, N4 so that only the 2-2 current control unit 122, the 4-2 current control unit 142, and the 6-2 current control unit 162 are turned on. And N6 are set to the HIGH level (see FIG. 6B, FIG. 6D and FIG. 6F), and the control signals N1, N3, and N5 are set to the LOW level (FIG. 6A, FIG. c) and FIG. 6 (e)).

  In this way, a current path as shown in FIG. 4B is formed at times T2 to T3. That is, the first LED block 110 and the second LED block 120 are connected in series between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12, and the third LED block 130 and the fourth LED block. A current path that is connected in parallel is formed between the one 140 connected in series and the fifth LED block 150 and the sixth LED block 160 connected in series, and the LEDs included in each LED block are lit.

  Further, at time T2 to T3, the control signal P1 from the first control unit 33 turns on only M1 and M2 of the first-1 current control unit 111, and the control signal P3 is output from the 3-1 current control unit 131. M6 and M7 are turned on, the control signal P4 turns on only M8 and M9 of the 4-1 current control unit 141, and the control signal P6 turns on M13 and M14 of the 6-1 current control unit 161 Is set to Similarly, the control signal N2 from the second control unit 43 turns on M21 and M22 of the 2-2 current control unit 122, and the control signal N3 turns on only M23 and M24 of the third-2 current control unit 132. The control signal N5 is set to turn on M28 and M29 of the 5-2 current control unit 152, and the control signal N6 is set to turn on only M30 and M31 of the 6-2 current control unit 162. Yes. That is, in this state, all current control units that are in the ON state each have two MOSFETs in the ON state so that two LED blocks are connected in series and the high-side side of the full-wave rectifier circuit 12 A current path is formed in which the power output 13 and the low-side power output 14 are connected in parallel.

[Operation from Time T3 to Time T4]
Between time T3 (see FIG. 3) and time T4 (see FIG. 3), the first-second comparator 35 detects that the output voltage of the full-wave rectifier circuit 12 is equal to or higher than the third forward voltage V3. To do. Accordingly, the first control unit 33 sets only the control signals P1 and P4 to the LOW level so that only the first-1 current control unit 111 and the 4-1 current control unit 141 are turned on (FIG. 5 ( a) and FIG. 5D), and the control signals P2, P3, P5 and P6 are set to the HIGH level (FIGS. 5B, 5C, 5E and 5F). reference).

  Similarly, between time T3 (see FIG. 3) and time T4 (see FIG. 3), the 2-2 comparator 45 causes the output voltage of the full-wave rectifier circuit 12 to be equal to or higher than the third forward voltage V3. Detect that. Accordingly, the second control unit 43 sets only the control signals N3 and N6 to the HIGH level so that only the third-2 current control unit 132 and the 6-2 current control unit 162 are turned on (FIG. 6 ( c) and FIG. 6F), and the control signals N1, N2, N4, and N5 are set to the LOW level (FIGS. 6A, 6B, 6D, and 6E). reference).

  In this way, a current path as shown in FIG. 4C is formed at times T3 to T4. That is, the first LED block 110, the second LED block 120, and the third LED block 130 are connected in series between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12, and the fourth LED block 140, and the fifth LED block 150 and the sixth LED block 160 connected in series form a current path connected in parallel, and the LEDs included in each LED block are lit.

  Further, at time T3 to T4, the control signal P1 from the first control unit 33 turns on all of M1 to M4 of the 1-1 current control unit 111, and the control signal P4 is the 4-1 current control unit 141. All of M8 to M11 are set to be in the ON state. Similarly, the control signal N3 from the second control unit 43 turns on all of M23 to M26 of the 3-2 current control unit 132, and the control signal N6 is the M30 to M34 of the 6-2 current control unit 162. All are set to turn on. That is, in this state, all current control units that are in the ON state each have four MOSFETs in the ON state so that three LED blocks are connected in series and the high-side side of the full-wave rectifier circuit 12 A current path is formed in which the power output 13 and the low-side power output 14 are connected in parallel.

[Operation from Time T4 to Time T5]
Between time T4 (see FIG. 3) and time T5 (see FIG. 3), the first-second comparator 35 detects that the output voltage of the full-wave rectifier circuit 12 has become less than the third forward voltage V3. To do. Accordingly, the first control unit 33 controls the control signals P1, P3 so that only the first-1 current control unit 111, the 3-1 current control unit 131, and the 5-1 current control unit 151 are turned on. And P5 only are set to the LOW level (see FIG. 5A, FIG. 5C and FIG. 5E), and the control signals P2, P4, and P6 are set to the HIGH level (FIG. 5B). 5 (d) and FIG. 5 (f)).

  Similarly, between time T4 (see FIG. 3) and time T5 (see FIG. 3), the 2-2 comparator 45 causes the output voltage of the full-wave rectifier circuit 12 to be less than the third forward voltage V3. Detect that. Accordingly, the second control unit 43 controls the control signals N2 and N4 so that only the 2-2 current control unit 132, the 4-2 current control unit 142, and the 6-2 current control unit 162 are turned on. And N6 are set to HIGH level (see FIG. 6B, FIG. 6D and FIG. 6F), and the control signals N1, N3 and N5 are set to LOW level (FIG. 6A, FIG. 6). (See (c) and FIG. 6 (e)).

  As described above, a current path as shown in FIG. 4D is formed at times T4 to T5. That is, the first LED block 110 and the second LED block 120 are connected in series between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12, and the third LED block 130 and the fourth LED block. A current path that is connected in parallel is formed between the one 140 connected in series and the fifth LED block 150 and the sixth LED block 160 connected in series, and the LEDs included in each LED block are lit.

  Further, at times T4 to T5, the control signal P1 from the first control unit 33 turns on only M1 and M2 of the first-1 current control unit 111, and the control signal P3 receives the control signal P3 of the 3-1 current control unit 131. M6 and M7 are turned on, the control signal P4 turns on only M8 and M9 of the 4-1 current control unit 141, and the control signal P6 turns on M13 and M14 of the 6-1 current control unit 161 Is set to Similarly, the control signal N2 from the second control unit 43 turns on M21 and M22 of the 2-2 current control unit 122, and the control signal N3 turns on only M23 and M24 of the third-2 current control unit 132. The control signal N5 is set to turn on M28 and M29 of the 5-2 current control unit 152, and the control signal N6 is set to turn on only M30 and M31 of the 6-2 current control unit 162. Yes. That is, in this state, all current control units that are in the ON state each have two MOSFETs in the ON state so that two LED blocks are connected in series and the high-side side of the full-wave rectifier circuit 12 A current path is formed in which the power output 13 and the low-side power output 14 are connected in parallel.

[Operation from Time T5 to Time T7]
Between time T5 (see FIG. 3) and time T7 (see FIG. 3), the 1-1 comparator 34 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V2. . Accordingly, the control signals P1 to P6 (see FIG. 5) supplied from the first control unit 33 are set so that the first-1 current control unit 111 to the 6-1 current control unit 161 are all turned on. All become LOW level. Similarly, the 2-1 comparator 44 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V2. Accordingly, the control signals N1 to N6 (see FIG. 6) supplied from the second control unit 43 so that all of the first-2 current control unit 112 to the 6-2 current control unit 162 are turned on. All become HIGH level.

  In this way, at time T5 to T7, a current path as shown in FIG. 4 (e) is formed. That is, a current path in which the first LED block 110 to the sixth LED block 160 are connected in parallel is formed between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12.

  Further, at time T5 to T7, the control signal P1 from the first control unit 33 turns on only M1 of the 1-1 current control unit 111, and the control signal P3 is only M6 of the 3-1 current control unit 131. Is set to ON state, the control signal P4 is set to turn on only M8 of the 1-1 current control unit 141, and the control signal P6 is set to turn on only M13 of the 6-1 current control unit 161. . Similarly, the control signal N2 from the second control unit 43 turns on only M21 of the 2-2 current control unit 122, and the control signal N3 turns on only M23 of the third-2 current control unit 132, The control signal N5 is set to turn on only M28 of the 5-2 current control unit 152, and the control signal N6 is set to turn on only M30 of the 6-2 current control unit 162. That is, in this state, all the current control units respectively turn on one MOSFET, so that each LED block and the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12 are connected in parallel. Current path is formed.

  When the output voltage of the full-wave rectifier circuit 12 is lower than the first forward voltage V1 at time T6 (see FIG. 3), the LEDs included in the first LED block 110 to the sixth LED block 160 are turned on. Since the voltage has not been reached, the LED does not light up.

  Thereafter, lighting control is performed so as to switch the series connection and the parallel connection of the first LED block 110 to the sixth LED block 160 while repeating the state from time T0 to time T7 (which corresponds to the time T0 of the cycle next).

[Explanation that total harmonic distortion can be suppressed]
FIG. 7 is a diagram illustrating the voltage and current supplied from the full-wave rectifier circuit 12 in the LED drive circuit 1.

  FIG. 7A shows the voltage waveform 50 supplied from the full-wave rectifier circuit 12 as in FIG. FIG. 7B shows a current waveform 51 supplied from the full-wave rectifier circuit 12. FIG. 7C shows that in the LED driving circuit 1, the 1-1 current control unit 111 to the 6-1 current control unit 161 and the 2-1 current control unit 112 to the 6-2 current control unit 162 include: It is a figure which shows the current waveform 52 at the time of assuming that it comprised from one MOSFET altogether.

  In the LED drive circuit 1, when switching to the current path shown in FIG. 4B at time T 2 and time T 5, two LED blocks are set with two MOSFETs that are turned on in all current control units that are turned on. Increases the amount of current supplied to those connected in series. Further, in the LED drive circuit 1, when the current path shown in FIG. 4C is obtained from time T3 to time T4, four MOSFETs that are turned on in all the current control units that are turned on are set to three. The amount of current supplied to the LED blocks connected in series is increased. Therefore, as shown in FIG. 7B, the current waveform at time T0 to time T7 is not greatly deviated from the sine curve.

  On the other hand, in the current waveform 52 shown in FIG. 7C, at time T2 and time T5, even if the voltage changes, the amount of current supplied to the LED blocks in which the two are connected in series is one. Since it is limited by the MOSFET, the amount of current is reduced. Similarly, from time T3 to time T4, the amount of current supplied to the three LED blocks connected in series is limited by one MOSFET, and thus the amount of current is further reduced. Therefore, in the current waveform 52 shown in FIG. 7C, the current waveform is greatly deviated from the sine curve.

  The total harmonic distortion included in the current waveform 51 shown in FIG. 7B is about 20%, and the total harmonic distortion included in the current waveform 52 shown in FIG. 7C is about 71%. As described above, in the LED drive circuit 1, in each current control unit, the number of MOSFETs to be turned on is controlled in synchronization with switching between parallel connection and series connection of LED blocks, and the maximum current passing amount is adjusted. This makes it possible to suppress total harmonic distortion.

  FIG. 8 is a schematic explanatory diagram of another LED driving device 2 according to the present invention.

  In the LED drive device 2 shown in FIG. 8, the same components as those of the LED drive device 1 shown in FIG. The LED driving device 2 is different from the LED driving device 1 shown in FIG. 1 in that the Zener diode 31 and the Zener diode 41 are connected by the resistor 25 except for the resistor 32 of the high-side control circuit 30 and the resistor 42 of the low-side control circuit 40. It is only the point which did.

  Also with the configuration as shown in FIG. 8, the reference voltage can be provided to the first control unit 33 of the high-side control circuit 30 and the second control circuit 43 of the low-side control circuit 40, respectively. Furthermore, the number of resistors can be reduced as compared with the LED driving device 1 shown in FIG.

  FIG. 9 is a schematic explanatory diagram of still another LED driving device 3 according to the present invention.

  In the LED drive device 3 shown in FIG. 9, the same components as those of the LED drive device 1 shown in FIG.

  As shown in FIG. 9, the LED drive device 3 includes a connection terminal 11 connected to a commercial power source (for example, AC 100 V) 10, a full-wave rectifier circuit 12, a resistance voltage dividing unit 20, a high side control circuit 30 ′, a low side It comprises a side control circuit 40 ', an LED drive circuit 200, and the like.

  9 is different from the high-side control circuit 30 shown in FIG. 1 only in that the high-side control circuit 30 ′ does not have the first-second comparator 35. is there. Further, the only difference between the low side control circuit 40 ′ shown in FIG. 9 and the low side control circuit 40 shown in FIG. 1 is that the low side control circuit 40 ′ does not have the 2-2 comparator 45. .

  The LED driving circuit 200 includes a first LED block 210 including a plurality of LEDs and a second LED block 220 including a plurality of LEDs. The first LED block 210 and the second LED block 220 are obtained by connecting nine white LEDs of Vf = 3.2V in series. Accordingly, in each LED block alone, when the applied voltage becomes equal to or higher than the first forward voltage (V11: 3.2V × 9 = 28.8V), the LEDs included in each block start to emit light. When two of the first LED block 210 and the second LED block 220 are connected in series, the applied voltage is equal to or higher than the second forward voltage (V12: 3.2 V × 9 × 2 = 57.6 V). In this case, the LEDs included in the two blocks connected in series start to emit light.

  In the LED drive circuit 200, the first LED block 210 is connected to the high-side power output 13 of the full-wave rectifier circuit 12 via the first-first current control unit 211, and the low-side power supply of the full-wave rectifier circuit 12. The output 14 is connected to the first-second current control unit 212. Similarly, the second LED block 220 is connected to the high-side power output 13 through the 2-1 current controller 221 and connected to the low-side power output 14 through the 2-2 current controller 222. Yes. Further, in the LED drive circuit 200, a reverse current prevention diode 271 is disposed between the first LED block 210 and the second LED block 220.

  FIG. 10 is a circuit diagram showing details of the LED drive circuit 200.

  The first-first current controller 211 includes two P-type MOSFETs M40 and M41. The 2-1 current controller 221 is composed of one P-type MOSFET M42. The P-type MOSFETs M40 to M42 are turned on when a voltage equal to or lower than a predetermined threshold voltage (−Vth) is applied to the gate with reference to the source potential, and the high-side power supply output 13 and each LED block are electrically connected. When a voltage having the same potential as that of the source is applied to the gate, the gate is turned off and the conduction between the high-side power supply output 13 and each LED block is cut off.

  As described above, the voltage (L) for the first control unit 33 of the high-side control circuit 30 ′ to turn on M40 to M42 is the threshold voltage (−Vth) from the voltage of the high-side power supply output 13. ) Is a voltage value obtained by subtracting more than minutes, and the voltage (H) for turning off M40 to M42 is the same voltage as the high-side power supply output 13. Since the high-side control circuit 30 ′ operates based on the potential of the high-side power supply output 13, control for supplying the first-first current control unit 211 and the 2-1 current control unit 221 is performed. When generating the signals P11 and P12, it is not necessary to perform voltage level shift or the like.

  The first-second current controller 212 is composed of one N-type MOSFET M50. The 2-2 current control unit 222 is composed of two N-type MOSFETs M51 and M52. The N-type MOSFETs M50 to M52 are turned on when a voltage higher than a predetermined threshold voltage (+ Vth) is applied to the gate with reference to the source potential, and the low-side power output 14 and each LED block are made conductive. When a voltage having the same potential as that of the source is applied to the gate, the gate is turned off, and conduction between the low-side power output 14 and each LED block is cut off.

  As described above, the voltage (L) for causing the second control unit 43 of the low-side control circuit 40 ′ to turn off M50 to M52 is the same voltage as the low-side power supply output 14, and M50 to M52 are The voltage (H) for setting the ON state is higher than the voltage of the low-side power supply output 14 by a threshold voltage (+ Vth) or more. Since the low-side control circuit 40 ′ operates with reference to the potential of the low-side power supply output 14, the control signal N 11 to be supplied to the first-2 current control unit 221 and the 2-2 current control unit 222. When generating N12 and N12, it is not necessary to perform voltage level shift or the like.

  As described above, the current control unit of the LED driving circuit 200 includes the P-type MOSFETs M40 to M42 and the N-type MOSFETs M50 to M52. Since the above-mentioned MOSFETs all have the same W / L size, it is possible to control the maximum amount of current passing through each current control unit by changing the number of MOSFETs that pass through the MOSFETs. . That is, the maximum current passage amount in the 1-1 current control unit 211 and the 2-2 current control unit 222 is larger than the maximum current passage amount of the 1-2 current control unit 212 and the 2-1 current control unit 221. It is set to be.

  FIG. 11 is a diagram illustrating another switching sequence example of the LED block.

  Hereinafter, the operation of the LED driving device 3 will be described with reference to FIG. In FIG. 11, for the sake of convenience, the reverse current prevention diode 271 is omitted.

  Until the output voltage of the full-wave rectifier circuit 12 reaches 0 (v) to V12 (v), the first-first comparator 34 determines that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V12. Is detected. In response thereto, control signals P11 and P12 are supplied from the first control unit 33 so that the 1-1st current control unit 211 and the 2-1st current control unit 221 are turned on. Similarly, the 2-1 comparator 44 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V12. In response thereto, control signals N11 and N12 are supplied from the second control unit 43 so that the first-second current control unit 212 and the second-second current control unit 222 are turned on.

  Therefore, a current path as shown in FIG. 11A is formed until the output voltage of the full-wave rectifier circuit 12 reaches 0 (v) to V12 (v). That is, a current path in which the first LED block 210 and the second LED block 220 are connected in parallel is formed between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12. In this state, when the output voltage of the full-wave rectifier circuit 12 becomes equal to or higher than the first forward voltage V11, the LEDs of the first LED block 210 and the second LED block 220 are lit.

  When the output voltage of the full-wave rectifier circuit 12 becomes equal to or higher than V12, the first-first comparator 34 detects that the output voltage of the full-wave rectifier circuit 12 becomes equal to or higher than the second forward voltage V12. Accordingly, the first control unit 33 supplies a control signal so that only the first-first current control unit 211 is turned on. Similarly, the 2-1 comparator 44 detects that the output voltage of the full-wave rectifier circuit 12 is equal to or higher than the second forward voltage V12. In response to this, the second control unit 43 supplies a control signal so that only the 2-2 current control unit 222 is turned on.

  Accordingly, a current path as shown in FIG. 11B is formed while the output voltage of the full-wave rectifier circuit 12 is equal to or higher than V12 (v). That is, a current path in which the first LED block 210 and the second LED block 220 are connected in series is formed between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12, and each LED block The LED included in is turned on.

  When the output voltage of the full-wave rectifier circuit 12 becomes less than V12 (v), the first-first comparator 34 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V12. In response thereto, a control signal is supplied from the first controller 33 so that the first-1 current controller 211 and the 2-1 current controller 221 are turned on. Similarly, the 2-1 comparator 44 detects that the output voltage of the full-wave rectifier circuit 12 is less than the second forward voltage V12. In response thereto, a control signal is supplied from the second control unit 43 so that the first-second current control unit 212 and the second-second current control unit 222 are all turned on.

  Therefore, when the output voltage of the full-wave rectifier circuit 12 is less than V12 (v), a current path as shown in FIG. 11C is formed. That is, a current path in which the first LED block 210 and the second LED block 220 are connected in parallel is formed between the high-side power output 13 and the low-side power output 14 of the full-wave rectifier circuit 12. In this state, the LEDs of the first LED block 210 and the second LED block 220 are lit until the output voltage of the full-wave rectifier circuit 12 becomes less than the first forward voltage V11.

  Thereafter, the lighting control is performed while repeating the above-described state, that is, while switching the series connection and the parallel connection of the first LED block 210 and the second LED block 220.

  The switching between the series connection and the parallel connection of the two LED blocks shown in FIGS. 9 to 11 is a minimum structural unit in the LED driving device according to the present invention. The LED driving device 1 shown in FIG. 1 has six LED blocks, and the lighting control is performed by switching the six LED blocks from parallel connection to serial connection in the order of 1 → 2 → 3. As described above, the number of LED blocks that the LED driving device according to the present invention can include and the number of LEDs included in one LED block depend on the type of commercial AC voltage to be used (100V, 220V, etc.). It is possible to set arbitrarily. Further, the switching of the LED blocks in series and in parallel is not limited to 1 → 2 → 3, but can be performed in various ways.

  In order to clarify the explanation, the increase / decrease of the current is represented by the number of ON states of the FET using the same size W / L. As is generally known, the FET flows between the source and the drain depending on the value of the gate voltage. It is possible to vary the saturation value of the current. Therefore, when the number of ON-state FETs shown in the embodiment of the present invention is large, the absolute value of the gate voltage is increased, and when the number of ON-state FETs is small, the absolute value of the gate voltage is decreased. Needless to say, a plurality of FETs arranged in parallel can be replaced by a single FET.

  The LED driving device 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 LED drive device 11 Terminal 12 Full-wave rectifier circuit 20 Resistance voltage dividing unit 30 High side control circuit 31 First control unit 40 Low side control circuit 41 Second control unit 100, 200 LED drive circuit 110, 120 , 130, 140, 150, 160, 210, 220 LED block 111, 121, 131, 141, 151, 161, 211, 221 High side current control unit 112, 122, 132, 142, 152, 162, 212, 222 Low-side current control unit 171, 172, 173, 174, 175, 271 Reverse current prevention diode

Claims (11)

A rectifier having a high-side power output and a low-side power output;
A voltage divider for dividing a voltage between the high-side power output and the low-side power output;
A first LED group including a plurality of LEDs;
A second LED group including a plurality of LEDs;
Connecting the first and second LED groups in series to the rectifier, or connecting the first and second LED groups in parallel to the rectifier;
A comparison unit that compares the partial pressure output of the voltage division unit with a threshold;
A control unit that controls the connection unit according to an output from the comparison unit, and switches the first and second LED groups from a parallel connection to a series connection with respect to the rectifier;
An LED driving device comprising:   The connecting portion includes at least a first current control circuit disposed between the first LED group and the high-side power output, and a second current circuit disposed between the first LED group and the low-side power output. A current control circuit; a third current control circuit disposed between the second LED group and the high-side power output; and a fourth current control disposed between the second LED group and the low-side power output. The LED driving device according to claim 1, comprising a circuit.   The control unit controls the first and second LED groups from parallel connection to series connection with respect to the rectifier by controlling the second current control circuit and the third current control circuit to cut off the current. The LED driving device according to claim 2, wherein the LED driving device is switched.   The control unit switches the first and second LED groups from a series connection to a parallel connection with respect to the rectifier by controlling the second current control circuit and the third current control circuit to pass current. The LED driving device according to claim 2.   The maximum current passing amount in the first current control circuit and the fourth current control circuit is set to be larger than the maximum current passing amount in the second current control circuit and the third current control circuit. The LED drive device as described in any one of -4.   The number of current control transistors constituting the first current control circuit and the fourth current control circuit is larger than the number of current control transistors constituting the second current control circuit and the third current control circuit. The LED driving device according to claim 2, wherein the LED driving device is set as follows.   The control unit generates a high-side control signal based on the high-side power supply output in accordance with an output from the comparison unit, and controls the first and third current control circuits; And a second control circuit that generates a low-side control signal based on the low-side power supply output in accordance with an output from the comparison unit and controls the second and fourth current control circuits. The LED drive device as described in any one of -6.   The comparison section includes a first comparison circuit that outputs a comparison signal to the first control circuit and a second comparison circuit that outputs a comparison signal to the second control circuit. LED drive device of clause.   The LED drive device according to claim 8, wherein the first control circuit, the first comparison circuit, the second control circuit, and the second comparison circuit are integrated into an IC.   The LED drive device according to claim 1, further comprising a reverse current prevention diode disposed between the first LED group and the second LED group.   5. The LED drive device according to claim 2, wherein a saturation current is controlled by varying a control voltage of a current control transistor that constitutes the first current control circuit and the fourth current control circuit. 6. .

Images