JP2010199201A - Led lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve control over a no-load voltage generated when the voltage across an LED rises or in the case of wire disconnection by a simple constitution, and to continuously change a current control mode and a voltage control mode. <P>SOLUTION: An LED lighting device detects a voltage outputted from a voltage converting circuit 13 for increasing the voltage of a DC power source 11 and also generates a drive voltage by a voltage detecting circuit 14. The LED 15 is displayed according to the drive voltage of the voltage detecting circuit 14. A drive current flowing through the LED 15 is detected by a current detecting circuit 16. An output voltage value is acquired by an operational amplifier OP on the basis of the value obtained by adding the detected voltage Vo detected by the voltage detecting circuit 14 and the detected current Io detected by the current detecting circuit 16, and a value for a reference voltage Vref, and the output voltage of the operational amplifier OP and the output of a triangular wave generator TG are compared by a comparator CP to determine the duty of a drive pulse (a), thereby controlling the output voltage of the voltage converting circuit 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an LED lighting device for lighting an LED (light emitting diode).

  The conventional LED lighting device reduces the stress on the LED by controlling the drive current of the LED so that the product of the both-end voltage and the drive current is constant when the voltage across the LED rises. I have to. (For example, Patent Document 1)

JP 2006-210836 A (pages 8 and 9 and FIG. 6)

  The technique disclosed in Patent Document 1 has a complicated configuration because separate operational amplifiers are used for the feedback loop for the driving current and the feedback loop for the both-ends voltage. In addition, the mode is switched from the current limiting region to the voltage limiting region.

  For this reason, when the voltage between both ends of the LED is in the vicinity of the switching voltage including temperature drift, there is a problem that the circuit operation is frequently switched and flickering is likely to occur.

  The object of the present invention is to realize control of no-load voltage generated when the voltage across the LED rises or breaks with a simple circuit configuration, and to change the current control mode and the voltage control mode continuously. It is to provide a lighting device.

  In order to solve the above-described problems, an LED lighting device according to the present invention includes a DC power supply, a voltage conversion circuit that boosts or reduces the voltage of the DC power supply, and a voltage detection circuit that detects an output voltage of the voltage conversion circuit. An LED driven by the output voltage of the voltage detection circuit, a current detection circuit for detecting a drive current flowing through the LED, a detection voltage detected by the voltage detection circuit, and a detection current detected by the current detection circuit And a control circuit that obtains an output voltage value based on a value obtained by adding and a value with respect to a reference voltage and controls the output voltage of the voltage conversion circuit with the output voltage value.

  According to the present invention, the use of the constant voltage element in the voltage detection circuit can simplify the PWM control circuit, and can continuously change the current control mode and the voltage control mode, thereby preventing flickering. It becomes.

It is a circuit block diagram for demonstrating 1st Embodiment regarding the LED lighting device of this invention. FIG. 2 is a circuit diagram for explaining a specific example of each circuit block in FIG. 1. 2 is a timing chart for explaining the operation of the voltage conversion circuit of FIG. 1. FIG. 2 is an explanatory diagram for explaining a relationship between a driving voltage and a driving current of the voltage detection circuit of FIG. 1. FIG. 2 is an explanatory diagram for explaining signals supplied from the voltage and current detection circuit of FIG. 1 to a PWM control circuit. FIG. 2 is an explanatory diagram for explaining an operation of the PWM control circuit of FIG. 1. It is a circuit diagram for demonstrating 2nd Embodiment regarding the LED lighting device of this invention. It is a circuit diagram for demonstrating 3rd Embodiment regarding the LED lighting device of this invention. It is explanatory drawing for demonstrating the operation | movement of FIG.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a conceptual circuit block diagram for explaining an embodiment relating to an LED lighting device of the present invention.

  In FIG. 1, reference numeral 11 denotes a DC power supply, and this power supply 11 is supplied to a voltage conversion circuit 13 via a power switch 12. The voltage conversion circuit 13 converts the DC voltage of the power source 11 into an AC voltage and boosts it, converts the AC voltage into a DC voltage, and outputs it as an output voltage. The voltage detection circuit 14 generates a drive voltage based on the output voltage Vd of the voltage conversion circuit 13, supplies the drive voltage to the LED 15 to which a plurality of LEDs are connected, detects the drive voltage, and extracts it as the detection voltage Vo. Reference numeral 16 denotes a current detection circuit for detecting a drive current flowing through the LED 15, and outputs a detection current Io detected by the current detection circuit 16.

  The detection voltage Vo of the voltage detection circuit 14 and the detection current Io of the current detection circuit 16 are supplied to the error amplifier 171 of the PWM control circuit 17, where the added value of the detection voltage Vo and the detection current Io and the reference voltage Vref The difference is amplified (α), and an error output (Vo + Io−Vref) × α is output from the error amplifier 171 to the PWM converter 172 in the next stage. The PWM converter 172 modulates the output pulse width based on the output level of the error amplifier 171 and supplies it to the voltage conversion circuit 13 as a drive pulse. The voltage conversion circuit 13 controls the output voltage based on the drive pulse width.

  With reference to FIG. 2, a circuit example more specifically showing the configuration of each circuit block in FIG. 1 will be described.

  The negative electrode of the DC power supply 11 is connected to the reference potential point, and the positive electrode is connected to one end of the choke coil L constituting the voltage conversion circuit 13 via the power switch 12. The voltage conversion circuit 13 connects the other end of the choke coil L to the anode of the diode D, and connects to the drain of the switching element Q using a MOS FET whose source is connected to the reference potential point. The gate of the switching element Q is connected to the source of the switching element Q via a resistor R1. The cathode of the diode D is connected to the reference potential point via the capacitor C.

  The connection point between the diode D and the capacitor C which is the output terminal of the voltage conversion circuit 13 is the connection point between the resistor R1 and the Zener diode ZD of the voltage detection circuit 14 in which the parallel circuit of the resistor R1 and the Zener diode ZD and the resistor R2 are connected in series. Connect one end to The other end of the resistor R2 having one end connected to the connection point of the resistor R1 and the Zener diode ZD is connected to the reference potential point. A detection voltage Vo is output as an output of the voltage conversion circuit 13 from a connection point between the resistor R1 and the parallel circuit of the Zener diode ZD and the resistor R2.

  The resistance values of the resistor R1 and the resistor R2 connected in parallel to the Zener diode ZD are R1> R2, and for example, when the resistor R1 is 1 MΩ, the resistor R2 is 1 KΩ.

  The other end of the parallel circuit of the resistor R1 having one end connected to the resistor R2 and the Zener diode ZD is connected to the anode of the LED at one end of the LED 15 formed by connecting a plurality of LEDs in series, and the cathode of the LED at the other end Are connected to a reference potential point via a resistor R3 constituting the current detection circuit 16. A detection current Io is output as an output of the current detection circuit 16 from the connection point between the LED 15 and the current detection circuit 16.

  The detection voltage Vo output from the voltage conversion circuit 13 and the detection current Io output from the current detection circuit 16 are supplied with the reference voltage Vref to the negative input − of the operational amplifier OP constituting the error amplifier 171 of the PWM control circuit 17. Supply to positive input + respectively. The output of the operational amplifier OP is supplied to the comparison input − of the comparator CP constituting the PWM converter 172 of the PWM control circuit 17. The comparison input + of the comparator CP is supplied with the output of the triangular wave generator TG that generates a triangular wave. The comparator CP supplies the output of the PWM control circuit 17 to the gate of the switching element Q of the voltage conversion circuit 13.

  Here, the operation of the voltage conversion circuit 13 will be described with reference to the timing chart of FIG.

  When the power switch 12 is turned on and the drive pulse a shown in FIG. 3A is supplied from the PWM control circuit 17 to the gate of the switching element Q1 of the voltage conversion circuit 13, the switching element Q1 is turned on / off. When the switching element Q1 is turned on, energy is stored in the choke coil L. At the moment when the switching element Q1 is turned off, the stored energy is transferred to the load side, and the boosted voltage output b as shown in FIG. can get. The transferred energy is rectified by the diode D and the capacitor C, and a DC output voltage Vd shown in FIG. The output voltage Vd varies depending on the duty of the voltage output b in FIG. That is, the output voltage Vd is large when the pulse width of the voltage output b is narrow, and the output voltage Vd is small when the pulse width is wide. FIG. 3C shows the current waveform of FIG.

  The value for converting the voltage in the voltage conversion circuit 13 varies depending on the number of LEDs connected in series with the LED 15 as a load. For this reason, in the above description, the value of the DC voltage 11 is increased, but it may be decreased.

  The output voltage Vd of the voltage conversion circuit 13 is applied across the resistor R2 connected in series with the parallel circuit of the resistor R1 and the Zener diode ZD of the voltage detection circuit 14, and is connected in series with the parallel circuit of the resistor R1 and the Zener diode ZD. The detection voltage Vo is taken out from the connection point with R2 and supplied to the positive input + of the error amplifier 171 which is the same as the detection current Io.

  The output voltage Vd of the voltage conversion circuit 13 is supplied to the LED 15 via the voltage detection circuit 14, and a drive current flows through the LED 15 to light the LED. The drive current flowing through the LED 15 is passed through the resistor R3 of the current detection circuit 16 so as to be taken out as the detection current Io and supplied to the positive input + of the error amplifier 171 of the PWM control circuit 17.

  The voltage detection circuit 14 to which the output voltage Vd is applied is extracted as a detection voltage Vo from the connection point between the resistor R2 and the resistor R2 connected in series with the parallel circuit of the resistor R1 and the Zener diode ZD, and the positive input of the error amplifier 171 that is the same as the detection current Io. Supplying to +.

  FIG. 4 is an explanatory diagram for explaining the relationship between the drive voltage and the drive current of the voltage detection circuit 14.

  That is, the Zener diode ZD is driven by current or voltage depending on whether the voltage applied to the Zener diode ZD of the voltage detection circuit 14 based on the output voltage Vd exceeds or does not exceed the Zener voltage Vz. At this time, since the resistance values of the resistors R1 and R2 connected in parallel to the Zener diode ZD are set in a relationship of R1> R2, a slight negative feedback is applied even before the operation of the Zener diode ZD. It will be.

  Therefore, the output of the voltage detection circuit 14 having the Zener diode ZD is a slightly smoother solid line in FIG. 4 than the conventional broken line characteristic in FIG. 4 in which the switching between current and voltage at the output of the voltage detection circuit 14 is steep. It becomes the characteristic. As shown by this characteristic, even in the part immediately after switching from the current to the voltage, the characteristic R is attached, and even in this part, the switching from the current to the voltage control mode becomes smooth.

  That is, the output voltage Vd rises, and the detection voltage Vo when the voltage applied to the Zener diode ZD is equal to or lower than the Zener voltage Vz has a value as shown in FIG. Further, the detection current Io has a value as shown in FIG. 5 when the voltage applied to the Zener diode ZD of the voltage detection circuit 14 is equal to or less than the Zener voltage Vz based on the output voltage Vd. The added value of the detection voltage Vo and the detection current Io when the voltage applied to the Zener diode ZD becomes equal to or higher than the Zener voltage Vz causes the detection voltage Vo to rapidly increase as shown in FIG.

  Therefore, a case where the voltage applied to the Zener diode ZD exceeds the Zener voltage Vz can be determined as a no-load voltage generated when the voltage across the voltage detection circuit 14 increases or is disconnected.

  The added value of the detection voltage Vo and the detection current Io is the difference between the reference voltage Vref supplied to the negative input − of the error amplifier 171 and the comparison input of the comparator CP as the output of the operational amplifier OP shown at 61 in FIG. -To supply. The triangular wave of the triangular wave generator TG indicated by 62 in FIG. 6A is supplied to the comparison input + of the comparator CP.

  The comparator CP compares 61 and 62 in FIG. 6A and outputs the comparison output shown in FIG. 6B from the output. As the output of the comparator CP from the output of the comparator CP, the drive pulse a corresponding to FIG. 3A is supplied to the gate of the switching element Q of the voltage conversion circuit 13, and the voltage conversion circuit 13 sets the duty of the drive pulse a. Based on the output voltage Vd.

  Here, when the voltage applied to the Zener diode ZD based on the value of the output voltage Vd is equal to or lower than the Zener voltage Vz, the added value of the detected voltage Vo and the detected current Io is equal to or lower than the reference voltage Vref. Accordingly, the level of the positive input + of the operational amplifier OP is equal to or lower than the reference potential Vref. For this reason, the level of the output 61 of the operational amplifier OP shown in FIG. 6A decreases in the direction of the arrow Ia in the figure. As a result, the duty of the drive pulse a spreads in the direction of arrow II in FIG. 6B, and the output voltage Vd of the voltage conversion circuit 13 rises based on this drive pulse a.

  Next, when the voltage applied to the Zener diode ZD exceeds the Zener voltage Vz based on the value of the output voltage Vd, the added value of the detection voltage Vo and the detection current Io becomes equal to or higher than the reference voltage Vref. Accordingly, the level of the positive input + of the operational amplifier OP becomes equal to or higher than the reference potential Vref. Therefore, the level of the output 61 of the operational amplifier OP shown in FIG. 6A increases in the direction of arrow Ib in the figure. As a result, the duty of the drive pulse a becomes narrower in the direction opposite to the arrow II in FIG. 6B, and the output voltage Vd of the voltage conversion circuit 13 decreases based on this drive pulse a.

  As described above, when the voltage applied to the Zener diode ZD of the voltage detection circuit 14 does not exceed the Zener voltage Vz, the current control mode can be continuously performed. It is possible to prevent flickering of the LED. Further, the output of the voltage detection circuit 14 can suppress frequent switching of the circuit operation by increasing the feedback amount to the PWM control circuit 17 when a voltage exceeding a certain level is output.

  In this embodiment, the Zener diode is used in the voltage detection circuit, so that the configuration of the PWM control circuit can be simplified, and the current control mode and the voltage control mode can be continuously changed to suppress flicker and the like. can do.

  By the way, the reference voltage Vref is supplied to the positive input + of the operational amplifier OP of the error amplifier 171, the added value of the detection voltage Vo and the detection current Io is supplied to the negative input −, and the output of the operational amplifier OP is supplied to the comparison input −. Even if the configuration is such that the comparison input + of the comparator CP is supplied, the same effect as described above can be obtained.

  FIG. 7 is a circuit diagram for explaining a second embodiment of the present invention. FIG. 7 shows only the voltage detection circuit 141, but the other parts are the same except for the voltage detection circuit 14 of FIG. 1, and illustration thereof is omitted here.

  That is, the voltage detection circuit 141 divides the resistor R1 into resistors R1a and R2a, the connection point between the resistors R1a and R2a is connected to the reference terminal REF of the shunt regulator SR, and the cathode K and the anode A of the shunt regulator SR are It is connected in the same way as the Zener diode ZD. The voltage detection circuit 141 has the same characteristics as in FIG.

  The resistors R1a and R1b are set to R1a = R1b, for example, and R1a + R1b is set to have a relationship of R1> R2 with respect to the resistor R2 similarly to the resistor R1.

  That is, when the drive voltage Vout decreases due to the influence of the LED 15 as a load, the voltage applied to the resistors R1a and R1b decreases. As a result, the voltage applied to the reference terminal REF of the shunt regulator SR obtained by dividing the drive voltage Vout by the resistors R1a and R1b decreases. By suppressing the current flowing through the cathode K of the shunt regulator SR, the drive voltage Vout is increased and the drive voltage Vout is stabilized.

  When the drive voltage Vout rises due to load fluctuation, the voltage applied to the reference terminal REf rises, the current flowing through the cathode K of the shunt regulator SR is increased, the drive voltage Vout is lowered, and the drive voltage Vout is stabilized.

  Also in this case, the detection voltage Vo of the voltage detection circuit 141 and the detection current Io of the current detection circuit 16 are added and supplied to the positive input + of the operational amplifier 171 of the PWM control circuit 17. Therefore, in the PWM control circuit 17, when the added value is higher than the reference voltage Vref, the duty of the drive pulse a is narrowed to lower the drive voltage Vd of the voltage conversion circuit 13. When the added value is lower than the reference voltage Vref, control is performed to increase the drive voltage Vd of the voltage conversion circuit 13 by increasing the duty of the drive pulse a.

  Also in this embodiment, the operational amplifier 171 can share the voltage control and current control mode loops to simplify the configuration of the PWM control circuit, and the voltage detection circuit 141 can perform the same current and voltage switching as in FIG. Therefore, the current control mode and the voltage control mode can be continuously changed, and flickering can be suppressed.

  8 and 9 are diagrams for explaining the third embodiment of the present invention, FIG. 8 is a circuit diagram, and FIG. 9 is a diagram for explaining the relationship between the drive voltage and drive current of the voltage detection circuit of FIG. FIG. FIG. 8 shows the configuration of only the voltage detection circuit, but the other parts are the same as those in FIG. 1 and are not shown here.

  That is, the voltage detection circuit 142 is a circuit in which Zener diodes ZD1 and ZD2 having different Zener voltages are connected in series, and the other end of the resistor R1 having one end connected to the output of the voltage conversion circuit 13 is connected to the connection point. .

  Even before the drive voltage Vout rises and exceeds the Zener voltage VD2 of the Zener diode ZD2 and the Zener diode ZD2 operates, a slight negative feedback is applied from the relationship of resistance R1> R2. If the drive voltage Vout further rises and exceeds the Zener voltage VD1 of the Zener diode ZD1, and if the drive voltage Vout exceeds VD1 + VD2, even before the Zener diode ZD2 operates, negative feedback is slightly caused by the relationship of the resistance R1> R2. This is done.

  As a result, as shown in FIG. 9, the drive voltage Vout is switched from the current control to the voltage control mode over two stages when the drive voltage Vout exceeds the Zener voltage VD1 and when the drive voltage Vout exceeds VD1 + VD2. It is possible to prevent an excessive drive voltage and drive current from being supplied.

  Further, since the resistance R1> R2, the switching characteristic is smooth at the points P1 and P2 at which the current control is switched to the voltage control mode, and the flickering at the time of switching to the voltage control mode at the current control. Can also be suppressed.

  The present invention is not limited to the above-described embodiment. For example, a Zener diode that is a non-linear element may exhibit characteristics similar to those of a non-linear element such as a shunt regulator circuit. In the voltage conversion circuit, a circuit for boosting a DC voltage has been described. However, a flyback circuit, a down chopper, or the like may be used.

  Further, although a plurality of LEDs are connected in series, they may be singular or connected in parallel. In the case of LEDs connected in parallel, a plurality of LEDs connected in series may be connected in parallel. When a plurality of LEDs connected in series are connected in parallel, it is necessary to connect a balancer (current limiting) resistor to each of the LEDs connected in series and adjust the drive current flowing through each of the LEDs connected in series.

11 Power supply 12 Power switch 13 Voltage conversion circuit 14 Voltage detection circuit 15 LED
16 Current detection circuit 17 PWM control circuit 171 Error amplifier 172 PWM converter ZD, ZD1, ZD2 Zener diodes R1 to R3, R1a, R1b Resistor Vref Reference voltage OP Operational amplifier CP Comparator TG Triangle wave generator SR Shunt regulator

Claims (6)

DC power supply,
A voltage conversion circuit for stepping up or down the voltage of the DC power supply;
A voltage detection circuit for detecting an output voltage of the voltage conversion circuit;
LEDs driven by the output voltage of the voltage detection circuit;
A current detection circuit for detecting a drive current flowing through the LED;
An output voltage value is obtained based on a value obtained by adding a detection voltage detected by the voltage detection circuit and a detection current detected by the current detection circuit, and a value with respect to a reference voltage, and the output of the voltage conversion circuit is obtained based on the output voltage value. An LED lighting device comprising: a control circuit for controlling voltage.   The control circuit supplies the detection voltage and the detection current to a positive (or negative) input of an operational amplifier to which a reference voltage is supplied negatively or (positive), and an output voltage of the operational amplifier is positive (or negative). A control signal for changing the duty of a driving pulse for controlling the output voltage of the voltage change circuit based on the output voltage of the operational amplifier based on the output voltage of the operational amplifier for comparison by supplying to the negative (or positive) input of a comparator whose triangular wave is supplied to the input The LED lighting device according to claim 1, wherein:   The voltage detection circuit is configured such that a voltage obtained by dividing the output voltage of the voltage conversion circuit by the first and second resistors is used as a detection voltage, and a constant voltage element is connected in parallel to the first resistor. The LED lighting device according to claim 1.   The LED lighting device according to claim 2, wherein the constant voltage element is a Zener diode.   3. The LED lighting device according to claim 2, wherein the constant voltage element includes Zener diodes having different Zener voltages connected in series, and the first resistor is connected in parallel to one higher Zener diode.   In the voltage element, the first resistor is divided into series-connected resistors, and a shunt regulator is connected in parallel to the divided resistors at the reference terminal, the cathode, and the anode at a connection point of the divided resistors. The LED lighting device according to claim 1.

Images