LIGHT EMITTING DIODE DRIVE APPARATUS

Abstract

There is provided a light emitting diode drive apparatus which decreases a conducted emission. The light emitting diode drive apparatus includes a light emitting diode to which a voltage is applied from a voltage source, a choke coil connected in series to the light emitting diode, a rectifier diode connected in parallel to the light emitting diode and the choke coil to supply a back electromotive force generated in the choke coil to the light emitting diode, and a switching drive circuit including a switching element and a control circuit block. The switching element determines whether a current is applied or not applied to the light emitting diode. The control circuit block controls on/off timing of the switching element to control the current flowing into the light emitting diode. The choke coil is connected between the light emitting diode and the switching element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a light emitting diode drive apparatus according to a first embodiment of the invention;

FIG. 2 shows waveforms of each voltage and each current in the first embodiment;

FIG. 3A shows a voltage and a current of the light emitting diode in the first embodiment;

FIG. 3B shows a voltage and a current of a conventional light emitting diode;

FIG. 4A shows a conducted emission waveform generated by the light emitting diode drive apparatus of the first embodiment;

FIG. 4B shows a conducted emission waveform generated by the conventional light emitting diode drive apparatus;

FIG. 5 is a circuit diagram showing a light emitting diode drive apparatus according to a second embodiment of the invention;

FIG. 6 shows waveforms of each voltage and each current in the second embodiment;

FIG. 7 is a circuit diagram showing a light emitting diode drive apparatus according to a third embodiment of the invention;

FIG. 8 shows a period during which the current is flowing into the light emitting diode in the third embodiment;

FIG. 9 is a circuit diagram showing a light emitting diode drive apparatus according to a fourth embodiment of the invention;

FIG. 10 is a circuit diagram showing a light emitting diode drive apparatus according to a fifth embodiment of the invention;

FIG. 11 shows a period during which the current is flowing into the light emitting diode in the fifth embodiment;

FIG. 12 is a circuit diagram showing a light emitting diode drive apparatus according to a sixth embodiment of the invention; and

FIG. 13 shows a schematic configuration of the conventional light emitting diode drive apparatus.

Claims

1. A light emitting diode drive apparatus comprising: at least one light emitting diode;a choke coil; anda switching drive circuit which includes a switching element and a control circuit block, the switching element determining whether a current is applied or not applied to the light emitting diode, the control circuit block controlling on/off timing of the switching element to control the current flowing into the light emitting diode,wherein the choke coil is connected between the light emitting diode and the switching drive circuit.

2. The light emitting diode drive apparatus according to claim 1, further comprising a rectifier diode which supplies a back electromotive force generated in the choke coil to the light emitting diode.

3. The light emitting diode drive apparatus according to claim 2, wherein an anode terminal of the light emitting diode is connected to a voltage source, one end of the choke coil is connected to a cathode terminal of the light emitting diode, an anode terminal of the rectifier diode is connected to other end of the choke coil, a cathode terminal of the rectifier diode is connected to the anode terminal of the light emitting diode, and the switching drive circuit is connected between the other end of the choke coil and a reference potential.

4. The light emitting diode drive apparatus according to claim 2, wherein a cathode terminal of the light emitting diode is connected to a reference potential, one end of the choke coil is connected to an anode terminal of the light emitting diode, a cathode terminal of the rectifier diode is connected to other end of the choke coil, an anode terminal of the rectifier diode is connected to the cathode terminal of the light emitting diode, and the switching drive circuit is connected between a voltage source and the other end of the choke coil.

5. The light emitting diode drive apparatus according to claim 1, further comprising a protective element which is connected in parallel to both terminals of the light emitting diode to protect the light emitting diode against the electrostatic discharge damage.

6. The light emitting diode drive apparatus according to claim 1, wherein the light emitting diode includes a light emitting element and a capacitor which are connected in parallel.

7. The light emitting diode drive apparatus according to claim 1, wherein the light emitting diode includes a light emitting element and a zener diode which is connected in antiparallel between the anode terminal and the cathode terminal of the light emitting element.

8. The light emitting diode drive apparatus according to claim 1, further comprising a rectifier which rectifies an alternating-current voltage when a voltage source is an alternating-current power supply which outputs the alternating-current voltage.

9. The light emitting diode drive apparatus according to claim 8, wherein the control circuit block includes: a constant current source of which one end is connected to the rectifier;a regulator which is connected to other end of the constant current source, the regulator outputting a start-up signal when an output voltage of the constant current source is not lower than a predetermined value, the regulator outputting a stop signal when the output voltage of the constant current source is lower than the predetermined value;a current detection circuit which detects a current flowing into the switching element;a control circuit which intermittently performs on/off control of the switching element at a predetermined oscillation frequency based on an output signal of the current detection circuit such that the current flowing into the light emitting diode is kept constant; anda start/stop circuit which controls a start and a stop of the control circuit based on the start-up signal and the stop signal from the regulator.

10. The light emitting diode drive apparatus according to claim 9, further comprising a capacitor of which one end is connected to the regulator and other end is connected to a reference potential of the rectifier or the choke coil.

11. The light emitting diode drive apparatus according to claim 9, further comprising an input voltage detection circuit which detects a voltage outputted from the rectifier and compares the detected voltage with a predetermined value to output a light emitting signal or an extinction signal for controlling light emission or extinction of the light emitting diode respectively, wherein the start/stop circuit outputs the stop signal to the control circuit when the regulator outputs the stop signal, and outputs the light emitting signal or the extinction signal of the input voltage detection circuit to the control circuit when the regulator outputs the start-up signal.

12. The light emitting diode drive apparatus according to claim 11, wherein the input voltage detection circuit includes: a plurality of resistors connected in series, the resistors being applied with the output voltage of the rectifier directly or through a resistor inserted between the rectifier and the input voltage detection circuit; anda comparator having a positive input terminal which is applied with a direct-current voltage divided by the plurality of resistors, and having a negative input terminal which is applied with an input reference voltage being a reference.

13. The light emitting diode drive apparatus according to claim 11, wherein the input voltage detection circuit includes: a plurality of resistors which are applied with the output voltage of the rectifier directly or through a resistor inserted between the rectifier and the input voltage detection circuit, the plurality of resistors outputting a first dividing voltage and a second dividing voltage lower than the first dividing voltage;a first comparator having a positive input terminal which is applied with the first dividing voltage, and having a negative input terminal which is applied with an input reference voltage being a reference;a second comparator having a negative input terminal which is applied with the second dividing voltage, and having a positive input terminal which is applied with the input reference voltage; andan AND circuit which receives output signals of the first and second comparators.

14. The light emitting diode drive apparatus according to claim 9, wherein the current detection circuit detects the current flowing into the switching element by comparing an on-state voltage of the switching element with a detection reference voltage being a reference.

15. The light emitting diode drive apparatus according to claim 9, wherein the switching drive circuit further includes: another switching element of which one end connected to a junction point between the choke coil and the switching element to switch by the same control as the switching element by the control circuit, a current flowing into the other switching device, the current being less than a current flowing into the switching element and having a constant current ratio to the current flowing into the switching element; anda resistor which is connected in series between other end of the other switching element and a reference potential, andthe current detection circuit detects the current of the switching element by comparing a voltage between both ends of the resistor with the detection reference voltage being reference.

16. The light emitting diode drive apparatus according to claim 14, wherein the switching drive circuit further includes an external detection terminal connected to the current detection circuit, and an on-period in the intermittent on/off control of the switching element is changed to adjust a level of a constant current flowing into the light emitting diode by changing a value of the detection reference voltage inputted to the external detection terminal.

17. The light emitting diode drive apparatus according to claim 16, further comprising a soft-start circuit which is connected between the current detection circuit and the external detection terminal to which the detection reference voltage is inputted, wherein the soft-start circuit outputs the detection reference voltage such that the detection reference voltage is gradually increased until the detection reference voltage reaches a constant value when the light emitting signal is inputted from the start/stop circuit.

18. The light emitting diode drive apparatus according to claim 15, wherein the switching drive circuit further includes an external detection terminal connected to the current detection circuit, and an on-period in the intermittent on/off control of the switching element is changed to adjust a level of a constant current flowing into the light emitting diode by changing a value of the detection reference voltage inputted to the external detection terminal.

19. The light emitting diode drive apparatus according to claim 18, further comprising a soft-start circuit which is connected between the current detection circuit and the external detection terminal to which the detection reference voltage is inputted, wherein the soft-start circuit outputs the detection reference voltage such that the detection reference voltage is gradually increased until the detection reference voltage reaches a constant value when the light emitting signal is inputted from the start/stop circuit.