Drive circuit for light-emitting diodes

• US 6,747,420 B2
• Filed: 09/13/2002
• Issued: 06/08/2004
• Est. Priority Date: 03/17/2000
• Status: Expired due to Term

• Current Assignee: Tridonicatco GmbH & Co. KG. (Zumtobel Group AG)
• Original Assignee: Tridonicatco GmbH & Co. KG. (Zumtobel Group AG)
• Inventors: Ludorf, Werner, Barth, Alexander, Hein, Peter
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Alemu, Ephrem
• Application Number:
  US10/242,704
• Publication Number:
  US 20030117087A1
• Time in Patent Office: 634 Days
• Field of Search: 315/291, 315/224, 315/307, 315/308, 315/169.3, 315/301, 315/129, 315/151, 315/158, 315/159
• US Class Current: 315/291
• CPC Class Codes: H05B 45/12 using optical feedback
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

The invention relates to a control circuit for at least one light-emitting diode (1) for adjusting the current and/or the voltage of the light-emitting diode (1) to a desired value adjusted by means of a controller (3), the current, the voltage and/or the luminescence of the light-emitting diode (1) being detectable and comparable with the desired value.

Claims

1. A drive circuit for at least one light-emitting diode, said circuit comprising:

a switched-mode regulator that can be supplied with a direct input voltage to drive said at least one light-emitting diode;

means for determining current through a light-emitting diode connected to said drive circuit and for determining the voltage across such light-emitting diode;

a regulating device to which a current setpoint value and a voltage setpoint value are fed and to which signals representative of the determined current and the determined voltage at the light-emitting diode are supplied, said regulating device being constructed to regulate the current and the voltage supplied to the light-emitting diode according to the respective setpoint values; and

a controller arranged for adjusting the setpoint values.

2. A drive circuit according to claim 1, and further including:

means for determining the brightness of said light-emitting diode and for adjusting said regulating device according to the determined brightness.

3. A drive circuit according to claim 1 or 2, and further including:

an AC/DC converter arranged to provide said direct voltage, said switched-mode regulator being integrated into said AC/DC converter.

4. A drive circuit according to claim 1 or 2, wherein:

said switched-mode regulator comprises a semiconductor switching element arranged to be driven by said controller.

5. A drive circuit according to claim 4, wherein:

said controller is connected to drive the said semiconductor switching element by one of amplitude modulation, pulse-width modulation and variable frequency modulation.

6. A drive circuit according to claim 4, wherein:

said controller is constructed and arranged to adjust said setpoint values in such a way that at least one of the switching frequency and said duty cycle of the switched-mode regulator is altered.

7. A drive circuit according to claim 1, and further including:

a measuring shunt arranged to be connected in series with a light-emitting diode, said measuring shunt being operative to determine current through said light-emitting diode.

8. A drive circuit according to claim 1, and further including:

a measuring shunt arranged to be connected in parallel with a light-emitting diode, said measuring shunt being operative to determine the voltage across said light-emitting diode.

9. A drive circuit according to claim 1, wherein:

said controller includes a variable resistor arranged to be connected in series with said light-emitting diode, said variable resistor being adjustable to adjust the setpoint value.

10. A drive circuit according to claim 9, wherein:

said variable resistor is a field-effect transistor.

11. A drive circuit according to claim 9 or 10, wherein:

said variable resistor is connected such that current through the light-emitting diode can be determined by means of the voltage drop across the variable resistor.

12. A drive circuit according to claim 1, and further including:

a photodiode connected and arranged to determine the brightness of said light emitting diode.

13. A drive circuit according to claim 1, wherein:

said switched-mode regulator is a step-up converter, a step-down converter or an insulating reverse converter.

14. A drive circuit according to claim 1, wherein:

said switched-mode regulator comprises a boost choke that is inductively coupled to a further coil, which in turn is connected to the output of the switched-mode regulator.

15. A drive circuit according to claim 1, wherein:

said switched-mode regulator includes a smoothing capacitor at its output.

16. A drive circuit according to claim 1, and including:

a further controllable switching element in the current path of the LED.

17. A drive circuit according to claim 1, wherein:

said switched-mode regulator is operable at frequencies in the range between 200 kHz and 1 MHz.

18. A drive circuit according to claim 1, wherein:

said circuit comprises at least one multilayer circuit into which passive components of said drive circuit are integrated.

19. A drive circuit according to claim 18, wherein:

said multilayer circuit comprises a plurality of conductor boards disposed above one another, to whose upper sides and/or lower sides conductor tracks composed of a conductive material are applied, said conductor boards having holes filled with a conductive material for connecting various conducting levels.

20. A drive circuit according to claim 19, wherein:

said multilayer circuit is an LTCC structure that comprises a plurality of low-sintering ceramic layers, said layers being disposed above one another and having therebetween, conductor tracks, said ceramic layers also having holes through which conductor tracks of different levels are connected.

21. A drive circuit according to claim 18, wherein:

said multilayer circuit is surrounded by a metallic housing.

22. A drive circuit according to claim 18, wherein:

semiconductor chips are mounted on a surface of said multilayer circuit flip-chip technology.