LED driver circuit

• US 8,680,778 B2
• Filed: 01/19/2007
• Issued: 03/25/2014
• Est. Priority Date: 04/21/2006
• Status: Active Grant

• Current Assignee: Tridoniticatco GmbH & Company KG
• Original Assignee: Tridoniticatco GmbH & Company KG
• Inventors: Stevens, Frederick, Wallhead, Geoff, Rohner, Daniel, Mair, Alexander
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): LUONG, HENRY T
• Application Number:
  US12/296,504
• Publication Number:
  US 20100060189A1
• Time in Patent Office: 2,622 Days
• Field of Search: 315/72, 315/129, 315/209.R, 315/291, 315/297, 315/307, 315/262, 315/274, 315/287, 315/185.R, 315/91
• US Class Current: 315/291
• CPC Class Codes: H02J 9/065 for lighting purposes
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

An emergency-lighting device for operating a light-source, in particular an LED, comprises an energy storage unit, a charging circuit, to be supplied with a mains supply voltage (U_in), for charging the energy storage unit during charging operation, the charging circuit comprising a potential separation, and also a driver circuit, supplied by the energy storage unit during emergency-light operation, for operating the light-source. Furthermore a control unit is provided which is designed for monitoring the state of the mains supply voltage (U_in) during charging operation and, when an emergency condition is detected, for activating emergency-light operation, the control unit ascertaining the state of the mains supply voltage (U_in) on the basis of operating variables of the emergency-lighting device which are measured on the output side of the charging circuit.

Claims

1. A circuit for operating at least one LED, comprising:

a driver circuit with a coil and with a switch which is connected in series with the coil and clocked at a high frequency, the switch being controlled by a control unit,

wherein when the switch is closed the coil is magnetized and when the switch is open the coil is demagnetized in a form of a current through the LED,

wherein in a demagnetizing-current path when the switch is open a current-registering means is provided which supplies a current-registering signal to the control unit, wherein the control unit is adapted to ascertain a temporally averaged value of the current through the LED on a basis of a value of the current-registering signal at an end of an on-time cycle and also on the basis of a value at an end of a demagnetizing phase, wherein for a purpose of dimming the LED the control unit superimposes a comparatively low-frequency modulation on a high-frequency timing of the switch.

2. The circuit according to claim 1, wherein the control unit adjusts a switching-frequency and/or a pulse duty factor in a manner depending at least on the registered temporally averaged value of the current through the LED.

3. The circuit according to claim 1, wherein for the purpose of dimming the LED, the control unit superimposes the comparatively low-frequency modulation on the high-frequency timing of the switch, and/or wherein, for the purpose of dimming, the mean value of the current through the LED is effected by adjustment of a pulse duty factor and/or of a switching-frequency of the switch which is clocked at the high frequency.

4. The circuit according to claim 1, wherein the low-frequency modulation is a pulse-width modulation.

5. The circuit according to claim 1, wherein the driver circuit is supplied from a battery voltage and/or from an AC mains voltage.

6. The circuit according to claim 5, comprising a unit for registering a battery-discharge current which is functionally connected to the control unit, wherein for a purpose of regulating the battery-discharge current the current through the LED is adjustable in a manner depending on the registered battery-discharge current.

7. The circuit according to claim 5, wherein the battery is connected to a charging circuit supplied with mains voltage.

8. The circuit according to claim 7, wherein the driver circuit dims the LED if a mean value of the mains voltage falls below a threshold value.

9. The circuit according to claim 7, wherein the charging circuit comprises a flyback converter.

10. The circuit according to claim 9, wherein the flyback converter is gated in pulsed manner if a mean value of the mains voltage falls below a threshold value.

11. The circuit according to claim 5, further comprising a circuit for registering the battery voltage.

12. The circuit according to claim 11, wherein the current through the LED is adjustable in a manner depending on an output signal of the circuit for registering the battery voltage.

13. The circuit according to claim 5, wherein a battery-charging current is registered.

14. The circuit according to claim 1, wherein the control unit registers an LED voltage.

15. The circuit according to claim 1, wherein the control unit carries out a test measurement of electrical parameters at start-up, to determine whether the LED or which LED is connected to the driver circuit.

16. The circuit according to claim 15, wherein the control unit adjusts an operating current through the LED in a manner depending on an outcome of the test measurement.

17. The circuit according to claim 15, wherein the test measurement comprises an application of a relatively small test current by appropriate triggering of the driver circuit and in the measuring of a resulting LED voltage.

18. The circuit according to claim 1, wherein the control unit increases the LED current at start-up, by appropriate triggering of the switch of the driver circuit, from a low value to a stationary operating value.

19. An emergency-lighting device, comprising the circuit according to claim 1.

20. A process for operating at least one LED with a circuit that comprises:

a driver circuit with a coil and with a switch which is connected in series with the coil and clocked at a high frequency, the switch being controlled by a control unit,

wherein when the switch is closed the coil is magnetized and when the switch is open the coil is demagnetized in a form of a current through the LED,

wherein in a demagnetizing-current path when the switch is open a current-registering means is provided which supplies a current-registering signal to the control unit, wherein the control unit is adapted to ascertain a temporally averaged value of the current through the LED on a basis of a value of the current-registering signal at an end of an on-time cycle and also on the basis of a value at an end of a demagnetizing phase, wherein for a purpose of dimming the LED the control unit superimposes a comparatively low-frequency modulation on a high-frequency timing of the switch.