Operating circuit for LEDs

• US 8,525,442 B2
• Filed: 10/16/2009
• Issued: 09/03/2013
• Est. Priority Date: 10/20/2008
• Status: Active Grant

• Current Assignee: Tridonic AG (Zumtobel Group AG)
• Original Assignee: Tridonic AG (Zumtobel Group AG)
• Inventors: Zimmermann, Michael, Pereira, Eduardo
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): Chen, Jianzi
• Application Number:
  US13/125,022
• Publication Number:
  US 20110199023A1
• Time in Patent Office: 1,418 Days
• Field of Search: 315/209.R, 315/119, 315/121, 315/122, 315/125, 315/127, 315/185.R, 315/186, 315/192, 315/193, 315/210, 315/225, 315/226, 315/291, 315/297, 315/299, 315/302, 315/306, 315/307, 315/308, 315/310, 315/312, 315/313, 315/360, 315/362
• US Class Current: 315/307
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology

Abstract

An operating circuit is provided for an LED, which receives a voltage, and which supplies a voltage for the LED via a coil, having a first switch clocked by a control/regulating unit. Power is stored temporarily in the coil when the first switch is activated so that the power is discharged via a diode and via the LED when the first switch is turned off. A capacitor is arranged in parallel to the LED and maintains current through the LED during the demagnetization of the coil. A first switch generates a first sensor signal dependent on the current flowing through the first switch, and/or a second sensor unit, which detects whether demagnetization of the coil unit has occurred and generates a sensor signal. The signals are fed to the control/regulating unit and processed. The control/regulating unit reactivates the first switch when the coil is demagnetized and/or the diode is blocking.

Claims

1. An operating circuit for at least one LED, which is supplied with direct current voltage or rectified alternating current voltage, and which provides a supply voltage for the at least one LED by a coil (L1) and a first switch (S1) that is clocked by a control/regulation unit (SR), where during the activated state of the first switch (S1), energy is temporarily stored in the coil (L1), which is discharged when the first switch (S1) is turned off through a free wheeling diode (D1) and through at least one LED, wherein a capacitor (C1) is provided, which is arranged in parallel to at least one LED, and which maintains the current through the LED during a demagnetization phase of the coil (L1), a first sensor unit (SE1) is provided, which generates a sensor signal (SES1) which is dependent on the current flowing through the first switch (S1), and with a second sensor unit (S2), which detects that the demagnetization of the coil (L1) has been reached and generates a sensor signal (SES2), the sensor signals (SES1, SES2) are supplied to and processed by a control/regulation unit (SR) at a point in time when the first switch (S1) is turned on again, when the coil (L1) is demagnetized and thereby the free wheeling diode (D1) is blocking.

2. The operating circuit according to claim 1, wherein the sensor unit (SR) uses a combination of the signal (SES1) of the first sensor unit (SE1) and a signal (SES2) of the second sensor unit (SE2) for determining the point in time for turning the first switch (S1) on and off.

3. The operating circuit according to claim 2, wherein the control/regulation unit (SR) of the first switch (S1) is turned off when the current flowing through the first switch (S1) exceeds a maximum reference value.

4. The operating circuit according to claim 1, wherein the first sensor unit (SE1) is a measurement resistor (shunt, RS).

5. The operating circuit according to claim 1, wherein the second sensor unit (SE2) comprises a secondary winding (L2) which is inductively coupled with the coil (L1).

6. The operating circuit according to claim 1, wherein the second sensor unit (SE2) is a Hall sensor.

7. The operating circuit according to claim 1, wherein the second sensor unit (SE2) determines whether demagnetization of the coil (L1) has been reached, as the unit monitors the voltage at the node (Ux) between the first switch (S1) and the coil (L1).

8. The operating circuit according to claim 7, wherein the detection of the voltage is realized by a resistive voltage distributor (R1/R2), a capacitive voltage distributor, or a combined voltage distributor comprising a resistance and a capacitance.

9. The operating circuit according to claim 1, further comprising a control circuit IC, which is provided with an input for determining whether the demagnetization of the coil (L1) has been reached and controls a first switch (S1).

10. The operating circuit according to claim 9, further comprising a microcontroller, which activates and/or deactivates by applying a voltage to an input of the control circuit IC this control circuit, and presets a reference voltage for the control circuit IC at another input.

11. The operating circuit according to claim 1, wherein the operating circuit can be controlled by a second switch (S2), which is arranged in parallel to the capacitor (C1) and to the LEDs and is independent of the first switch (S1).

12. The operating circuit according to claim 11, wherein the second switch is closed in order to accelerate a discharging operation of the capacitor (C1).

13. A method for operating at least one LED by a switching regulator circuit, which is supplied with direct current voltage or rectified alternating current voltage and which provides a supply voltage for at least one LED by a coil (L1) and a first switch (S1) that is clocked by a control/regulation unit (SR), where during the activated state of the first switch (S1), energy is temporarily stored in the coil (L1), which is discharged when the first switch (S1) is turned off through a free wheeling diode (D1) and through at least one LED, where a capacitor (C1) is provided, which is arranged in parallel to at least one LED, and which maintains the current through the LED during the phase of the demagnetization of the coil (L1), the method comprising:

providing a first sensor unit (SE1), which generates a sensor signal (SES1) that is dependent on the current flowing through the first switch (S1), and a second sensor unit (SE2), which detects demagnetization of the coil (L1),

turning the first switch (S1) on again, via the control/regulation unit (SR), at a point in time when the coil (L1) is demagnetized and thereby the free wheeling diode (D1) is blocking.

14. The method for operating at least one LED according to claim 13 wherein the control/regulation unit (SR) of the first switch (S1) is turned off when the current flowing through the first switch (S1) exceeds a maximum reference value.