Drive circuit for at least one LED strand

• US 20030227265A1
• Filed: 06/10/2003
• Published: 12/11/2003
• Est. Priority Date: 06/10/2002
• Status: Active Grant

• Current Assignee: ABL IP Holding LLC (Acuity Brands, Inc.)
• Original Assignee: Patent-Treuhand-Gesellschaft Fur Elektrische Gluhlampen mbH (Ams-Osram AG)
• Inventors: Biebl, Alois
• Granted Patent: US 7,061,394 B2
• Time in Patent Office: Days
• US Class Current: 315/291
• 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: H05B 45/385 using flyback topology

Abstract

Drive circuit for at least one LED strand (D1 to D4), with a switch (T1) being arranged in series with each LED strand and with each LED strand having a supply connection via which it can be connected to a supply voltage, in which case each switch (T1) can be driven so as to allow a current to flow in the associated LED strand, having a first control loop which is designed to drive the switch (T1) of the at least one LED strand such that an adjustable mean value ({overscore (i)}_LEDnom) is achieved for the current (i_LED) flowing through the LED strand, with the drive circuit also having: a second control loop which is designed to provide a supply voltage (U_A) for the at least one LED strand (D1 to D4) as a function of the peak value (î_LED) of the current (i_LED) flowing through the at least one LED strand. The present invention also relates to a corresponding method for operating at least one LED strand.

Claims

1. A drive circuit for at least one LED strand, with a switch being arranged in series with each LED strand and with each LED strand having a supply connection via which it can be connected to a supply voltage, in which case each switch can be driven so as to allow a current to flow in the associated LED strand, having

a first control loop which is designed to drive the switch of the at least one LED strand such that an adjustable mean value is achieved for the current flowing through the LED strand,

characterized in that the drive circuit also has:

a second control loop which is designed to provide a supply voltage for the at least one LED strand as a function of the peak value of the current flowing through the at least one LED strand.

2. The drive circuit as claimed in claim 1, characterized

in that the second control loop has a peak value detector for the current flowing through the at least one LED strand, in which case a peak value can be preset for the current flowing through the at least one LED strand, and the second control loop is designed to provide a supply voltage so that the peak value which can be preset is achieved.

3. The drive circuit as claimed in one of claims 1 or 2, characterized

in that the second control loop has a DC/DC converter whose output voltage is coupled to the at least one supply connection.

4. The drive circuit as claimed in claim 3, characterized

in that the DC/DC converter is, in particular, in the form of a step-up converter, step-down converter or a flyback converter.

5. The drive circuit as claimed in claim 3, characterized

in that an inductance is arranged in series with the output of the second control loop.

6. The drive circuit as claimed in claim 1, characterized

in that the at least one LED strand is operated in a pulsed manner.

7. The drive circuit as claimed in claim 1, characterized

in that the mean value of the current flowing through the at least one LED strand is adjusted by pulse width modulation.

8. The drive circuit as claimed in claim 1, characterized

in that the second control loop is designed to match the supply voltage to the strand voltage of the at least one LED strand.

9. The drive circuit as claimed in claim 1, characterized

in that the first and the second control loops are designed to determine the actual values for the mean value and the peak value only a first LED strand, with an at least second LED strand being operated on the basis of the actual values) determined for the first LED strand.

10. The drive circuit as claimed in claim 1, characterized

in that the first control loop has a first comparator which is used to compare the actual value of the mean value of the current flowing through the at least one LED strand with a nominal value which can be preset, with the output signal from the first comparator being coupled to the first input of a second comparator, to whose second input a triangular waveform signal is applied, with the output signal from the second comparator being coupled to the at least one switch.

11. The drive circuit as claimed in claim 3, characterized

in that the second control loop has a third comparator which is used to compare the actual value of the peak value of the current flowing through the at least one LED strand with a nominal value which can be preset, with the output signal from the third comparator being coupled to the first input of a fourth comparator, to whose second input a triangular waveform signal is applied, with the output signal from the fourth comparator being coupled to the DC/DC converter.

12. The drive circuit as claimed in claim 1, characterized

in that the mean value of the current flowing through the at least one LED strand can be varied by an operator for dimming purposes.

13. The drive circuit as claimed in claim 1, characterized

in that the peak value of the current flowing through the at least one LED strand can be varied by an operator in order to adjust the wavelength of the light which is emitted from the LED strand.

14. A method for operating at least one LED strand with a switch being arranged in series with each LED strand and each LED strand having a supply connection via which it can be connected to a supply voltage, in which case each switch can be driven so as to allow a current to flow in the associated LED strand, comprising the following steps:

a) determination of the mean value of the current flowing through the at least one LED strand;

b) driving of the switch for the at least one LED strand so as to achieve an adjustable mean value for the current flowing through the LED strand;

characterized in that the method also includes the following steps;

c) determination of the peak value of the current flowing through the at least one LED strand; and

d) provision of a supply voltage to the at least one LED strand as a function of the peak value of the current flowing through the at least one LED strand.