Control circuit for LED and corresponding operating method

• US 6,515,434 B1
• Filed: 06/06/2001
• Issued: 02/04/2003
• Est. Priority Date: 10/18/1999
• Status: Expired due to Term

• Current Assignee: Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MbH (Siemens AG)
• Original Assignee: Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen MbH (Siemens AG)
• Inventors: Biebl, Alois
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Alemu, Ephrem
• Application Number:
  US09/857,502
• Time in Patent Office: 608 Days
• Field of Search: 315/169--16, 315/200.A, 315/185.R, 315/224, 315/241.S, 315/241.P, 315/291, 315/307, 315/360, 362/555, 362/800, 362/235, 362/227, 313/500
• US Class Current: 315/291
• CPC Class Codes: B60Q 1/2696 Mounting of devices using LEDs
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: H05B 45/58 involving end of life detection of LEDs
• CPC Class Codes: Y10S 362/80 Light emitting diode

Abstract

A drive circuit for an LED array, comprising at least two clusters of LEDs, in which one cluster comprises a number of LEDs arranged in series which are connected to a supply voltage (U_Batt), with a semiconductor switch (T) being arranged in series between each LED cluster and the associated supply voltage, which semiconductor switch (T) allows the LED current to be supplied in a pulsed manner, with a measurement resistor (R_Shunt) being arranged in series with the LEDs in the path for the forward current I_F between the LEDs and ground. A control loop controls the semiconductor switch (T1) in a first LED cluster, referred to as the master cluster in the following text, such that a constant mean value of the LED current is achieved, wherein the master cluster has a predetermined number X of LEDs in its cluster, and with this control loop also driving at least the semiconductor switch (T2) in a further, LED cluster, referred to in the following text as the slave cluster.

Claims

1. A drive circuit for LED arrays comprising:

at least two clusters of LEDs, in which one cluster comprises a number of LEDs arranged in series which are connected to a supply voltage,

a semiconductor switch being arranged in series between each LED cluster and the supply voltage for allowing LED current to be supplied in a pulsed manner,

means for measuring a forward current including a measurement resistor arranged in series with the LEDs in at least one first LED cluster, in a path for the forward current, between the LEDs and ground, and

a control loop controlling the semiconductor switch in the first LED cluster referred to as a master cluster such that a constant mean value of the LED current is achieved, wherein the master cluster has a predetermined number X of LEDs in the cluster, the control loop also driving at least a semiconductor switch in a second LED cluster referred to as a slave cluster.

2. The drive circuit as claimed in claim 1, wherein all the LED clusters which are additionally present each have the same number of LEDs as the master cluster, with the control loop of the master cluster also driving all the additional LED clusters.

3. The drive circuit as claimed in claim 1, wherein all the LED clusters which are additionally present have a number X_n of LEDs, with the number X_n being equal to X, and with an additional load including a resistor R_xn, being arranged in series with the LEDs in the LED cluster, if X_n<

X.

4. The drive circuit as claimed in claim 1, wherein at least two groups of LED clusters whose numbers of LEDs differ each have an associated master cluster, with the number X of LEDs in a group of slave clusters matching the number in the associated master cluster.

5. The drive circuit as claimed in claim 1, wherein one of the slave clusters is in the form of a reserve master cluster, in that a means is provided for identifying an interruption in the control loop of the master cluster and this means, for its part, is connected to a changeover switch in the control loop, with the changeover switch being connected on the one hand to the master cluster and on the other hand to the reserve master cluster, and being suitable for switching to the reserve master cluster if an interruption occurs in the master cluster.

6. The drive circuit as claimed in claim 1, wherein each LED cluster includes means for fault identification.

7. A method for operating a number of LED clusters, the method comprising the steps of:

providing a master LED cluster equipped with a control loop which predetermines a clock frequency, and

providing at least one slave LED cluster controlled by the clock frequency.