Driver circuit for light-emitting diodes

• US 9,351,361 B2
• Filed: 11/28/2012
• Issued: 05/24/2016
• Est. Priority Date: 01/17/2012
• Status: Active Grant

• Current Assignee: ams AG (Ams-Osram AG)
• Original Assignee: ams AG (Ams-Osram AG)
• Inventors: Teufel, Mario
• Primary Examiner(s): Hammond, Crystal L
• Application Number:
  US14/372,442
• Publication Number:
  US 20150008837A1
• Time in Patent Office: 1,273 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G03B 15/05 Combinations of cameras with electronic flash apparatus; Electronic flash units
• CPC Class Codes: H02M 1/0087 adapted for receiving as input a current source
• CPC Class Codes: H02M 3/158 including plural semiconductor devices as final control devices for a single load
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

In one embodiment, a driver circuit for light-emitting diodes has a first DC/DC converter (DCDC1) with an input (IN) for feeding a supply voltage (VBAT) and with a first output (OUT), a second DC/DC converter (DCDC2), which is coupled on the output side to the first output (OUT) and is designed for operation with energy supplied in advance, a current source (IFlash) that is connected to the first output (OUT), and a main output (LED_OUT), which is coupled to the current source (IFlash) and is designed to be connected to the light-emitting diodes. The first DC/DC converter (DCDC1) is designed for operation in a current-limiting mode. The second DC/DC converter (DCDC2) is designed for regulation to a nominal voltage (Vds) of the current source (IFlash).

Claims

1. A driver circuit for light-emitting diodes, comprising:

a first DC/DC converter (DCDC1) with an input (IN) for feeding a supply voltage (VBAT) and with a first output (OUT);

a second DC/DC converter (DCDC2), which is coupled on the output side to the first output (OUT) and is designed for operation with energy supplied in advance;

a current source (IFlash), which is connected to the first output (OUT); and

a main output (LED_OUT), which is coupled to the current source (IFlash) and is designed for connecting to the light-emitting diodes;

wherein the first DC/DC converter (DCDC1) is designed for operation in a current-limiting mode and wherein the second DC/DC converter (DCDC2) is designed for regulation to a nominal voltage (Vds) of the current source (IFlash),

wherein the driver circuit is designed for operation in a flash mode, in which a flash is triggered with the aid of the light-emitting diodes, for which a constant power for the light-emitting diodes is provided at the main output (LED_OUT) for the duration of the flash, and

wherein the first DC/DC converter (DCDC1) and the a second DC/DC converter (DCDC2) are designed to operate towards the first output (OUT).

2. The driver circuit according to claim 1,

wherein the first and second DC/DC converters (DCDC1, DCDC2) are operated at a respective constant frequency.

3. The driver circuit according to one of claim 1 or 2, wherein a voltage (VLED) provided at the main output (LED_OUT) is a difference between a voltage (VOUT) provided at the first output (OUT) and the nominal voltage (Vds) of the current source (IFlash).

4. The driver circuit according to one of claim 1 or 2, wherein the light-emitting diodes to be operated are photoflash light-emitting diodes, which are connected in series and are referenced to a reference potential terminal (10).

5. The driver circuit according to one of claim 1 or 2, wherein the first DC/DC converter (DCDC1) comprises the following:

a first inductive storage unit (L1), which is connected to the input;

a first capacitive storage unit (C1), which is connected to the first output (OUT) and the reference potential terminal (10);

a first control unit (Strg1);

a first switch (T1), which is connected to the first inductive storage unit (L1), the first control unit (Strg1) and the reference potential terminal (10);

a second switch (T2), which is connected to the first inductive storage unit (L1), the first control unit (Strg1) and the first capacitive storage unit (C1); and

a measuring unit (M), which is coupled to the first switch (T1) and the first control unit (Strg1) and is designed to detect a level of a current (IL1) through the first switch (T1).

6. The driver circuit according to claim 5,

wherein the first control unit (Strg1) is designed to limit the current (IL1) through the first switch (T1) to an adjustable maximum value (Imax) and to provide corresponding control signals for the first and second switches (T1, T2).

7. The driver circuit according to one of claim 1 or 2, wherein the second DC/DC converter (DCDC2) comprises the following:

a second control unit (Strg2);

a third switch (S1), which is connected to the first output (OUT) and the second control unit (Strg2);

a fourth switch (S2), which is connected to the third switch (S1), the second control unit (Strg2) and the reference potential terminal (10);

a second inductive storage unit (L2), which is coupled to a node point (SW2) between the third and the fourth switches (S1, S2); and

a second capacitive storage unit (C2), which is connected to the second inductive storage unit and the reference potential terminal (10).

8. The driver circuit according to claim 7, wherein the second control unit (Strg2) is designed to provide trigger signals for the third and fourth switches (S1, S2) on the basis of the regulation to the nominal voltage (Vds) of the current source (IFlash).

9. The driver circuit according to claim 7, wherein the second control unit (Strg2) has a proportional-integral controller.

10. The driver circuit according to claim 7, wherein the second capacitive storage unit (C2) has a series circuit comprising two capacitors (SC1, SC2).

11. The driver circuit according to claim 10, wherein the two capacitors (SC1, SC2) each have a supercapacitor.