Adaptive direct current (DC) to DC (DC-to-DC) light emitting diode (LED) driver for dynamic loads

Patent metadata

Field	Value
Publication number	US-9485818-B2
Application number	US-201414575125-A
Country	US
Kind code	B2
Filing date	Dec 18, 2014
Priority date	Dec 18, 2014
Publication date	Nov 1, 2016
Grant date	Nov 1, 2016

Abstract

Current spikes may occur when dynamically shortening a light emitting diode chain. These current spikes can be avoided by using a voltage control loop to regulate the output of the LED driver just prior to the transition period. Specifically, regulation of the LED driver is switched from a current control loop (e.g., a control loop regulating the output current of the led driver) to a voltage control loop (e.g., a control loop regulating the output voltage of the led driver) just before the LED chain is shortened. The voltage control loop then reduces the voltage of the LED driver to a target voltage prior to shortening the LED chain, thereby allowing the LED chain to be shortened without eliciting a current spike.

First claim

What is claimed is:

1. A method comprising:
receiving an indication of a changed load condition or voltage characteristic of a power supply driving a chain of series connected circuit elements; and
switching regulation of the power supply from a current control loop to a voltage control loop in response to receiving the indication of the changed load condition or voltage characteristic, wherein the chain of series connected circuit elements includes a first number of circuit elements during a first period, and wherein the indication of the changed load condition or voltage characteristic is received prior to a length of the chain of series connected circuit elements being changed from the first number of circuit elements to a second number of circuit elements at a beginning of a second period.

2. The method of claim 1 , further comprising:
switching regulation of the power supply back to the current control loop after the length of the chain of series connected circuit elements has been changed from the first number of circuit elements to the second number of circuit elements.

3. The method of claim 1 , further comprising:
determining a target voltage of the power supply for the second period in accordance with a ratio between the first number of circuit elements and the second number of circuit elements; and
changing an output of the power supply from an initial voltage to the target voltage prior to the length of the chain of series connected circuit elements being changed from the first number of circuit elements to the second number of circuit elements.

4. The method of claim 3 , wherein determining the target voltage of the power supply for the second period comprises:
dividing the initial voltage by the ratio between the first number of circuit elements and the second number of circuit elements.

5. The method of claim 3 , wherein changing the output of the power supply from the initial voltage to the target voltage comprises:
receiving a feedback signal indicating an output voltage of the power supply;
producing an compensating error voltage signal in accordance with a difference between the output voltage of the power supply and the target voltage; and
providing the compensating error voltage signal to a control port of the power supply until the difference between the output voltage of the power supply and the target voltage is less than a threshold.

6. The method of claim 1 , wherein the chain of series connected circuit elements comprises a chain of light emitting diodes (LEDs) that is shortened from a first number of LEDs to a second number of LEDs at the beginning of the second period.

7. The method of claim 6 , wherein the power supply is a direct current (DC) to DC (DC-to-DC) LED driver having an output that is reduced from an initial voltage to a target voltage prior to the chain of LEDs being shortened from a first number of LEDs to a second number of LEDs.

8. The method of claim 7 , wherein an output capacitor coupled in parallel with the chain of LEDs is at least partially discharged when the output of the DC-to-DC LED driver is reduced from the initial voltage to the target voltage.

9. An apparatus comprising:
a port adapted to receive an indication of a changed load condition or voltage characteristic for a power supply driving a chain of series connected circuit elements; and
a controller configured to switch regulation of the power supply from a current control loop to a voltage control loop in response to receiving the changed load condition or voltage characteristic indication, wherein the chain of series connected circuit elements includes a first number of circuit elements during a first period, and wherein the changed load condition or voltage characteristic indication is received prior to a length of the chain of series connected circuit elements being changed from the first number of circuit elements to a second number of circuit elements at a beginning of a second period.

10. The apparatus of claim 9 , wherein the controller is further configured to switch regulation of the power supply back to the current control loop after the length of the chain of series connected circuit elements has been changed from the first number of circuit elements to the second number of circuit elements.

11. The apparatus of claim 9 , further comprising:
the voltage control loop, wherein the voltage control loop is configured to determine a target voltage of the power supply for the second period in accordance with a ratio between the first number of circuit elements and the second number of circuit elements, and to change an output of the power supply from an initial voltage to the target voltage prior to the length of the chain of series connected circuit elements being changed from the first number of circuit elements to the second number of circuit elements during the second period.

12. The apparatus of claim 11 , wherein the voltage control loop is adapted to determine the target voltage of the power supply for the second period by dividing the initial voltage by the ratio between the first number of circuit elements and the second number of circuit elements.

13. The apparatus of claim 11 , wherein the voltage control loop is adapted to change the output of the power supply from the initial voltage to the target voltage by:
receiving a feedback signal indicating an output voltage of the power supply;
producing a compensating error voltage signal in accordance with a difference between the output voltage of the power supply and the target voltage; and
providing the compensating error voltage signal to a control port of the power supply until the difference between the output voltage of the power supply and the target voltage is less than a threshold.

14. A power supply comprising:
an output adapted to power a chain of series connected circuit elements, the chain of series connected circuit elements including a first number of circuit elements during a first period, wherein a length of the chain of series connected circuit elements is changed to a second number of circuit elements at a beginning of a second period; and
a first controller configured to switch regulation of the output from a current control loop to a voltage control loop before the length of the chain of series connected circuit elements is changed from the first number of circuit elements to the second number of circuit elements.

15. The power supply of claim 14 , wherein the first controller is further configured to switch regulation of the output back to the current control loop after the length of the chain of series connected circuit elements is changed from the first number of circuit elements to the second number of circuit elements.

16. The power supply of claim 14 , wherein the power supply is a direct current (DC) to DC (DC-to-DC) LED driver adapted to drive a chain of light emitting diodes (LEDs) that is shortened from a first number of LEDs to a second number of LEDs at the beginning of the second period.

17. The power supply of claim 14 , further comprising the voltage control loop, the voltage control loop including:
an input port configured to receive a feedback signal comprising an output voltage being provided over the output of the power supply;
a first voltage divider coupled to the input port;
a second voltage divider coupled to the input port, the second voltage divider being coupled in parallel with the first voltage divider;
an error amplifier configured to sample outputs of the first voltage divider and the second voltage divider, and to provide a compensati

Assignees

• Infineon Technologies Dresden Gmbh
• Infineon Technologies Ag

Inventors

• Galvano Maurizio
• Penzo Roberto
• Milanesi Paolo

Classifications

• H05B45/48 Primary

  having LEDs organised in strings and incorporating parallel shunting devices · CPC title

• H05B45/37

  Converter circuits · CPC title

• H05B45/44

  with an active control inside an LED matrix · CPC title

• H05B45/10

  Controlling the intensity of the light · CPC title

• H05B33/0824

  Electricity · mapped topic