LED system with driver voltage clamping

Patent metadata

Field	Value
Publication number	US-9949327-B2
Application number	US-201414569094-A
Country	US
Kind code	B2
Filing date	Feb 28, 2014
Priority date	Feb 28, 2014
Publication date	Apr 17, 2018
Grant date	Apr 17, 2018

Abstract

One example includes a light-emitting diode (LED) system. The LED system includes an LED array comprising a plurality of LEDs that are each activated via an LED current provided therethrough to provide illumination. The system also includes an LED controller configured to sequentially activate the plurality of LEDs via at least one LED driver system configured to selectively provide the LED current through each sequential one of the plurality of LEDs in an activated state in response to an activation signal. The at least one LED driver system includes a voltage clamp configured to maintain a substantial constant amplitude difference of a driver voltage associated with the LED current from the activated state to a deactivated state.

First claim

What is claimed is:

1. A light-emitting diode (LED) system comprising:
an LED array comprising a plurality of LEDs that are each activated via an LED current provided therethrough to provide illumination; and
an LED controller configured to sequentially activate the plurality of LEDs via at least one LED driver system configured to selectively provide the LED current through each sequential one of the plurality of LEDs in an activated state in response to an activation signal, the at least one LED driver system comprising a voltage maintenance circuit configured to maintain a substantially constant amplitude difference of a driver voltage associated with the LED current from the activated state to a deactivated state where off times of the LEDs that vary per cycle with some off times being longer than others and the maintained voltage is substantially constant over off times that are shorter or longer, wherein the plurality of LEDs of the LED array are arranged in a plurality of rows and a plurality of columns, wherein the LED controller further comprises an activation controller configured to sequentially activate each of the plurality of rows of the plurality of LEDs and to provide the activation signal in response to a digital input to activate a respective one of the plurality of LEDs in a given activated one of the plurality of rows, and wherein a darkness of a first line corresponding to a first row of sequentially activated LEDs is reduced or eliminated.

2. The system of claim 1 , wherein the voltage maintenance circuit is configured as one of a current source and a resistor configured to conduct a clamping current to set a maximum amplitude of the driver voltage in the deactivated state.

3. The system of claim 1 , wherein the voltage maintenance circuit is programmable to set a value of the amplitude difference of the driver voltage from the activated state to the deactivated state.

4. The system of claim 1 , wherein the activation controller is configured to sequentially activate each of the plurality of rows during a first time duration based on a clock signal, and is further configured to deactivate the plurality of rows during a second time duration based on the clock signal, wherein the activation controller is alternates between the first time duration and the second time duration, and wherein the second time duration is greater than a time duration between the activation of consecutive rows of the plurality of rows.

5. The system of claim 1 , wherein the LED driver system comprises an activation switch coupled to one of the plurality of columns of the plurality of LEDs via an intermediate node, the activation switch being configured to conduct the LED current in response to the activation signal, wherein the driver voltage is a voltage associated with the intermediate node.

6. The system of claim 5 , wherein the voltage maintenance circuit is configured as one of a current source and a resistor configured to conduct a clamping current from the intermediate node to set a maximum amplitude of the driver voltage in the deactivated state.

7. The system of claim 6 , wherein the clamping current is selected to be approximately equal to a leakage current associated with the respective one of the plurality of columns of the plurality of LEDs.

8. The system of claim 1 , wherein the LED driver system comprises an amplifier configured to activate an activation switch that is coupled to the LED array via an intermediate node having the driver voltage to conduct the LED current in response to the activation signal, wherein the voltage maintenance circuit is configured as one of a current source and a resistor configured to conduct a clamping current from the intermediate node.

9. An LED display system comprising the LED system of claim 1 .

10. A method for providing substantially uniform illumination in a light-emitting diode (LED) system, the method comprising:
sequentially activating a plurality of rows of LEDs arranged in an array;
activating a switch in response to an activation signal to conduct an LED current through an LED in a respective activated one of the plurality of rows of LEDs to activate the LED, the switch being coupled to the LED via an intermediate node having a driver voltage;
deactivating the switch via a deactivation signal to deactivate the LED; and conducting a maintaining current from the intermediate node to set a maximum amplitude of the driver voltage while the switch is deactivated, where off times of the LEDs that vary per cycle with some off times being longer than others and the amplitude of the driver voltage is substantially constant over off times that are shorter or longer, wherein a darkness of a first line corresponding to a first row of sequentially activated LEDs is reduced or eliminated.

11. The method of claim 10 , wherein conducting the maintaining current comprises conducting the clamping current via one of a current source and a resistor interconnecting the intermediate node and a low voltage rail.

12. The method of claim 10 , further comprising dynamically setting an amplitude of the maintaining current to dynamically set the maximum amplitude of the driver voltage.

13. The method of claim 12 , wherein setting the amplitude of the maintaining current comprises setting the amplitude of the maintaining current approximately equal to a leakage current associated with at least one LED in a respective column of LEDs in the array.

14. The method of claim 10 , wherein the sequentially activating the plurality of rows comprises:
sequentially activating each of the plurality of rows during a first time duration based on a clock signal;
deactivating the plurality of rows during a second time duration based on the clock signal; and
alternating between the first time duration and the second time duration, and wherein the second time duration is greater than a time duration between the activation of consecutive rows of the plurality of rows and varies per cycle.

15. The method of claim 10 , wherein activating the switch and deactivating the switch comprises activating the switch and deactivating the switch via an amplifier configured to set a bias voltage for the switch based on a reference voltage.

16. A controller for a light-emitting diode (LED) system comprising an LED array comprising a plurality of LEDs arranged in a plurality of rows and a plurality of columns that are each activated via an LED current provided therethrough to provide illumination, an LED controller comprising:
an activation controller configured to sequentially activate each of the plurality of rows and to provide activation signals in response to a digital input; and
a plurality of LED driver systems that are each associated with a respective one of the plurality of columns, each of the plurality of LED driver systems being configured to activate one of the plurality of LEDs in a respective activated one of the plurality of rows in response to a respective one of the activation signals, each of plurality of LED driver systems comprising a voltage maintenance circuit configured to maintain a substantial constant amplitude difference of a driver voltage associated with the LED current between activation of one of the plurality of LEDs in the respective one of the plurality of columns and deactivation of the plurality of LEDs in the respective one of the plurality of columns, where off times of the LEDs that vary per cycle with some off times being longer than others and the maintained voltage is substantially constant over off times that are shorter or longer and wherein a darkness of a first line

Assignees

• Texas Instruments Inc

Inventors

• Xie Makalo
• Shen Feifei
• Tan Richard
• Ruan Alex

Classifications

• H05B45/44

  with an active control inside an LED matrix · CPC title

• H05B47/16

  by timing means · CPC title

• H05B47/155

  Coordinated control of two or more light sources · CPC title

• G09G3/32

  semiconductive, e.g. using light-emitting diodes [LED] · CPC title

• H05B45/34

  Voltage stabilisation; Maintaining constant voltage · CPC title