Method and device for supplying power to leds

• US 20060234779A1
• Filed: 06/28/2004
• Published: 10/19/2006
• Est. Priority Date: 07/16/2003
• Status: Active Grant

• Current Assignee: DSP Group Switzerland AG (Synaptics Incorporated)
• Original Assignee: DSP Group Switzerland AG (Synaptics Incorporated)
• Inventors: Haener, Lukas, Fries, Juerg
• Granted Patent: US 7,479,741 B2
• Time in Patent Office: Days
• US Class Current: 455/566
• CPC Class Codes: H05B 45/38 using boost topology

Abstract

The invention relates to a device for lighting at least one light emitting diode to be supplied with predefined minimum forward voltage and maximum current. It comprises: voltage supply means for supplying voltage to the light emitting diode, a pulse generator for generating a cyclic pulse signal having predefined on-times and off-times, a switch, controlled by the pulse generator to be turned on during said on-times to short-circuit the light emitting diode and turned off during said off-times, an inductive device for increasing the forward voltage over the light emitting diode when the switch is turned off, so that said forward voltage gets higher thatn the minimum forward voltage and for decreasing said forward voltage when the switch is turned on, so that the current through the light emitting diode remains below the maximum current.

Claims

1. A device for lighting at least one light emitting diode (LED) to be supplied with predefined minimum forward voltage and maximum current, comprising:

voltage supply means for supplying voltage to the light emitting diode,

a pulse generator for generating a cyclic pulse signal having predefined on-times and off-times,

a switch controlled by the pulse generator to be turned on during said on-times to short-circuit the light emitting diode and turned off during said off-times,

an inductive device for being charged when the switch is turned on and for increasing the forward voltage over the light emitting diode when the switch is turned off.

2. A device as claimed in claim 1, comprising a diode before the light emitting diode to prevent the voltage over the light emitting diode from going down to zero.

3. A device as claimed in claim 1, wherein the inductive device is a coil having an inductance defined by the number of light emitting diodes and their maximum current and voltage requirements as well as the available frequency of the pulse generator.

4. A device as claimed in claim 1, wherein the cyclic pulse signal has a frequency from 0.1 kHz to 30 Mega hertz.

5. A device as claimed in claim 1, wherein the pulse generator is a pulse width modulation generator.

6. A device as claimed in claim 1, wherein the switch is a MOS FET or an NPN bipolar.

7. A battery-supplied apparatus comprising a display and a device as claimed in claim 1 for backlighting said display.

8. A method of lighting at least one light emitting diode to be supplied with predefined minimum forward voltage and maximum current, comprising the steps of:

supplying a forward voltage to the light emitting diode,

generating a cyclic pulse signal having predefined on-times and off-times for controlling a switch to be turned on during said on-times to short-circuit the light emitting diode and turned off during said off-times,

charging an inductive device when the switch is turned on,

increasing the forward voltage over the light emitting diode when the switch is turned off so that said forward voltage gets higher than the minimum forward voltage.