US 7,843,148 B2 · Driving multiple parallel LEDs with reduced power supply ripple

Abstract

An LED driver is disclosed that drives LEDs connected in parallel. Instead of applying current to all the parallel-connected LEDs at the same time, under control of a common PWM brightness control signal, the application of current to each parallel path is staggered by using staggered brightness control signals. The turning on of the LEDs in the different parallel paths will have the same duty cycle but will be out of phase. This reduces ripple in the power supply by reducing the magnitude of the instantaneous current sink. In one embodiment, a shift register contains a binary representation of the PWM duty cycle, and a clock shifts the bits along the shift register. The PWM brightness control signals for each parallel path of LEDs are tapped from different positions along the shift register so that the PWM brightness control signals are identical but staggered.

Claims22

Dependent claims

A light emitting diode (LED) driver for driving LEDs connected to different parallel paths, the driver comprising:

a voltage source for connection to first ends of LEDs in a plurality of parallel paths;
a plurality of current set circuits, one current set circuit per parallel path, each current set circuit controlling a peak current through one or more LEDs connected in each parallel path;
and
a pulse-width modulated (PWM) brightness control signal generator connected to the plurality of current set circuits, the brightness control signal generator being configured to generate staggered PWM brightness control signals to the plurality of current set circuits,
each current set circuit being configured to draw the peak current through its associated one or more LEDs at a duty cycle substantially corresponding to a duty cycle of a PWM brightness control signal applied to it, such that the plurality of current set circuits conduct current through their associated one or more LEDs at the same duty cycle but out of phase with each other.

2 more elements

A method for driving light emitting diodes (LEDs) connected to different parallel paths, the method comprising:

supplying a voltage to first ends of LEDs in a plurality of parallel paths;
setting a peak current through one or more LEDs connected in each of the parallel paths, the peak current being set by a current set circuit for each parallel path;
generating staggered pulse width modulated (PWM) brightness control signals;
applying a different staggered PWM brightness control signals to each current set circuit;
and
drawing the peak current through the one or more LEDs in each parallel path, set by its associated current set circuit, at a duty cycle corresponding to a duty cycle of an associated PWM brightness control signal, such that the parallel paths of LEDs conduct current at substantially the same duty cycle but out of phase with each other.

3 more elements

Dependencies are inferred from the claim text.

Driving multiple parallel LEDs with reduced power supply ripple

Life of this patent

Driving multiple parallel LEDs with reduced power supply ripple

Life of this patent

Abstract

Claims22