TECHNICAL FIELD

The present invention relates to driving of light emitting diodes (LED). More particularly, relates to driving LEDs using sinusoidal pulse sequences to enhance lumen output and reduce EMI (electromagnetic interference).

BACKGROUND

An LED is a semiconductor device with a PN junction, which can emit light when a forward current flows through. The LEDs have an important property, which is the direct proportion relationship between the luminous intensity and forward current. In other words, the larger the forward current is for the LEDs, the higher is the luminous intensity. However, a larger forward current is also accompanied with higher heat. Also, the excessive heat results in permanent damage or durability shortening for LEDs. Therefore, LED manufactures always rate an average forward current IAVG for each model of LED under continuous operation and a peak pulsed forward current IPK under momentary operation. When an LED performs a high frequency blink, a forward current higher than IAVG and up to IPK can be applied to obtain an instantaneous luminous intensity. When an LED lights up continuously, only a forward current not greater than IAVG can be applied. The luminous intensity generated by continuous forward current is continuous and consistent but must be lower than the instantaneous luminous intensity.
Presently, the LED drivers operate in constant current mode with switched mode power supplies (SMPS). The power supply voltage and current are continuously available to the LED circuits as shown in the figures 1(a) and 1(b).

The LEDs are designed for pulsed operation with much higher current compared to the continuous mode operation current as shown in the figure 2. The conventional rectangular pulse schemes have the following disadvantages:

• The fast rise and fall times of the rectangular pulses give rise to a large EMI, and

• The dwell time of the peak depends on the rectangular pulse width.

In light of the foregoing discussion, there is a need for a method and system to solve the above mentioned problems.

BRIEF DESCRIPTION OF DRAWINGS

The novel features and characteristic of the disclosure are set forth in the appended claims. The embodiments of the disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. One or more embodiments are now described, by way of example only, with reference to the accompanying drawings.

Figure 1(a) shows a block diagram of conventional LED driver in one embodiment.
Figure 1(b) shows a block diagram of conventional LED driver in another embodiment.

Figure 2 illustrate a block diagram of LED driver using rectangular pulses.

Figure 3 illustrate a block diagram of LED driver using sinusoidal pulses.

Figure 4 shows rectified sinusoidal pulses which trigger the MOSFETS.

Figure 5 shows a flow chart of 2-level multiplexing.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION

The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

The primary embodiment of the present disclosure is a light emitting diode (LED) driver system 300 comprising plurality of LED arrays (302A to 302P); LED driver circuit 304 connected to the LED arrays through switches 306 (Ql and Q2) to provide required power; and a control unit 310 to generate pulse sequences and control the switches through wave shaping circuit 308 to drive the LED arrays, said wave shaping circuit 308 converts the pulse sequences into rectified sinusoidal pulses.

In yet another embodiment of the present disclosure each LED array comprises of at least one LED.

In still another embodiment of the present disclosure the LED arrays are connected in series parallel combination.

In still another embodiment of the present disclosure the sinusoidal pulse sequences have 50% duty cycle.

In still another embodiment of the present disclosure the switches are MOSFET 306 (Ql, Q2).

In still another embodiment of the present disclosure the control unit 310 is a microcontroller 310.

Another embodiment of the present disclosure is a method of driving light emitting diodes (LED) arrays using sinusoidal pulses, said method comprising acts of generating
rectified sinusoidal pulse sequence with equal periods and duty cycle, wherein said rectified sinusoidal pulse sequence has a peak current equal to the peak rated current of the LEDs; and driving each LED array for a predefined duty cycle with the rectified sinusoidal pulses, thereby reducing the power consumption.

In yet another embodiment the LED arrays are driven at higher rate than a visual perception rate to increase perceived luminous output as compared to driving of LEDs continuously.

In still another embodiment the driving of LEDs using rectified sinusoidal pulses reduces electromagnetic interference (EMI) as compared to the driving of LEDs using rectangular pulses.

In still another embodiment the LED arrays driven by the sinusoidal pulses reduce the EMI (electromagnetic interference) compared to rectangular pulses.

In yet another embodiment the driving of LEDs using sinusoidal pulsed increases luminous output as compared to driving of LEDs using rectangular pulses.

Exemplary embodiments of the present disclosure relates to a method and system of driving LEDs using sinusoidal pulse sequences to reduce power consumption and EMI (electromagnetic interference).

The brightness of LEDs increases in a proportional way to the applied current. Since the human eye responds to the peak light output and due to persistence of vision the luminous output corresponds to the peak light output, with a slight decay between excitation pulses. The duty cycle of the applied current ensures safe average current for the operation of the LED.

In one embodiment, the pulsed operation of LED matrix array results in more perceivable luminous output for a given LED driver, compared to a non-pulsed operation. Usually rectangular pulses are used in the pulsed LED drivers wherein the safe peak current is pumped into LED for the duration of the pulse width. The driving of LED lighting panel

rectified sinusoidal pulse sequence with equal periods and duty cycle, wherein said rectified sinusoidal pulse sequence has a peak current equal to the peak rated current of the LEDs; and driving each LED array for a predefined duty cycle with the rectified sinusoidal pulses, thereby reducing the power consumption.

In yet another embodiment the LED arrays are driven at higher rate than a visual perception rate to increase perceived luminous output as compared to driving of LEDs continuously.

In still another embodiment the driving of LEDs using rectified sinusoidal pulses reduces electromagnetic interference (EMI) as compared to the driving of LEDs using rectangular pulses.

In still another embodiment the LED arrays driven by the sinusoidal pulses reduce the EMI (electromagnetic interference) compared to rectangular pulses.

In yet another embodiment the driving of LEDs using sinusoidal pulsed increases luminous output as compared to driving of LEDs using rectangular pulses.

Exemplary embodiments of the present disclosure relates to a method and system of driving LEDs using sinusoidal pulse sequences to reduce power consumption and EMI (electromagnetic interference).

The brightness of LEDs increases in a proportional way to the applied current. Since the human eye responds to the peak light output and due to persistence of vision the luminous output corresponds to the peak light output, with a slight decay between excitation pulses. The duty cycle of the applied current ensures safe average current for the operation of the LED.

In one embodiment, the pulsed operation of LED matrix array results in more perceivable luminous output for a given LED driver, compared to a non-pulsed operation. Usually rectangular pulses are used in the pulsed LED drivers wherein the safe peak current is pumped into LED for the duration of the pulse width. The driving of LED lighting panel using the pulses is shown in the figure 2. When the sinusoidal pulse shape is used rather than the rectangular pulses, the energy pumped into the LED per pulse is less by about 10 %. Since the perceived lux level depends on the peak value of the excitation current, no drop of the perceived flux output occurs. The LEDs are arranged in series parallel configuration so as to match the LED drivers for pulsed operation. A microcontroller generates the required sinusoidal pulse sequences and through suitable buffers drives the MOSFET gates, providing power to the LED array.

The LED lighting panels driven using sinusoidal pulses instead of rectangular pulses provide higher lumen output as compared to constant current mode and reduce the EMI as compared to driving LED light panels using rectangular pulses with higher current.
In one embodiment, the method of the present disclosure provides a sinusoidal pulsated current to drive LEDs which is an integral multiple of the constant current mode level. Further, the method includes adjusting the duty cycle appropriately; the average power consumed by the LEDs remains same as compared to continuous mode operation.
In one embodiment, sinusoidal pulse mode operation as shown in the figure 3, uses two arrays having the configuration of 8 x 4 LEDs i.e. 8 Strings of 4 series LEDs (302A to 302P). The figure 3 illustrates that the connection between the major blocks of LED arrays to provide more luminous output, with reduced power consumption and EMI. Figure 4 shows the waveforms used to perform the operations in the figure 3. The anodes of all the LEDs are connected to positive of the supply and the cathode goes to negative via the switches 306. The switches are MOSFET gates. The gate of MOSFET is triggered by the control unit 310 which provides the required pulse train of required frequency and duty cycle.

The control unit 310 has 8-bit timer which gives the required resolution for generating the pulses. The control unit 310 is a microcontroller, i.e. PIC18f2520 microcontroller as an example. Appropriate buffer circuits are used to protect the microcontroller. In this mode the pulses of required frequency and duty cycle is first generated using a microcontroller. using the pulses is shown in the figure 2. When the sinusoidal pulse shape is used rather than the rectangular pulses, the energy pumped into the LED per pulse is less by about 10 %. Since the perceived lux level depends on the peak value of the excitation current, no drop of the perceived flux output occurs. The LEDs are arranged in series parallel configuration so as to match the LED drivers for pulsed operation. A microcontroller generates the required sinusoidal pulse sequences and through suitable buffers drives the MOSFET gates, providing power to the LED array.

The LED lighting panels driven using sinusoidal pulses instead of rectangular pulses provide higher lumen output as compared to constant current mode and reduce the EMI as compared to driving LED light panels using rectangular pulses with higher current.
In one embodiment, the method of the present disclosure provides a sinusoidal pulsated current to drive LEDs which is an integral multiple of the constant current mode level. Further, the method includes adjusting the duty cycle appropriately; the average power consumed by the LEDs remains same as compared to continuous mode operation.
In one embodiment, sinusoidal pulse mode operation as shown in the figure 3, uses two arrays having the configuration of 8 x 4 LEDs i.e. 8 Strings of 4 series LEDs (302A to 302P). The figure 3 illustrates that the connection between the major blocks of LED arrays to provide more luminous output, with reduced power consumption and EMI. Figure 4 shows the waveforms used to perform the operations in the figure 3. The anodes of all the LEDs are connected to positive of the supply and the cathode goes to negative via the switches 306. The switches are MOSFET gates. The gate of MOSFET is triggered by the control unit 310 which provides the required pulse train of required frequency and duty cycle.

The control unit 310 has 8-bit timer which gives the required resolution for generating the pulses. The control unit 310 is a microcontroller, i.e. PIC18f2520 microcontroller as an example. Appropriate buffer circuits are used to protect the microcontroller. In this mode the pulses of required frequency and duty cycle is first generated using a microcontroller.

The generated pulses are passed through RC filter or wave shaping circuit 308 which is appropriately designed to shape the pulses as required.

In one embodiment, the LEDs are operated at double the current with half the duty cycle. Hence, the power consumed will remain the same but increases the lumen level as compared to constant current mode. Each array is switched on and off by means of pulses with a duty cycle of 50%. When one of the array is off the other one is pumped with 2 times the current as compared to constant current and switched off for 50% duty cycle to cool down. The switching is performed at a very high rate to avoid the presence of flicker.

The figure 5 shows the flow chart for the multiplexed driving scheme of the LED arrays or LED lighting panels. As illustrated in the figure one time-slot energizes one LED array at a time. The peak current is set two times the normal average operating current. The perceived flux output corresponds to the peak light output. The human eye-response remembers the peak lux output till the next excitation pulse refreshes the lux output again.

The following are the advantages of using the sinusoidal pulsed operation for driving LED lighting panels or LED arrays:

• The rise time and fall time are shaped into a sinusoidal fashion which slow-down the fast rise and fall time of rectangular pulse scheme. Hence, the pulse shaping EMI effect reduces.

• The energy consumption per pulse is less due to the reduced time at the peak excitation current, resulting in an overall energy saving (about 10%).

• The perceived enhanced brightness of the rectangular pulse scheme of operation is preserved.

The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and devices within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.
While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

We claim

1. A light emitting diode (LED) driver system comprising:

a. plurality of LED arrays;

b. LED driver circuit connected to the LED arrays through switches to provide
required current; and

c. a control unit to generate pulse sequences and control the switches through
wave shaping circuit to drive the LED arrays, said wave shaping circuit
converts the pulse sequences into rectified sinusoidal pulses.

2. The system as claimed in claim 1, wherein each LED array comprises of at least one LED.

3. The system as claimed in claim 1, wherein the LED arrays are connected in series parallel combination.

4. The system as claimed in claim 1, wherein the sinusoidal pulse sequences have 50% duty cycle.

5. The system as claimed in claim 1, wherein the switches are MOSFET.

6. The system as claimed in claim 1, wherein the control unit is a microcontroller.

7. A method of driving light emitting diodes (LED) arrays using sinusoidal pulses, said method comprising acts of:

a. generating rectified sinusoidal pulse sequence with equal periods and duty
cycle, wherein said rectified sinusoidal pulse sequence has a peak current
equal to the peak rated current of the LEDs; and

b. driving each LED array for a predefined duty cycle with the rectified
sinusoidal pulses, thereby reducing the power consumption.

8. The method as claimed in claim 7, wherein the LED arrays are driven at higher rate than a visual perception rate to increase perceived luminous output as compared to driving of LEDs continuously.

9. The method as claimed in claim 7, wherein the driving of LEDs using rectified sinusoidal pulses reduces electromagnetic interference (EMI) as compared to the driving of LEDs using rectangular pulses.

10. The method as claimed in claim 7, wherein the LED arrays driven by the sinusoidal pulses reduces power consumption compared to the driving of LEDs using rectangular pulses.