[1] The present disclosure relates, in general, to control of operation of light emitting devices. In particular, the present disclosure relates to a means to operate a light emitting diode (LED) to reduce flickering in LEDs due to ripple effect.

BACKGROUND
[2] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[3] Most LED drivers and modern power supplies are switching convertors. Often, they have a PWM signal to control light dimming levels. The output voltage of such convertors, typically, has minute oscillations called ripple, which can cause flickering in LED light output, which are fluctuations in light flux output from the LEDs. Flickering, in turn, can cause a stroboscopic effect, which occurs when a flashing light source illuminates a moving object. This effect can be harmful for vision, and can cause physiological effects such as discomfort, visual fatigue, headaches, nausea and can lead to hazardous accidents in industrial setups, during automobile travel etc. It is thus imperative to reduce the flickering of LEDs.
[4] Solutions available to reduce ripple in output of LED drivers generally suffer from having a low operating range of currents and voltages and having low reliability. Additionally, some solutions are very expensive and have large form factors.
[5] There is, therefore, a requirement in the art for a means to reduce ripple in the output of an LED driver that can operate over a wide range of currents and voltages and has a long operating life.

OBJECTS OF THE DISCLOSURE
[6] A general object of the present disclosure is to provide a system for a light emitting diode (LED) driver that can reduce ripple in output of the LED driver.
[7] Another object of the present disclosure is to provide a system that can operate reliably across a wide range of currents and voltages.
[8] Another object of the present disclosure is to provide a system that has a long operating life.
[9] Another object of the present disclosure is to provide a system that is economical to implement.

SUMMARY
[10] The present disclosure relates, in general, to control of operation of light emitting devices. In particular, the present disclosure relates to a means to operate a light emitting diode (LED) to reduce flickering in LEDs due to ripple effect.
[11] In an aspect, the present disclosure provides a system to reduce ripple in output of a light emitting diode (LED) driver. The system includes: an input configured to receive an input current; an output coupled to a load comprising one or more LEDs, the output configured to supply a current to the load; a first metal oxide field effect transistor (MOSFET) coupled in series with the input and the output; and a first biasing circuit comprising a resistor (R1) and a first capacitor (C1), the first biasing circuit configured to provide a bias to a gate of the first MOSFET. The first MOSFET is configured to attenuate at least a part of ripple in input current to generate an output current with reduced ripple.
[12] In an embodiment, the system includes: a first inductor (L1) coupled in series between the first MOSFET and the output; and a second capacitor (C2) and a third capacitor (C4) connected in series with the first inductor (L1) and connected in parallel with each other such that the second capacitor (C2), the first inductor (L1) and the third capacitor (L4) form a PIE filter. The PIE filter is configured to receive current from the first MOSFET and attenuate at least a part of ripple remaining in the current from the first MOSFET to generate an output current with reduced ripple.
[13] In another embodiment, the system can include a second MOSFET, and wherein, during short circuit across the output, the first inductor (L1) can be configured to trigger the second MOSFET to switch off the first MOSFET and discharge the first capacitor (C1).
[14] In another embodiment, the first biasing circuit can include a first diode (D1) and a second resistor (R2), which can be configured to protect gate of the first MOSFET during event of sudden discharge of the first capacitor (C1).
[15] In another embodiment, the current and voltage rating of the first MOSFET can be selected based on current at input and load at output.
[16] In another embodiment, the values of the first resistance (R1) and the first capacitance (C1) can be selected such that time constant frequency of the first biasing circuit is higher than a maximum ripple frequency.
[17] In another embodiment, the first MOSFET can be configured to have fast switching speed.
[18] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF DRAWINGS
[19] The accompanying drawings are included to provide a further understanding of the present disclosure and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present invention and, together with the description, serve to explain the principles of the present disclosure.
[20] FIG. 1 illustrates a representation of a first conventional means to reduce ripple in output of an LED driver.
[21] FIG. 2 illustrates a representation of a second conventional means to reduce ripple in output of an LED driver.
[22] FIG. 3 illustrates a representation of a third conventional means to reduce ripple in output of an LED driver.
[23] FIG. 4 illustrates an exemplary representation of a system for reducing ripple in an output of an LED driver, in accordance with an embodiment of the present disclosure.
[24] FIG. 5 illustrates an exemplary representation of a system for reducing ripple in an output of an LED driver, which is operable over a wide range of wattages, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION
[25] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[26] Flickering occurs in light sources such as LED when there is fluctuations in light flux output from the LEDs, which may be caused due to peak-to-peak oscillations in output voltage signal of an LED driver. Flickering, in turn, can cause a stroboscopic effect, which occurs when a flashing light source illuminates a moving object. This effect can be harmful for vision, and can cause physiological effects such as discomfort, visual fatigue, headaches, nausea and can lead to hazardous accidents in industrial setups, during automobile travel etc. It is thus imperative to reduce the flickering of LEDs.
[27] One way to reduce ripple in the output of an LED driver is to use a bulk electrolytic capacitor with a high capacity and a low equivalent series resistance (ESR). However, in such a case, the ripple component of the load current flows entirely through the bulk capacitor, which causes deterioration in capacitor lifetime.
[28] FIG. 1 illustrates a representation of a first conventional means to reduce ripple in output of an LED driver. The setup 100 makes use of an integrated IC 102 connected in series between an input 104 and an output 106 of the LED driver. A disadvantage of such a setup 100 is the requirement of a separate IC biasing circuit. Further, the reliability of IC behaviour is dependent on tolerances of biasing components, which degrade over time. Additionally, IC components are prone to damage and failure during testing of the product.
[29] FIG. 2 illustrates a representation of a second conventional means to reduce ripple in output of an LED driver. The setup 200 includes a two stage driver including an AC-DC converter 202 and a DC-DC converter 204 connected in series between an input 206 and an output 208 of the LED driver. However, the setup 200 has a large form factor and is expensive. Further, the setup 200 has a reduced mean time between failure (MTBF).
[30] FIG. 3 illustrates a representation of a third conventional means to reduce ripple in output of an LED driver. The setup 300 includes a bipolar junction transistor (BJT) 302, connected in series between an input 104 and an output 106 of the LED driver. The BJT 302 is biased by a circuit having a resistor R1 308 and a capacitor C1 310.
[31] BJTs operate in an active region when being used as ripple remover. In active region, collector current IC is proportional to base current IB by a factor called BHT hFE. However, hFE is not a constant value over the entire operating current and temperature range of the BJT, thereby making a BJT not a suitable component for reducing ripple in a wide temperature and current range.
[32] The present disclosure relates, in general, to control of operation of light emitting devices. In particular, the present disclosure relates to a means to operate a light emitting diode (LED) to reduce flickering in LEDs due to ripple effect.
[33] FIG. 4 illustrates an exemplary representation of a system for reducing ripple in an output of an LED driver, in accordance with an embodiment of the present disclosure. The system 400 includes a MOSFET 402 connected in series between an input 404 and an output 406 of the LED driver. A MOSFET has a wider operating range of current and temperature along with having faster switching speeds, which allows the MOSFET 402 to operate on a larger bandwidth of ripple in the output. In the system 400, the current and voltage rating of the MOSFET 402 is selected based on current at input 404 and load at output 406. The MOSFET gate is biased by a first biasing circuit having a first resistor R1 408 and a first capacitor C1 410. The values of R1 408 and C1 410 are selected such that time constant frequency of the RC circuit is higher than a maximum ripple frequency. Here, only a fraction of ripple current passes through the first capacitor C1 410, thereby limiting deterioration of C1 410 and increasing its operating life.
[34] However, the system 400 is suitable largely for lower wattages, and exhibits reliability issues when ripple current increases over time, where the drain and source of the MOSFET 402 begin to exhibit permanent shorting. This may cause the gate of the MOSFET 402 to be damaged.
[35] FIG. 5 illustrates an exemplary representation of a system for reducing ripple in an output of an LED driver, which is operable over a wide range of wattages, in accordance with an embodiment of the present disclosure. The system 500 is a hybrid system, where a conventional L-C filtering is used along with optimised protection of gate of first MOSFET 502 used in the system 500.
[36] In the system 500, the first MOSFET 502 and a post filter 504 are connected in series between an input 506 and an output 508 of the LED driver. The post filter 504 may be a ferrite inductor. The current and voltage rating of the first MOSFET 502 is selected based on current at input 504 and load at output 508. The use of a MOSFET enables the system 500 to be used in high current and high voltage applications. The MOSFET gate is biased by a first biasing circuit having a first resistor R1 510 and a first capacitor C1 512. The values of R1 510 and C1 512 are selected such that time constant frequency of the RC circuit is higher than a maximum ripple frequency. Here, only a fraction of ripple current passes through the first capacitor C1 512, thereby limiting deterioration of C1 512 and increasing its operating life.
[37] In another embodiment, a second circuit including C2 (514) - L1 (504) – C4 (516) forms an L-C PIE type filter, which is adapted to further attenuate ripple current from the input 506. The PIE filter offers high impedance for AC current but low resistance for DC current. The inductor L1 504 further acts as a sense resistor during short circuit across the output 508 and is adapted to trigger a second MOSFET 518 to turn of the first MOSFET 502 and discharge the first capacitor C1 512.
[38] In another embodiment, the first biasing circuit of the system 500 includes a first diode D1 520 and a second resistor R2 522, which are adapted to protect gate of the first MOSFET 502 in case of conditions such as sudden discharge of first capacitor C1 510, for instance. The additional protection also improves reliability of the system 500.
[39] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE DISCLOSURE
[40] The present disclosure provides a system for a light emitting diode (LED) driver that can reduce ripple in output of the LED driver.
[41] The present disclosure provides a system that can operate reliably across a wide range of currents and voltages.
[42] The present disclosure provides a system that has a long operating life.
[43] The present disclosure provides a system that is economical to implement.

Claims:1. A system to reduce ripple in output of a light emitting diode (LED) driver, the system (400, 500) comprising:
an input (404, 506) configured to receive an input current;
an output (406, 508) coupled to a load comprising one or more LEDs, the output (406, 508) configured to supply an output current to the load;
a first metal oxide field effect transistor (MOSFET) (402, 502) coupled in series with the input (404, 506) and the output (406, 508); and
a first biasing circuit comprising a resistor (R1) (408, 510) and a first capacitor (C1) (410, 512), the first biasing circuit configured to provide a bias to a gate of the first MOSFET (402, 502),
wherein the first MOSFET (402, 502) is configured to attenuate at least a part of ripple in input current to generate an output current with reduced ripple.
2. The system as claimed in claim 1, wherein the system comprises:
a first inductor (L1) (504) coupled in series between the first MOSFET (402, 502) and the output (406, 508); and
a second capacitor (C2) (514) and a third capacitor (C4) (516) connected in series with the first inductor (L1) (504) and connected in parallel with each other such that the second capacitor (C2) (514), the first inductor (L1) (504) and the third capacitor (L4) form a PIE filter,
wherein the PIE filter is configured to receive current from the first MOSFET (402, 502), and attenuate at least a part of ripple remaining in the current from the first MOSFET (402, 502) to generate an output current with reduced ripple.
3. The system as claimed in claim 2, wherein the system comprises a second MOSFET (518), and wherein, during short circuit across the output (406, 508), the first inductor (L1) (504) is configured to trigger the second MOSFET (518) to switch off the first MOSFET (402, 502) and discharge the first capacitor (C1) (410, 512).
4. The system as claimed in claim 1, wherein the first biasing circuit comprises a first diode (D1) (520) and a second resistor (R2) (522), which are configured to protect gate of the first MOSFET (402, 502) during event of sudden discharge of the first capacitor (C1) (410, 512).
5. The system as claimed in claim 1, wherein the current and voltage rating of the first MOSFET (402, 502) is selected based on current at input (404, 506) and load at output.
6. The system as claimed in claim 1, wherein the values of the first resistance (R1) (408, 510) and the first capacitance (C1) (410, 512) are selected such that time constant frequency of the first biasing circuit is higher than a maximum ripple frequency.
7. The system as claimed in claim 1, wherein the first MOSFET (402, 502) is configured to have fast switching speed.