TECHNICAL FIELD
Embodiments of the present invention relate generally to field of electrical overstress damage protection and specifically to an electrical circuit for protection against voltage overstress in driver of LED Bulb.
BACKGROUND OF THE INVENTION
Electrical overstress is stress to a component or circuit caused by overvoltage or overcurrent condition. Electrical overstress is a major cause for damage to circuit components. Particularly, the modern electronic equipment requires special protection against electrical overstress as they are more sensitive to currents and voltages. Like any other electrical system, LED lightings are also susceptible to electrical overstress (EOS).
Conventional electrical overstress management techniques involve common types of devices like metal-oxide varistors (MOV), transient surge suppressors (TVS), GDT and fuses. One shortcoming of MOV is their limited energy handling capacity and relatively high capacitance, which delays response time. TVS are fast and have efficient clamping capability but have limited surge robustness. They can undergo catastrophic failure under overstress condition. Gas Discharge Tube (GDT) is normally used on signal lines. However, these devices can only protect against short-duration events. Longer duration, higher-energy events will result in the device overheating and ultimate failure, sometimes catastrophic.
Accordingly, there remains a need in the prior art to have a protection against short duration and long duration high-energy events.
OBJECT OF THE INVENTION
An object of the present invention is to provide a generic voltage overstress protection circuit.

SUMMARY OF THE INVENTION
Embodiments of the present invention aim to provide a circuit, which can provide protection against voltage overstress of shorter and longer duration. An overvoltage stress of shorter duration is caused by lightning phenomenon and/ or by sudden switching. A voltage stress of longer duration is of 50/60Hz grid frequency, can go up to 400V, and is generally caused by disconnection of neutral wire from earth in a 3-phase system.
An overvoltage protection module is provided as part of the electrical overstress protection circuit, which provides protection against high voltage. Further, MOVs (used in prior art for protection) are not needed in this invention, avoiding MOV induced failure in the circuit. MOVs fail short under sustained high voltage condition causing fuse failure in the upstream circuit and hence interrupting the power supply to the downstream circuit.
In accordance with an embodiment of the present invention, a voltage overstress protection circuit connected to a bulb driver unit, the voltage overstress protection circuit comprises a neutral conductor, a line conductor, a fusible resistor or a fuse connected with the neutral conductor or the line conductor, a capacitor connected between the neutral conductor and the line conductor, a resistor-inductor (R-L) circuit, connected with the line conductor, the R-L circuit comprising an inductor and a resistor connected in parallel, a plurality of diodes connected with the resistor-inductor circuit, the plurality of diodes being configured to form a bridge configuration. Additionally, a reservoir capacitor is connected in parallel with the bridge configuration. Moreover, a high voltage diode is connected in series with a high voltage capacitor, an arm having the high voltage diode and the high voltage capacitor being in parallel with the reservoir capacitor. The fusible resistor or the fuse is adapted to melt and disrupt flow of current in an overcurrent condition. Also, the capacitor is configured to store energy in a form of electrical charge. Additionally, the reservoir capacitor is configured to reduce a high frequency input current.
In accordance with an embodiment of the present invention, the bridge configuration is further configured to provide unipolar voltage supply.
In accordance with an embodiment of the present invention, the bulb driver unit comprises an integrated circuit, an inductor, a plurality of first resistors connected with the inductor, the plurality of first resistors being arranged in parallel, a plurality of second resistors connected with the plurality of first resistors and the inductor, a diode connected with the plurality of second resistors. Further, the integrated circuit is configured to regulate a current in the bulb driver unit. Also, the inductor is configured to store electrical energy in a magnetic field. Furthermore, the diode is configured to provide an uninterrupted path to the inductor current when the integrated circuit switches off an internal MOSFET.
In accordance with an embodiment of the present invention, the plurality of second resistors is configured to regulate current in the circuit.
In accordance with an embodiment of the present invention, the plurality of first resistors is configured to regulate voltage in the circuit.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred by embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
These and other features, benefits, and advantages of the present invention will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:
Fig. 1 illustrates a schematic view of a voltage overstress protection circuit, in accordance with an embodiment of the present invention;
Fig. 2 illustrates a graph showing voltage surge capacity of the voltage overstress protection circuit of the present invention for Up Max;
Fig. 3 illustrates another graph showing voltage surge capacity of the voltage overstress protection circuit of the present invention for Up Min; and
Fig. 4 illustrates yet another graph showing high duration voltage capacity of the voltage overstress protection circuit of the present invention with 388Vac, 50 Hz applied across the input terminal of circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the present invention is described herein by way of example using embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described, and are not intended to represent the scale of the various components. Further, some components that may form a part of the invention may not be illustrated in certain figures, for ease of illustration, and such omissions do not limit the embodiments outlined in any way. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the present invention as defined by the appended claim. As used throughout this description, the word "may" is used in a permissive sense (i.e. meaning having the potential to), rather than the mandatory sense, (i.e. meaning must). Further, the words "a" or "an" mean "at least one” and the word “plurality” means “one or more” unless otherwise mentioned. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention. In this disclosure, whenever a composition or an element or a group of elements is preceded with the transitional phrase “comprising”, it is understood that we also contemplate the same composition, element or group of elements with transitional phrases “consisting of”, “consisting”, “selected from the group of consisting of, “including”, or “is” preceding the recitation of the composition, element or group of elements and vice versa.
The present invention is described hereinafter by various embodiments with reference to the accompanying drawing, wherein reference numerals used in the accompanying drawing correspond to the like elements throughout the description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. In the following detailed description, numeric values and ranges are provided for various aspects of the implementations described. These values and ranges are to be treated as examples only, and are not intended to limit the scope of the claims. In addition, a number of materials are identified as suitable for various facets of the implementations. These materials are to be treated as exemplary, and are not intended to limit the scope of the invention.
Referring to the drawings, the invention will now be described in more detail. Figure 1 illustrates a schematic view of a voltage overstress protection circuit (67), in accordance with an embodiment (100) of the present invention. As shown in figure 1, the voltage overstress protection circuit (67) is connected to a bulb driver unit (69). The voltage overstress protection circuit (67) comprises a neutral conductor (3), a line conductor (1), a capacitor (25) connected between the neutral conductor (3) and the line conductor (1), a resistor-inductor (R-L) circuit (41, 31) connected with the line conductor (1), the R-L circuit comprising an inductor (41) and a resistor (31) connected in parallel. Further, connected with the neutral conductor (3) is a fusible resistor (or a fuse) (47). The fusible resistor or the fuse (47) is adapted to melt and disrupt flow of current in an overcurrent condition. In an alternate embodiment, the fusible resistor or the fuse (47) may be connected with the line conductor (1). The line conductor (1) material is selected from a group comprising, but not limited to, copper and aluminum.
The capacitor (25) is configured to store energy in a form of electrical charge. In general, the capacitor (25) is made of two close conductors (usually plates) that are separated by a dielectric material. Also, the capacitor (25) disconnects current in direct current (DC) circuits and short circuit in alternating current (AC) circuits. Further, currents flowing in resistor (31) and inductor (41) are different. Additionally, the plurality of diodes (5, 7, 9, 11) are connected with the R-L circuit (41, 31). The plurality of diodes (5, 7, 9, 11) are configured to form a bridge configuration (10) connected at a terminal (13) with the neutral conductor (3). Further, the bridge configuration (10) is configured to provide unipolar voltage supply. In general, for conversion of an alternating current (AC) input into a direct current (DC) output, the plurality of diodes (5, 7, 9, 11) in the bridge configuration (10) is known as a bridge rectifier.
Further, the voltage overstress protection circuit (67) comprises a reservoir capacitor (15) connected in parallel with the bridge configuration (10) towards an output end of the bridge configuration (10) for reducing the high frequency input current. The reservoir capacitor (15) releases stored energy present in the reservoir capacitor (15) during the part of the AC cycle when the AC source does not supply any power, that is, when the AC source changes its phase resulting in change in 'direction of flow of current'. The change in 'direction of flow of current' of the AC source takes a very small amount of time. In this short gap of time, the continuous flow of current gradually moves to the state when it ceases. Using the reservoir capacitor (15), the gap is filled; since the capacitor (25) releases the stored energy (gets discharged) in that gap of time. This allows the load to be powered at all times without any interruption.
In accordance with an embodiment of the present invention, the voltage overstress protection circuit (67) further comprises a high voltage diode (49) connected in series with a high voltage capacitor (61). Further, an arm (50) comprises the high voltage diode (49) and the high voltage capacitor (61) being in parallel with the reservoir capacitor (15), the arm being connected with a ground terminal (27) at one end. In accordance with an embodiment of the present invention, the voltage overstress protection circuit (67) is connected to the bulb driver unit (69) and provides protection against high voltage (short and long duration) surges. Preferably, the bulb driver unit (69) is meant to drive a Light-Emitting Diode (LED) bulb.
In accordance with an embodiment of the present invention, the bulb driver unit (69) comprises an integrated circuit (55), a plurality of capacitors (17, 19, 21) connected between the integrated circuit (55) and a second ground terminal (65), an inductor (43), a plurality of first resistors (37, 39, 63) connected with the inductor (43), the plurality of first resistors (37, 39, 63) being arranged in parallel. Further, a plurality of second resistors (33, 35) are connected with the plurality of first resistors (37, 39, 63) and the inductor (43), and a common junction between the plurality of second resistors (33, 35) and the inductor (43) is kept at ground potential via a third ground terminal (53). Also, a diode (51) is connected with the plurality of second resistors (33, 35). Further, an additional capacitor (23) has been provided between the inductor (43) and a fourth ground terminal (29). Also, an additional resistor (45) has been provided parallel to the additional capacitor (23) and end terminals (57, 59).
In one embodiment, the integrated circuit (55) comprises, but not limited to, one or more terminals, voltage feedback sense input (FB), supply voltage (Vcc), current sense input (ISEN), no connection pin (NC), ground (GND) and compensation terminal for current loop (COMP). Further, the voltage from bridge rectifier diodes reaches the integrated circuit (55) to automatically trigger the power “ON”. The output of the integrated circuit (55) is collected by the plurality of first resistors (37, 39, 63) and the plurality of second resistors (33, 35) and the diode (51) which further connects with the inductor (43) forming power supply section of the circuit. Also, the integrated circuit (55) is configured to regulate current and assists in proper functioning of the bulb driver unit (69). The inductor (43) is configured to store electrical energy in a magnetic field. Also, the diode (51) is configured to provide an uninterrupted path to the inductor (43) current when the integrated circuit (55) switches off an internal MOSFET.
In accordance with an embodiment of the present invention, the plurality of first resistors (37, 39, 63) is configured to regulate voltage in the circuit. Also, the plurality of second resistors (33, 35) is adapted to regulate current in the circuit. By tapping the plurality of first resistors (37, 39, 63) and the plurality of second resistors (33, 35) as per the predefined setting, the bulb driver unit (69) is further adapted to load current and maximum load voltage. In accordance with an exemplary embodiment of the present invention, the voltage overstress protection circuit (67) of the present invention can protect from the high AC voltage (up to 450V, 50/60 Hz) and different voltage surge (peak voltage ranging from 500V to 3KV) as shown in Figure 2, Figure 3 and Figure 4. But by using the proper rated high voltage capacitor (61) and the high voltage diode (49), the voltage overstress protection circuit (67) can work with any high voltage and voltage surge.
The present invention offers a number of advantages. The present invention comprises the voltage overstress protection circuit (67) which is configured to provide protection against high voltage. Further, MOVs (used in prior art for protection) are not needed in this invention, avoiding MOV induced failure in the circuit. MOVs fail short under sustained high voltage condition causing fuse failure in the upstream circuit and hence interrupting the power supply to the downstream circuit.
Various modifications to these embodiments are apparent to those skilled in the art from the description and the accompanying drawings. The principles associated with the various embodiments described herein may be applied to other embodiments. Therefore, the description is not intended to be limited to the embodiments shown along with the accompanying drawings but is to be providing broadest scope of consistent with the principles and the novel and inventive features disclosed or suggested herein. Accordingly, the invention is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present invention and appended claims.

We Claim:
1. A voltage overstress protection circuit (67) connected to a bulb driver unit (69), the voltage overstress protection circuit (67) comprising:
a neutral conductor (3);
a line conductor (1);
a fusible resistor or a fuse (47) connected with the neutral conductor (3) or the line conductor (1);
a capacitor (25) connected between the neutral conductor (3) and the line conductor (1);
a resistor-inductor (R-L) circuit (41, 31) connected with the line conductor (1), the R-L circuit comprising an inductor (41) and a resistor (31) connected in parallel;
a plurality of diodes (5,7,9,11) connected with the resistor-inductor circuit (41, 31), the plurality of diodes (5, 7, 9, 11) being configured to form a bridge configuration (10);
a reservoir capacitor (15) connected in parallel with the bridge configuration (10);
a high voltage diode (49) connected in series with a high voltage capacitor (61), an arm (50) having the high voltage diode (49) and the high voltage capacitor (61) being in parallel with the reservoir capacitor (15);
wherein the fusible resistor or the fuse (47) is adapted to melt and disrupt flow of current in an overcurrent condition;
wherein the capacitor (25) is configured to store energy in a form of electrical charge; and
wherein the reservoir capacitor (15) is configured to reduce high frequency input current.

2. The voltage overstress protection circuit (67) as claimed in claim 1, wherein the bridge configuration (10) is further configured to provide unipolar voltage supply.

3. The voltage overstress protection circuit (67) as claimed in claim 1, wherein the bulb driver unit (69) comprises:
an integrated circuit (55);
an inductor (43);
a plurality of first resistors (37, 39, 63) connected with the inductor (43), the plurality of first resistors (37, 39, 63) being arranged in parallel;
a plurality of second resistors (33, 35) connected with the plurality of first resistors (37, 39, 63) and the inductor (43);
a diode (51) connected with the plurality of second resistors (33, 35);
wherein the integrated circuit (55) is configured to regulate current in the bulb driver unit (69);
wherein the inductor (43) is configured to store electrical energy in a magnetic field; and
wherein the diode (51) is configured to provide an uninterrupted path to the inductor (43) current when the integrated circuit (55) switches off an internal MOSFET.

4. The voltage overstress protection circuit (67) as claimed in claim 3, wherein the plurality of first resistors (37, 39, 63) is configured to regulate voltage in the circuit.

5. The voltage overstress protection circuit (67) as claimed in claim 3, wherein the plurality of second resistors (33, 35) is configured to regulate current in the circuit.