FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
Title of invention:
RECTIFIER AND REGULATOR (RR) DRIVEN CLASS D PROJECTOR
HEADLAMP
APPLICANT:
VARROC ENGINEERING LIMITED
An Indian entity having address as:
L-4, MIDC Waluj,
Aurangabad-431136,
Maharashtra, India
.
The following specification describes the invention and the manner in which it is to be performed.

TECHNICALFIELD
The present disclosure relates to headlamps of automobile.
BACKGROUND
The subject matter discussed in the background section should not be assumed to be prior art merely because of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.
In the conventional headlamps, a linear driver regulator with constant DC input is used. The linear driver regulator with constant DC input is illustrated. The linear driver regulators of high beam and low beam headlamps receives constant DC input from vehicle battery having input voltage within range of 9V to 16V. Typical voltage of the vehicle battery is 13.5V. Each linear driver regulator includes an input protection circuitry and LED driver linear regulator to drive LEDs. The linear driver regulator with constant DC input achieves 1.5A high beam (HB) LED current, 2.1A low beam (LB) LED current, 57W maximum input power, 32W driver losses, and 60% efficiency. It must be understood that conventional linear driver regulator results in high driver losses and high thermal rise. The linear driver regulator topologies are not preferable for DC applications.
Specifically, the function of optimized electrical performance in the conventional headlamp assembly are typically achieved using DC-DC converter, which uses high frequency switching. The DC-DC convertor also includes inductors, transformers and capacitors in closed feedback loop which results in increased noise and complexity in the system and hampers the Electromagnetic Compatibility (EMC) performance. Further, presence of a greater number of parts in the headlamp assembly results in a complex design which further leads to overall increase in manufacturing cost. Further, the linear driver regulators respond quickly to changes in input voltage, producing a constant output voltage along with heat dissipation.

The heat dissipation generates need of heat sinks, thereby increasing the product cost.
Therefore, there is an utmost need of an improved headlamp assembly with a lesser number of parts and/or components thereby making the entire headlamp assembly simple to build with reduced cost and yet meeting the statutory requirements of light projection. And there is an utmost need of a headlamp with improved driver regulators and provision for heat management.
SUMMARY
This summary is provided to introduce concepts related to a rectifier and regulator driven class D projector in two-wheeler headlamp and the concepts are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.
In one implementation, a circuit for driving a plurality of light emitting diode (LEDs) of a lighting device is disclosed. The circuit may comprise an input protection circuit, a voltage limiting circuit, an active thermal management circuit, and a current linear regulator. The input protection circuit may be configured to receive negative half wave rectified dc signal and protect the circuit from reverse polarity. The voltage limiting circuit may be configured to receive the negative half wave rectified dc signal and maintain a rectified rippled DC voltage. The active thermal management circuit may be configured to receive the rectified rippled DC voltage and drop down excess voltage to obtain to a constant voltage, if the rectified rippled DC voltage exceeds a predetermined threshold. The current linear regulator may be configured to receive the constant voltage from the active thermal management circuit and provide constant output LED current to the plurality of LEDs.
BRIEF DESCRIPTION OF DRAWINGS
The detailed description is described with reference to the accompanying Figures. In the figures, the same numbers are used throughout the drawings to refer like features and components.

Figure 2 illustrates a basic block diagram of a circuit (10) for driving a plurality of light emitting diode (LEDs) of a lighting device, in accordance with an embodiment of the present disclosure.
Figure 3A illustrates a schematic diagram of an input protection circuit (103), in accordance with an embodiment of the present disclosure.
Figure 3B illustrates a schematic diagram of a voltage limiting circuit (104), in accordance with an embodiment of the present disclosure.
Figure 3C illustrates a schematic diagram of an active thermal management circuit (107), in accordance with an embodiment of the present disclosure.
Figure 3D illustrates a schematic diagram of a current linear regulator (106), in accordance with an embodiment of the present disclosure.
Figure 4 illustrates a waveform representation 400 of different input and output parameters, in accordance with an embodiment of the present disclosure.
DETAILEDDESCRIPTION
Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment” in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
Referring to figure 2, a block diagram of a circuit (10) for driving a plurality of light emitting diode (LEDs) of a lighting device is illustrated, in accordance with an embodiment of the present subject matter. The circuit (10) may comprise an input protection circuit (103), a voltage limiting circuit (104), an active thermal management circuit (107), and a current linear regulator (106). The circuit (10) may

be driven by a negative half wave rectified dc signal from a Regulator and Rectifier (RR) unit. The negative half wave rectified dc signal may be a pulsating DC signal.
In one exemplary embodiment, the negative half wave rectified dc signal may be received by the input protection circuit (103). The input protection circuit of low beam headlamp circuit and high beam headlamp circuit are denoted by (103L) and (103H), respectively. The negative half wave pulsating DC input is utilized to generate a constant DC output as the pulsating DC input goes to zero periodically. The voltage limiting circuit (104) may be configured to receive the negative half wave rectified dc signal and maintain a rectified rippled DC voltage. The voltage limiting circuit of low beam headlamp and high beam headlamp are denoted by (104L) and (104H), respectively. The active thermal management circuit (107) may be configured to receive the rectified rippled DC voltage and drop-down excess voltage to obtain to a constant voltage if the rectified rippled DC voltage exceeds a predetermined threshold. The active thermal management circuit of low beam headlamp and high beam headlamp are denoted by (107L) and (107H), respectively. The current linear regulator (106) may be configured to receive the constant voltage from the active thermal management circuit (107) and provide constant output LED current to the plurality of LEDs (108a-d) (108e-k). The current linear regulator of low beam headlamp and high beam headlamp are denoted by (106L) and (106H), respectively.
Now referring to figure 3A, a schematic diagram of an input protection circuit (103) is illustrated. The input protection circuit (103) may comprise at least one reverse polarity diode. Figure 3A shows two reverse polarity diodes D1 and D2 according to one embodiment. The input protection circuit (103) may be configured for protecting the circuitry from reverse polarity.
Now referring to Figure 3B, a schematic diagram of a voltage limiting circuit (104), is illustrated. The voltage limiting circuit (104) may configured to receive the negative half wave rectified dc signal and maintain a rectified rippled DC voltage. The voltage limiting circuit (104) may comprise a MOSFET Q1 (204), a transistor Q3 (202), a Zener diode ZD3 (203), and a bulk capacitor C2 (212). The transistor

Q3 (202) and the Zener diode ZD3 (203) may be configured to control a switch operation of the MOSFET Q1 (204). The resistors R5 and R10 may be configured for biasing of the transistor Q3 (202). The resistors R7 and R17 may be configured for biasing of the MOSFET Q1 (204). Further, Ton time of MOSFET Q1 (204) may be dependent on the value of the Zener diode ZD3 (203) such that the voltage at the bulk capacitor C2 (212) may be limited to less than the breakdown voltage of the Zener diode ZD3 (203).
In one embodiment, when Zener diode ZD3 (203) clamps at a predefined voltage, the MOSFET Q1 (204) turns off and cuts down excess voltage and generates constant voltage at the output of Q1. Further, Zener diode ZD2 may be configured for the protection of the MOSFET Q1 (204).
In one embodiment, the bulk capacitor C2 (212) may be configured to maintain a minimum voltage required for driving the plurality of LEDs, when the MOSFET Q1 (204) is turned off. Now referring to figure 4, a waveform representation 400 of RR negative rectified input voltage and an output voltage at the bulk capacitor C2 of the voltage limiting circuit (104) and a constant output LED current, is illustrated. The output voltage of the bulk capacitor C2 is maintained to provide the constant output LED current.
Now referring to Figure 3C, a schematic diagram of an active thermal management circuit (107), is illustrated. The active thermal management circuit (107) may be configured to receive the rectified rippled DC voltage of the voltage limiting circuit (104). In one embodiment, the active thermal management circuit (107) may comprise a switch Q2 (210), a transistor Q4 (205), a Zener diode ZD1(206), a Zener diode ZD4(211), and a plurality of resistors (R1-R4) and R6, R11, R8, R18. The resistors R6 and R11 may be configured for biasing of the transistor Q4 (205). The resistors R8 and R18 may be configured for biasing of the MOSFET Q2 (210). When a voltage across the bulk capacitor C2 (212) of the voltage limiting circuit (104) is below the predetermined threshold, the switch Q2 (210) enters into saturation region and the voltage of the bulk capacitor C2 (212) is directly transferred to the plurality of LEDs. When the voltage across the bulk capacitor C2

(212) exceeds the predetermined threshold, the transistor Q4 (205) and a Zener diode ZD1 (211) are configured to turn-off the switch Q2 (210). When the switch Q2 (210) enters into cut-off region, the plurality of resistors (R1-R4) across the switch Q2 (210) may be in series connection with the plurality of LEDs and configured to absorb the excess voltage. Therefore, the active thermal management circuit (107) may be configured for reducing thermal stress on linear regulator.
In one exemplary embodiment, when the voltage across the bulk capacitor C2 (212) is below 24V, the switch Q2 (210) enters into saturation region and voltage of the bulk capacitor C2(212) is directly transferred to the plurality of LEDs. When the voltage across the bulk capacitor C2 (212) is above 24 V, the plurality of resistors (R1-R4) across the switch Q2 (210) comes in series connection with the plurality of LEDs and are configured to absorb the excess voltage.
The Ton time of transistor Q4 (205) is dependent on the value of ZD4 (211) of the active thermal management circuit (107) in order to maintain a constant voltage across the current linear regulator (106). In one embodiment, the current linear regulator (106) comprises a Zener diode Z D5 (207), resistor R12, R13, a transistor Q5 (208), and transistor Q6 (214). The constant output LED current is dependent at least on the breakdown voltage of the Zener diode ZD5 (207) and the resistors R12, R13. In one non-limiting embodiment, the number of transistors may increase with an increase in the number of LEDs.
The transistor Q5 (208) and transistor Q6(214) are configured to receive the input voltage from the active thermal management circuit (107). Further, transistor Q5 (208) and transistor Q6 (214) are configured to receive the base voltage from Zener diode ZD5 (207). The resistors R12 and R13 may be configured to vary collector current Ic of the transistor Q5 (208) and transistor Q6 (214). Further, the resistors R12, R13 may be configured to come in series connection with the LED loads for multiple number of times, when RPM of the vehicle is increased.
The characteristics of the conventional linear driver regulator with constant DC input and the circuit (10) for driving a plurality of light emitting diode (LEDs) of a lighting device is compared in table 1 shown below:

Sr. Characteristic Conventional linear driver Circuit (10) for driving a plurality of
No regulator with constant DC light emitting diode (LEDs) of a
input lighting device
1 Input source Vehicle battery Phase controlled RR
2 Input voltage Range 9V ~16V 13.5V±0.5V (RMS)
3 Typical Input 13.5V Ideal RPM (MIN)- 1350 RPM, VIN
Voltage (Min)=-20V

Typical RPM (TYP) - 5000 RPM,
VIN (Min)=-30V

Maximum RPM (MAX) - 9000
RPM, VIN (Min)=-32V
Table 1: Characteristics
Now referring to following table 2, comparison of power and efficiency calculations of the conventional linear driver regulator with constant DC input and the circuit (10) for driving a plurality of light emitting diode (LEDs) of a lighting device is depicted:

Sr. Feature Conventional linear driver Circuit (10) for driving a plurality of
No regulator with constant DC light emitting diode (LEDs) of a
input lighting device
1 High Beam (HB) LED Current 1.5A 0.75A
2 Low Beam (LB) LED Current 2.1A 0.75A
3 Maximum input power 57W 33W
4 Driver losses 57- 25= 32W 33- 25= 8W
5 Efficiency 40% 76%

6 Losses 60% 24%
Table 2: Power and Efficiency calculations
It can be noted that, the aforementioned comparison table clearly shows improvement in the efficiency due to less driver loss in the circuit (10) for driving a plurality of light Emitting Diode (LEDs) of a lighting device.
Further, the aforementioned illustrated embodiments offer the following advantages over the conventional Headlamp Assembly, which may include but are not limited to:
• Some embodiments of the present disclosure may provide a headlamp package for providing an optimized efficiency of nearly 75 percent in the electronic circuit of the headlamp in the automobile.
• Some embodiments of the present disclosure may employ lesser components thereby producing a low form factor which causes reduced power consumption in the system.
• Some embodiments of the present disclosure are free of high frequency switching components thereby there is noise free output in Electromagnetic interference/Electromagnetic compatibility (EMI/EMC) requirements, and there is cost optimization.
• Some embodiments of the present disclosure may provide a constant light output in the headlamp in the automobile at wide range (around 1000 RPM to 8000 RPM) of RPM values of the vehicle.
Although implementations of the rectifier and regulator driven class D projector in two-wheeler headlamp have been described in language specific to structural features and/or methods, it is to be understood that the appended claims are not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as examples of implementations of the rectifier and regulator driven class D projector in two-wheeler headlamp.

WE CLAIM:
1. A circuit (10) for driving a plurality of light emitting diode (LEDs) of a
lighting device, the circuit (10) comprising:
an input protection circuit (103) configured to receive negative half wave
rectified dc signal and protect the circuit (10) from reverse polarity;
a voltage limiting circuit (104) configured to receive the negative half
wave rectified dc signal and maintain a rectified rippled DC voltage;
an active thermal management circuit (107) configured to:
receive the rectified rippled DC voltage; and
drop down an excess voltage to a constant voltage, if the rectified rippled
DC voltage exceeds a predetermined threshold; and
a current linear regulator (106) configured to:
receive the constant voltage from the active thermal management circuit
(107); and
provide constant output LED current to the plurality of LEDs.
2. The circuit (10) as claimed in claim 1, wherein the negative half wave rectified dc signal is received from a Regulator and Rectifier (RR) unit, and wherein the negative half wave rectified dc signal is a pulsating DC signal.
3. The circuit (10) as claimed in claim 2, wherein the input protection circuit
(103) comprises at least one reverse polarity diodes (D1 and D2).
4. The circuit (10) as claimed in claim 1, wherein the voltage limiting circuit
(104) comprises a MOSFET Q1 (204), a transistor Q3 (202), a Zener diode
ZD3 (203), and a bulk capacitor C2 (212), and wherein the transistor Q3
(202) and the Zener diode ZD3 (203) are configured to control a switch
operation of the MOSFET Q1 (204).
5. The circuit (10) as claimed in claim 4, wherein the Ton time of MOSFET
Q1 (204) is dependent on the value of the Zener diode ZD3 (203) such that
the voltage at the bulk capacitor C2 (212) is limited to less than the
breakdown voltage of the Zener diode ZD3 (203).

6. The circuit (10) as claimed in claim 5, wherein the bulk capacitor C2 (212) is configured to maintain a minimum voltage required for driving the plurality of LEDs, when the MOSFET Q1 (204) is turned off.
7. The circuit (10) as claimed in claim 1, wherein the active thermal management circuit (107) comprises a switch Q2 (210), a transistor Q4 (205), and a Zener diode ZD1(206), ZD4 (211), and a plurality of resistors.
8. The circuit (10) as claimed in claim 7, wherein the switch Q2 (210) enters into saturation region and the voltage of the bulk capacitor C2 (212) is directly transferred to the plurality of LEDs, when a voltage across the bulk capacitor C2 (212) is below the predetermined threshold.
9. The circuit (10) as claimed in claim 7, wherein the transistor Q4 (205) and a Zener diode ZD4 (211) are configured to turn-off the switch Q2 (210), when the voltage across the bulk capacitor C2 (212) is exceeds the predetermined threshold.
10. The circuit (10) as claimed in claim 9, wherein the plurality of resistors are in series connection with the plurality of LEDs and are configured to absorb the excess voltage, when the switch Q2 (210) enters into cut-off region.
11. The circuit (10) as claimed in claim 7, wherein the Ton time of transistor Q4 (205) is dependant on the value of ZD4 (211) to maintain a constant voltage across the current linear regulator.
12. The circuit (10) as claimed in claim 1, wherein the current linear regulator (106) comprises a Zener diode ZD5 (207), Resistor R12, R13, a transistor Q5 (208), and transistor Q6 (214), and wherein the constant output LED current is dependent at least on the breakdown voltage of the Zener diode ZD5 (207) and the resistors R12, R13.