FORM 2
THE PATENTS ACT, 1970
(39of l970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
An automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai 400 030, Maharashtra, India, an Indian Company
Inventors
Naman Raval of Crompton Greaves Ltd, Electronic Design centres, Global R&D Centre, Kanjurmarg (East), Mumbai - 400042, Maharashtra, India and Jaishankar Nirody of Al Nandanvan, MG Road, Mulund (west), Mumbai-400080, Maharashtra, India, both Indian Nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the nature of this invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
This invention relates to an automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast. BACKGROUND OF THE INVENTION
An electronic ballast of a High Intensity Discharge (HID) Lamp usually comprises of a Power Factor Corrector (PFC) IC connected to a Buck Regulator which in turn is connected to the HID Lamp through a Full Bridge circuit. A lamp igniter is usually connected in parallel with the HID Lamp and the Full Bridge circuit. The Buck Regulator usually comprises of a Buck MOSFET and a Power Control IC such that the input end of the Buck MOSFET is connected to the output end of the Power Control IC. The PFC IC is fed input AC supply which converts it into power factor corrected DC supply which is fed into the Buck MOSFET. The Buck MOSFET outputs a regulated DC voltage based on the input from the Power Control IC. The regulated DC voltage from the Buck MOSFET is fed into the Full Bridge circuit which converts the DC voltage into an AC voltage to be fed to the HID Lamp and the Lamp Igniter to ignite the HID Lamp at the start up. The Power Control IC takes feedback from the actual current and voltage being fed to the Full Bridge Circuit and compares it to the reference current and voltage (which is based on the set value of the required power) and accordingly adjusts the Pulse Width Modulation of the Buck MOSFET to maintain the set levels of current and voltage being fed to the Full Bridge Circuit and thus maintains the set power being fed to the Lamp.
A plurality of such HID Lamps is used in street light systems which are found not only on city roads and highways, but also on college campuses, around commercial and industrial centers, in public and private parks and amusement centers, and any other locations where safety of people and property is a significant concern. Normally, switching ON/OFF and varying the intensity of brightness in such HID lamps at different times is a manual process and labour intensive. For example, each

time at dusk and dawn, a person has to go and switch ON/OFF the lamps. Moreover, in order to save energy, the lamps are required to be dimmed at a time near the dawn. Having a manual attendant for performing the above functions is costly and time consuming. There is a need for an automatic control device for such HID Lamps having electronic ballast.
OBJECTS OF THE INVENTION
An object of the invention is to provide an automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast.
Another object of the invention is to obviate the need of a manual attendant for switching ON/OFF or varying the power supply to HID Lamps having electronic ballast.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, there is provided an automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast, the device comprising a processor based controller, a timer configured to provide time details to the controller, at least one sunlight detecting sensor interfaced with the controller and a Digital to Analog Convertor (DAC) interfaced with the controller, wherein the controller being pre-programmed to output a digital pulse of a pre-determined pulse width to the DAC based on the inputs from the sensor and timer, the analog pulse from the DAC corresponding to the digital pulse from the controller being fed to an electronic ballast of the HID Lamp which being configured to provide a regulated power supply to the HID Lamp based on the input from the DAC.
Preferably, the controller is a microprocessor based controller and the electronic ballast comprises of a Power Factor Corrector (PFC) IC for converting the AC input supply being fed thereto for converting the AC input supply into Power

Factor corrected DC supply, a buck regulator connected to the output end of the PFC IC and having a feedback mechanism for generating a regulated DC supply based on the said feedback and input from the DAC and a full bridge circuit connected to the output end of the buck regulator for converting the regulated DC supply in to regulated AC supply to be fed to the HID Lamp through a Lamp Igniter connected in parallel with the HID Lamp.
Preferably, the Buck Regulator comprises of a Power Control IC and a Buck MOSFET wherein the outputs from the PFC IC and the Power Control IC are connected to the input ends of the Buck MOSFET, the output from the Buck MOSFET being fed to the Full Bridge Circuit and the Power Control IC as feedback input, the output from the DAC being fed as another input to the Power Control IC which being configured to generate a control signal based on the said inputs thereto, the control signal being fed to the Buck MOSFET, wherein the Buck MOSFET being configured to regulate the input DC supply being fed thereto based on the control signal from the Power Control IC and output thereof to the Full Bridge circuit
These and other aspects, features and advantages of the invention will be better understood with reference to the following detailed description, accompanying drawings and appended claims, in which,
Fig 1 is a block diagram of an automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast.
Fig 2 is a block diagram of a power supply system to a High Intensity Discharge (HID) Lamp.
As shown in Fig 1, an automatic control device 1 for a High Intensity Discharge (HID) Lamp having an electronic ballast comprises a microcontroller based processor 2, a timer device 3 i.e. a Real Time Clock (RTC), a sunlight sensor 4 and a digital to analog convertor (DAC) 5 interfaced with the microcontroller 2 through

known interfacing techniques such as by a single port driven resistor - capacitor network or by using a dedicated digital to analog converting IC, The microcontroller 2 is usually a low cost microcontroller like PIC12F675 or AT89C2C2051 or similar pre-programmed to receive inputs from the timer device 3 and sunlight sensor 4. The input from the timer device 3 is about the current time details and that from the sunlight sensor 4 is the presence/absence/intensity of the sunlight. There may not be a need of the timer device 3 if the microcontroller 2 comprises an internal clock and configured to fetch time details from therein. The sunlight sensor 4 is a preferably a TSL2550 sensor made by TAOS Inc and/or other sensors for example an Light Dependent Resistor sensor (LDR) and/or Infrared sensor with a spectra] response nearer to the visible spectrum of sunlight or a Digital Ambient Light Sensor capable of sensing the visible spectrum of the sunlight. The sunlight sensor 4 may also be of a type which can filter the normal artificial light by other lamps in the vicinity. A combination of above described sensors may also be used. Based on the inputs from the timer device 3 and sunlight sensors 4, the microcontroller 2 is pre-programmed to generate an output digital pulse of a pre-determined pulse width. For example, the microcontroller 2 can be pre-programmed in the following way: i) generate digital pulses of unique pre-determined pulse widths as soon as a particular instances of time is reached such as dusk, dawn, midnight etc, for example, at dawn and dusk, a digital pulse of 50% pulse width and 3 volts is generated to give a half dimmed level of the lamp. Between 7 PM and 11 PM a digital pulse of 100% pulse width and 5 volts can be generated for giving full brightness of the lamp and so on. ii) generate a digital pulse of a unique pre-determined width as soon as the sensor fails to detect any ambient light overriding any other condition such as i) above iii) generate a digital pulse of a unique pre-determined width as soon as a predetermined intensity of sunlight is detected, overriding any other condition such as i)

above. The output from the microcontroller 2 is fed to a DAC 5 which converts the digital pulse from the microcontroller 2 into a corresponding analog signal. The DAC 5 could be a discrete circuit using just a resistor and capacitor combination or a digital to analog converter IC such as DAC0808 made by National Semiconductors or similar.
Fig 2 is a block diagram of a power supply system to an HID Lamp having an electronic ballast according to a preferred embodiment. The electronic ballast 7 comprises of a Power Factor Corrector (PFC) IC 10, Buck Regulator 9 and a Full Bridge Circuit 12. The Buck Regulator 9 comprises of a Power Control (PC) IC 8 and Buck MOSFET 11. The PFC IC 10 is fed input AC supply which converts it into power factor corrected DC supply which is fed into the Buck MOSFET 11. The Buck MOSFET 11 is typically a device such as IRF840 or STP10N60 which outputs a variable regulated DC voltage from the fixed DC voltage being fed thereto based on the inputs from the PC JC 8. The PC JC 8 is fed two inputs, one being the output from the DAC 5 and the other being the output from the Buck MOSFET 11 as feedback input. The PC IC 8 is typically a Transition Mode Controller IC, such as the L6562 made by ST Microelectronics, but used for regulating DC voltage outputted by the Buck MOSFET 11. This is done by using feedback from the output of the Buck MOSFET 11 and comparing it with the reference input coming from the DAC 5. The current through the Buck MOSFET 11 is held constant by the PC IC 8. For example, if the input from the DAC 5 is 0 V, 5 V or 3 V, the corresponding output DC voltage configured to be outputted from the Buck MOSFET II is 0 V (off), 100 volts (maximum brightness) or 75 volts (half brightness) assuming that the feedback divider is so configured as to give a voltage of OV, 5 V and 3 V feedback to the PC IC 8 when the output voltage of the Buck Mosfet 11 is 100 volts and 15 volts respectively. This DC voltage from the Buck MOSFET 11 is then converted to AC

voltage by means of a Full Bridge Circuit 12, connected between the output end of the Buck MOSFET 11 and input end of the HID Lamp 13, and fed to the HID Lamp 13 thus switching OFF, brightening to the maximum or halving the maximum brightness of the HID Lamp 13 respectively. Most preferably, a Lamp igniter 14 is connected to the HID Lamp 13 and in parallel to the Full Bridge Circuit 12 for igniting the HID Lamp 13.
It may be noted that the structure of the electronic ballast and the Buck Regulator as describe above may vary. Similarly, the programming of the microcontroller may vary from as described above. Instead of a microcontroller, some other processor based device may be used as controller.
According to the invention, an automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast is provided which obviates the need of a manual intervention to switch ON/OFF and vary the power supply to the HID Lamps thereby saving costs and making the process simpler.
Although the invention has been described with reference to a specific embodiment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that such modifications can be made without departing from the scope of the invention as defined in the appended claims.

We claim:
1. An automatic control device for a High Intensity Discharge (HID) Lamp having an electronic ballast, the device comprising a processor based controller, a timer configured to provide time details to the controller, at least one sunlight detecting sensor interfaced with the controller and a Digital to Analog Convenor (DAC) interfaced with the controller, wherein the controller being pre-programmed to output a digital pulse of a pre-determined pulse width to the DAC based on the inputs from the sensor and timer, the analog pulse from the DAC corresponding to the digital pulse from the controller being fed to an electronic ballast of the HID Lamp which being configured to provide a regulated power supply to the HID Lamp based on the input from the DAC.
2. The device as claimed in claim 1, wherein the electronic ballast comprises of:
a. a Power Factor Corrector (PFC) IC for converting the AC input
supply being fed thereto for converting the AC input supply into Power
Factor corrected DC supply;
b. a buck regulator connected to the output end of the PFC IC and having
a feedback mechanism for generating a regulated DC supply based on
the said feedback and input from the DAC; and
c. a full bridge circuit connected to the output end of the buck regulator
for converting the regulated DC supply in to regulated AC supply to be
fed to the HID Lamp through a Lamp Igniter connected in parallel with
the HID Lamp.

3. The device as claimed in claim 2, wherein the Buck Regulator comprises of a Power Control IC and a Buck MOSFET wherein the outputs from the PFC IC and the Power Control IC are connected to the input ends of the Buck MOSFET, the output from the Buck MOSFET being fed to the Full Bridge Circuit and the Power Control IC as feedback input, the output from the DAC being fed as another input to the Power Control IC which being configured to generate a control signal based on the said inputs thereto, the control signal being fed to the Buck MOSFET, wherein the Buck MOSFET being configured to regulate the input DC supply being fed thereto based on the control signal from the Power Control IC and output thereof to the Full Bridge circuit.
4. The automatic control device as claimed in claim 1, wherein the processor based controller is a microcontroller.
5. The automatic control device as claimed in claim 1, wherein the processor based controller comprises an internal timer.
6. The automatic control device as claimed in claim 1, wherein the timer is provided externally to the controller and interfaced therewith.
7. The automatic control device as claimed in claim 1, wherein the sunlight detecting sensor is a LDR sensor or an Infrared sensor or a combination of such sensors.
8. The automatic control device as claimed in claim 1, wherein the controller is pre-programmed to generate a digital pulse of a pre-determined pulse width for switching ON the power supply to the HID Lamp, if OFF, in the event of no sunlight being detected by the sunlight detecting sensor.

9. The automatic control device as claimed in claim 1, wherein the controller is pre-programmed to generate a digital pulse of a pre-determined pulse width for varying the power supply to the HID Lamp at pre-determined times.