Electronic ballast with low voltage output

Abstract

The present invention provides a high frequency electronic ballast with low voltage output, comprising a high voltage power supply ( 200 ) generating high voltage power ( 234 ) at a voltage and a frequency; a low voltage microcontroller ( 214 ) which is responsive to the voltage and the frequency of the high voltage power ( 234 ) and generates a low voltage drive signal ( 240 ); and a switch ( 216 ) operably connected to the high voltage power supply ( 200 ) and responsive to the low voltage drive signal ( 240 ). The low voltage output of the switch ( 216 ) can be used to drive auxiliary low voltage loads ( 220 ), such as a back-up incandescent lamp ( 116 ). The low voltage output can be responsive to HID lamp power, so that the back-up incandescent lamp ( 116 ) is energized when the HID lamp is not providing illumination.

1 . A low voltage output circuit for an electronic ballast comprising:
 a high voltage power supply ( 200 ), the high voltage power supply ( 200 ) generating high voltage power ( 234 ) having a voltage and a frequency;   a low voltage microcontroller ( 214 ), the low voltage microcontroller ( 214 ) being responsive to the voltage and the frequency of the high voltage power ( 234 ) and generating a low voltage drive signal ( 240 ); and   a switch ( 216 ), the switch ( 216 ) being operably connected to the high voltage power supply ( 200 ) and being responsive to the low voltage drive signal ( 240 ).   
   
   
       2 . The low voltage output circuit of  claim 1  wherein the high voltage power supply ( 200 ) is a power supply for mains voltage ( 120 ). 
   
   
       3 . The low voltage output circuit of  claim 1  wherein the low voltage microcontroller ( 214 ) is responsive to a switching signal ( 232 ). 
   
   
       4 . The low voltage output circuit of  claim 3  further comprising a ballast microcontroller ( 206 ), the ballast microcontroller ( 206 ) being responsive to a ballast signal ( 204 ) and generating the switching signal ( 232 ). 
   
   
       5 . The low voltage output circuit of  claim 4  wherein the ballast signal ( 204 ) is an HID lamp power signal and the ballast microcontroller ( 206 ) switches the switching signal ( 232 ) when the HID lamp power signal reaches a predetermined setpoint. 
   
   
       6 . The low voltage output circuit of  claim 5  wherein the predetermined setpoint is about 50% nominal HID lamp power. 
   
   
       7 . The low voltage output circuit of  claim 1  wherein the switch ( 216 ) provides low voltage output ( 218 ) to an incandescent lamp ( 116 ). 
   
   
       8 . The low voltage output circuit of  claim 1  wherein the switch ( 216 ) is a triac. 
   
   
       9 . A method of producing a low voltage output for an electronic ballast comprising:
 providing a high voltage power supply ( 200 ), the high voltage power supply ( 200 ) generating high voltage power ( 234 );   determining voltage of the high voltage power ( 234 );   determining frequency of the high voltage power ( 234 );   determining a low voltage drive signal ( 240 ) based on the voltage and the frequency; and   switching a switch ( 216 ) operably coupled to the high voltage power supply ( 200 ) in response to the low voltage drive signal ( 240 ).   
   
   
       10 . The method of  claim 9  wherein determining frequency of the high voltage power ( 234 ) comprises:
 rectifying the high voltage power ( 234 ) to generate a high voltage (HV) voltage signal ( 236 );   comparing the HV voltage signal ( 236 ) to a reference voltage signal ( 208 ) to generate an HV zero crossing signal ( 238 ) indicative of the frequency.   
   
   
       11 . The method of  claim 9  wherein determining a low voltage drive signal ( 240 ) based on the voltage and the frequency further comprises:
 providing a low voltage microcontroller ( 214 ) having a look-up table; and   looking up the low voltage drive signal ( 240 ) for the voltage and the frequency on the look-up table.   
   
   
       12 . The method of  claim 9  further comprising switching the low voltage drive signal ( 240 ) in response to a switching signal ( 232 ). 
   
   
       13 . The method of  claim 12  further comprising providing a ballast microcontroller ( 206 ), the ballast microcontroller ( 206 ) generating the switching signal ( 232 ) in response to a ballast signal ( 204 ). 
   
   
       14 . The method of  claim 9  further comprising providing a low voltage output ( 218 ) from the switch ( 216 ) to an incandescent lamp ( 116 ). 
   
   
       15 . The method of  claim 14  further comprising:
 determining power to an HID lamp; and   switching off the incandescent lamp ( 116 ) when the power to the HID lamp exceeds a predetermined power.   
   
   
       16 . The method of  claim 15  wherein the predetermined power is about 50% nominal HID lamp power. 
   
   
       17 . A system for producing a low voltage output for an electronic ballast comprising:
 means for providing high voltage power ( 234 );   means for determining voltage of the high voltage power ( 234 );   means for determining frequency of the high voltage power ( 234 );   means for determining a low voltage drive signal ( 240 ) based on the voltage and the frequency; and   means for switching operably coupled to the high voltage power providing means, the switching means being responsive to the low voltage drive signal ( 240 ).   
   
   
       18 . The system of  claim 17  wherein the frequency determining means further comprises:
 means for rectifying the high voltage power ( 234 ) to generate a HV voltage signal ( 236 );   means for comparing the HV voltage signal ( 236 ) to a reference voltage signal ( 208 ) to generate an HV zero crossing signal ( 238 ) indicative of the frequency.   
   
   
       19 . The system of  claim 17  wherein the low voltage drive signal ( 240 ) determining means further comprises:
 means for storing a look-up table; and   means for looking up the low voltage drive signal ( 240 ) for the voltage and the frequency from the look-up table.   
   
   
       20 . The system of  claim 17  further comprising means for switching the low voltage drive signal ( 240 ), the low voltage drive signal ( 240 ) switching means being responsive to a switching signal ( 232 ). 
   
   
       21 . The system of  claim 17  further comprising means for backup lighting operably connected to the switching means. 
   
   
       22 . The system of  claim 21  further comprising:
 means for determining power to an HID lamp; and   means for switching off the backup lighting means when the power to the HID lamp exceeds a predetermined power.   
   
   
       23 . The low voltage output circuit of  claim 1  wherein the switch ( 216 ) provides low voltage output ( 218 ) to an insulation detector. 
   
   
       24 . The method of  claim 9  further comprising providing a low voltage output ( 218 ) from the switch ( 216 ) to an insulation detector. 
   
   
       25 . The system of  claim 17  further comprising means for detecting insulation operably connected to the switching means.