Integrated circuit for lamp heating and dimming control

• US 6,531,831 B2
• Filed: 04/03/2001
• Issued: 03/11/2003
• Est. Priority Date: 05/12/2000
• Status: Expired due to Fees

• Current Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Original Assignee: O2 Micro International Limited (O2 Micro Incorporated)
• Inventors: Chou, John, Lin, Yung-Lin
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): TRAN, CHUC
• Application Number:
  US09/825,034
• Publication Number:
  US 20020140371A1
• Time in Patent Office: 707 Days
• Field of Search: 315/224, 315/244, 315/243, 315/DIG.4, 315/307, 315/209.R, 315/291, 315/DIG.2, 315/DIG.5, 315/225, 315/277, 315/119
• US Class Current: 315/225
• CPC Class Codes: H05B 41/295 with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
• CPC Class Codes: H05B 41/2985 against abnormal lamp operating conditions
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations
• CPC Class Codes: H05B 41/3927 by pulse width modulation H05B41/3922 takes precedence
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

An electronic ballast for lamps or tubes is provided. In one embodiment the present invention includes a ballast controller that includes filament heating circuitry and dimming circuitry. The filament heating circuitry may include preheat dimming circuits which preheat the filaments for a predetermined time period prior to striking the lamp, and steady-state heating circuitry that continually heats the filaments during steady state operation of the lamp. The steady state heating circuitry may be adapted to heat the filaments inversely proportional to the dim desired value of the lamp. The dimming circuitry may include conventional analog dimming and/or burst mode dimming to define a wide range of dimming characteristics for the lamp.

Claims

1. An electronic ballast system, comprising:

a variable voltage source generating a first signal indicative of a desired dim value for a hot cathode fluorescent lamp, and a second signal indicative of the average power of said variable voltage source;

a ballast controller comprising;

lamp filament current control circuitry comprising preheat filament current control circuitry generating a preheat filament current to the filaments of said lamp for a predetermined time period and steady state filament current control circuitry generating a steady state filament heating current in reverse proportion to said desired dim value during times after said predetermined period of time;

dimming circuitry comprising a burst PWM (pulse width modulated) signal generator receiving said first signal and generating a PWM dimming signal proportional to a desired dim value;

current feedback circuitry receiving a signal indicative of the current supplied to said lamp and comparing said signal indicative of the current supplied to said lamp and said PWM dimming signal to generate a variable power control signal;

inverter circuitry receiving said variable power control signal and generating an AC signal proportional to said power control signal by inverting said second signal; and

a resonant tank circuit coupled to said inverter circuitry receiving said AC signal to deliver striking and steady state sinusoidal power to said lamp.

2. An electronic ballast system as claimed in claim 1, wherein said preheat filament current control circuitry comprising a selector switch;

said selector switch being controlled by an enable signal, said selector switch operable to cast through a predetermined filament preheat signal to generate a predetermined filament current for preheating the filaments of said lamp.

3. An electronic ballast system as claimed in claim 2, wherein said predetermined period of time being controlled by preheat timing control circuitry comprising a comparator that compares a voltage generated by a charging capacitor to a predetermined reference voltage, wherein said preheat filament current control circuitry operable for a time period for when the voltage on said charging capacitor is less than said reference voltage.

4. An electronic ballast system as claimed in claim 1, wherein said steady state filament current control circuitry operable to generate said steady state filament heating current between a predetermined minimum value and predetermined maximum value.

5. An electronic ballast system as claimed in claim 1, wherein said inverter circuitry comprising a full bridge inverter circuit.

6. An electronic ballast, comprising:

a variable voltage source generating a first signal indicative of a desired dim value for a hot cathode fluorescent lamp, and a second signal indicative of the average power of said variable voltage source;

a ballast controller comprising;

open loop lamp filament current control circuitry comprising preheat filament current control circuitry generating a preheat filament current to the filaments of said lamp for a predetermined time period and a steady state filament heating current during times after said predetermined period of time;

dimming circuitry to vary the power delivered to said lamp as a function of the value of said first signal; and

a full bridge inverter circuit generating an AC signal from said second signal based on said dimming circuitry; and

a resonant tank circuit coupled to the output of said full bridge inverter receiving said AC signal and generating a sinusoidal signal to deliver striking and steady state power to said lamp.

7. An electronic ballast system as claimed in claim 6, wherein said preheat filament current control circuitry comprising a selector switch;

said selector switch being controlled by an enable signal, said selector switch operable to cast through a predetermined filament preheat signal to generate a predetermined filament current for preheating the filaments of said lamp.

8. An electronic ballast system as claimed in claim 7, wherein said predetermined period of time being controlled by preheat timing control circuitry comprising a comparator that compares a voltage generated by a charging capacitor to a predetermined reference voltage, wherein said preheat filament current control circuitry operable for a time period for when the voltage on said charging capacitor is less than said reference voltage.

9. An electronic ballast system as claimed in claim 6, wherein said steady state filament current control circuitry operable to generate said steady state filament heating current between a predetermined minimum value and predetermined maximum value.

10. An electronic ballast system, wherein said lamp filament current control circuitry further comprising a high frequency pulse with modulation circuit comprising a comparator that compares an output signal generated by said preheat filament current control circuitry or said steady state filament current control circuitry to a high frequency saw tooth to signal and generating a signal having a duty cycle based on said output signal and said high frequency saw tooth to signal.

11. An electronic ballast system, wherein said lamp filament current control circuitry further comprising a high frequency pulse with modulation circuit comprising a comparator that compares an output signal generated by said preheat filament current control circuitry or said steady state filament current control circuitry to a high frequency saw tooth to signal and generating a signal having a duty cycle based on said output signal and said frequency saw tooth to signal.