Floating IC driven dimming ballast

• US 6,218,788 B1
• Filed: 08/20/1999
• Issued: 04/17/2001
• Est. Priority Date: 08/20/1999
• Status: Expired due to Term

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Chen, Timothy, Nerone, Louis R.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): Lee, Wilson
• Application Number:
  US09/378,193
• Time in Patent Office: 606 Days
• Field of Search: 315/209.R, 315/219, 315/224, 315/225, 315/244, 315/247, 315/291, 315/307, 315/308, 315/360, 315/DIG.4, 315/DIG.5, 315/207
• US Class Current: 315/225
• CPC Class Codes: H05B 41/3921 with possibility of light intensity variations

Abstract

Ballast circuit 10 for lamp 52 has a switching network consisting of a complimentary pair of switches 30, 32 which are driven by a low-power universally available controller IC 26. The controller IC 26 is configured with a floating ground arrangement 36. A current sensor 72 assists in generating a negative feedback signal 79 which is provided to an inverting input of operational amplifier 86 of controller IC 26. Prior to being supplied, the negative feedback signal 79 is summed at summing node 80 with a level shifted signal 92, generated by a level shifting circuit 22 which received an input dimming signal 16. The level shifting circuit 22 shifts the dimming signal 16 from a ground reference system to a floating ground design. The level shifted signal 92 and feedback signal 79 are designed to cancel each other whereby the input to operational amplifier 86 is maintained constant as the non-inverting input has a constant internally supplied voltage.

Claims

1. A dimming ballast circuit designed to use a phase dimmer signal to control output of a fluorescent lamp, the dimming ballast comprising:

a controller integrated chip (IC) having an internal operational amplifier with a non-inverting input tied to a steady state voltage, and a Class D output, the controller integrated chip configured in a floating ground arrangement, and configured to generate a drive signal from the phase dimmer signal;

a switching network which receives a drive signal from the controller IC for operating the switching network, to control operation of the fluorescent lamp;

a level shifter designed to receive the phase dimmer signal from the input, and to shift the received phase dimmer signal from a level of the reference around to a level of the floating ground; and

a load circuit including the fluorescent lamp, connected to a series configured resonant inductor and resonant capacitor.

2. The invention of claim 1 further including:

a feedback signal generated from current of the switching network.

3. The invention of claim 2 further including:

a summing node which sums the shifted signal of the level shifter with the feedback signal from the current sensor, such that the level shifted signal and the feedback signal are summed at the summing node, whereby the error is input to the operational amplifier.

4. The invention according to claim 1:

wherein the switching network includes a pair of switches.

5. The invention according to claim 4:

wherein the pair of switches are configured as a common source complementary pair of transistors.

6. The invention according to claim 5:

wherein gates of the common source complementary pair of transistors are driven from a single drive signal.

7. The invention according to claim 1:

wherein the fluorescent lamp is driven by a pulse width modulated signal.

8. The invention according to claim 1:

wherein the switching frequency of the ballast circuit is 100KHz or greater.

9. The invention according to claim 1 wherein the phase dimmer signal is a chopped input voltage, which is shifted from circuit ground to floating ground.

10. A dimming ballast circuit designed to receive a phase dimmer signal to control output of a fluorescent lamp, the dimming ballast comprising:

an input configured to generate the phase dimmer signal;

a controller integrated chip (IC) having an internal operation amplifier with a non-inverting input tied to a steady state voltage, within the integrated chip, and a Class D output the controller integrated chip configured in a floating ground arrangement;

a coupling capacitor connected at one end to the output of the integrated chip;

a complementary pair of power switches, wherein the gates of the switches receive the output of the integrated chip through a second end of the coupling capacitor;

a resistor connected to the second end of the coupling capacitor, and to the floating ground;

a switching current sensor which senses current of the switching network and generates a feedback signal;

a level shifter designed to receive the phase dimmer signal from the input, and to shift the received phase dimmer signal from a level of the reference ground to a level of the floating ground;

a summing node which sums the shifted signal of the level shifter with the feedback signal from the current sensor, such that the level shifted signal and the feedback signal are summed at the summing node, whereby the error is input to the operational amplifier; and

a resonant network configured to receive the output from the switching network.

11. The invention according to claim 10:

wherein the complementary a pair of switches are configured as a common source complementary pair of transistors.

12. The invention according to claim 11:

wherein gates of the common source complementary pair of transistors are driven from a single drive signal.

13. The invention according to claim 10:

wherein the fluorescent lamp is driven by a pulse width modulated signal.

14. The invention according to claim 10:

wherein the switching frequency of the ballast circuit is 100 K Hz or greater.

15. The invention according to claim 11:

wherein the phase dimmer signal is a chopped input voltage, which is shifted from circuit ground to floating ground.

16. A method of controlling an output supplied to a fluorescent lamp by a ballast:

supplying a square wave signal to an input of the ballast;

configuring an integrated control chip of the ballast with a floating ground;

placing a non-inverting input of an internal operational amplifier of the integrated control chip with a steady state input;

sensing an average switching signal of a switching network of the ballast;

forming a feedback signal based on the sensed average switching current;

feeding the input signal to a level shifter circuit of the ballast;

generating a level shifted signal from the input signal feed to the level shifting circuit;

summing the feedback signal and the level shifted signal, such that the difference between the feedback signal and the level shifted signal are amplified and compensated;

supplying the summed signal to an inverting input of the operational amplifier, wherein the operational amplifier receives constant inputs on its non-inverting and inverting inputs; and

energizing the fluorescent lamp via the switching network.

17. The method according to claim 16:

wherein dimming is accomplished by fixed frequency current mode controlled pulse width modulated signals.

18. The method according to claim 16 wherein:

a negative RMS switching current sensing method is used for obtaining dimming.

19. The method according to claim 16:

wherein the switching frequency is 100K Hz or greater.