Electronic ballast circuit for igniting, supplying and dimming a gas discharge lamp

• US 5,925,985 A
• Filed: 07/23/1997
• Issued: 07/20/1999
• Est. Priority Date: 07/27/1996
• Status: Expired due to Fees

• Current Assignee: Singapore Productivity and Standards Board
• Original Assignee: Singapore Productivity and Standards Board
• Inventors: Zeng, Xiaoming, Chia, Che Lock, Tan, Kia Tong
• Primary Examiner(s): KINKEAD, ARNOLD M
• Application Number:
  US08/899,253
• Time in Patent Office: 727 Days
• Field of Search: 315/225, 315/219, 315/DIG. 4, 315/224, 315/DIG. 7, 315/307
• US Class Current: 315/224
• CPC Class Codes: H05B 41/298 Arrangements for protecting lamps or circuits against abnormal operating conditions
• 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
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

An electronic ballast circuit for igniting, supplying and dimming a gas discharge lamp which comprises an oscillation control circuit, an IR2155 self-oscillating half-bridge driver, a dimming control circuit, a load circuit including at least one gas discharge lamp and an over-current protection circuit, wherein the oscillation control circuit controls a current through the lamp by pulse width modulation of a drive signal during a pre-heating stage and the normal operation to control the dimming of the gas discharge lamp.

Claims

1. An electronic ballast circuit for igniting, supplying and dimming a gas discharge lamp, the circuit comprising:

an oscillation control circuit, a self-oscillating half-bridge driver, a dimming control circuit, a load circuit including at least one gas discharge lamp and an over-current protection circuit, wherein the oscillation control circuit controls a current through the lamp by pulse width modulation of a drive signal during a preheating stage and normal operation to control the dimming of the gas discharge lamp;

wherein said circuit comprises;

first and second input terminals (A and B) for connection to a source of DC voltage;

a controlled semiconductor switching element having a drain electrode, a source electrode and a control electrode;

a IR2155 self-oscillating half-bridge driver having an oscillator timing resistor input RT, an oscillator timing capacitor input CT, a high side floating supply VB, a high side gate drive output HO, a high side floating supply return VS, a low side supply VCC, a low side gate drive output LO and a low side return GND;

a choke transformer having a primary winding and a secondary winding;

first means for connecting first and second semiconductor switching elements in a first series circuit across said first and second terminals;

second means for connecting one end of the load circuit and one end of a snubber circuit to a junction point between said first and second semiconductor switching elements and further connecting the other end of said load circuit to said second terminal (B) and the other end of said snubber circuit to said first terminal (A);

said load circuit comprising a first capacitor, the gas discharge lamp and a choke transformer;

said snubber circuit having a first resistor and a second capacitor connected in series;

third means for connecting the input terminals of a first DC supply circuit across said first and second terminals;

said first DC supply circuit having a second resistor and a third capacitor connected in series;

fourth means for connecting said VCC pin of the IR2155 self-oscillating half-bridge driver to a junction point of said second resistor and said third capacitor of said first DC supply via a first diode, and then to said second terminal via a fourth capacitor; and

further connecting said GND pin of the IR2155 self-oscillating half-bridge driver to said second terminal;

fifth means for connecting said VB pin of IR2155 to said VCC pin of the IR2155 self-oscillating halfbridge driver via a second diode, and further connecting said VS pin of the IR2155 self-oscillating half-bridge driver to a junction point between said first and second semiconductor switching elements, and then connecting a fifth capacitor across said VB pin and said VS pin of the IR2155 self-oscillating half-bridge driver;

sixth means for connecting said HO pin of IR2155 to a control electrode of said first semiconductor switching element via a third resistor, and further connecting said LO pin of the IR2155 self-oscillating half-bridge driver to a control electrode of said second semiconductor switching element via a fourth resistor;

seventh means for connecting one end of a second DC supply to said VCC pin of the IR2155 self-oscillating half-bridge driver, and further connecting the other end of said second DC supply to said second terminal;

said second DC supply comprising a secondary winding of said choke transformer, a third diode, a fourth diode and a fifth resistor connecting in series, and a sixth capacitor between one end of said secondary winding and a cathode of said third diode;

eighth means for connecting a resistive voltage divider between said VCC pin of the IR2155 self oscillating half-bridge driver and said second terminal;

said resistive voltage divider having sixth and seventh resistors connected in series, and a seventh capacitor in parallel with said seventh resistor;

ninth means for connecting a first part of the oscillation control circuit to said RT pin of the IR2155 self-oscillating half-bridge driver, and then connecting a second part of said oscillation control circuit to said CT pin of the IR2155 self-oscillating half-bridge driver, and then connecting a third part of said oscillation control circuit to said second terminal, and further connecting a fourth part of said, oscillation control circuit to a junction point of said resistive voltage divider;

said oscillation control circuit comprising a pulse-width limiting circuit, a pulse width control circuit and an oscillation circuit;

said pulse-width limiting circuit having an eighth resistor and a fifth diode connected in series and then connected in parallel with a ninth resistor;

said pulse width control circuit having a sixth diode, a third semiconductor switching element and a tenth resistor connected in series and then connected to an eleventh resistor in parallel with an emitter electrode and a collector electrode of said third switching element;

said oscillation circuit having a twelfth resistor and an eighth capacitor connected in series;

tenth means for connecting one end of said pulse width limiting circuit to said first part of said oscillation control circuit, and then connecting the other end of said pulse-width limiting circuit to one end of said pulse-width control circuit and one end of said oscillation circuit, and then connecting a collector electrode of said third semiconductor switching element to a junction point of said oscillation circuit and to the second part of said oscillation control circuit, and then connecting the other end of said pulse width control circuit and the other end of said oscillation circuit together to the third part of said oscillation control circuit, and further connecting a base electrode of said third semiconductor element to the fourth part of said oscillation control circuit;

eleventh means for connecting one end of the dimming control circuit to a junction point of said resistive voltage divider, and then connecting the other end of said dimming control circuit to said second terminal;

said dimming control circuit comprising a thirteenth resistor and an optotransistor connected in series, a ninth capacitor across the base electrode and emitter electrode of said optotransistor, and a fourteenth resistor connected in series with an opto-diode of said optotransistor;

twelfth means for connecting one end of the protection circuit to a junction point of said first DC supply, and connecting the other end of said protection circuit to said second terminal;

said protection circuit having a fifteenth resistor, a silicon controlled rectifier and a sixteenth resistor connected in series, and a tenth capacitor connected in parallel with the sixteenth resistor and a fourth semiconductor switching element with a base electrode connected to a junction point of said sixteenth resistor and said silicon controlled rectifier, and a collector electrode connected to the base electrode of said third semiconductor switching element;

thirteenth means for connecting one end of a current sensing circuit to a control electrode of said silicon controlled rectifier and other end to a junction point of said third diode and said fourth diode;

said current sensing circuit comprising a seventeenth resistor, a zener diode and an eighteenth resistor connected in series, and an eleventh capacitor connected parallel with said seventeenth resistor and a twelfth capacitor connected between a junction point of said zener diode and said eighteenth resistor.

2. An electronic ballast circuit according to claim 1, wherein the oscillation control circuit of the electronic ballast circuit controls the pulse-width of the drive signal through the third semiconductor switching element.

3. An electronic ballast circuit according to claim 1, wherein the off-time of the drive signal is fixed by the ninth resistor and twelfth resistor and the eighth capacitor.

4. An electronic ballast circuit according to claim 1, wherein the tenth resistor is placed in parallel with the eighth capacitor to control the off-time to near a fixed value during a starting stage.

5. An electronic ballast circuit according to claim 1, wherein the on-time of the drive signal can be varied by the third semiconductor switching element and the sixth diode by setting the base current of the third semiconductor switching element through the resistive voltage divider.

6. An electronic ballast circuit according to claim 1, wherein the value of the sixth resistor and seventh capacitor in the resistive voltage divider determines the preheating time during a starting stage.

7. An electronic ballast circuit according to claim 1, wherein the eighth resistor and the fifth diode control the minimum pulse-width of the drive signal when the third semiconductor switching element is almost fully on.

8. An electronic ballast circuit according to claim 1, wherein the eleventh resistor across the third semiconductor switching element controls the maximum pulse-width of the drive signal when the third semiconductor switching element is almost fully off.

9. An electronic ballast circuit according to claim 1, wherein the dimming control circuit can control a wide range of light output, the dimming control circuit comprising an opto-transistor and the control signal input terminals of said opto-transistor.

10. An electronic ballast circuit according to claim 9, wherein the input voltage across said control signal input terminals of the opto-transistor control the base current of the opto-transistor which controls the base current of the third semiconductor switching element, and then modulates the pulse-width of the drive signal.

11. An electronic ballast circuit according to claim 9, wherein the dimming control circuit can be implemented by providing the voltage across the control signal input terminals of the opto-transistor by remote control.

12. An electronic ballast circuit according to claim 1, wherein the over-current protection circuit comprises at least a silicon controlled rectifier and a zener diode is connected to the secondary winding of the choke transformer that is shared with the second DC supply.

13. An electronic ballast circuit according to claim 12, wherein the secondary winding of the choke transformer is used to supply the power for the half-bridge driver and control circuit and to sense the output current.

14. An electronic ballast circuit according to claim 13, wherein when the output current increases to a maximum value and the voltage of the secondary winding across the zener diode reaches its breakdown voltage, the zener diode starts to conduct and charges up the eleventh capacitor and when the voltage across the eleventh capacitor reaches a firing voltage of the silicon controlled rectifier, the silicon controlled rectifier conducts and provides a large base current to turn on the fourth semiconductor switching element thus fully turning on the third semiconductor switching element and stopping the oscillation of the oscillation control circuit.

15. An electronic ballast circuit according to claim 14, wherein the protection circuit is latched until the ballast is reset.

16. An electronic ballast circuit according to claim 14, wherein the maximum current value of the ballast can be set by selecting the breakdown voltage of the zener diode.

17. An electronic ballast circuit according to claim 1 wherein the at least one gas discharge lamp comprises a low-pressure mercury vapour discharge lamp.