Resonant flyback ignitor circuit for a gas discharge lamp control circuit

• US 6,323,603 B1
• Filed: 02/17/1999
• Issued: 11/27/2001
• Est. Priority Date: 02/18/1998
• Status: Expired due to Fees

• Current Assignee: Nicollet Technologies Corporation (Badger Transformer Co., Inc.)
• Original Assignee: Nicollet Technologies Corporation (Badger Transformer Co., Inc.)
• Inventors: Persson, Eric G.
• Primary Examiner(s): Wong, Don
• Assistant Examiner(s): VO, TUYET THI
• Application Number:
  US09/251,551
• Time in Patent Office: 1,014 Days
• Field of Search: 315/307, 315/244, 315/276, 315/274, 315/224, 315/219, 315/209.R, 315/209.SC, 315/194, 315/DIG.4, 315/290, 315/289, 315/240, 315/209.T, 315/207.CD, 315/204.M, 315/209.PZ, 315/209.CS
• US Class Current: 315/290
• CPC Class Codes: H05B 41/042 using semiconductor devices
• CPC Class Codes: H05B 41/3924 by phase control, e.g. using a triac H05B41/3922 takes precedence

Abstract

A gas discharge lamp control circuit includes a series circuit formed by first and second AC input terminals, an inductance and first and second lamp terminals. An ignitor circuit is coupled to the series circuit and selectively couples and decouples at least a portion of the inductance in parallel with the first and second AC input terminals to generate a flyback voltage in the inductance.

Claims

1. A gas discharge lamp control circuit comprising:

a first and second alternating-current (AC) input terminals;

first and second lamp terminals;

a capacitor coupled in parallel across the first and second lamp terminals;

a transformer comprising a primary winding coupled in a first series loop with the first and second AC input terminals and a secondary winding coupled in a second series loop with the first and second lamp terminals, wherein the secondary winding comprises a plurality of turns;

an inductance coupled within the first series loop; and

an ignitor circuit having first and second ignitor inputs which are coupled across at least a portion of the plurality of turns of the secondary winding, and adapted to provide a temporary current path between the first and second ignitor inputs.

2. The gas discharge lamp control circuit of claim 1 wherein the inductance comprises an inductor winding which is coupled in series with the primary winding.

3. The gas discharge lamp control circuit of claim 1 wherein the inductance is a primary winding-referred leakage inductance of the transformer.

4. The gas discharge lamp control circuit of claim 1 wherein the first and second ignitor inputs are coupled across the entire secondary winding.

5. The gas discharge lamp control circuit of claim 1 wherein the secondary winding comprises first and second sets of turns which are coupled together in series and the ignitor circuit first and second ignitor inputs are coupled across only the first set of turns of the secondary winding.

6. The gas discharge lamp control circuit of claim 1 wherein the ignitor circuit comprises:

an ignitor switch having a control terminal;

a current sensor coupled in series with the ignitor switch between the first and second ignitor inputs; and

a switch control circuit coupled between the current sensor and the control terminal of the ignitor switch.

7. The gas discharge lamp control circuit of claim 6 and further comprising a bridge rectifier coupled between the first and second ignitor inputs and coupled to the ignitor switch and the current sensor such that current received through the first and second ignitor inputs flows through the ignitor switch in only one direction.

8. The gas discharge lamp control circuit of claim 6 wherein the switch control circuit further comprises:

a trigger circuit coupled to the control terminal for selectively switching the ignitor switch from an open state to a closed state until the current sensor senses that a current flowing through the ignitor switch reaches a threshold level;

a peak detector circuit which measures a representation of a peak voltage generated across the first and second ignitor inputs when the trigger circuit switches the ignitor switch from the closed state to the open state; and

an adjustment circuit which compares the measured representation of the peak voltage to a representation of a selected peak voltage and responsively adjusts the threshold voltage.

9. The gas discharge lamp control circuit of claim 6 wherein the switch control circuit selectively switches the ignitor switch from an open state to a closed state until the current sensor senses that a current flowing through the ignitor switch reaches a threshold level.

10. The gas discharge lamp control circuit of claim 9 wherein the switch control circuit comprises:

a set-reset flip-flop having a set input for receiving a trigger signal, a reset input coupled to a comparator output, and a trigger output coupled to the control terminal;

a comparator having a non-inverting input, an inverting input and the comparator output, wherein the non-inverting input is coupled to the current sensor; and

a reference circuit coupled to the inverting input for providing a signal to the comparator which is representative of the threshold level.

11. A method of igniting a gas discharge lamp, the method comprising:

receiving an AC drive signal through first and second AC inputs;

applying the AC drive signal to a primary winding of a transformer through an inductance;

applying a voltage produced on a secondary side of the transformer in response to the AC drive signal across the gas discharge lamp;

shorting a plurality of turns in the secondary side of the transformer to store energy from the AC drive signal in the inductance; and

un-shorting the plurality of turns to generate a flyback voltage in the inductance in response to the energy stored in the inductance from the step of shorting.

12. A gas discharge lamp control circuit comprising:

first and second AC inputs for receiving an AC drive signal;

first and second lamp terminals for coupling to a gas discharge lamp;

a capacitor coupled in parallel across the first and second lamp terminals;

a transformer comprising a primary winding coupled in a first series loop with the first and second AC inputs and a secondary winding coupled in a second series loop with the first and second lamp terminals, wherein the secondary winding comprises a plurality of turns;

an inductance coupled in the first series loop; and

means for temporarily shorting and then un-shorting at least a portion of the plurality of turns of the secondary winding to generate a flyback voltage in the inductance.

13. A gas discharge lamp control circuit comprising:

a series circuit formed by first and second alternating-current (AC) input terminals, an inductance and first and second lamp terminals; and

an ignitor circuit which is coupled to the series circuit and selectively couples and decouples at least a portion of the inductance in parallel with the first and second AC input terminals, wherein the ignitor circuit comprises;

first and second ignitor inputs which are coupled to the series circuit;

an ignitor switch having a control terminal;

a current sensor coupled in series with the ignitor switch between the first and second ignitor inputs; and

a switch control circuit coupled between the current sensor and the control terminal of the ignitor switch and comprising a comparator having a first compare input coupled to the current sensor and a second compare input coupled to a reference input indicative of a reference current level through the ignitor circuit.