Low voltage power supply for spark igniter and flame sense

• US 7,944,678 B2
• Filed: 09/11/2008
• Issued: 05/17/2011
• Est. Priority Date: 09/11/2008
• Status: Expired due to Fees

• Current Assignee: Robertshaw Controls Company (Schneider Electric SE)
• Original Assignee: Robertshaw Controls Company (Schneider Electric SE)
• Inventors: Kaplan, Yelena N., Rodda, Dale Thomas
• Primary Examiner(s): SALCE, PATRICK R
• Application Number:
  US12/208,856
• Publication Number:
  US 20100061034A1
• Time in Patent Office: 978 Days
• Field of Search: 361/253, 361/256, 361/263, 361/268, 315/209.T, 315/209.CD, 315/209.SC, 431/46, 431/71, 431/78
• US Class Current: 361/253
• CPC Class Codes: F23Q 3/004 Using semiconductor elements
• CPC Class Codes: H02M 3/33507 with automatic control of the output voltage or current, e.g. flyback converters H02M3/33561, H02M3/33569 take precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A low voltage power supply circuit for intermittent pilot and/or direct spark ignition systems utilized in gas burning appliances is provided. The circuit utilizes a single transformer and a resonant circuit to supply power to both a flame sense circuit as well as the spark generation circuit. The resonant circuit allows the use of low power sources such as batteries or self-supplied voltage systems such as thermopiles or hydro generators. Recognizing that power draw from the low power source is high during a sparking event and recharging of a sparking capacitor, the flame sensing is suspended during the sparking event and for a short recharge time thereafter.

Claims

1. A power supply circuit for use with intermittent pilot and direct spark ignition systems for gas burners, comprising:

a low voltage DC power source;

a resonant circuit coupled to the power source, the resonant circuit including as an inductive element thereof a primary coil of a transformer;

an electronic switching circuit coupled in series with the resonant circuit;

a control circuit operatively coupled to the switching circuit to control switching thereof, the control circuit utilizing a low duty cycle control signal to control switching of the switching circuit; and

wherein the transformer includes a first secondary coil coupled to a flame sense electrode and flame sense circuit; and

wherein the transformer includes a second secondary coil coupled through a voltage doubler circuit to a spark capacitor in parallel with a primary coil of a step-up transformer and trigger circuit, the secondary coil of the step-up transformer being coupled to a spark electrode.

2. The power supply circuit of claim 1, wherein the control circuit generates a pulse width modulated (PWM) control signal to control switching of the switching circuit.

3. The power supply circuit of claim 2, wherein the duty cycle of the control signal is between about 1% to about 15%.

4. The power supply circuit of claim 1, wherein the control signal has a frequency approximately equal to a resonant frequency of the resonant circuit.

5. The power supply circuit of claim 1, wherein the switching circuit is an N-channel MOSFET.

6. The power supply circuit of claim 1, further comprising a filter circuit coupled between the power source and the resonant circuit.

7. The power supply circuit of claim 1, wherein the trigger circuit is an SCR having a gate coupled to the control circuit.

8. The power supply circuit of claim 1, wherein the control circuit is operatively coupled to the flame sense circuit to read an output thereof, and wherein the control circuit does not read the flame sense circuit during a sparking event.

9. The power supply circuit of claim 8, wherein the control circuit does not read the flame sense circuit for a predetermined period following the sparking event.

10. The power supply circuit of claim 9, wherein the predetermined period is approximately 50 ms.

11. The power supply circuit of claim 9, wherein the predetermined period is between approximately 50 ms and 100 ms.

12. The power supply circuit of claim 9, wherein the predetermined period is set to allow recharging of the spark capacitor after the sparking event.

13. The power supply circuit of claim 1, wherein the first secondary coil and the second secondary coil of the transformer are identical.

14. The power supply of claim 1, wherein the low voltage DC power source is a battery.

15. The power supply of claim 1, wherein the low voltage DC power source is a thermopile.

16. The power supply of claim 1, wherein the low voltage DC power source is a hydro generator.

17. A power supply circuit for use with intermittent pilot and direct spark ignition systems for gas burners powered from a low voltage DC power source, comprising:

an input filter circuit adapted to receive low voltage DC;

a transformer having coupled in parallel with a primary coil thereof a capacitor to form a resonant circuit;

a switching circuit operatively coupled to the resonant circuit to induce resonance therein;

wherein the transformer includes a first secondary coil configured to power a flame sense circuit utilizing flame rectification to detect the presence of flame; and

wherein the transformer includes a second secondary coil coupled to a spark capacitor, the spark capacitor being coupled to a primary coil of a step-up transformer and trigger circuit, the secondary coil of the step-up transformer configured to drive a spark electrode of an intermittent pilot or direct spark ignition system.

18. The power supply circuit of claim 17, further comprising a control circuit operatively coupled to the switching circuit and configured to generate a low duty cycle pulse width modulated (PWM) signal to drive the switching circuit.

19. The power supply circuit of claim 18, wherein a frequency of the PWM signal is approximately equal to a resonant frequency of the resonant circuit.

20. The power supply circuit of claim 17, further comprising a voltage doubler circuit interposed between the second secondary coil and the spark capacitor.