PULSED HIGH VOLTAGE IGNITER CIRCUIT

Cross-Reference to Related Application This application claims the benefit of United States Provisional Patent

Application 60/909,392 filed March 30, 2007, the benefit of the earlier filing date of which is hereby claimed under 35 U.S. C. §119(e) and which is further incorporated by reference.

Field of the Invention

The present invention generally relates to high voltage generator circuits, and more specifically, but not exclusively, to a pulsed, high voltage generator circuit used to provide a spark for igniting a combustible gas.

Background of the Invention

High voltage generator circuits are used for many different applications, including lighting applications and igniter circuits as just a few examples. In the case of igniter circuits, the voltage generated must be sufficiently high in order to cause electrical breakdown of air and create a spark. Since the breakdown voltage of air is typically 30 kV per centimeter, a voltage of several thousand volts or even tens of thousands of volts may be needed to create a spark across a gap on the order of a centimeter or less.

For most igniter circuits, the high voltage needed to create the breakdown or spark is generated from a low voltage power source, since most power

sources are of relatively low voltage, on the order of tens of volts. One method of producing a high voltage from a low voltage source is to incrementally build up the high voltage on a temporary charge or voltage storing component, such as a capacitor. A switching circuit is utilized in conjunction with the voltage source and the capacitor. A common problem associated with such switching circuits used to generate high voltage for igniter circuits is that they generate electrical noise in the circuit due to the switching involved, and since the switching involves high voltages, the voltage and/or power of the electrical noise generated is unnecessarily high. This may impact the operation of other circuitry located nearby or on the same circuit board. Additionally, the problem is especially significant when the adjacent circuitry is sensitive high speed electronic circuitry. A typical example of how to cope with this electrical noise is to physically separate the spark generator from the rest of the electronics, frequently by placing it on a different PCB, which adds cost and complexity. Thus, there is a need for a high voltage generator circuit which is able to generate high voltage, such as that used in igniter circuits, but without causing unnecessary electrical noise or disturbance for adjacently located electronic circuitry.

Summary of the Invention

The present invention is related to a high voltage generator circuit which can generate a high voltage suitable for use with an igniter. While generating the required high voltage, the circuit results in a significantly reduced amount of electrical noise such that the disruption of adjacent, sensitive circuitry is minimized.

Specifically, at least one embodiment of the present invention periodically generates a high voltage on an inductor and causes the high voltage generated to incrementally charge up and build up the voltage on a capacitor connected to the inductor. The capacitor is isolated from the adjacent, sensitive circuitry by way of a relay. Also, to minimize the number of components and complexity of the high voltage generator circuit, the inductor which is used to generate the high voltage is the inductor located within the relay, which is also used to switch the contacts of the relay.

Description of the Drawings

These and other objects and features of the invention will become more apparent by referring to the drawings, in which:

Figure 1 is a block diagram of a high voltage generator circuit according to an embodiment of the present invention; and Figure 2 is an electrical schematic of an embodiment of the high voltage generator circuit of Figure 1 according to aspects of the present invention.

Detailed Description of a Preferred Embodiment

Various embodiments of the present invention will be described in detail with reference to the drawings, where like reference numerals represent like parts and assemblies throughout the several views. Reference to various embodiments does not limit the scope of the invention, which is limited only by the scope of the claims attached hereto. Additionally, any examples set forth in this specification are not intended to be limiting and merely set forth some of the many possible embodiments for the claimed invention.

Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of "a," "an," and "the" includes plural reference, and the meaning of "in" includes "in" and "on." The phrase "in one embodiment," as used herein does not necessarily refer to the same embodiment, although it may. Similarly, the phrase "in some embodiments," as used herein, when used multiple times, does not necessarily refer to the same embodiments, although it may. As used herein, the term "or" is an inclusive "or" operator, and is equivalent to the term "and/or," unless the context clearly dictates otherwise. The term "based, in part, on", "based, at least in part, on", or "based on" is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. The term "coupled" means at least either a direct electrical connection between the items connected, or an indirect connection through one or more passive or active intermediary devices. The term "circuit" means at least either a single component or a multiplicity of components, either active and/or passive, that are

coupled together to provide a desired function. The term "signal" means at least one current, voltage, charge, temperature, data, or other signal. Where either a field effect transistor (FET) or a bipolar junction transistor (BJT) may be employed as an embodiment of a transistor, the scope of the words "gate", "drain", and "source" includes "base", "collector", and "emitter", respectively, and vice versa.

Figure 1 illustrates a block diagram of circuit 100, which may be employed as a high voltage generator circuit. Circuit 100 includes relay Kl , switch

Sl, rectifier 110, capacitor C9, and transformer Xl. Relay Kl has five contacts

(numbered 1, 2, 3, 4, and 5 in the example illustrated in Figure 1), and includes inductor Ll.

In operation, switch Sl is turned on and off, for example, at a frequency on the order of 30Hz. The exact frequency may be dependent on both the supply voltage and response time of the relay. The pulsing frequency, as well as the ON time of the cycle, is sufficiently timed such that relay Kl is not tripped. Switch S 1 is coupled between contact 1 of the relay and a reference voltage — the reference voltage may be ground, VSS, some other fixed DC voltage, or the like.

As switch S 1 is turned on and off at a periodic rate on the order of

30Hz, relay Kl is untripped. While relay Kl is untripped, it provides a connection between contact 4 and contact 3 of relay Kl . As explained in greater detail below, while switch Sl is turned on and off at a periodic rate on the order of about 30Hz, a large voltage builds up on capacitor C9.

Once a sufficient voltage has been built up on capacitor C9, switch Sl is turned ON for a sufficiently long period of time to trip relay Kl (instead of turning on and off at a period rate of about 30Hz, as it did prior to capacitor C9 reaching the

target voltage). When relay Kl is tripped, relay Kl provides a connection between contact 4 and contact 2 of the relay (instead of between contact 4 and contact 3). This causes capacitor C9 (and the voltage across capacitor C9) to be presented at the primary side of the igniter transformer Xl. In turn, this causes a high voltage to be presented at the secondary side of transformer Xl (the voltage multiplication from primary to secondary dependent on the relative number of turns of the primary and secondary windings of transformer Xl).

In various embodiments, determining when the voltage across capacitor C9 has reached the target voltage may be accomplished in different ways in different embodiments. In one embodiment, circuit 100 includes a clock in the software that determines both the build up and the number of clock cycles. The known component values are used to estimate when the target voltage is reached. These embodiments and others are within the scope and spirit of the invention.

Referring now to Figure 2, therein is illustrated an electrical schematic of a high voltage generator circuit 200, which may be employed as an embodiment of circuit 100 of Figure 1. Circuit 200 further includes capacitor C8 and resistor R20. Switch Sl includes transistor Q4. Rectifier 210 includes diode D6.

In operation, transistor Q4 is pulsed ON and OFF, for example, at a frequency on the order of 30Hz. The exact frequency is dependent on both the supply voltage and response time of the relay. The pulsing frequency, as well as the ON time of the cycle, is sufficiently timed such that relay Kl is not tripped. Relay Kl includes an inductor, which has one side connected to a typical voltage supply, for example, +5 V, or +12V. The voltage, VCC provided at one side of the inductor may be provided by a DC power supply circuit (not shown). The other side of the coil within

relay Kl is connected to the drain of transistor Q4 when Q4 is implemented as an N- channel FET (Field Effect Transistor). Alternatively, if transistor Q4 is a bipolar junction transistor, then the coil would be connected to the collector of the transistor.

Each time that transistor Q4 is turned OFF and caused to cease conducting, an extremely high voltage is developed at the coil within the relay Kl due to the transient effect of the flow of current through the coil, i.e., the energy stored within the coil creates a high voltage at one end of the coil. This high voltage is passed through diode D6 and onto capacitor C9 where it causes charge (and correspondingly voltage) to accumulate on capacitor C9. Diode D6 prevents capacitor C9 from discharging or losing its charge. For each cycle, transistor Q4 is turned OFF to cause voltage to build up on capacitor C9, and then caused to turn ON, to set up the transient high voltage effect for the next cycle when transistor Q4 turns off. In this way, the voltage built up on capacitor C9 can be controlled based on the number of ON/OFF cycles of transistor Q4. Once a sufficient voltage has been built up on capacitor C9, transistor

Q4 is turned ON for a sufficiently long period of time to trip relay Kl . This causes capacitor C9 (and the voltage across capacitor C9) to be presented at the primary side of the igniter transformer Xl . In turn, this causes a high voltage to be presented at the secondary side of transformer Xl (the voltage multiplication from primary to secondary dependent on the relative number of turns of the primary and secondary windings of transformer Xl).

One advantage of circuit 200 is that the high voltage circuit (capacitor C9 and transformer Xl) is isolated from the rest of the circuit, by way of relay Kl.

This helps in reducing the unwanted effects of electrical noise on the rest of the circuitry.

Another advantage of circuit 200 is that the coil inside relay Kl is used for two different purposes. One purpose is to assist in the tripping or switching of the relay. Anther purpose is to create the transient high voltage which is used to charge the capacitor.

The above specification, examples and data provide a description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention also resides in the claims hereinafter appended.