Patent Application
20080054819
These and other advantages of the invention will be more apparent from the following description in view of the drawings that show:
The inventors of the present invention have innovatively recognized a lighting ignition circuit for igniting and then operating (e.g., during steady state operation) a gas discharge lamp, such as an automotive high intensity discharge (HID) headlamp. The circuit includes a dual stage resonant circuit that in one aspect thereof allows effective utilization of a single inverter both during an ignition mode of a gas discharge lamp, and then during steady state operation of the lamp, (e.g., to drive the lamp during normal operation after ignition has been completed). One of the circuit stages advantageously serves as a current-suppression stage. Consequently, a resonant current Ir that forms in the resonant circuit is prevented from fluxing into the inverter and as result the magnitude of a switching current is in the inverter is relatively small when compared to the resonant current Ir. This aspect should bring advantages, such as lower voltage stress for the semiconductor power switches in the inverter, and reduced power losses and higher efficiency of the entire circuit.
In one example embodiment, circuit 10 comprises an inverter 14, such as a full bridge inverter, half bridge inverter, class-D inverter, etc. The inverter comprises a plurality of power switches set to operate at a first switching frequency during a lamp ignition mode and outputs a variable voltage signal 15, e.g., a square wave signal. The inverter is connected to a resonant circuit 16 embodying aspects of the present invention. More particularly, resonant circuit 16 comprises a first circuit stage 18 including in one example embodiment an inductor L1. This inductor functions during the ignition mode as a current-suppressing element for reducing an effect of a resonant current in the resonant circuit on a switching current in the inverter. The input signal to first circuit stage 18 is the variable voltage signal 15 supplied by inverter 14. For readers desirous of general background information regarding examples of inverter architectures reference is made to textbook titled “Power Electronics Circuits, Devices and Applications, 2nd Ed., by M. H. Rashid, which textbook was published by Prentice-Hall, Inc., and is herein incorporated by reference.
Resonant circuit 16 further comprises a second circuit stage 20 including in one example embodiment an inductor L2, a first capacitor C1 and a second capacitor C2 connected to form a tank resonant circuit. In one example embodiment, the resonant frequency f is defined by the following equation: f=1/(2*3.14*sqrt(L2*C)), where C=C1*C2/(C1+C2). In one example embodiment, L1=0.47 mH, L2=0.525 mH, C1=0.044 uF, C2=2.2 nF. In this example embodiment, the resonant frequency will be f=150 kHz. And in this example embodiment the switching frequency can be set to about 150 kHz during the ignition phase, and then the switching frequency can be changed to a value in the order of several hundreds Hz during steady state operation when used to drive a lamp such as an automotive HID headlamp, etc.
When the switching frequency of inverter 14 is set to match the resonant frequency, a high resonant voltage is generated across the second capacitor C2 being that the capacitance value of the second capacitor C2 is chosen to be substantially smaller relative to the capacitance value of the first capacitor C1. It is noted that in a two stage circuit embodying aspects of the present invention, the resonant current Ir essentially flows just through inductor L2, and first and second capacitors C1, and C2, but does not flow through the current-suppressing inductor L1 being that the inductance value of the first inductor L1 comprises a relatively small inductance value and L1 effectively acts as a current suppressor. Consequently, the resonant current Ir advantageously cannot flux into the inverter circuit and as result the magnitude of the switching current is of the inverter circuit is relatively small when compared to the resonant current Ir.
In one example embodiment, the resonant output voltage (Vo_ac) can be optionally rectified by a rectifier circuit 30 to a DC voltage by a diode rectifier D1 connected to a resistor R1 and a third capacitor C3, which stores the resonant peak voltage. The DC voltage from third capacitor C3 (Vo_dc) may be connected to a voltage pulse circuit 32 (e.g., an ignition module) to actuate a switch S1, and then transfer the electrical energy stored in third capacitor C3 to a high voltage (HV) transformer T1 to ignite the lamp. It will be appreciated that switch S1 is used as a generic representation of various examples of switching means, such as a spark gap, break down diode, sidac, thyristor, insulated gate bipolar transistor (IGBT), metal oxide semiconductor field effect transistor (MOSFET), relay, etc.
At the secondary side of HV transformer T1, a high voltage pulse (e.g., >25 kv) will be generated so that lamp 12 is ignited. It is contemplated that in this example embodiment ignition circuit 10 can realize a hot re-strike of HID lamp 12. After an ignition event is executed, during steady state operation the lamp will be directly supplied a drive signal by inverter 14, such as conceptually represented by connecting wires c and d. The switching frequency of the inverter circuit can be set from a first value suitable for the ignition phase to a second frequency value suitable for the steady state operation of the lamp. In the foregoing example embodiment, the lamp is triggered by DC voltage (e.g., uni-polar voltage, Vo_dc)). In operation, this circuit embodiment can supply very high DC ignition voltage (e.g., >25 kV) for the lamp, and during steady state operation can supply a lower voltage suitable for normal operation of the lamp. This circuit embodiment may be used in applications where high re-restrike (e.g., >25 kv) and uni-polar voltage ignition of a HID lamp is desired, such as for automotive HID headlamps. It will be appreciated that the connecting wires a, b, c, and d can be adapted to two or three wire connecting arrangements based, for example, on the circuit architecture of the inverter circuit.
It will be appreciated that in another example embodiment, that does not use rectifier 30, the resonant output voltage (Vo_ac) from the resonant circuit can be directly connected to voltage pulse circuit 32 to trigger switch S1. In this case, the energy stored in second capacitor C2 is transferred to the primary winding of HV transformer T1 to ignite the lamp. After an ignition event is executed, during steady state operation the lamp will be supplied a drive signal by inverter 14 through connecting wires c and d. The switching frequency of the inverter circuit can be adjusted from a first value suitable for the ignition phase to a second value suitable for the steady state operation of the lamp. In the foregoing example embodiment, the lamp is triggered by AC voltage (e.g., bi-polar voltage). This circuit embodiment can supply very high AC ignition voltage (e.g., >25 kV) for the lamp, and during steady state operation can supply a lower voltage suitable for normal operation of the lamp. This circuit embodiment may be used in applications where the HID lamp needs a high re-strike with bi-polar voltage ignition. It will be appreciated that the connecting wires a,b,c,d can be combined to two or three wire connecting arrangements based, for example, on the circuit architecture of the inverter circuit.
In yet another example embodiment, the resonant output voltage from the resonant circuit 12 can be directly applied to the lamp without use of either a rectifier 30 and a voltage pulse circuit 32. In this case, the lamp will be triggered by AC voltage (e.g., bi-polar voltage, Vo_ac). This circuit embodiment can supply high ignition voltage (e.g., several kV) for triggering the lamp. After an ignition event is executed, during steady state operation the lamp will be also directly driven by AC voltage (e.g., bi-polar voltage, Vo_ac). The switching frequency of the inverter can be adjusted from a first value suitable for the ignition phase to a second value suitable for the steady state operation of the lamp. The circuit embodiment may be suitable for applications where the HID lamp does not need a hot re-strike.
In view of the foregoing description of example embodiments, it should be appreciated that rectifier circuit 30 and/or voltage pulse circuit 32 constitute optional circuitry (as represented by the dashed line blocks in
While the preferred embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
