Patent ID: 7821207

Claim:
A lighting unit having a circuit composed of a plurality of electronic components for operating a low-pressure discharge lamp having filament electrodes, wherein the circuit includes: a rectifier/smoothing circuit portion having a smoothing capacitor; an inverter circuit portion having a switching element; a resonance circuit portion having a foil-type resonance capacitor, and a preheating circuit portion having a positive temperature coefficient element configured to preheat one or both of the electrodes at startup of the low-pressure discharge lamp, the plurality of electronic components are mounted on a substrate and include one or more heat receiving capacitors and one or more heat generating components, each heat receiving capacitor is configured to (i) perform a predetermined function during normal lamp operation and (ii) break down when raised to a predetermined temperature or higher responsive to heat from another of the electronic components, so that lamp operation is terminated or abnormal heat generation in said another electronic component is eliminated, each heat generating component is configured to undergo an excessive temperature rise when the lamp is operated under a predetermined condition, and one of the heat receiving capacitors is the resonance capacitor, one of the heat generating components is the positive temperature coefficient element configured to undergo a temperature rise when the low-pressure discharge lamp is operated under the predetermined condition that either of the electrodes is at an end of life, the resonance capacitor is connected in parallel to the preheating circuit portion and is disposed on the substrate at a position that is (i) close to or in contact with the positive temperature coefficient element and (ii) positioned nearer to a peripheral edge of the substrate than the positive temperature coefficient element, so that the resonance capacitor breaks down in a short-mode when raised to the predetermined temperature or higher.