Patent ID: 6404990
Filing Date: 2002-06-11
Classification: G03B,H05B

Abstract:
A flash device comprising an oscillation circuit that starts oscillating when a flash charge switch is turned on, the oscillation circuit comprising an oscillation transformer having a primary coil connected to a power source and a secondary coil connected to a main capacitor, the secondary coil being inductively coupled to the primary coil such that a high voltage current is induced in the secondary coil while the oscillation circuit oscillates, and that the main capacitor is charged with the high voltage current up to a set charge voltage, the flash circuit being characterized by comprising:a tap point located at an intermediate position of the secondary coil, the tap point having a potential that changes proportionally to the charge voltage across the main capacitor; a Zener diode connected to the tap point, to conduct a Zener current when the potential at the tap point reaches a value that corresponds to the set charge voltage of the main capacitor; and a stopping transistor activated by the Zener current to stop the oscillation circuit from oscillating and thus stop charging the main capacitor when the main capacitor reaches the set charge voltage.