Flash circuit

A flash circuit comprising:

• an oscillation transformer having a primary coil connected to a power source and a secondary coil connected to a main capacitor, for boosting a low power source voltage up to a high voltage for charging the main capacitor;
• an oscillation transistor connected between the power source and the oscillation transformer and oscillating in cooperation with the oscillation transformer to conduct oscillating current through the oscillation transformer;
• and
• an oscillation stopping device which taps out voltage proportional to but less than charge voltage in the main capacitor from the oscillation transformer, and which is driven to deactivate the oscillation transistor when the charge voltage in the main capacitor reaches a set voltage;
• wherein the oscillation stopping device comprises a stopping transistor and a Zener diode connected between a tap point located at an intermediate position of the secondary coil and a base of the stopping transistor, the stopping transistor being turned on in response to a Zener current conducted through the Zener diode when the main capacitor is charged up to the set voltage, the stopping transistor being connected to the oscillation transistor such that the oscillation transistor is deactivated when the stopping transistor is turned on;
• wherein the primary coil is connected at one terminal to a plus pole of the power source and at the other terminal to a minus pole of the power source through collector-emitter circuit of the oscillation transistor, and the secondary coil is connected at one terminal to a base of the oscillation transistor, and wherein emitter and collector of the stopping transistor are connected to the base and the emitter of the oscillation transistor respectively, a potential difference between the tap point and the base of the oscillation transistor being the voltage proportional to the charge voltage, and causing the Zener diode to conduct the Zener current when the main capacitor is charged up to the set voltage, and the stopping transistor is turned on to connect the base of the oscillation transistor to the emitter thereof, thereby deactivating the oscillation transistor.

A flash circuit comprising:

• an oscillation transformer having a primary coil connected to a power source and a secondary coil connected to a main capacitor, for boosting a low power source voltage up to a high voltage for charging the main capacitor up to a set voltage;
• an oscillation transistor connected between the power source and the oscillating transformer and oscillating in cooperation with the oscillation transformer to conduct oscillating current through the oscillating transformer;
• a Zener diode connected to a tap point located at an intermediate position of the secondary coil for tapping out a voltage that is proportional to but less than the charge voltage in the main capacitor, the Zener diode conducting a Zener current when the voltage tapped out from the tap point reaches a predetermined value corresponding to the set charge voltage of the main capacitor;
• a stopping capacitor connected to the Zener diode so that the stopping capacitor is charge only with the Zener current;
• and
• a stopping transistor connected to the stopping capacitor through a resistor so that the stopping transistor is turned on while the stopping capacitor discharges through the resistor and the stopping transistor, thereby deactivating the oscillation transistor.

A flash circuit comprising:

• an oscillation transformer having a primary coil connected to a power source and a secondary coil connected to a main capacitor, for boosting a low power source voltage up to a high voltage for charging the main capacitor;
• an oscillation transistor connected between the power source and the oscillation transformer and oscillating in cooperation with the oscillation transformer to conduct oscillating current through the oscillation transformer;
• and
• an oscillation stopping device detecting oscillation frequency of the oscillating current as being proportional to charge voltage in the main capacitor, and deactivating the oscillation transistor when it is determined based on the oscillation frequency that the charge voltage in the main capacitor reaches a set voltage.