Regulated strobe with hysteresis

A capacitor charging circuit for use in electronic flash apparatus of the type having a flashtube together with means for effecting the selective discharge of the capacitor through the flashtube to produce a flash of light, said capacitor charging circuit comprising:

• a d-c to d-c converter oscillator;
• means for facilitating the connection of said d-c to d-c converter to a direct current voltage source;
• a first energy storage capacitor connected to receive an output voltage and charging current from said oscillator;
• and
• control circuit means for effectively terminating the operation of said d-c to d-c converter oscillator when said output voltage increases to a predetermined maximum value and for restarting the operation of said oscillator when said output voltage thereafter decays to a predetermined minimum value, said control circuit means including:
• first transistor having a collector terminal, an emitter terminal and a base terminal;
• a circuit element connected to become conductive upon the application thereto of a voltage at least equal to a predetermined potential proportional to said predetermined maximum value and connected to render said transistor at least partially conductive in response to the output voltage of said oscillator reaching said predetermine maximum value, said circuit element also being connected to be thereafter substantially non-conductive in response to said output voltage decaying below said predetermined maximum value to render said transistor substantially non-conductive;
• a second capacitor connected with respect to said transistor so as to be charged to a first select potential in response to the rendering of said transistor at least partially conductive, said charging of said second capacitor occurring before said output voltage can decay below a value at which said circuit element again becomes substantially non-conductive, and electrical means connected between said transistor and oscillator for terminating the operation of said oscillator in response to the rendering of said transistor at least partially conductive, said electrical means also operating in response to the discharge of said second capacitor from said first select potential to a second select potential subsequent to the rendering of said transistor substantially non-conductive to maintain the termination of the operation of said oscillator, said electrical means operating thereafter to restart the operation of said oscillator in response to the voltage of second capacitor reaching said second select potential, said second select potential being determined so as to occur at a time generally corresponding to the time at which said output voltage decays to said predetermined minimum value.

An electronic flash apparatus comprising:

• a flash tube;
• a d-c to d-c oscillator;
• means for facilitating the connection of said d-c to d-c converter to a direct current voltage source;
• a first energy storage capacitor connected to receive an output voltage and charging current from said oscillator;
• means for effecting the selective discharge of said first capacitor through said flash tube to produce a flash of light;
• and
• a control circuit for effectively terminating the operating of said d-c to d-c converter oscillator where said output voltage increases to a predetermined maximum value and for restarting the operation of said oscillator when said output voltage thereafter decays to a predetermined minimum value, said control circuit comprising:
• a first transistor having a collector terminal, an emitter terminal and a base terminal;
• a circuit element connected to become conductive upon the application thereof of a voltage at least equal to a predetermined potential corresponding to said predetermined maximum value and connected to render said transistor at least partially conductive in response to the output voltage of said oscillator reaching said predetermined maximum value, said circuit element also being connected to be thereafter substantially non-conductive in response to said output voltage decaying below said predetermined maximum value to render said transistor substantially non-conductive;
• a second capacitor connected with respect to said transistor so as to charge to a first select potential in response to the rendering of said transistor at least partially conductive, said charging of said second capacitor occurring before said output voltage can decay below a value at which said circuit element again becomes substantially non-conductive, and circuit means connected between said transistor and oscillator for terminating the operation of said oscillator in response to the rendering of said transistor at least partially conductive, said circuit means also operating in response to the discharge of said second capacitor from said first select potential to a second select potential subsequent to the rendering of said transistor substantially nonconductive to maintain the termination of the operation of said oscillator, said circuit means operating thereafter to restart the operation of said oscllator in response to the voltage of said second capacitor reaching said second select potential, said second select potential being determined so as to occur at a time generally corresponding to the time at which said output voltage decays to said predetermined value.