US 6,674,247 B1 · Efficient photographic flash

Abstract

Photographic flashes use the major portion of available energy in modern cameras. A series of innovations within a photographic flash system improves the energy efficiency by a factor of 3, and thereby extends battery life. The flash system includes a precise flash-termination circuit, a high-efficiency charging circuit, a low-leakage coupled inductor, and a battery-saving charge-circuit drive. Flash termination is controlled by a majority-carrier switching device. This circuit allows termination of the flash current without the timing uncertainty or parasitic leakage associated with previous designs. Multiple flashes also can be produced by the circuit, which may be interfaced with through-the-lens flash controls. A flyback-converter charging circuit uses a coupled inductor that has an alternately layered winding pattern to lower leakage inductance drastically, and uses appropriately selected wire types to decrease skin-effect resistance losses. Because of the low leakage inductance, the charge circuit can make use of simple energy-efficient overshoot-damping circuitry. The charge circuit also increases battery life by smoothing peaks in current drawn from the battery. A new drive circuit operates the flyback converter efficiently, maintains battery current below a damage-threshold level to extend battery life, and efficiently holds the flash capacitor in a maximum charge state.

Claims39

Dependent claims

A photographic flash, comprising:

a flash tube filled with an ionizable gas;
a photoflash capacitor connected to supply energy to said flash tube;
a majority-carrier switching device, responsive to a control signal, connected to conduct current through said flash tube;
a trigger circuit, responsive to a trigger signal, connected to said flash tube;
and
a controller configured to send said trigger signal to said trigger circuit thereby to cause said gas in said flash tube to ionize, and configured to send said control signal to said majority-carrier switching device thereby to allow a flow of a current through said flash tube, thereby to initiate a flash discharge, and further configured to turn on and turn off said majority-carrier switching device a plurality of times while said gas in said flash tube remains ionized, thereby to cause a plurality of flash discharges.

3 more elements

A driving circuit for providing an on-off control signal for controlling a charging circuit for charging a photoflash capacitor,

wherein said charging circuit comprises a DC power source, an inductor having a primary winding, and a switching transistor operative to turn on and turn off a primary current through said primary winding;
and
wherein said driving circuit comprises:
a DC voltage input from said DC power source of said charging circuit;
a charge-state input, representing a voltage on said photoflash capacitor;
a model capacitor having a model voltage;
a first current source, configured to charge said model capacitor in a first direction, said first current source capable of producing a first model current substantially in proportion to said charge-state input when said charge-state input is below a first threshold, increasing said first model current less than proportionately to said charge-state input when said charge-state input is above said first threshold and below a second threshold, and producing a substantially zero value of said first model current when said charge-state input is above said second threshold;
a second current source, configured to charge said model capacitor in a second direction, said second current source capable of producing a second model current proportional to said DC voltage input;
a bistable controller having an on state and an off state;
and
an electronic switch circuit for connecting said model capacitor alternately to said first current source when said bistable controller is in said off state and to said second current source when said bistable controller is in said on state, such that said first and second model currents charge said model capacitor alternately in opposite directions at rates determined by said charge-state input and said DC voltage input, respectively;
wherein said bistable controller is responsive to said model voltage, such that said on state is entered when said model voltage reaches a first reference voltage, and such that said off state is entered when said model voltage reaches a second reference voltage, said bistable controller thereby capable of effecting a cyclic on-off action and producing said on-off control signal as its output;
and
wherein said on-off control signal has an on level when said bistable controller is in said on state and an off level when said bistable controller is in said off state, said on level operative to control said switching transistor of said charging circuit to turn on said primary current, and said off level operative to control said switching transistor of said charging circuit to turn off said primary current.

11 more elements

A charging circuit for charging a photoflash capacitor, comprising:

a DC power source;
a coupled inductor, comprising:
a primary winding comprising a plurality of primary winding layers, said primary winding layers electrically connected in parallel;
a secondary winding comprising a plurality of secondary winding layers, said secondary winding layers electrically connected in series;
and
a magnetic core;
wherein said primary winding layers and said secondary winding layers are alternately layered around said magnetic core;
a switching transistor operative to turn on and turn off a primary current through said primary winding, thereby generating a charging current in said secondary winding by induction;
a rectifier for charging said photoflash capacitor with said charging current;
and
a driving circuit for controlling said switching transistor, wherein said driving circuit comprises:
a DC voltage input from said DC power source;
a charge-state input, representing a voltage on said photoflash capacitor;
a model capacitor having a model voltage;
a first current source, configured to charge said model capacitor in a first direction, said first current source capable of producing a first model current substantially in proportion to said charge-state input when said charge-state input is below a first threshold, increasing said first model current less than proportionately to said charge-state input when said charge-state input is above said first threshold and below a second threshold, and producing a substantially zero value of said first model current when said charge-state input is above said second threshold;
a second current source, configured to charge said model capacitor in a second direction, said second current source capable of producing a second model current proportional to said DC voltage input;
a bistable controller having an on state and an off state;
and
an electronic switch circuit for connecting said model capacitor alternately to said first current source when said bistable controller is in said off state and to said second current source when said bistable controller is in said on state, such that said first and second model currents charge said model capacitor alternately in opposite directions at rates determined by said charge-state input and said DC voltage input, respectively;
said bistable controller being responsive to said model voltage, such that said on state is entered when said model voltage reaches a first reference voltage, and such that said off state is entered when said model voltage reaches a second reference voltage, said bistable controller thereby capable of effecting a cyclic on-off action;
and
wherein said bistable controller is operative to control said switching transistor to turn on said primary current when said bistable controller is in said on state, and to turn off said primary current when said bistable controller is in said off state.

19 more elements

Dependencies are inferred from the claim text.

Efficient photographic flash

Life of this patent

Efficient photographic flash

Life of this patent

Abstract

Claims39