Method and circuit for charging of super capacitor as energy source for flash diodes
AssigneeNational Semiconductor Corporation
InventorsWilliam J. McIntyre, John Philip Parry, Nathanael Griesert
Life of this patent
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Abstract
A circuit and method for charging a super capacitor to an optimal voltage that provides a desired flash diode current value while minimizing power dissipation in circuit elements other than the flash diode. One embodiment uses periodic sampling of the current through the flash diode and termination of the charging upon the super capacitor having been charged to a voltage value that produces the desired flash diode current. Another embodiment includes a current regulator in the flash diode firing circuit that keeps the current at a substantially constant level during the time that the flash diode is being fired.
Claims20
A circuit for a photo flash, comprising:
- a super capacitor;
- a charging circuit arranged to charge the super capacitor;
- a flash diode coupled to the super capacitor;
- and
- a first circuit arranged to (i) set a target voltage value to which the super capacitor is to be charged, (ii) provide a current flow through the flash diode at a target current value as the flash diode is being fired, and (iii) terminate charging of the super capacitor at the target voltage value;
- wherein the first circuit includes a sampling circuit arranged to periodically sample the current flow through the flash diode and to terminate charging of the super capacitor when the current flow through the flash diode reaches the target current value.
A circuit for a photo flash, comprising:
- a super capacitor;
- a charging circuit arranged to charge the super capacitor;
- a flash diode coupled to the super capacitor;
- a first circuit arranged to (i) set a target voltage value to which the super capacitor is to be charged, (ii) provide a current flow through the flash diode at a target current value as the flash diode is being fired, and (iii) terminate charging of the super capacitor at the target voltage value;
- and
- a current regulator arranged to regulate the current flow through the flash diode;
- wherein the first circuit includes a sampling circuit arranged to (i) periodically sample a voltage across the current regulator and (ii) terminate charging of the super capacitor by the charging circuit when the sampled voltage across the current regulator reaches a specified value, wherein the sampled voltage across the current regulator is based on the current flow through the flash diode.
A method, comprising:
- setting a voltage value to which a super capacitor is to be charged for firing of a flash diode at a target current value;
- charging the super capacitor, the super capacitor having an output coupled to the flash diode;
- sampling a voltage on the super capacitor using a current flowing through the flash diode;
- and
- terminating the charging when the voltage on the super capacitor has reached the voltage value.
Dependencies are inferred from the claim text.