Driver circuit for a solid state optical emitter device
First Claim
1. A driver circuit for a solid state optical emitter, the circuit comprising a current supply path and a current return path to which the optical emitter is connected, and current limit means to limit a maximum current that flows through one of the current paths, characterised in that the current limit means has a current mirror circuit comprising at least a first transistor and a second transistor, said first transistor comprising an input portion of the current mirror circuit and said second transistor comprising an output portion of the current mirror circuit, said first transistor and second transistor connected so that when a first current flows through the input portion, the second portion is predisposed to supply a second current up to a maximum which tracks the first current, such that the maximum current through the current paths is limited to be no greater than the maximum of the second current.
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Accused Products
Abstract
The present invention relates to a circuit for driving a solid state optical emitter device such as a laser diode, and in particular a circuit which limits the maximum current which may be drawn through the device. The circuit comprises a current supply path and a current return path to which the optical emitter may be connected, and a current limit device to limit a maximum current that may flow through one of the current paths. The current limit device has a current mirror with an input portion and an output portion, the circuit being arranged so that when a first current flows through the input portion, the second portion is predisposed to supply a second current up to a maximum which mirrors the first current. The maximum current through the paths is thereby limited in accordance with the maximum of the second current.
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Citations
14 Claims
- 1. A driver circuit for a solid state optical emitter, the circuit comprising a current supply path and a current return path to which the optical emitter is connected, and current limit means to limit a maximum current that flows through one of the current paths, characterised in that the current limit means has a current mirror circuit comprising at least a first transistor and a second transistor, said first transistor comprising an input portion of the current mirror circuit and said second transistor comprising an output portion of the current mirror circuit, said first transistor and second transistor connected so that when a first current flows through the input portion, the second portion is predisposed to supply a second current up to a maximum which tracks the first current, such that the maximum current through the current paths is limited to be no greater than the maximum of the second current.
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14. A method of driving a solid state optical emitter with a circuit comprising a current supply path and a current return path to which the optical emitter is connected, and current limit means to limit a maximum current that may flow through one of the current paths, characterised in that the current limit means has a current mirror circuit comprising at least a first transistor and a second transistor, said first transistor comprising an input portion of the current mirror circuit and said second transistor comprising an output portion of the current mirror circuit, comprising the steps of:
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i) generating a first current in the first transistor of the current mirror circuit; ii) predisposing said second transistor of the current mirror circuit to supply a second current up to a maximum which mirrors the first current; and iii) using the maximum second current to limit the maximum current through the current paths.
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Specification