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US 4,787,087 AGranted
Circuit for driving a laser diode
AssigneeCitizen Watch Co., Ltd.
InventorsNobuyuki Hashimoto, Kazuya Ohike
Life of this patent
Estimating the term…
Abstract
A driving circuit for a laser diode has an exciting circuit for intermittently exciting the laser diode. A photodiode is provided for detecting the beam power emitted from the laser diode, and a resistor is connected to the photodiode in series. Voltage across the resistor is stored in a capacitor of a charging circuit. The stored voltage is applied to a constant current circuit to control a current supplied to the laser diode to stabilize beam power of the laser diode.
Claims4
A circuit for driving a laser diode comprising:
- an exciting circuit for energizing said laser diode, including a first transistor connected to said laser diode in parallel and supplied with clock pulses so as to be intermittently turned on and off;
- a photodiode for detecting the power of a beam emitted from said laser diode upon energization;
- a first resistor serially connected to said photodiode;
- a charging circuit for storing a voltage appearing across said first resistor that is representative of the power detected by said photodiode, said charging circuit being a one-way charging circuit including a diode and a capacitor connected in parallel to said first resistor;
- and
- a constant current circuit, responsive to the voltage stored in said capacitor, for supplying a constant energization current to said laser diode, said constant current circuit including
- an operational amplifier having a non-inverting terminal coupled to the voltage stored in said capacitor, and
- a second transistor serially connected to said laser diode, a base terminal of which is connected to an output terminal of said operational amplifier so as to control the amount of energization current flowing in said laser diode.
5 more elements
Dependencies are inferred from the claim text.