Importance

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Abstract

A constant power laser driver for a laser diode in a laser printer reduces laser shadow by maintaining the junction temperature of the laser diode at a constant level. The constant temperature is maintained by a reverse or zener current through the laser diode when the laser is in an off state. The zener current is determined so that the product of the reverse laser current and reverse breakdown voltage is equal to the product of the forward bias voltage drop and forward current when the laser is on. Since these products are substantially equal to the current dissipated in the diode, equal amounts of power are dissipated as heat in the laser diode junction both when the laser is in a writing state and in a non-writing state. As a result, the junction temperature remains relatively constant and the light output remains constant when the laser is turned on, regardless of the length of time it was previously in the opposite state.

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First Claim