Current driver and power control for electrophotographic devices

A laser driver comprising:

• a laser source;
• a bias current source coupled to said laser source;
• a first switched current source switchably coupled to said laser source;
• a first laser power control signal that corresponds to a first desired laser output power for said first switched current source;
• a second switched current source switchably coupled to said laser source;
• a second laser power control signal that corresponds to a second desired laser output power for said second switched current source;
• a sampler arranged to store:
• a first sampled measure of output power from said laser source when said first switched current source is driving said laser source and said second switched current source is not driving said laser source,
• a second sampled measure of output power from said laser source when said second switched current source is driving said laser source and said first switched current source is not driving said laser source, and
• a third sampled measure of output power when both said first and second switched current sources are driving said laser source;
• and
• a compensator that adjusts a magnitude of each of said first and second switched current sources and said bias current source such that output power error measures of said first sampled measure of output power relative to said first laser power control signal, said second sampled measure of output power relative to said second laser power control signal and said third sampled measure of output power relative to a combination of said first and second laser power control signals combine to change a magnitude of each of said two switched current sources and said one bias current source such that said output power error measures converge over time.

A method of controlling a laser driver in an electrophotographic device comprising:

• providing a laser source;
• providing a bias current source coupled to said laser source;
• providing a first switched current source switchably coupled to said laser source;
• providing a second switched current source switchably coupled to said laser source;
• providing a first laser power control signal corresponding to a first desired laser power output level when said first switched current source is applied to said laser source;
• providing a second laser power control signal corresponding to a second desired laser power output level when said second switched current source is applied to said laser source;
• sampling laser output power for each of said first and second switched current sources during a non-printing portion of a scan operation;
• and
• adjusting said magnitudes of said first and second switched current sources and said bias current source based upon said sampled laser output power for each of said first and second switched current sources such that said output power error measures between said sampled laser output power and said first and second desired laser output power levels converge over time;
• writing a plurality of Pels across a scan line by sweeping said laser source across a photoconductive drum, wherein each written Pel comprises at least two data signals that determine if each Pel is Off, or is written using said first switched current source, said second switched current source, or both said first and second switched current sources.