| 摘要 |
A fixing device, such as a halogen bulb fuser or an instant on fuser, includes a first heating element supplied with substantially constant average power by a power control circuit in preparation for and during fusing. Additionally, the instant on fuser includes a second heating element supplied by the power control circuit. The power control circuit measures the average voltage across and the average current through the first heating element to detect changes in the thermal load applied to the first heating element. In preparation for fusing, the power control circuit applies sufficient power to the second heating element for fusing the expected average thermal load. If the power control circuit detects a level of thermal loading on the instant on fuser different than the expected average thermal load, the power control circuit adjusts the power supplied to the second heating element to compensate for the level of thermal loading different than the average expected thermal load. The power control circuit includes a pulse width modulator that adjusts the duty cycle of a drive signal applied to the gate terminal of a first triac coupled in series with the first heating element to maintain substantially constant power dissipation in the first heating element. To compensate for thermal loading different than the average expected thermal load, the pulse width modulator adjusts the duty cycle of a drive signal applied to the gate terminal of a second triac coupled in series with the second heating element.
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