| 摘要 |
A fuser temperature control using a resistive bridge driven power circuit. At the beginning of each positive half cycle of the AC line voltage, the possible firing of a triac (104) is delayed by 1090 microseconds. During this delay, the fuser temperature is checked by measuring the foil heaters resistance with a DC bridge circuit (102). One leg of this bridge circuit contains the foil heater (100). The other leg of the bridge has a potentiometer (110) to set the temperature of the fuser. The output of the bridge circuit is fed into a differential comparator (102) and D-type flip-flop (112). This combination gives high gain with very little sensitivity to noise. The differential comparator checks the fuser temperature (foil resistance) relative to the set point temperature (set point potentiometer). It determines whether the fuser temperature is above or below the set point temperature. The D-type flip-flop latches this information to either enable or disable the triac triggering circuitry for each full cycle of the line voltage. When the fuser temperature is below the set point temperature, power is enabled to heat the fuser. When the fuser temperature is above the set point temperature it is disabled to cool the fuser. This power decision is made at a rate of 60 Hz in order to keep up with the fusers instant-on characteristics. |
