Toshiba DP120F, Service Manual

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March 2000 © TOSHIBA TEC 7-99 DP120F/DP125F Circuit Description
7.4 Heater Drive Circuit
The heater drive circuit delivers and controls AC power to the heater tube in the fuser.
The heater tube may be damaged due to sudden supply of a high voltage. To prevent it, this
circuit performs control so that power is delivered only when the AC power is around 0V.
When the HTON signal output from the fuser control circuit on the Main PBA goes LOW, the
LED of the photo-coupler (PC1) lights and the light detector attempts to conduct. At this time,
if the AC power is a high voltage, the light detector of PC1 does not conduct due to zero-cross
and TRC1 does not turn off so that no power is delivered to the heater tube. When the AC
power is around 0V, the light detector of PC1 conducts due to zero-cross and TRC1 turns on so
that power is delivered to the heater tube.
If high power is about to be applied to the heater tube due to a sudden rise in the input voltage,
and so on the fuse (FS2) will blow to prevent damage to the heater tube.
Fig. 7-7-5
07-07-04