Canon NP2120 Service Manual page 97

A. DC Power Supply
1. Mechanism
The DC power supply PCB is supplied with AC
turned ON.
lowered by the transformer (T201); thereafter, it is
made available in 24V, 12V. and 5V by filters and
regulator.
For 24V power, the output voltage is checked; it
of a photocoupler (Q205) for stabilization.
5V power is stabilized by the regulator (Q207).
3-52
2. Protection Mechanism for Power Supply
The DC powersupply is equipped with protection
mechanisms to cut off the power should any of the
The protection mechanism for 24V power is the
over-current detection mechanism in the switching
regulator (Q204); upon activation, the circuit also
current fuse serves to protect against an over-cur-
rent.
The protection mechanism for 5V power makes
use of the over-current detection circuit of the regu-
isadditionallyprovidedusing
and thyristor (Q208).
The output, after activation of these protection
mechanisms, can be recovered by turning the door
switch OFF, correctingthe relevant load, and turning
the door switch ON once again.
If only 12V has been cut out, the door switch
should be turned OFF, the relevant load should be
corrected, fuse (FU202) should be replaced. and the
door switch should be turned ON once again.
Q207
Figure 3-52
C A N O N NPZl20/2MU RN.0 MAY 1930 PRINTEU IN JAPAN IIMPNIME AU JAPUNI d
aZenerdiode(ZD201)
protection circuit
24V