Overvoltage - Sharp SF-2052 Serviceanleitung

(9)-2. +10V
For the +10V also, the LC filter is composed of the reactor L711 and
the capacitor C747 for ripple compression.
(9)-3. –20V
The –20V is stabilized by the regulator IC yZ702 and the capacitor
C752 as pre-regulate.
(10) FW signal
The FW signal generates rectangular waveforms in synchronization
with the AC input.
After full-wave rectifying with the AC input diodes D701, D702, D741,
and D742, the edge section of the AC full-wave rectifying waveform is
transmitted to the secondary side by the photo coupler PC701
through the resistors R706 and R707 and the zenor diode D703. In
the secondary side, the signal of the photo coupler PC701 is ampli-
fied by the transistor Q708, rectified into the rectangular waveform,
and outputted.
After full-wave rectification with the AC input diodes D701, D702,
D741, and D742, the circuit is in common with the starting circuit of
the control IC Z701 up to the resistors R706 and R707.

(11) Overvoltage

If the output voltage increases abnormally for some reasons (a trou-
ble in the photo coupler PC703 in the control system or in he transis-
tor Q711), it is transmitted to 8 pin of the control IC Z701 in the
primary side by the photo coupler PC702 to be shut off through zenor
diodes D722 and D723 for the +38V, through the zenor diode D720
and the diode D721 for the +24V, through the zenor diode D726 and
the diode D725 for the +10V, and through the zenor diode D728 and
the diode D727 for the +5V.
To resume in this case, supply the AC power again.
(12) Short protecting function
(12)-1. +38V
The +38V is protected with the fuse F702 in it. However, in the case
of an instantaneous short, the fuse may not be blown off.
In that case, the control IC Z701 protects the circuit. A signal is
applied through detection resistors R722 ∼ R725, resistor R726, vari-
able resistor RV701, capacitor CX701 and resistor RX701 to the
control IC Z701 3 pin. Protection is made with this signal level (sup-
posing that only the +38V line is subject to an overcurrent by the
rated output.)
If the protection is operated for a certain duration, the control IC Z701
stops oscillation. To resume, supply the AC power again.
(12)-2. +24V
The +24V includes fuses F704, F705, F708, and F709, which protect
the circuit.
However, in the case of an instantaneous short, the fuse may not
blow off.
In that case, the control IC Z701 protects the circuit. A signal is
applied through detection resistors R722 ∼ R725, resistor R726, vari-
able resistor RV701, capacitor CX701 and resistor RX701 to the
control IC Z701 3 pin. Protection is made with this signal level (sup-
posing that only the +38V line is subject to an overcurrent by the
rated output.)
If the protection is operated for a certain duration, the control IC Z701
stops oscillation. To resume, supply the AC power again.
(12)-3. +10V
The +10V is protected by the D/D convertor protecting function de-
scribed in item 8.
In this case, the electric field effect transistor Q710 is turned off by the
transistor Q712 through the detecting resistor R766, resistor RX708,
and capacitor CX706 to narrow the pulse width and reduce the fre-
quency. The protection is performed with this signal level (supposing
that only the +10V line is subject to the overcurrent.)
This protection is automatically resumed.
(12)-4. +5V
The +5V is protected by the D/D convertor protecting function de-
scribed in item 8.
In this case, the electric field effect transistor Q710 is turned off by the
transistor Q712 through the detecting resistor R766, resistor RX708,
and capacitor CX706 to narrow the pulse width and reduce the fre-
quency. The protection is performed with this signal level (supposing
that only the +10V line is subject to the overcurrent.)
This protection is automatically resumed.
(12)-5. –20V
For the –20V protection, in addition to the D/D convertor protection
function described in item 8, protection is provided by the three-termi-
nal regulator IC Z703. In either case, the operation is automatically
resumed. The regulator IC has the priority in operation.
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