Sharp R-9320 Service Manual page 51

R-9320
R-9450
TEMPERATURE MEASUREMENT CIRCUIT (On R-9450 Alone)
Fig. 15 shows the temperature measurement circuit. The
thermistor in the temperature probe varies in resistance ac-
cording to the cooking temperature and this variation is con-
verted to analog voltage variation
to be delivered to the
K4
terminal of LSI which contains an A/D converter. In the LSI
there are produced "H" level signal and "L" level signal at
its
output terminal D7, as shown in Fig. 16.
When the output signal of
the
terminal D7
is at "H" level, the
transistor Q5 turns on
to get
R62 shorted,
and the circuit
equivalent to that shown in Fig. 17-(a) is set
up.
With
this
equivalent circuit in operation, the LSI can
perform the tem-
perature measurement through the temperature
probe.
When the output signal of the terminal D7 is at "L" level, the
transistor Q5 turns off to get R62 and R61 connected in series
with each other, and the circuit equivalent to that shown in
Fig. 17-(b) is set up. With this equivalent circuit in operation,
.
the LSI judges whether the temperature probe is opened or
not: that is, when the temperature probe is opened, the
voltage almost
equal to VREF/~ is applied
to the
K4 terminal
of LSI; when it is not opened (at its normal state), the voltage
lower than VREF/~ is applied thereto. With the temperature
probe opened, the temperature indicator and numeral indi-
cator flash to indicate this
state.
TEMP.
PROBE
LSI
Figure 15. Temperature Measurement Circuit
"H"
t
GND
i Judge)
(Temp. Measurement)
I
I
I
I
Figure 16. Signal Output Timing at 08 Terminal
;yk- K4 (To LSI, v;Tb-- K4 (To Lsl)
(a) D7
terminal "H" lb)
D7
terminal "I-'*
Figure 17. Circuit Equivalent to Temperature Measurement Circuit
49