D2.8
T869 Circuit Operation
M860-00-Preliminary
30/06/98
Copyright TEL
2.3.5
Forward And Reverse Power Metering
Forward and reverse power signals from the two IC1 buffers are available for metering
purposes. The output currents are adjustable via RV43 (forward power) and RV57
(reverse power).
2.3.6
Fan Control Circuitry
Figure 2.4 T869 Fan Control Logic Diagram
Comparator IC3 pins 12, 13 & 14 are set to trigger at heatsink temperatures greater than
+70
°
C, and pins 1, 2 & 3 at temperatures greater than -10
°
C.
A logic AND function is applied to the comparator outputs by Q10 and Q15, thereby
turning on the fan unconditionally (via Q12 and Q13) if the heatsink temperature
e70
°
C.
A logic OR function is applied to comparator IC3 pins 12, 13 & 14 and Tx KEY signals,
thereby turning on the fan when the transmitter is keyed and the temperature is
between -10
°
C and +70
°
C.
If the temperature drops below -10
°
C, Q15 is turned off, preventing Q10 from activating
the fan.
Q12 Q13
Fan
Ref
+
High Temp.
Sense
Comparator
IC3
R193
Ref
+
Low Temp.
Sense
Comparator
IC3
R40
NTC
NTC
Tx Key
Invert
Q9
OR
Q10,
R28, R38
NAND
Q10, Q15,
R29, R30
Fan Driver
13.8V
Filtered
Содержание T860 Series II
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