Ecler PAM2000, Service Manual

Page: 14 / 107

11
TEMPERATURE DETECTOR
This circuit is calculated to operate over the output relay opening it if any of both modules' temperature
excedes 90
E
C, approximately. It is made with a comparator per channel (L-R), resident in the same IC306. Both
share a reference voltage provided by D306 (TL431A), which gives excellent stability at that voltage " 1%. These
comparators reveive, like the DC amplifiers, the signal from their probes, comparing them with the Vref.Once this
voltage is surpassed by any of both probes, the output of the corresponding comparator is balanced to the power
supply (+10V), acting through D307, R318, D308 and R319 over the respective bases of transistors Q301 y
Q307, which makes the corresponding relay open. This output is also connected to the THERMAL LEDs, which
light up as the relays are open.
Note that each time the relay is open through any of the variables which act upon it the PROTECT LED
must light up. The circuit acting over this LED is made of R327, R328, R329, R4, R5 and Q303. When Q302
stops conducting (open relay), Q303 receives its base current through R327, R326, R6 and the relay's coil,
putting this transistor into saturation. This way the LED is linked to the power supply (+V) by means of the group
of resistances R328, R329, R4 and R5.
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