Ecler PAM2000, Service Manual

Page: 12 / 107

9
PROTECTION CIRCUIT 11.0411 OPERATION - DESCRIPTION
The circuit is configured by:
- A POWER SUPPLY.
- A THERMAL PROBE DC AMPLIFIER.
- A TEMPERATURE DETECTOR.
- A DC OUT DETECTOR PER CHANNEL.
- A CLIP CIRCUIT PER CHANNEL.
- A RESET (TURN OFF/TURN ON) CIRCUIT.
- A BINARY COUNTER PER CHANNEL.
- TWO MONOSTABLE CIRCUITS PER CHANNEL.
The circuit power supply is performed through various sources: +V, module's power supply. This voltage
feeds the relays circuit, manual reset circuit and part of the clip circuit. Alternate voltage from a transformer's
secondary (manual reset circuit).
There is also a stabilized 10V power supply which feeds the card's circuitry, made of IC301 (7805) plus
the zener D302 (Z4.7) 4.7+5
.
10V. We will also need a regulated power supply to get 14Vmax at 0.7A, which
can be obtained with IC302 (7805) plus an auxiliary circuitry that will be analysed below.
The cooling fan speed is automatically regulated in relation to the power module's temperature, which is
read by a thermal probe (LM35D), jointly linked to the heat sink.
This high sensitivity thermal probe gives variations of 10mV for every
E
C. This voltage is picked up and
amplified by the IC305 (LM358). Of course, there is a probe for each L and R heatsink. The output of both
amplifiers is linked through two diodes D304 and D305, making an O gate, whose cathodes go to the regulator,
applying the DC of any of them to the regulator. This provides a variable voltage at its output which oscillates from
a minimum of approximately 7V for a temperature of 20
E
C (cold heatsink) to a maximum of 14V for temperatures
of 76
E
C or higher.
The gain of the amplifiers has been calculated for this temperatures window. The maximum voltage
allowed by the heatsink in order to work properly is 14V. This maximum is given by the zener D305 (Z9.1/1); as
the regulator is a 7805 the voltage will be -as maximum- 9.1+5 = 14.1V. When the zener is not working (not
enough voltage) the voltage on the fan will be the output amplifiers', less 0.6V (diodes fall), plus the 5V of the
IC302.
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