VITALAB MICRO & MICROLAB 200 THEORY OF OPERATION
VITAL SCIENTIFIC SERVICE MANUAL
2.14
two FET switches (IC3C and IC3D) and control each one half of
the bridge driver.
Depending which output of the followers is positive, one half
of the bridge driver is active. This means that the two outputs
are controlling the current direction through the Peltier
elements, and therefore select heating or cooling.
Peltier element driver circuit.
The Peltier driver circuit is built-up around four FET
transistors (T1 to T4), which form together a bridge driver
circuit.
If the measured temperature is lower than the requested
temperature, the output voltage of IC5 is positive. The output
voltage of IC4B will also be positive, driving transistor T4
via FET switch IC3C.
Transistor T6, will take away the gate voltage of transistor
T3. The current through the Peltier elements is then going via
T1, the Peltier elements and via T4 to ground.
If the measured temperature is higher than the requested
temperature, the output voltage of IC4C will be positive,
driving transistor T2. The current through the Peltier elements
is then going via T3, the Peltier elements and via T2 to
ground.
The two Peltier elements are connected in series between pin 1
and 3 of connector PL10.
The microprocessor can monitor if the temperature is within 0.1
C. by means of the 'TEMP-OK` signal. If the temperature is not
reached within 20 seconds the microprocessor will switch off
the Peltier element driving circuit by means of the two FET
switches (IC3C and IC3D) and the 'TEMP-OFF' signal (T-set0 and
T-set1 both 0).
Reference voltage circuits.
There are three circuits which provide the necessary reference
voltages.
First of all, there is an pin-programmable precision voltage
source, IC12 (REF01) which produces a very stable 10 Volts
reference supply. This 10 Volts is used as the main reference
Summary of Contents for Vitalab Micro
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