Datex-Ohmeda F-LM1 Technical Reference Manual page 156

Datex-Ohmeda S/5 Light Monitor
Isolated section
Signal isolation
There are two opto isolators to isolate serial communication between LM-STP and CPU board.
Reset line is an open collector type with a pull-up resistor. With that signal the processor is able to
use its internal watch-dog function. CPU board can reset LM-STP board processor. On the isolated
section there is a supply voltage monitor connected to the reset signal.
Power supply section
Both LM-ECG and LM-STP boards have the same kind of switching mode power supply. Note that
generated isolated voltages are different in LM-STP and LM-ECG board. Both power supplies use
the same oscillator, which is located on the LM-STP board. The synchronization signal is transferred
to the LM-ECG board via a module bus cable.
The core of the power supply is a PWM controller which controls a FET transistor. The transistor
supplies the power to a special pulse transformer. The controller uses a feedback signal from the
analog optocoupler to stabilize isolated +5 V voltage. All other voltages, except +5 V for
microprocessor section, are stabilized with linear regulators.
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Document No. 8000060-1