Hill-Rom Advanta P1600, Service Manual

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Theory of Operation
Chapter 3: Theory of Operation
Advanta™ Bed Service Manual (man168ra) Page 3 - 25
3
through R82, are used to configure the transformer’s primary coil for either
115V AC or 230V AC operation. Relay K1 acts as a supervisory switch for
solenoid power and logic power to the valve/sensor module. The relay is on
continuously during normal operation. It is turned off onlyif the cable is
disconnected, if a system failure is detected, or if the air system switch is
turned off.
The 4 amp triacs, Q3 - Q8 are driven by the opto-triac drivers U20 through
U25. Fuses F3 through F8 provide overcurrent protection for the cable and
valve/sensor module.
The circuitry surrounding U18 provides an O-ring feedback function to the
microprocessor. This circuit detects whether a triac is conducting. Resistors,
R50 through R55 are sized so that only when a triac is conducting will the U18
opto’s detector output switch. When a triac is conducting, the output of the
opto is a 50 or 60 Hz square wave. This square wave keeps capacitor C27
discharged so that the output of the Schmitt-Trigger Inverter is HI. When all
triacs are in the blocking state, C27 charges up via R66 and R69 which allows
the inverter output to go LO.
Compressor and Crossover Valve Drivers
The circuitry surrounding Q9, Q10, U26, and U27 makes up the compressor
and cross-over valve drivers. Q9 and Q10 are 800V, 8A, high noise immunity
triacs. The circuitry around U19 is another O-ring function similar to the one
previously mentioned.
Electrostatic Discharge (ESD) Protection
Some integrated circuits have a 100 ohm resistor in series with its Vcc pin to
limit Icc to 50 mA. This helps prevent latch-up. Switched inputs have RC
protection for debounce and static. Digital outputs have a 5.0v TVS zener, 1K
ohm resistor, and (Harris SP720) diode clamps.
LON Connector (P112, P113)
Pins 2 and 7 provide unregulated logic power to the board from the central
power supply.
Pins 3 and 8 are for unregulated logic power return.
Pins 4 and 5 are the Echelon net signal lines.
Pin 9 is the net shield connection.