System Control
System Control
System Control
System Control
LP6 Plus, LP10, and LP20 Technical Manual
November 2000
Page 4-14
Page 4-14
Page 4-14
Page 4-14
Another important U10/U4 input (A3) originates from the motor
control chip, U9 on the older through-hole board, or U12 on the
newer surface-mount board. It:
•
controls how much power is supplied to the motor. It turns the
motor power on and off at a 16 kHz rate and acts as a speed con-
trol. A speed input signal (J4 on the older through-hole board or
J2 on the newer surface-mount board, pin 1) comes from the
microprocessor, through an analog switch, U6 on the older
through-hole board or R13 on the newer surface-mount board,
and enters a control input of U9 or U12. The other U9 or U12
control input comes from U7 on the older through-hole board, or
U2 on the newer surface-mount board, a tachometer generator.
This is a speed feedback signal to U9 or U12.
•
Two other inputs to U9 or U12 (pins 15 and 16) provide current
limiting to the motor so that it cannot be driven harder than it is
intended, particularly if it is stalled. The U9 or U12, pin 16 cir-
cuitry sets the motor drive power to approximately the same level
regardless of source (a 12V battery, or from the AC line). This
puts about 22V output on the drive circuitry (from AC power);
12V (from DC power sources).
A8 on U10 on the older through-hole board, or U4 on the newer sur-
face-mount board, is the backup line (the line on the logic board
that monitors whether the microprocessor is functioning properly).
If this line goes high, the three CPU lines, A4, A5, and A6 are
ignored by U10 or U4. The exhalation solenoid will be de-energized
and all six motor-drive transistors will be off. No air will be deliv-
ered.
Three nearly identical power supplies provide: 1) 5V for much of the
system circuitry, particularly on the boards; 2) 12V for several IC’s
on the logic board, for the solenoid, for the fan, and for the magnetic
sensor; 3) 13.8V or 14.4V for charging the battery.
The external power system is also shown on this schematic, with AC
power passing through the power switch/circuit breaker, through
the transformer and full wave rectifier, and onto the motor board
where it is filtered and becomes system power.
The internal and external batteries also connect directly to the
motor board through the two parts of CR13 on the older through-
hole board, or D32 on the newer surface-mount board, (dual diode)
to the system power common. If AC power is connected, its voltage is
much higher than that of the batteries and therefore overrides the
batteries in supplying power to the system. AC operation is supply-
ing approximately 22V, where the battery is supplying around 12V.
Therefore, no current flows from the battery during AC operation.