GE Medical Systems Solar 9500 Service Manual page 150

+12 Volt Linear Regulator
-12/-5 Volt Regulators
External 16.75V Protect Circuit
Battery Control/Charging Circuit
8-4
Theory of Operation: Subassemblies
U17 and associated circuitry form a +12 volt linear regulator. U17 is the
same regulator that is used in the 3.3 volt circuit. The output voltage is
determined by the values of R138 and R139 and filtered by C54. The
output is clamped by zener transient suppressor CR2.
U6 is a fixed voltage output negative regulator. The input is from an
auxiliary winding of the main switching transformer T2. R107 and R106
are required to provide a minimum load for regulation. C4 filters the
output voltage and zener transient suppressor CR1 clamps the output
voltage.
U1 is a -5 volt low current linear regulator. C103 provides filtering for
the output and transients suppressor CR5 protects the output from
overvoltage transients.
Since the 16.75 volt rail is the source for all of the other voltages it is
necessary that the external +16.75 volt output be protected against short
circuits or overloads. U8 and associated circuitry form a auto-reset
electronic circuit breaker. In the event of an overload the breaker will
remain tripped for a period of time determined by the value of C112 and
C114. The output of U8 at pin 6 drives an N-channel mosfet U9 which is
the pass element for the circuit. R110, C2, and R111 are used to control
the turn-on time of U9.
R110 and R111 are bypassed by CR7 so U9 can be turned off rapidly
when a overload occurs. The feedback sense voltage is developed across
sense resistor R8 and filtered by R112 and C8. The additional filtering is
required to prevent nuisance tripping due to transients. L1, C3 and C113
are used to filter the input to the circuit. Transient suppressor CR9
protects the output from over voltage.
Comparator U7 and associated circuitry control the connection of the
battery to the main rail. Q3 and Q4 both have to be on in order for the
battery to be connected. BATCON* is a signal that is controlled by the
main processor board. When BATCON* goes low Q2 turns off which
allows Q4 to turn on. U7 monitors the battery voltage. If the voltage is
high enough the output at U7-1 will be high and Q3 will be turned on.
When both Q3 and Q4 are on, the gate of P-channel mosfet Q1 is near
ground turning it on. This connects the battery to the main rail via or'ing
diode CR3.
The battery is continuously trickle charged from the main 16.75 volt rail
via current limiting resistors R6 and R7. CR6 is used to prevent the
battery from driving the 16.75 volt rail when it drops below the battery
voltage.
Solar 9500 Information Monitor
2001085-061
Revision A