GE Cardiocap 5 Service Manual

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5.2.2 Main structure 
The general schematic structure of the SR92A720 power supply is shown below.  
RFIINPUTFILTER
L
N
PE
100...240V~
V7R16
V1
C9
V8
L1V26V12T1
L2
15.7V/4A
C18
X12-4
+
X12-5
X12-1
X12-2
-
X12-3
X12-6
Externalshutdownsignal
feedbackExternal
signal
GatedriveGatedrive
Inrushresistor
 
Figure 5-2. General schematic structure of SR92A720 
This AC/DC converter contains two converter stages: a preconverter and a postconverter.  The 
preconverter is an AC/DC converter which...

Cardiocap/5 Technical Reference Manual 
The PFC converter controls the intermediate voltage.  The intermediate voltage has been set to about 
370 V.  In addition, there is a small (

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Output voltage is controlled by a two-loop system.  This means that there is a fast inner-voltage-
control loop and a slow outer-voltage-control loop.  The slow-voltage control is an external voltage 
signal, which, by setting the offset to the inner-control loop, determines the level of the output voltage.  
If the external feedback signal is not connected to pin 6 of connector X12, the output voltage 
measured from connector X12 settles to approximately 10 V.  The external...

Cardiocap/5 Technical Reference Manual 
5.3 DC/DC board functional description 
5.3.1 Introduction 
The DC/DC board converts the output voltage of the AC/DC power supply or the battery voltage to 
various supply voltages for the electronics of Cardiocap/5 monitor. Another main task of the board is 
battery charging.  
 
Figure 5-5. DC/DC board  
5-6  

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5.3.2 DC/DC board block diagram 
The input voltages of the board are VDD (from the AC/DC power supply) and BAT (the battery voltage). 
The DC/DC board trims the level of VDD. Switching power supplies convert VDD or BAT to supply 
voltages for monitor electronics. The board output voltages are +3.3V, +5V, +12V, +15V, -15V and 
+15VD.  
The battery is charged when VDD is present. During mains dropouts, the monitor is powered by a 12V, 
sealed, lead-acid type battery.  
There is no CPU...

Cardiocap/5 Technical Reference Manual 
 
Figure 5-7. DC/DC board power supplies 
5-8  

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5.4 Detailed description of the power supplies 
Synchronous switching is used in all step-down (buck) type switching power supplies in order to 
improve the efficiency. In synchronous switching (or synchronous rectification), the normal schottky 
diode of a buck converter is bypassed by a FET conducting at the same time as the diode. This reduces 
diode loss remarkably. 
All regulated output voltages of the DC/DC board are short-circuit protected. Protection is based on 
current...

Cardiocap/5 Technical Reference Manual 
5.4.5 +15VD power supply 
+15VD is used as a “dirty” +15V supply in the monitor. It powers the thermal printer, DC motors, 
pneumatic valves, and isolated switching power supplies.  
On the DC/DC board, the regulated voltage is actually +15VB, which is named +15VD after circuit 
breaker electronics. During mains usage, +15VB is taken from VDD via a diode. When the mains 
voltage drops, the monitor continues operation on battery. In battery use +15VB is converted...

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CPU power connector (X6) 
PIN  SIGNAL/VOLTAGE I/O DESCRIPTION 
X6/1 GND   
X6/2 GND   
X6/3 +3.3V out To CPU and 3.3V LCD display 
X6/4 +3.3V out  
X6/5 +3.3V out  
X6/6 +3.3V out  
X6/7 GND   
X6/8 GND   
X6/9 +5V out To CPU and 5V LCD display 
X6/10 +5V out  
X6/11 GND   
X6/12 GND   
X6/13 +12V out To LCD backlight inverter 
X6/14 GND   
Mother board power connector (X2) 
PIN  SIGNAL/VOLTAGE I/O DESCRIPTION 
X2/1 VDD/BAT out Not utilized 
X2/2 GND   
X2/3 +15VD out To parameter...

Cardiocap/5 Technical Reference Manual 
AC/DC power supply connector (X8) 
PIN  SIGNAL/VOLTAGE I/O DESCRIPTION 
X8/1 VDD_SHUTDOWN/ out Shut AC/DC power s. 
X8/2 GND   
X8/3 GND   
X8/4 TRIM_VDD out Adjust VDD 
X8/5 VDD in AC/DC output voltage 
X8/6 VDD in  
5.4.6 Fan control 
The supply voltage VFAN is linearly regulated from +15VD. The operating voltage range of the fan used 
is 10.2 to 13.8V. The fan is CPU controlled by signal FAN_ON. In the circuit used, VFAN drops to the 
level of 1.2 to 1.3V when...