144/ 266 3CIRCUIT DESCRIPTION
Low voltage supply
Slot J2
The following assemblies are located on the PCB:
• Voltage regulator for +24 volts
• Voltage regulator for +15 volts
• Voltage regulator for +5 volts
• Voltage regulator for –15 volts
• Three sound generators for the acoustic signals
• Circuit for tone selection
• Tone output amplifier with volume control.
Voltage regulator for +24 volts
The unstabilized DC voltage, gained on the motherboard via transformer TR1 and bridge-connected rectifier
BR2, moves to the input of a switched-mode power supply unit. This consists of the integrated switching
controller IC3, the memory choke L1 and the free-wheeling diode D1 with the necessary wiring. The
output voltage is adjusted via the voltage divider R22, R23.
At the output of the switching controller, a stabilized DC voltage of +24 volts is available. The presence of
this voltage is indicated by the LED6.
This voltage is mainly used to operate the relays in the surgical unit.
Voltage regulation for +15 volts
The instable input voltage, the presence of which is indicated by LED 4, moves to the switching
controller IC 1. The circuit extensively corresponds to the +24 volt regulation, however the transformer
UE 1 is used here as the memory choke which simultaneously taps a part of the connector voltage
occurring there for the operation of the – 15 volt regulation.
The output voltage of 15 volts prescribed by the divider ratio of the resistors R30 and R31 is used to
operate the CMOS circuits and the operation amplifier. Its proper presence is signaled by the LED 2.
Voltage regulation for – 15 volts
The negative operation voltage of – 15 volts is mainly required for the negative voltage supply of the
operation amplifier. Since the capacity of this voltage source is just minimal due to the circuit, a simple
regulating circuit could be used. The principle of analog regulation is thus sufficient, and the resulting
losses are minimal.
The switched-mode voltage tapped from the switched-mode power unit for + 15 volts at transformer UE 1
is rectified through the diode D6 such that a negative DC voltage is present at the input of the analog
regulator IC10. This voltage is stabilized by the fixed voltage controller IC10 to –15 volts. The proper
presence of this voltage is indicated by the LED1.
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