25/08/2004 ©
Söring
Service-Manual Arco- and RF-units
1
not valid for A-3000/ -2000
2
not valid for Arco-2000
-30-
3
not valid for MBC600
4
not valid for Arco-1000
5. Description of high-power supply
5.1. General description
Purpose of the high-power supply is the feeding of the power modules. It delivers three
voltages, two of these are fixed voltages: +15v and -15v and one is a variable voltage of
0 - 80v controlled by the CPU with a resolution of 6 bit via the equipment bus. In order to
produce only little heat the high-power supply is designed as a switching regulator.
Furthermore this board contains the following components:
-
Analogue signal output of momentary current and voltage values in order to detect
overload respectively an output power error at the patient.
- Short-circuit-/overload-protection of the switching regulator.
5.2. High-power supply, design and function
The module is supplied with 2 x 18v~ and 1 x 15v~ from the mains transformer via a 6-
pole plug. These voltages are rectified, filtered and stabilized to ± 15v and 12v by means
of fixed voltage regulators and supply the internal circuits. The vo15v and -15v
are led out for supplying the Cut- and Coagulator-module. Via another plug smoothed but
unregulated 130v= are fed to the MOS-switch. By varying the duty cycle the MOS-switch
together with its storage-choke and freerun diode delivers the desired output voltage. The
regulation is done by comparing the actual voltage to the nominal voltage. The nominal
voltage comes from the processor interface which contains the necessary address
decoding, galvanic isolation (opto-coupler) and a D/A-converter.
The current limiter limits the current to 7a by switching-off the MOS-switch. If the current
limiter is continuously active for more than 0.3 to 0.4 seconds, e.g. due to a defective
module or extreme overload, the switching regulator is switched off for approx. 5 seconds
and then restarted.
The value of the mains-transformer voltage (15v-winding) is monitored before the
smoothing capacitor for the limits
≥
15v and
≤
27v. In case of overvoltage or undervoltage
the monitoring circuit cuts off the switching regulator and delivers a power-fail signal.
