ULTRATHERM 908i
29
gbo Medizintechnik AG 2004
Version 1.2
5.1.3.8. Cable voltage monitoring circuit
This circuit includes N201/2 and the externally connected components of which.
The sum voltage at X212 is a measure of the maximum RF voltage along the cable at X222.
Integrated circuit N201/2 monitors this voltage. In the standard case, i. e. the load is matched to
X222 and power requirement below 250 W, about +14 V apply at the output pin 7.
The cable voltage monitoring is active when extreme mismatching occurs at X222 and high RF
power is required at the same time.
For checking, R219 can be bridged for a short time. This results in blocking the level control and,
thus, the RF power becomes zero.
5.1.3.9. Analogous OR interconnection
It includes: V201, V202, R229.
Via R229 a current is fed into the basis of V210 trying to increase the level. When the RF voltage
level is sufficient one of the control systems becomes active and takes over a component current
through V201 or V202. In this way, the output power is stabilised. V201 and V202 are used to
decouple the outputs of the operational amplifier.
5.1.4. Operation of the power supply
The power supply delivers the voltage at X205 which depends on the AC collector voltage of the
final stage transistor. Tthis is obtained by feeding a current at pin 10 of N203 through V215/V216,
R258. In case of matching the following relations apply:
Output power [W]
Voltage at X205 [V]
0
about 13
50
about 29
100
about 36
150
about 41
250
about 48
Be careful when working at the power supply. With full output power a direct short-circuit
between X205 and earth can damage the integrated circuit N203!
