Valleylab CUSA EXcel-8 - Bias Circuitry; Feedback Signal; Frequency Selection Circuitry

Ultrasonics Board-Ultrasonic Generator
The RUN_HPO signal from the machine control board via switch U4D
enables the whole frequency loop.
U2A and U2B connect as non-inverting and inverting current sources via
the
feedback of the 0.25 Ohm resistors. Maximum current in the output
transistors (20 amps peak) depends on the gain set by R13 and RIS for the
positive half-cycle, and R41, R36, R18, and R17 for the negative half-cycle.
Amplifier compensation for the positive half-cycles depends on R14 and
C21; for the negative half cycles, R40, C35 and C15.
CR7 and CR2 protect output transistors Q15 and Q16 from the output
transformer flyback; R38 protects the output transistors from open-circuit
loading (like a short-circuit for voltage based designs). The output
transformer is center tapped with a ratio of 1:4.6 for each half coil.
C10 provides AC coupling to the DC biased handpiece and its value is
selected low enough to avoid resonant circuit interactions with the
handpieces.
Feedback Signal
U13B, U11, U14, and U18 filter and convert the feedback signal to digital.
The signal level depends on the gain of the amplifier U13B, R77, and R78.
Bias Circuitry
The bias circuit consists of the following items:
© A pass transistor switch, Q1
+ Filter components L5 and C9
* CRI.
The filter prevents ultrasonic signal leakage from returning to the power
supply, while CRI acts as a free wheeling diode when Q1 is turned off.
Frequency Selection Circuitry
Handpiece interlock jumpers in the handpiece connectors enable
frequency selection. A signal, filtered and “wired OR” for the HP_PRES
signal, goes to the Machine Control board when either handpiece is
present. The 23 PRES and 23_PRES signals select analog switches. The
default frequency selection is the 35.75 kHz circuit.
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CUSA
EXcel-8
System
Service
Manvel
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