Phase Compensator; Driver Stage - Integra Cusa Excel Service Manual

CUSA EXcel Ultrasonic Surgical Aspiration System Service Manual
nominal error output. Under maximum load, the gain should be sufficiently large
to allow stroke, even if the stroke is at reduced levels. If the gain is too large,
however, a large enough feedback will force the error amplifier output to 0,
whereby control is lost.
RV11 is for calibration purposes only.

Phase Compensator

The two-pole, active filter, U9, provides loop phase compensation. This is a
Bessel filter characteristic implemented with a "low sensitivity" configuration. It
is "low sensitivity" in that it has low operational amplifier (op-amp) slew rate and
drive requirements, while component temperature and tolerance sensitivities also
remain low. The phase for the 23 kHz circuit depends on the RC value of RV5,
R52, and C41 selected by the analog switch U5A; the phase for the 35.75 kHz
circuit depends on RV4, R300, and C41 selected by U5D. The nominal -3 dB
point of the filter is 37.30 kHz.
The alignment of these filter poles with the BPF determines the amount of phase
at the undesired longitudinal modes. Too little phase from the BPF makes it
difficult to adjust these modes out; too much phase allows the center frequency to
remain mis-adjusted and, therefore, may sacrifice mid-band gain flatness.

Driver Stage

The driver stage consists of the following components:
• A pre-amp, U1B
• A push-pull rectifier or phase splitter, U1A
• A positive half-cycle driver, U2B
• A negative half cycle driver U2A.
For the 23 kHz circuit, output stage gain depends on the combination of two
gains:
• The pre-amp gain (R10 and R11)
• The phase-splitter gain (R19, R20, R24, and RV3).
For the 35.75 kHz circuit, output stage gain depends on RV2, selected by switches
U5C and U5B.
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 R15 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.
Ultrasonics Board–Ultrasonic Generator
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