Biomedical Engineering Reference
In-Depth Information
Figure 8.34
This prototype instrument is a demonstrator of the internal workings of an implantable
de
brillation energies of up to 50 J to the heart. This
energy level is suitable when at least one of the electrodes is in direct contact with the ventricular
muscle.
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brillator. This circuit is capable of delivering de
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Lead impedance is estimated prior to delivery of a shock or under command from the
control computer. Inappropriate lead impedances cause the de
brillation command to be
aborted since delivering high energies into inappropriately low loads can be dangerous,
because the developed currents pose
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erent modules of the
circuit are presented in the following sections. The interconnection between these modules
takes place as depicted in Figure 8.36.
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fire or explosion risks. The di
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Power Supply Section
A Condor medical-grade (low-leakage, redundantly insulated) power supply is used to gen-
erate
brillation module. The power line is applied to the power supply
input terminals through a medical-grade connector/switch/fuse/
15 V dc for the de
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lter/voltage-selector mod-
ule. The power supply has low leakage and a redundant isolation on the power transformer,
and its linear regulator is capable of producing 15 V at 0.4 A.
As shown in Figure 8.37, a Power Convertibles HB04U15D15Q (C&D Power Tech-
nologies) isolated dc/dc converter powers the battery charger circuitry. The isolation bar-
rier of this converter is rated at 3000 V (continuous) and tested at 8000 V with a maximum
60-Hz leakage of 2
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A. This dc/dc isolation rating is the main power line leakage barrier
for the applied part of the circuit. The output of the dc/dc converter is
µ
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filtered through a
Murata BNX002
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filter block and a 470-
µ
F capacitor (C22). A TIP42 transistor and a 33-V
zener diode are con
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gured as an “ampli
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ed zener diode” to clamp the dc/dc output of the
dc/dc converter at approximately 34 V.
A single-chip gel-cell charge controller is used to charge two sealed, leakproof gel cells
in series. Charging of the two 12-V batteries is controlled through a Unitrode (now owned
by Texas Instruments) UC3906 IC, which implements an optimal-charge algorithm with
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