Biomedical Engineering Reference
In-Depth Information
+5V
4.7
IC_Enable_1
8
7
6
5
Out 1-
Out 1+
Out 2-
Out 2+
2
3
Anode
Cathode
+HV
PVI1050
IC_Enable_2
Load
8
7
6
5
Out 1-
Out 1+
Out 2-
Out 2+
2
3
Anode
Cathode
2
C
PVI1050
1
Q_Kick
2
IGBT
Kick
1
39
3
G
E
1
Q_Enable
2
3
R_Gate_Bleed_IGBT
Enable
10M
Q_Disable
1
3
2
IC_Disable
3
R_Gate_Bleed_FET
8
7
6
5
470k
Out 1-
Out 1+
Out 2-
Out 2+
150
2
3
Anode
Cathode
Disable
HV Gnd
PVI1050
Figure 8.39
Implantable defibrillators commonly use insulated-gate bipolar transistors (IGBTs) to switch defibrillation energy to the heart.
In a shock-box circuit, photovoltaic optocouplers are used to control the IGBTs. The two photovoltaic cells inside each PVI1050 are wired
in series to produce up to 16 V. Two PVI1050s (U_Enable_1 and U_Enable_2) are wired in parallel to charge the IGBT gate capacitance to
the saturation voltage. R_Gate_Bleed_IGBT bleeds charge accumulated at the IGBT gate to ensure that it remains off until turned on by acti-
vating the photovoltaic isolators. Fast IGBT turn-off is accomplished by discharging the IGBT gate through a FET (Q_Disable).
There is no need for further protection of the gate since the 10 M
loaded output of the
photovoltaic cells in series/parallel is approximately 24 V, and the allowed transient
VGEM of the IGBT is
Ω
is accomplished by discharging the
IGBT gate through a FET (Q_DISABLE). This FET is actuated via a third photovoltaic
isolator.
As shown in Figure 8.39, a switching stage is available on the prototype to enable fast
dump of stored energy into a 50-
30 V. Fast IGBT turn-o
ff
load. This feature may be used to deliver sequential
shocks with decreasing energy (since the remaining energy of the previous shock may be
larger than the energy desired for the succeeding shock) or to return the module to a safe
state after aborting the delivery of a shock.
As shown in Figure 8.40, an H-bridge switch con
Ω
fi
guration was used in the proto-
type to generate biphasic waveforms onto the de
fi
brillation load. Each switch acts as
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