Biomedical Engineering Reference
In-Depth Information
Figure 8.35 Block diagram of the 50-J defibrillator. Power is supplied by a medical-grade power supply. A current of 15 V from this sup-
ply operates a dc/dc converter to charge two 12-V gel-cell batteries. Battery power is supplied to the microcontroller constantly. The battery
is also used to power a high-voltage power supply which charges the energy-storage capacitor bank (165 µF) up to 50 J, as selected through a
DAC. A defibrillation pulse is generated by commuting the capacitor bank onto the defibrillation load through an H-bridge switch matrix.
Capacitor bank voltage and current can be monitored by way of isolation amplifiers. Parameter information and commands are entered via a
control computer through isolated RS232 line. The instrument includes circuitry to measure load impedance without delivering shock currents.
fast,
float, and trickle-charge phases to charge the gel cells safely. Two Yuasa NP1.2-12
batteries are connected in series to generate approximately 24 V for the high-voltage power
supply. Each battery has a nominal voltage of 12 V and a capacity of C
fl
1.2 Ah.
Lead-acid batteries with a gelled electrolyte are best kept charged and maintained by a
charger at a
float voltage of 2.25 to 2.3 V per cell. To obtain a full charge, the battery is
charged to about 2.4 V per cell. Therefore, the charger IC switches back to the
fl
fl
float level
when necessary. Terminal voltages that exceed the
float level place the battery in what is
known as the overcharge region . During fast charge, the charger limits the current to a safe
level known as the bulk rate and then tapers o
fl
ff
to the overcharge region at about one-tenth
of the bulk rate.
Search WWH ::




Custom Search