Page 443 - Handbook of Biomechatronics

The Artificial Pancreas 437

Basal delivery is
spring-driven 24-h basal
rate begins
with the push
of a button
Viscous
fluid
Insulin
Basal rate flow Viscous fluid Needle
restrictor

On-demand bolus function, user
pushes a button to deliver two
units of insulin per push

Fig. 18 V-Go spring-driven disposable insulin pump. (Courtesy Valeritas Inc.)

Pressure sensors are incorporated into most insulin pumps to ensure nor-
mal operation and detect occlusions. These are usually based on silicon strain
gauges that provide signals in the millivolt range, rather than the microvolt
level provided by bonded-wire strain gauges. The strain gauges are config-
ured in a bridge configuration, which provides a differential signal at a
common-mode voltage that is about half of the supply voltage. Differential
instrumentation amplifiers followed by programmable gain amplifiers and
analogue to digital converters interface pressure measurements to the micro-
controller. Precision pressure measurements are not required as they are only
used to verify normal operation and are not concerned with actual drug
delivery (Mossman, 2010; Ganesan, 2013).

4.2.3 Power Management
Power is generally provided using a single 1.5V alkaline or rechargeable
LiPo cell that is boosted to a nominal operating voltage of 2V to obtain
the most life from a cell. Typical boost regulators used in insulin pumps
can run from voltages as low as 0.6V. An example of the genre is the
MAX1947 has a 0.7–3.6V input-voltage range. Its 2-MHz switching fre-
quency and current-mode control reduces component sizes, achieves over
94% efficiency while integrating all the required switches (power switch,
synchronous rectifier, and reverse-current blocker) to minimize solution