|Title:|| Circuits for increasing the reliability of an iontophoretic system|
|Abstract:||Circuits are provided for increasing the reliability of an iontophoretic drug delivery system. Such circuits detect the failure of a crystal oscillator of the system, the failure of a voltage reference of the system, or the impending failure of a battery power source of the system.|
|Inventor(s):|| Flower; Ronald J. (Atlanta, GA), Garde; Kenneth E. (New Windsor, NY), Walter; Steven D. (Vernon, NJ) |
|Assignee:|| Vyteris, Inc. (Fair Lawn, NJ) |
1. An iontophoretic drug delivery device comprising a controller, a high voltage supply, and a patch for delivering drugs electrically connected therebetween, the controller
having a circuit comprising:
a microprocessor selectively switchable between an operational state and a reset state for controlling delivery of current to the patch according to preprogrammed software instructions in said operational state, said microprocessor having an
output line, said output line being set low in the operational state and set high in the reset state;
a crystal oscillator connected to the microprocessor to clock the microprocessor;
a transistor, a gate of which being connected to the output line, wherein current delivery to the patch is allowed to occur when the output line is low and the transistor is turned off, and current delivery is stopped when the output line is high
and the transistor is turned on, wherein
the microprocessor includes a watchdog timer which switches the microprocessor from the operational state to the reset state, thereby causing current delivery to be stopped by the transistor.
2. The iontophoretic delivery device of claim 1 wherein said watchdog timer switches the microprocessor from the operational state to the reset state upon a failure of the crystal oscillator.
3. The iontophoretic delivery device of claim 1 wherein said watchdog timer switches the microprocessor from the operational state to the reset state upon a failure of said preprogrammed software instructions.
4. A circuit for disabling delivery of current to a patch of an iontophoretic system, comprising:
a microprocessor for controlling an amount of current to be delivered to the patch, said microprocessor clocked by a crystal oscillator, wherein an input/output line of said microprocessor is caused to be in a hi-impedance state upon power being
initially supplied to said microprocessor; and
first and second transistors, said first transistor having a gate connected to said input/output line and a source connected to a gate of a second transistor, said second transistor having a source and drain in the current delivery pathway of the
wherein when said power is initially supplied to said microprocessor, said input/output line is in the hi-impedance state and said first transistor is turned on, thereby turning off said second transistor and causing the current delivery pathway
to be in an open, disabled-delivery state.
5. A circuit according to claim 4, wherein when said crystal is in operation and said microprocessor processes current control instructions, the input/output line is in a low-impedance state, thereby turning off said first transistor and turning
on said second transistor, causing the current delivery pathway to be in a closed, abled-delivery state.
6. A circuit according to claim 4, wherein after said crystal fails, a watchdog timer in said microprocessor times out, causing the microprocessor to power-on reset and the input/output line to be in a hi-impedance state, thereby causing the
current delivery pathway to be in an open, disabled-delivery state.