High voltage therapy system with transformer primary current control
Improved devices, circuits and methods of operation in implantable stimulus systems. An implantable defibrillator may comprise a charging circuit using a transformer to store and build up energy on an HV capacitor or capacitor stack, with the HV capacitor in turn coupled to an H-bridge output circuit having low and high sides for issuing therapy. A current monitoring circuitry is provided on the low side of the H-Bridge and used to form a feedback loop to control current into a transformer that converts battery voltage to a signal that charges the HV capacitor to control current through the H-bridge.
1. An implantable pacemaker-defibrillator comprising:
a battery;
a transformer having a primary winding and at least one secondary winding;
a capacitor stack coupled to the at least one secondary winding;
an H-bridge to deliver electrical signals from the capacitor stack to outputs of the defibrillator, the H-bridge including first and second high side switches and first and second low side switches;
a current sensing subcircuit coupled to the H-bridge and positioned between the first and second low side switches and a reference or ground node to measure current flow out of the first and second low side nodes;
a charge control circuit configured to control electrical coupling of the primary winding to the battery;
a system controller for the implantable defibrillator having control outputs to control operation of the H-Bridge and the charge control circuit; and
a housing containing the battery, transformer, capacitor stack, H-bridge, current sensing subcircuit, charge control circuit and system controller;
wherein the system controller is configured to selectively operate the charge control circuit in a pacing mode in which a feedback signal from the current sensing subcircuit is used to control current through the primary winding by operation of the charge control circuit;
wherein the at least one secondary winding includes a first secondary winding and a second secondary winding, the capacitor stack includes at least a first capacitor and a second capacitor, the first capacitor is coupled to the first secondary winding, and the second capacitor is coupled to the second secondary winding;
the implantable pacemaker-defibrillator further comprising a defibrillation enable switch coupling the capacitor stack to the H-bridge, and a pacing enable switch coupling only one of the first capacitor and the second capacitor to the H-bridge, and
wherein the system controller is configured to:
operate in the pacing mode by selectively closing the pacing enable switch and not the defibrillation enable switch, and
to operate in a defibrillation mode by selectively closing the defibrillation enable switch and not the pacing enable switch.
2. The implantable pacemaker-defibrillator of claim 1 wherein the charge control circuit is configured to operate, in the pacing mode, by selective enabling and disabling of current through the primary winding in response to the feedback signal.
3. The implantable pacemaker-defibrillator of claim 1 in which the system controller is configured to bypass the current sensing subcircuit to issue defibrillation signals.
4. The implantable pacemaker-defibrillator of claim 1 wherein the charge control circuit is operable in a defibrillation mode in which the charge control circuit ignores the feedback signal.
5. The implantable pacemaker-defibrillator of claim 1 wherein the charge control circuit is configured to issue charger enable pulses that enable electrical coupling of the battery to the primary winding, and to modulate one or more characteristics of the charger enable pulses in response to the feedback signal in the current controlling mode.
6. The implantable pacemaker-defibrillator of claim 5 wherein the charge control subcircuit is configured to modulate one or more characteristics of the charger enable pulses by adjusting a period between successive ones of the charger enable pulses.
7. The implantable pacemaker-defibrillator of claim 5 wherein the charge control subcircuit is configured to issue the charger enable pulses as a series of bursts of charger enable pulses, and, to modulate characteristics of the charger enable pulses, the charge control subcircuit is configured to omit at least one burst of the series of bursts.
8. The implantable pacemaker-defibrillator of claim 5 wherein the charge control subcircuit is configured to issue the charger enable pulses as a series of bursts of charger enable pulses, and, to modulate characteristics of the charger enable pulses, the charge control subcircuit is configured to change how many pulses are in each of the series of bursts.
9. The implantable pacemaker-defibrillator of claim 1 further comprising a lead, wherein the outputs of the pacemaker defibrillator include a first output coupled to a conductor in the lead, and a second output coupled to the housing, wherein at least a portion of the housing is conductive.
10. The implantable pacemaker-defibrillator of claim 5 wherein the charge control subcircuit is configured to modulate one or more characteristics of the charger enable pulses by adjusting a width of one or more charger enable pulses.