Defibrillator with uncontrolled solid state switching
A defribrillator comprises first and second electrodes (A, B) for application to a patient, a voltage source ( 60 ), and an output circuit for connecting the voltage source across the electrodes upon the occurrence of a control signal ( 64 ). The output circuit includes a first current path connecting one side of the voltage source to the first electrode (A) and a second current path connecting the other side of the voltage source to the second electrode (B). Each of the current paths contains at least one solid state switching device USD 1 (bo) or IGBT 1. The switching device(s) USD 1 (bo) in at least one of the current paths has no external control and characteristics similar to a Shockley diode.
1. A defibrillator comprising first and second electrodes for application to a patient, a voltage source, and an output circuit for connecting the voltage source across the electrodes upon the occurrence of at least one control signal, wherein the output circuit includes a first current path connecting one side of the voltage source to the first electrode and a second current path connecting the other side of the voltage source to the second electrode, a third current path connecting the one side of the voltage source to the second electrode, and a fourth current path connecting the other side of the voltage source to the first electrode, each of the first to fourth current paths containing at least one solid state switching device that is an uncontrolled two-terminal device which automatically undergoes a transition from a high impedance state to a low impedance state when a voltage greater than a predetermined threshold is applied across its terminals, the at least one switching device in the first current oath transitioning to a low impedance state unconditionally when the applied voltage exceeds a predetermined threshold, and the at least one switching device in the third current oath transitioning to a low impedance state if the applied voltage exceeds a predetermined first threshold but not a second, higher threshold.
2. A defibrillator as claimed in claim 1 , wherein each of the second and fourth current paths contains a controlled solid state switching device.
3. A defibrillator as claimed in claim 1 , wherein the the at least one switching device in the second current path transitions to a low impedance state unconditionally when the applied voltage exceeds a predetermined threshold and the at least one switching device in the fourth circuit path transitions to a low impedance state if the applied voltage exceeds a predetermined first threshold but not a second, higher threshold, the output circuit also including a controlled solid state switching device common to the second and fourth current paths.
4. A defibrillator as claimed in claim 1 , wherein the voltage source is a capacitor.
5. A defibrillator as claimed in claim 1 , wherein the voltage source is a programmable voltage source.
6. A defibrillator as claimed in claim 1 , wherein the output circuit is a single integrated solid state device.