CN218961597U

CN218961597U - Defibrillator device

Info

Publication number: CN218961597U
Application number: CN202221591152.XU
Authority: CN
Inventors: 李萍; 单纯玉
Original assignee: Shanghai University of Medicine and Health Sciences
Current assignee: Shanghai University of Medicine and Health Sciences
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2023-05-05
Anticipated expiration: 2032-06-24

Abstract

The utility model belongs to the technical field of medical appliances, and particularly relates to a defibrillator, which comprises a direct current power supply, a voltage converter, a rectifying circuit, a charging and discharging circuit and a pair of electrodes which are sequentially connected. The charge-discharge circuit includes: the first charging and discharging switch, the first stationary end connects the output end of the rectifier circuit; the second charge-discharge switch, the first stationary end connects another output end of the rectifier circuit; one end of the first energy storage capacitor is connected with the movable end of the first charge-discharge switch, and the other end of the first energy storage capacitor is connected with the movable end of the second charge-discharge switch; the positive electrode of the diode is connected with the second motionless end of the second charge-discharge switch, and the negative electrode of the diode is connected with the second motionless end of the first charge-discharge switch; and one end of the second energy storage capacitor is connected with the second motionless end of the first charge-discharge switch, the other end of the second energy storage capacitor is connected with the second motionless end of the second charge-discharge switch, and two ends of the second energy storage capacitor are respectively connected with two electrodes. The utility model adds the second energy storage capacitor to smooth the defibrillation waveform, and releases the defibrillation waveform by using the first charge-discharge switch according to the requirement, thereby being convenient for generating the defibrillation waveform.

Description

Defibrillator device

Technical Field

The utility model belongs to the technical field of medical appliances, and particularly relates to a defibrillator.

Background

External defibrillators provide devices for electrical defibrillation of the heart by applying electrical pulses through electrodes to the patient's skin (external electrodes) or exposed heart (internal electrodes). Is used for emergency treatment of patients suffering from ventricular fibrillation, ventricular tachycardia and suspected cardiac arrest. The duration of the external defibrillation pulse is typically 4-20 ms and the energy is within 40-360J (joules). The pulse power is up to tens of kilowatts. The voltage amplitude is around 2000V. The defibrillation electric pulse has the characteristics of high voltage, high power and short time. The external defibrillator is a three-type medical instrument, and requires stability, reliability, accuracy and safety of defibrillation electric pulse.

A defibrillator is an energy storage device, and is generally composed of a low-voltage power supply, an energy storage capacitor, a high-voltage charging circuit, a discharging circuit, electrodes and the like. At present, defibrillation discharge control can be divided into two methods, namely a total amount control method and a process control method.

The total amount control means that the total amount of stored energy and released energy is controlled, and the release rate (discharge power) is not actively regulated in the release process, thereby being natural. The discharge waveform is generally an exponential wave. Defibrillation is performed by first determining the total amount of memory, called preset energy, according to some rule. Such as CN202010941353 defibrillation discharging device and defibrillation method, CN202110778506 a method and system for automatically adjusting external defibrillation current and defibrillation energy, and CN201810865883 a bridge discharging circuit of defibrillator for accurately controlling the conducting process. The control objective is to control the total released energy, indirectly by controlling the stored energy, in such a way that the initial voltage of the storage capacitor is changed. The advantage of the method of controlling total energy is good compliance. The main disadvantages are as follows:

the control variable is not identical to the variable that plays the role of defibrillation. The control variable of the total amount control method is energy, only total energy is controlled, and the application mode is not controlled. Numerous literature studies have shown that the variable that actually plays a role in defibrillation is current, not energy. The ordinate of the defibrillation waveform is current and the abscissa is time. The energy is equal to the integral of power over time. If a voltage of 5V is applied to a 50 ohm transthoracic resistor, a current of 0.1A is obtained. The pulse power is 0.5W for a duration of 720s, 360J of energy can be applied. Although the human body obtains 360J of energy, defibrillation cannot be achieved with a 5V power supply. Because a current of 0.1A belongs to the subthreshold stimulus. According to the electrophysiological principle, in the case of subthreshold stimulation, even if the stimulation time is longer, the tissue excitation is not caused, and defibrillation cannot be realized.

The process control continuously adjusts the release rate during the release of current to obtain the desired waveform. An output stage of an H-bridge defibrillator and a method for defibrillation high-voltage discharge of a biphasic sawtooth square wave according to patent CN201210556832 employ a process control method. However, the existing process control has a relatively slow adjustment speed and insufficient adjustment instantaneity, so that sawtooth waves are output.

Disclosure of Invention

Aiming at the technical problems of poor defibrillation effect and poor real-time performance of defibrillation control and regulation of the existing defibrillator, the utility model aims to provide the defibrillator.

A defibrillator comprises a direct current power supply, a voltage converter, a rectifying circuit and a pair of electrodes which are sequentially connected;

the defibrillator further includes:

the charging and discharging circuit is positioned between the rectifying circuit and the electrode;

the charge-discharge circuit includes:

the first charge-discharge switch is provided with a first fixed end, a second fixed end and a movable end, the movable end can be switched between the first fixed end and the second fixed end, and the first fixed end is connected with the output end of the rectifying circuit;

the second charge-discharge switch is provided with a first fixed end, a second fixed end and a movable end, the movable end can be switched between the first fixed end and the second fixed end, and the first fixed end is connected with the other output end of the rectifying circuit;

one end of the first energy storage capacitor is connected with the movable end of the first charge-discharge switch, and the other end of the first energy storage capacitor is connected with the movable end of the second charge-discharge switch;

the anode of the diode is connected with the second motionless end of the second charge-discharge switch, and the cathode of the diode is connected with the second motionless end of the first charge-discharge switch;

one end of the second energy storage capacitor is connected with the second stationary end of the first charge-discharge switch through an inductor, the other end of the second energy storage capacitor is connected with the second stationary end of the second charge-discharge switch, and two ends of the second energy storage capacitor are respectively connected with two electrodes.

Preferably, the defibrillator has a charging process, the charging process being:

when defibrillation begins, the movable end of the first charge-discharge switch is connected with the first fixed end of the first charge-discharge switch, the movable end of the second charge-discharge switch is connected with the first fixed end of the second charge-discharge switch, the direct-current low voltage provided by the direct-current power supply is increased to a preset high voltage through the voltage converter, and the first energy storage capacitor is charged after rectification by the rectification circuit;

the defibrillator has a discharge process that is:

after receiving a discharging instruction, the defibrillator connects the movable end of the first charging and discharging switch with the second fixed end of the first charging and discharging switch, connects the movable end of the second charging and discharging switch with the second fixed end of the second charging and discharging switch, energy of the first energy storage capacitor is transferred to the second energy storage capacitor through the first charging and discharging switch, the inductor and the diode, the second energy storage capacitor forms voltage, and defibrillation current is generated by releasing the voltage to a human body through a pair of electrodes.

Preferably, the charge and discharge circuit further includes:

and the one watt stopwatch is connected in series with a one watt-second meter resistor and then connected in parallel with the second energy storage capacitor so as to detect the defibrillation voltage and the defibrillation current at two ends of the pair of electrodes.

Preferably, after receiving the discharge instruction, the defibrillator drives the watt-hour meter to start metering or timing, when detecting that the total energy reaches a preset target energy or a preset time, the defibrillator disconnects the moving end of the first charge-discharge switch from the second fixed end of the first charge-discharge switch, disconnects the moving end of the second charge-discharge switch from the second fixed end of the second charge-discharge switch, and after the second energy storage capacitor completely releases energy to a pair of electrodes, defibrillation discharge is completed.

As a preferable scheme, the first charge-discharge switch adopts a field effect transistor, the drain electrode of the first charge-discharge switch is used as a movable end thereof, the grid electrode of the first charge-discharge switch is used as a first fixed end thereof, and the source electrode of the first charge-discharge switch is used as a second fixed end thereof;

the defibrillator also includes a feedback control circuit, the feedback control circuit comprising:

the current sampling resistor is connected in series with the load resistor, and the load resistor is an equivalent resistor of a human body;

the non-inverting input end of the error amplifier is connected with the reference voltage end, and the inverting input end of the error amplifier is connected with the common end of the current sampling resistor and the load resistor;

the inverting input end of the comparator is connected with the output end of the error amplifier, and the non-inverting input end of the comparator is connected with a sawtooth wave generator;

and one end of the driver is connected with the output end of the comparator, and the other end of the driver is connected with the grid electrode of the first charge-discharge switch.

Preferably, the first charge-discharge switch is an N-channel field effect transistor, and preferably a silicon carbide type field effect transistor.

Preferably, the driver is an isolated driver.

Preferably, the feedback control circuit further includes:

one end of the first resistor is connected with the common end of the current sampling resistor and the load resistor, and the other end of the first resistor is connected with the inverting input end of the error amplifier;

one end of the feedback resistor is connected with the inverting input end of the error amplifier;

and one end of the feedback capacitor is connected with the other end of the feedback resistor, and the other end of the feedback capacitor is connected with the output end of the error amplifier.

Preferably, the defibrillator further includes a feedforward control circuit, the feedforward control circuit including:

one end of the timing resistor is connected with the second fixed end of the first charge-discharge switch;

one end of the timing capacitor is connected with the other end of the timing resistor, and the other end of the timing capacitor is connected with the second fixed end of the second charge-discharge switch;

the grid electrode of the MOS tube is connected with the clock signal end, the drain electrode of the MOS tube is connected with the common end of the timing resistor and the timing capacitor, and the source electrode of the MOS tube is grounded;

and the drain electrode of the MOS tube is used as the output end of the sawtooth wave generator.

As a preferable scheme, the MOS tube adopts a PMOS tube.

The utility model has the positive progress effects that: the utility model adopts the defibrillator and has the following advantages:

1. the defibrillator of the utility model can charge the energy of the first energy storage capacitor to the maximum value before discharging, and after receiving a discharging instruction, the defibrillator can generate defibrillation current by forming voltage through the second energy storage capacitor and releasing the voltage to a human body through a pair of electrodes.

2. The structure is provided with the watt stopwatch to detect defibrillation voltage and defibrillation current, the measurement result is more accurate, the released energy is irrelevant to the impedance of the human body, the transthoracic impedance of the patient does not need to be detected, and the structure compliance is better.

3. By adding a feedback control circuit, the defibrillation current can be controlled to be at a desired value.

4. By additionally arranging the feedforward control circuit, the first energy storage capacitor immediately reacts when the voltage starts to drop, the peak current of discharge can be effectively reduced, and the damage to myocardial cells of a patient is avoided.

5. According to the combination of the feedforward of the voltage of the first energy storage capacitor and the feedback of the output current, the dynamic regulation capability of defibrillation current is obviously improved. The defibrillation current is enabled to track the setting current, and the defibrillation current can be changed by changing the setting current. Thus, the defibrillation waveform can be changed according to clinical needs.

6. In the discharging process, the control variable is controlled by current, and the defibrillation effect has good correlation.

7. The released energy can be matched according to different impedance conditions of the patient, so that personalized accurate defibrillation is realized.

8. The utility model is applicable to various external defibrillators.

Drawings

FIG. 1 is a schematic diagram of an overall structure of the present utility model;

FIG. 2 is a schematic circuit diagram of a feedback control circuit according to the present utility model;

FIG. 3 is a schematic circuit diagram of a feedforward control circuit according to the present utility model.

Detailed Description

In order that the manner in which the utility model is practiced, as well as the features and objects and functions thereof, will be readily understood and appreciated, the utility model will be further described in connection with the accompanying drawings.

Referring to fig. 1, a defibrillator includes a dc power supply (not shown), a voltage converter 1, a rectifying circuit 2, a charge-discharge circuit 3, and a pair of electrodes 4, which are connected in this order.

The charge-discharge circuit 3 includes a first charge-discharge switch K1, a second charge-discharge switch K2, a first energy storage capacitor C1, a diode D, a second energy storage capacitor C2, and an inductance L. Where the voltage VC represents the voltage across the first storage capacitor C1.

The first charge-discharge switch K1 has a first stationary end, a second stationary end and a movable end, the movable end of the first charge-discharge switch K1 can be switched between the first stationary end of the first charge-discharge switch K1 and the second stationary end of the first charge-discharge switch K1, for example, the first charge-discharge switch K1 adopts a switch with a switchable function such as a single-pole double-throw switch or a field effect transistor, and the first stationary end (1 end) of the first charge-discharge switch K1 is connected with one output end of the rectifying circuit 2. The second charge-discharge switch K2 has a first stationary end, a second stationary end and a movable end, the movable end of the second charge-discharge switch K2 can be switched between the first stationary end of the second charge-discharge switch K2 and the second stationary end of the second charge-discharge switch K2, for example, the second charge-discharge switch K2 adopts a switch with a switchable function such as a single-pole double-throw switch or a field effect transistor, and the first stationary end (1 end) of the second charge-discharge switch K2 is connected with the other output end of the rectifying circuit 2. One end of the first energy storage capacitor C1 is connected with the movable end of the first charge-discharge switch K1, and the other end of the first energy storage capacitor C1 is connected with the movable end of the second charge-discharge switch K2. The positive pole of diode D connects the second motionless end (2 ends) of second charge-discharge switch K2, and the negative pole of diode D connects the second motionless end (2 ends) of first charge-discharge switch K1. One end of the second energy storage capacitor C2 is connected with the second stationary end of the first charge-discharge switch K1 through the inductor L, the other end of the second energy storage capacitor C2 is connected with the second stationary end of the second charge-discharge switch K2, and two ends of the second energy storage capacitor C2 are respectively connected with two electrodes 4.

In some embodiments, referring to fig. 1, the defibrillator has a charging process of:

at the beginning of defibrillation, the movable end of the first charge-discharge switch K1 is connected with the first fixed end of the first charge-discharge switch K, the movable end of the second charge-discharge switch K2 is connected with the first fixed end of the second charge-discharge switch K, the direct-current low voltage provided by the direct-current power supply is increased to a preset high voltage through the voltage converter 1, and the first energy storage capacitor C1 is charged after rectification by the rectification circuit 2. For example, by charging the energy of the first storage capacitor C1 to the maximum allowable value 360J after the charging.

The defibrillator has a discharge process of:

after receiving the discharging instruction, the defibrillator connects the moving end of the first charging and discharging switch K1 with the second fixed end thereof, and connects the moving end of the second charging and discharging switch K2 with the second fixed end thereof, so that the first energy storage capacitor C1, the first charging and discharging switch K1, the inductor L, the diode D and the second energy storage capacitor C2 form a typical buck converter. The inductor L is used for converting the electric energy of the first energy storage capacitor C1 into magnetic energy when the first charge-discharge switch K1 is turned on, and converting the magnetic energy into electric energy to be supplied to the second energy storage capacitor C2 when the first charge-discharge switch K1 is turned off. The diode D functions to provide a current path for the inductor current. Thus, part of the energy of the first energy storage capacitor C1 is transferred to the second energy storage capacitor C2 through the first charge-discharge switch K1, the inductor L and the diode D, a voltage is formed in the second energy storage capacitor C2, and the voltage is discharged to the human body through the pair of electrodes 4 to generate a defibrillation current.

In some embodiments, the charge-discharge circuit 3 further includes a Watt stop watch WS, a Watt stop watch WS and a Watt stop watch resistor R _ws In parallel with the second storage capacitor C2 after series connection to detect the defibrillation voltage and defibrillation current across the pair of electrodes 4.

Among the variables that can be controlled in a defibrillator are voltage, current, and energy. The relation among the three is:

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where W is defibrillation energy, U is voltage across the output pair of electrodes 4, and I is defibrillation current. t0 is the discharge start time, and t1 is the discharge end time.

As can be seen from the equation, the released energy is independent of the body impedance. Therefore, the transthoracic impedance need not be measured, nor does the defibrillation energy need to be adjusted.

In some embodiments, if the discharge energy is used as a control variable, the wattmeter WS is driven from t0 to start metering or timing after the defibrillator receives the discharge command, and the discharge is considered to be stopped when the metered total energy is detected to reach a preset target energy or a preset time, so as not to be excessively wide. At this time, the moving end of the first charge/discharge switch K1 is disconnected from the second stationary end thereof, the moving end of the second charge/discharge switch K2 is disconnected from the second stationary end thereof, and the defibrillation discharge is completed after the second energy storage capacitor C2 releases all the energy to the pair of electrodes 4.

The preset target energy or preset time can be obtained by user input in the manual defibrillator or can be a machine preset value of the automatic defibrillator.

The error due to the smaller capacitance value of the second storage capacitor C2 is less than 1%. The mode is simple in principle, accurate in control, good in compliance and fixed in preset energy, the transthoracic impedance does not need to be measured, and only the connection condition of the defibrillation electrode needs to be judged qualitatively.

In some embodiments, controlling the defibrillation current may be accomplished by adjusting the closing time of the discharge switch. For example, the first charge/discharge switch K1 is switched at a fixed frequency of 100kHz or more, and when the first charge/discharge switch K1 is turned on (the movable end of the first charge/discharge switch K1 is connected to the second stationary end thereof), the first energy storage capacitor C1 transfers energy to the second energy storage capacitor C2 and stores energy in the inductor L, and when the first charge/discharge switch K1 is turned off (the movable end of the first charge/discharge switch K1 is turned off from the second stationary end thereof), the inductor L transfers the stored energy to the second energy storage capacitor C2 via the diode D. The longer the first charge-discharge switch K1 is turned on each time, the more energy the inductor L stores, the more energy the first energy storage capacitor C1 transfers to the second energy storage capacitor C2, the higher the voltage across the second energy storage capacitor C2, and the greater the defibrillation current. Accordingly, the defibrillation current can be changed by changing the on time of the first charge-discharge switch K1.

The utility model can control the defibrillation current to the expected value through the feedback control circuit. Referring to fig. 2, the first charge-discharge switch K1 employs a field effect transistor, a drain electrode of the first charge-discharge switch K1 is used as a movable end thereof, a gate electrode of the first charge-discharge switch K1 is used as a first stationary end thereof, and a source electrode of the first charge-discharge switch K1 is used as a second stationary end thereof. The first charge/discharge switch K1 is preferably an N-channel fet, and more preferably a silicon carbide fet.

Referring to fig. 2, the feedback control circuit includes a current sampling resistor RS, an error amplifier EA, a comparator A1, a driver U1, a reference voltage terminal, and a sawtooth generator U2. Wherein the reference voltage terminal provides a reference voltage Vref.

The current sampling resistor RS is connected in series with the load resistor RL, which is the equivalent resistance of the human body. Defibrillation current I _RL A feedback voltage VFB is generated at the current sampling resistor RS. The non-inverting input end of the error amplifier EA is connected with a reference voltage end, and the inverting input end of the error amplifier EA is connected with the common end of the current sampling resistor RS and the load resistor. The feedback voltage VFB is compared with the reference voltage Vref by an error amplifier EA, which outputs a signal VX for adjusting the duty cycle of the PWM signal of the driver U1. The feedback voltage VFB (representing the present output current) is subtracted from the reference voltage Vref in the error amplifier EA. Thus, the error amplifier EA is performed onceAnd (5) subtracting operation.

The inverting input end of the comparator A1 is connected with the output end of the error amplifier EA, and the non-inverting input end of the comparator A1 is connected with the sawtooth wave generator U2. One end of the driver U1 is connected with the output end of the comparator A1, and the other end of the driver U1 is connected with the grid electrode of the first charge-discharge switch K1. The driver U1 employs an isolated driver U1.

Referring to fig. 2, signal VX represents the difference between the feedback voltage VFB generated by the defibrillation current and the reference voltage Vref. At steady state, the average value of signal VX changes slowly. In the comparator A1, the signal VX is compared with the sawtooth wave VS generated by the sawtooth wave generator U2, if VS < VX, the comparator A1 outputs a high level, and the first charge-discharge switch K1 is turned on by the driving of the driver U1, and the first energy storage capacitor C1 discharges to the second energy storage capacitor C2. If VS > VX, the comparator A1 outputs the low level first charge-discharge switch K1 to be closed, and the discharge stops. The higher the signal VX, the longer the sawtooth wave reaches VX, and the longer the discharge time.

The working principle of closed loop steady flow is as follows: if the output current drops, the feedback voltage VFB is lower than the reference voltage Vref, which will cause the error amplifier EA output voltage VX to rise. The rise of the voltage VX increases the time for which the comparator A1 outputs the high level, and the discharge time increases. The output current increases until vfb=vref and vice versa.

In some embodiments, the feedback control circuit further includes a first resistor R1, a feedback resistor RF, and a feedback capacitor CF. One end of the first resistor R1 is connected with a common end of the current sampling resistor RS and the load resistor RL, and the other end of the first resistor R1 is connected with an inverting input end of the error amplifier EA, namely, the inverting input end of the error amplifier EA is connected with the common end of the current sampling resistor RS and the load resistor RL through the first resistor R1. One end of the feedback resistor RF is connected to the inverting input of the error amplifier EA. One end of the feedback capacitor CF is connected with the other end of the feedback resistor RF, and the other end of the feedback capacitor CF is connected with the output end of the error amplifier EA.

The first resistor R1, the feedback resistor RF, the feedback capacitor CF and the error amplifier EA form a proportional-integral (PI) controller, also called compensation circuit. The effect is to improve the stability of the circuit so as not to swing the output current around the set value.

In steady state: vfb=vref=i _RL ×RS

The current sampling resistor RS is fixed, so that the defibrillation current I can be changed by changing Vref _RL 。

In some embodiments, referring to fig. 3, when the discharge peak in the circuit is too high, a feedforward method can be added, that is, the defibrillator of the present utility model further includes a feedforward control circuit including a timing resistor RT, a timing capacitor CT, and a MOS transistor Q1.

One end of the timing resistor RT is connected with the second motionless end of the first charge-discharge switch K1. One end of the timing capacitor CT is connected with the other end of the timing resistor RT, and the other end of the timing capacitor CT is connected with the second stationary end of the second charge-discharge switch K2. The grid electrode of the MOS tube Q1 is connected with a clock signal end, the drain electrode of the MOS tube Q1 is connected with the common end of the timing resistor RT and the timing capacitor CT, and the source electrode of the MOS tube Q1 is grounded. The drain electrode of the MOS transistor Q1 is used as the output end of the sawtooth wave generator U2. Wherein, the MOS tube Q1 is preferably a PMOS tube.

Referring to fig. 2 and 3, the voltage VC represents the voltage on the first storage capacitor C1, and the comparator A1, the sawtooth wave generator U2, the MOS transistor Q1, and the clock signal terminal serve as a PWM circuit in which the clock signal generated at the clock signal terminal controls the frequency of the sawtooth wave. The feedforward control circuit works as follows:

after the clock signal controls to clear the voltage of the timing capacitor CT, the comparator A1 outputs a high level, and the first charge-discharge switch K1 is turned on. The voltage on the timing capacitor CT starts to rise. The rising speed is related to the current of the timing resistor RT, and the higher the current of the timing resistor RT is, the faster the rising speed is. After the voltage on the timing capacitor CT reaches VX, the comparator A1 outputs a low level, the first charge-discharge switch K1 is closed, and the discharge is ended.

The timing resistor RT is connected with the voltage VC point and directly senses the voltage on the first energy storage capacitor C1. The higher the voltage on the first storage capacitor C1, the faster the voltage on the first storage capacitor CT reaches VX, the shorter the discharge time. When defibrillation begins, the voltage on the first energy storage capacitor C1 is higher, the discharge time is short each time, the average discharge speed is slow, and the peak current of discharge can be effectively reduced.

The foregoing has shown and described the basic principles, principal features and advantages of the utility model. It will be understood by those skilled in the art that the present utility model is not limited to the embodiments described above, and that the above embodiments and descriptions are merely illustrative of the principles of the present utility model, and various changes and modifications may be made without departing from the spirit and scope of the utility model, which is defined in the appended claims. The scope of the utility model is defined by the appended claims and equivalents thereof.

Claims

1. A defibrillator comprises a direct current power supply, a voltage converter, a rectifying circuit and a pair of electrodes which are sequentially connected;

wherein the defibrillator further comprises:

the charge-discharge circuit includes:

2. The defibrillator of claim 1 wherein said charge and discharge circuit further comprises:

and the one watt stopwatch is connected in series with the one watt-second meter resistor and then connected in parallel with the second energy storage capacitor.

3. The defibrillator of claim 1 or 2 wherein the first charge-discharge switch employs a field effect transistor, the drain of the first charge-discharge switch being the active terminal thereof, the gate of the first charge-discharge switch being the first inactive terminal thereof, the source of the first charge-discharge switch being the second inactive terminal thereof;

4. The defibrillator of claim 3 wherein the first charge-discharge switch is an N-channel fet.

5. The defibrillator of claim 4 wherein said first charge-discharge switch is a silicon carbide field effect transistor.

6. The defibrillator of claim 3 wherein the driver employs an isolated driver.

7. The defibrillator of claim 3 wherein the feedback control circuit further comprises:

8. The defibrillator of claim 3 wherein the defibrillator further comprises a feed forward control circuit, said feed forward control circuit comprising:

9. The defibrillator of claim 8 wherein the MOS transistor is a PMOS transistor.