CARDIAC PACING AND DEFIBRILLATION - Design and Development of Medical Electronic Instrumentation - page 436

+5SW

R60
33K

R61
33K

R62
33K

R63
330K

R64
33K

R65
33K

R66
33K

R68

R67

Q27
2N2222

Q40
2N2222

1K 1K

R69 10

J8
1

J7
1

R70
10

Q41
MTP3N100E

Q30
MTP3N100E

R71
33K

R72
33K

R73
33K

R74
330K

R75
33K

R76
33K

R77
33K

Q31
2N2222

R79
1K

R78
1K

Q32
2N2222

R80 10

J9
1

J10
1

R81
10

Q33
MTP3N100E

Q34
MTP3N100E

Figure 8.47 The input of the impedance measurement circuit of Figure 8.46 is connected to the defibrillation electrode terminals by
way of a self-activated isolation circuit. A solid-state switching circuit that reacts to current flow protects both the impedance
measurement circuit from defibrillation pulses as well as the patient from faults in the impedance measurement circuit. The gates of
Q29 and Q30 are held at a positive voltage in excess of the conduction threshold by the 5-V source through resistor R63. This allows
impedance measurement to take place via these FETs and resistor R70. However, when a defibrillation pulse is applied, current
increases through R70, causing one of the bipolar transistors (Q7 or Q28) to conduct and place its associated FET in the high-impedance
state.

2. If the switches are pressed, takes appropriate action, including:
a. Initiates charge.
b. Checks for completion of charge cycle.
c. Awaits front-panel command to shock.
d. Dumps remaining stored energy after shock.
e. Informs GUI of charge due to manual request, and de fi brillates due to manual

request.
f. Checks for GUI information requests.