JAJU873 August   2020

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1 System Description
    1. 1.1 Medical Respiratory Systems
    2. 1.2 Respirator System Components
    3. 1.3 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Brushless DC Motor (BLDC)
        1. 2.2.1.1 DRV8323RS BLDC Motor Driver Design Calculations
        2. 2.2.1.2 BLDC Motor Driver Circuit
      2. 2.2.2 Solenoid Valve Drivers
        1. 2.2.2.1 DRV8847 Solenoid Driver Design Calculations
        2. 2.2.2.2 Solenoid Driver Circuit
      3. 2.2.3 Power Tree Architecture
        1. 2.2.3.1 Input protection - overvoltage and reverse voltage
        2. 2.2.3.2 LM5122 Boost Design Calculations
        3. 2.2.3.3 LMR33630 Buck Design Calculations
        4. 2.2.3.4 Secondary Power Stage – TPS62840 3.3V Buck
        5. 2.2.3.5 Secondary Power Stage – TPS7A02 3.3V LDO
        6. 2.2.3.6 Power Tree Circuit
    3. 2.3 Highlighted Products
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware and Software Requirements
    2. 3.2 Test Setup
      1. 3.2.1 Hardware Configuration
      2. 3.2.2 Software Configuration
    3. 3.3 Test Results
      1. 3.3.1 Motor Test Result
      2. 3.3.2 Valve Test Result
      3. 3.3.3 Power Tree Test Result
      4. 3.3.4 Key Test Summary
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 サポート・リソース
    4. 4.4 Trademarks
  10. 5About the Author

1.1 Medical Respiratory Systems

There are several instances where it may become medically necessary for machines to assist with patient respiration, and these machines may require motors and valves depending on the specific application. For example, ventilators use motors to generate pressurized air and a system of valves to either deliver pressurized air or release air in the lungs back to the atmosphere to mechanically assist respiration. Ventilators can also be coupled with anesthesia delivery systems to keep the patient in a safe and anesthetized state. Anesthesia delivery systems incorporate numerous valves for drug mixing and patient protection. Ventilators are typically used in hospital, institutional, transport, and home environments.

There are three basic drive mechanisms in a ventilator system: bellows, piston, and turbine. For a bellows system, typically the air compression of a bellows is from a pneumatic force controlled by servo valves. For a piston system, typically the air compression is achieved from a BLDC or DC servo motor to move a piston. For a turbine system, typically a BLDC motor is used to drive a turbine (blower).

GUID-20200801-CA0I-6HLT-ZC2B-WDQ0TGHD91GJ-low.jpg Figure 1-1 Ventilator system showing patient vital parameters.

The key system requirements for a ventilator system are shown in Table 1-1.

Table 1-1 Ventilator System Requirements
KEY REQUIREMENTSTYPICAL
System reliability and functional safetyIEC 60601-1, ISO 80601-2
Accurate sensing of key parametersflow, pressure, respiration rate, FiO2, temperature, and humidity
Power sourceAC or DC
Efficient system design for portable systems8-10 hours of continuous use on battery
DC power input voltage6-28 V
Input power150-200 W
Operation temperature range5-40 °C
Operating pressure range0 – 90 cmH2O
Operating flow range0-200 L/m
Flow accuracy± 5 L/min or 20% of reading
Pressure accuracy± 0.5 cmH2O or 10% of reading
Minimum inspiratory/expiratory time200 ms
Valve response time< 5ms
Motor operating voltage24 V
Motor operating current3-5 A continuous
High speed operation40-60 kRPM
Wide operating speed range1-60 kRPM
High accelerations and braking150-200 kRPM/s

Note, many medical ventilators will also support continuous positive airway pressure (CPAP) operating mode and include an oxygen concentrator (for example, Ventec VOCSN, Medtronic Puritan Bennett™ 980). However, there are many standalone CPAP machines (for example, Philips DreamStation, ResMed AirMini™) and oxygen concentrators used for home healthcare. For CPAP machines, the pressurized air is delivered to sleeping patients through a mask to treat sleep apnea by helping to prevent the throat from closing.

Similar to ventilators, many CPAP machines and oxygen concentrators rely on a BLDC motor in their application to pressurize the air due their reliability, efficiency, and audible noise characteristics. In general, these standalone machines are designed to be portable and many weights less than 10 lbs. Standalone CPAP machines have less stringent motor requirements compared to ventilators. In addition, CPAP machines typically specify a lower sound level (~29 dBA) compared to ventilators (~50 dBA) and they have a narrower operating pressure range compared to ventilators.

The key system requirements for a CPAP system are shown in Table 1-2.

Table 1-2 CPAP System Requirements
KEY REQUIREMENTSTYPICAL
System reliability and functional safetyIEC 60601-1, ISO 80601-2
Accurate sensing of key parametersFlow, pressure, temperature, and humidity
Power sourceAC or DC
Efficient system design for portable systems8-12 hours of continuous use on battery
DC power input voltage6-28 V
Input power30-80 W
Operation temperature range5 to 35 °C
Operating pressure range4-20 cmH2O, sensor range 0-40 cmH2O
Operating flow range0-150 L/min
Flow accuracy± 1.5 L/min or ± 2.7 % of reading (ISO 80601-2-70)
Static and dynamic pressure accuracy± 0.15 , ± 0.27 cmH2O (ISO 80601-2)
Sound level / noise emissions<29 dBA (ISO 4871)
Service life5 years
Physical weight1-4 lbs
Motor operating voltage12 or 24 V
Motor operating current2-3 A continuous
High speed operation30-40 kRPM
Wide operating speed range1-40 kRPM

Standalone oxygen concentrators will similarly use a motor to pressurize air and will use multiple valves to mix air with pure oxygen to increase the oxygen concentration in the mixture delivered to the patient. One of the key differences in requirements compared to the previous applications is the lower motor speed (2-4 kRPM) due to a lower flow rate requirement (typically less than 2 L/min).

The key system requirements for an oxygen concentrator are shown in Table 1-3.

Table 1-3 Oxygen Concentrator System Requirements
KEY REQUIREMENTSTYPICAL
System reliability and functional safetyIEC 60601-1, ISO 8359, ISO 80601-2-67
Accurate sensing of key parametersFlow, pressure, FiO2, temperature, and humidity
Power sourceAC or DC
Efficient system design for portable systems4-10 hours of continuous use on battery
DC power input voltage10-28V
Input power100-150W
Operation temperature range5 to 35 °C
Maximum outlet pressure30 to 90 psi
FiO2 Range 21-100 %
O2 sensor accuracy3-6 %
Operating flow range0-10 L/min
Flow accuracy+/- 15 %
Sound level / noise emissions40 dBA
Service life5 years
Physical weight5-10 lbs
Motor operating voltage12 or 24 V
Motor operating current2-5 A continuous
Motor speed2-4 kRPM