Handheld medical equipment power supply system solution analysis

When the range of applications for medical devices extends from hospitals to emergency and home healthcare environments, its mobility will be determined by a variety of factors. In addition, medical equipment in hospitals often requires battery support to facilitate patient transfer in different wards. Moreover, people born at the peak of childbirth have entered the old age, and they still want to move around, which creates a need for portable applications of traditional fixed devices that can facilitate the activities of sick elderly people. They include diagnostic instruments such as fiber vibrators, ultrasound equipment and blood analyzers; and patient-oriented devices, including insulin syringes, left ventricular assist devices (LVADs), and wireless vital signal monitors.

In addition, when multiple surgical instruments can only be used within a certain range, some devices are freed from this limitation by using battery pack power. When surgical devices such as electric orthopedic tools or endoscopes are powered by batteries, surgeons feel the great convenience of this flexibility.

Traditional battery packs include batteries that provide primary energy and boards that integrate residual fuel gauges, protection circuits, temperature sensors, LED drivers that display battery pack or cell status, and serial data communication buses. The exterior of the battery pack is a typical plastic case with an external contact that provides an electrical interface to the connection to the main device and absorbs external oscillations and keeps the internal components insulated.

1 Overview of use

The first step in designing a safe and reliable system is to accurately understand the characteristics of the medical device usage model, including temperature range, discharge curve, charging method, shelf life, and transmission needs. All external and internal operating temperatures are also important considerations when selecting the best battery for mobile applications.

Manufacturers have shown the performance of the cell at the ideal C/5 constant current and external temperature of +20 °C. However, many medical devices are expected to operate between -20 ° C and +60 ° C temperature range, and heat can be dissipated during charging and discharging, thus when the battery system is placed together with the temperature sensitive component, the assembled battery The system and device enclosures have maximum temperature thresholds.

An inconsistent pulse discharge or a typical defibrillator pulse can cause the cell to generate more heat, which can reduce battery capacity faster than a non-uniform discharge curve. The charging method affects the way the battery heat is dissipated and should also be considered in the system design of the battery.

2 optimal chemical properties

Choosing the best battery for the battery pack determines whether the field medical equipment can work properly. This requires a full understanding of the battery performance curve. Understanding voltage, charge and discharge cycles, load current, energy density, charge time, and discharge rate are the first steps in selecting a cell for a handheld device. Several batteries are described below.

The first is a sealed lead acid battery (SLA). Charging SLA features include: 2V rated voltage, prismatic or cylindrical construction, high capacity, low cost and simple charging conditions. The biggest challenges of SLA batteries include: bulky bulk factor, linear voltage decay, lack of fast charging technology and sensitivity to high temperatures and high self-discharge (which affects shelf life).

Followed by NiMH batteries. Its features include: rated voltage of 1.25V, 500 charge and discharge cycles during the lifetime, average energy density of 100Wh/kg, charging time less than four hours, close to 30% monthly discharge rate and strict size factor. In places where low voltage is required or price sensitive, NiMH batteries have a good performance. Ten NiMH batteries can be connected in series to increase the voltage so that the total voltage reaches 12.5V.

The last is a lithium-ion battery. Lithium-ion battery features include: 3.6V rated voltage, 500-1000 charge and discharge cycle during the lifetime, the average energy density is 160Wh / kg, charging time is less than 4 hours, the monthly average discharge rate is 10%; Seven lithium-ion batteries can be connected in series to achieve a total voltage of 25.2V.

3 battery pack intelligence

Handheld and outdoor are the development trend of medical equipment today. Lithium-ion batteries have higher energy density, lighter weight, longer duty cycle, superior capacity retention and wide ambient temperature adaptability. Compared to NiMH and SLA solutions of the same power, they require batteries. The number is smaller.

Many advanced accessories on the board facilitate the intelligence of the system, including residual fuel gauges, protection circuits, temperature sensors, and serial data buses. A smart battery pack that provides higher power utilization when the end user's discharge profile or characteristics are adjusted. One reason battery packs are valuable for medical applications is their ability to monitor their status, accurately predict remaining runtime and send their workgroup status to medical devices. These features allow end users to intelligently manage device usage while avoiding unexpected failures or shutdowns. An intelligent battery pack can provide feedback based on its history of use, which facilitates traceability and warranty issues.

4 Security

Medical battery packs must integrate multiple safety systems and reliable protection circuitry. Among them, the active safety circuit is a necessary factor to ensure that the chemical of the battery remains stable. The safety circuit protects the battery pack from overcharging, overdischarging, short circuits and extreme temperatures, which limits the voltage to a tight operating range. The safety circuit uses a temperature sensor to open the battery at a specific temperature to prevent heat dissipation and overheating.

For multi-battery battery packs, it is wise to have an active battery balancing circuit. Placing the circuit in the battery pack is especially critical as it leaves the battery no longer in danger of overheating.

Reverse Conducting Thyristor(RCT)

Reverse Conducting Thyristor(RCT) is also called Reverse- appreciation Thyristor.The characteristic is that a diode is connected in reverse parallel between the anode and cathode of thyristor, so that the transmitting junction of anode and cathode is short-circuited.As a result of this special circuit structure, it has high voltage resistance, high temperature resistance, short turn-off time, low switching voltage and other good performance.For example, the turn-off time of the reverse thyristor is only a few microseconds, and the working frequency is dozens of KHZ, which is better than the fast thyristor (FSCR).This device is suitable for switching power supply and UPS uninterrupted power supply. One RCT can replace one thyristor and one continuous current diode respectively.

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