How to effectively reduce the power consumption of medical electronic equipment

Designers of portable medical devices are facing some unique challenges. The examination and control of electronic products in the field of medical care is quite strict, especially in the life of the product design, the life cycle, and the stability of use, all have high specifications. In addition, the design use of electronic devices, once relevant to medical devices, has produced significant significance.

For example, low power consumption is a common goal for all designers. Low power means that batteries can be smaller and lighter, thereby improving product portability. For medical devices, portability is improved. The patient's quality of life, and the patient's life needs to rely directly on the life of the battery.

In this article, we will show how designers can design with microcontrollers (MCUs) and meet the low power requirements of medical devices.

In low-power applications, the microcontroller's static power consumption is an important choice; some microcontrollers with high-order processing technology can consume less than 50 nA in sleep mode. To be suitable for a variety of low power designs, microcontrollers must be able to operate over a wide range of power supplies. For example, when using an alkaline battery, an operating voltage of 1.8 V is usually specified because two alkaline batteries with an end voltage of 0.9 V are usually used in the application. By choosing a microcontroller that operates over a wide range of voltages, you can extend the life of your portable device. In addition to the operating voltage range of the microcontroller, Table 1: In addition to the components listed in Figure 1 and their measured current consumption values, the designer can also consider the overall system operation. The voltage range, including the periphery of the microcontroller. If the periphery of the system is very power hungry, then reducing the power consumption of the microcontroller has little effect on the total system power consumption.

Figure 1: In the medical data logger application, the microcontroller's I/O pins can be used to power EEPROM and sensors.

Table 1: Estimating the power supply of the medical data logger using the components listed in Figure 1 and their measured current consumption values

The power management principle for portable embedded systems is to allow the microcontroller to control the power consumption of the internal and external peripherals. When designing a portable medical device, determine the required operating mode or state and then decompose the design to eliminate unwanted circuitry. Choosing the right microcontroller from many different vendors can help you eliminate redundant external components and reduce costs. As mentioned earlier, microcontrollers that operate over a wide range of voltages will make your system design more flexible.

Try to use a medical monitor that contains a microcontroller to record data to illustrate how to minimize the power consumption of the entire system: this monitor contains sensors, EEPROM, and batteries (see Figure 1). In practical applications, the sensor can perform measurements of temperature, oxygen saturation, blood pressure, blood glucose concentration, and many items. The medical device will continuously monitor the patient's relevant index for several hours or longer. In this example, the microcontroller reads the sensor's measured data every 2 seconds and converts it, stores the data in an external EEPROM, and waits for the sensor to output the next reading. If power consumption is not required, it is of course possible to always power the EEPROM, the sensor and its bias circuits; however, for portable medical devices, efficient use of the power supply is very important. Therefore, in order to effectively reduce the power consumption of such systems, designers often turn them off when the microcontroller does not need these peripherals.

As shown in Figure 1, the designer can use the microcontroller's I/O pins and some program code to power the EEPROM and sensors when needed. Since the I/O pins of the selected microcontroller can supply up to 20mA, no additional power is required.

A common method of saving power in embedded applications is to let the microcontroller enter sleep mode when the system has low resource requirements for the microcontroller. In the example, the system takes measurements every 2 seconds; if it actually takes 11ms to measure and store the results, the MCU can sleep 1.989ms between measurements. The longer the microcontroller sleeps, the lower the average power consumption. The system microcontroller is responsible for waking up by setting interrupts or by the watchdog timer; therefore, ensuring that the appropriate watchdog timer is important. In general, if the application requires the microcontroller to process the data samples at regular intervals, the watchdog timer should wake up the MCU for the required time period; therefore, select the micro-control that matches the watchdog timer period. The device is also very important.

Designers use power budgeTIng to estimate the possible current consumption and battery life in the application. Also taking Figure 1 as an example, the data logger continues to experience various modes such as sleep, sensor warm-up, detection, data conversion, and storage. The analytical processing loop will assist the designer in determining the time taken by the various modes in a single cycle. Then, with the component data provided by the manufacturer, you can know the current consumption status of each component. By multiplying the total current required in each mode by the duration of the mode, the amount of charge consumed by the mode in each cycle can be obtained.

According to Table 1, the application of the data logger is about 2000 ms per cycle, and the total amount of charge required is 18.8 e-6 amps* sec. According to the data in Table 1, it can be inferred that the average current is 0.009 mA, as follows:

Average current (mA) = total charge (ampere * seconds) / total time (seconds) = 18.8 e-6/2000 e-3 = 0.009 mA peak current = 2.048 mA Conclusion:

Through the choice of MCU, designers can successfully manage medical electronic devices, thereby reducing power consumption; reducing power consumption can effectively reduce heat generation when using products, and reduce battery size, thereby extending the life of the device and increasing the device's Reliability, improved patient fit, and reduced overall device size.