Application of the hottest DCDC power module in me

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The application of dc/dc power modules in medical sensor circuits I. Introduction at present, with the continuous development of modern medical devices, especially the electronic instruments directly connected to the human body, in addition to the increasingly high requirements for the performance of the instruments themselves, more and more attention has been paid to the consideration of human safety, such as life monitors, maternal and Infant monitors, infant heat preservation instruments and other instruments that are in close contact with the human body, That is to say, when using the instrument, the patient shall not cause electric shock or other risks to the human body because of the instrument used

II. Application of ECG detection circuit

the following briefly introduces the common ECG detection circuit as an example, as shown in figure 1:

Figure 1: common ECG detection circuit

Figure 1 is the practical circuit of ina115 in ECG detection circuit. The positive and negative inputs of the amplifier are respectively connected to the left arm (LA) and the right arm (RA) of the human body through the ECG sensor, and the driving circuit composed of the operational amplifier N and the resistors R1-R4 is connected to the right leg (RL) of the human body to form a "floating ground". Due to the weak biological signal and polarization potential, the amplification factor of this stage should not be too high. It is generally taken as between and can only be used as pre amplification. In order to detect safety, the later stage should be isolated by isolation amplification circuit, and the power supply voltage of this stage should preferably be provided by isolation power module to achieve complete isolation of power supply and signal. As shown in Figure 2 at the 2016 German plastic industry exhibition - k2016, which is similar to the temperature of the machine head, figure 2: isolated ECG detection preamplifier circuit

the above circuit is an isolated ECG detection preamplifier circuit composed of t6235d and ina115 of Hanwei company, which has high input impedance, low leakage current The detection accuracy is high and the indicators such as human safety can fully meet the required standards for the use of medical devices. This circuit is generally used as a pre amplification circuit. The device is in direct contact with the human body. After picking up the ECG signal, it is amplified through ina115. Finally, it is isolated and transmitted to the post amplification circuit by iso122 to realize the isolation and amplification of the human body signal, output and power supply

the working power supply of the amplifier shall have sufficient safe creepage distance, high isolation voltage characteristics and extremely low isolation capacitance value, so as to better ensure the safety performance of the system. Here, it is recommended to use 6000vdc isolated G Series (constant voltage input, 6000vdc positive and negative voltage output) or H series products (constant voltage input, 6000vdc single circuit voltage output) of jinshengyang company, Due to its extremely high isolation voltage characteristic (6000vdc) and extremely low isolation capacitance (≤ 10PF), this series of products are widely used in Baiyin medical electronic equipment industry due to its high thermal conductivity, electrical conductivity and corrosion resistance. G1515s-1w is used to truly disconnect the ground wire that ina115 contacts with the human body from the input power line, so as to achieve the effect of complete isolation, that is, complete isolation of power supply and signal

III. selection of isolated dc/dc power supply module:

Description: the above scheme is made under the condition that the working voltage of the isolation amplifier is ± 15V. If the working voltage is ± 5V, ± 12 or other voltages, just select the product with the corresponding output voltage

IV. the following problems should be paid attention to during the use of dc/dc power module:

1. The external capacitors C2 and C3 of dc/dc power module adopt tantalum capacitors with low internal resistance. The recommended capacitance value is 0.47uf. Excessive capacitance should be avoided to prevent the module from being damaged due to the overcurrent at the moment of startup caused by excessive capacitance

2. In order to ensure the reliability of the module for long-term operation, the module shall work above 10% of the rated power to prevent the unstable output voltage of the module due to no-load or light load from affecting the circuit operation. If the load power consumption is really small, a dummy load of 10% of the rated power can be added between +vo and 0V and -vo and 0V at the output end by connecting an external dummy load (the following is a small method for maintenance), To improve product reliability

3. Since the dc/dc power supply module is realized by switching oscillation circuit, it will also generate common mode and differential mode noise interference. For occasions with high requirements for ripple noise, the output end of the dc/dc power supply module can be externally connected with passive LC filter network or RC (with large loss) to further reduce the ripple noise of the power supply. However, it should be noted that the resonant frequency of L itself is much higher than the switching frequency of the module, The allowable current should be more than twice the input current of the module, and the internal resistance should be small to reduce the DC loss. For details, please refer to the following figure:

v. conclusion

the above mainly introduces the characteristics, application and precautions of dc/dc module power supply in the medical electronics industry, especially in the sensor detection circuit. At present, there are many dc/dc module power supplies in the market, but because medical electronics belongs to a special industry, the requirements for its power supply are very high. In order to ensure the safety performance of human body and equipment, The selected dc/dc module power supply is particularly important. (end)

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