Common Problems and Analysis in DC/DC Applications (Figure)-EEWORLD

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At present, with the continuous development of China's electronic industry, the application of switching power supplies has received more and more attention from technicians in the application field of this product. The products include AC/DC, DC/DC and DC/AC, among which PWM mode is the main one. In actual use, some technical problems are often encountered, such as interference, voltage instability, poor reliability, etc. The following takes the low-power DC/DC used in general communication interfaces and instruments as an example to discuss the common problems and solutions of DC/DC in actual applications.

1. DC/DC power module Application in RS485 interface circuit (DC/DC power module: isolation 1000VDC, In:5V, Out:5V, P:1W), the circuit is as follows:

RS485 uses DC/DC power module and optocoupler isolation, which can suppress electromagnetic interference and eliminate ground loops, protecting system circuits from external network influences. The DC/DC output end supplies power to the optocoupler and MAX485 chip, and its current is very small (6-8MA/optocoupler, MAX485 current is only about 20MA), so the DC/DC often works under light load conditions, especially when the optocoupler is cut off, the DC/DC power module only supplies power to the MAX485, which may cause the output voltage to be high and the ripple to be large. In severe cases, it may also affect the performance of the MAX485, and the reliability of the DC/DC will also be reduced. Therefore, when selecting a DC/DC module, the rated power of the DC/DC power supply, the minimum power of the load, and the stability of its output voltage should be considered. Because the common isolated DC/DC power modules on the market have a minimum load requirement for reliability (currently the minimum load requirement is ≥15-20% of the rated power, MORNSU's B0505LM-1W can achieve ≥5%, and special products can be used at no load). When selecting a power module, it is best to make the load work at around 40-70% of the rated power of the module. Under this load condition, the output voltage stability is better.

In many cases, manufacturers generally recommend that customers choose standard 1W products. In this case, the load may be too light, resulting in a high output voltage, or even much higher than the normal voltage. In severe cases, it will affect the normal operation of the circuit and the performance of components. Therefore, the following suggestions are provided:

1. If the load is light or may be no-load, it is best to connect a dummy load to the output end of the DC/DC power module, which is about 5-10% of the rated power. For example, a 1W product can be connected to a 470 ohm resistor, as shown in the figure above;

2. If the product requires lower power consumption, you can choose a smaller power DC/DC power module from MORNSUN, such as B0505LS-W5 or B0505LS-W25, etc., which can avoid the increase of no-load power consumption and improve voltage stability;

3. If the transmission speed is high (>9.6K) and the circuit stability is required, it is recommended to use products with high output voltage stability and low ripple noise, such as MORNSUN's IB0505LS-W75 (isolated 1000VDC, regulated output). This product can meet the requirements of ripple and voltage accuracy at high transmission speeds due to its extremely low ripple and high voltage accuracy.

The following are some DC/DC power module models used in RS485/232 and other interface circuits for reference:

Second, for the discussion of DC/DC power supply in the amplifier, the circuit is as follows:

This circuit uses a DC/DC power supply module to power the isolated amplifier. Considering that the amplifier uses voltage or current as a medium, the requirements for power isolation, output voltage accuracy, and ripple noise are relatively high. If an ordinary power supply is used as the power supply part of the amplifier, it will affect or interfere with the amplifier due to its large ripple noise and low voltage accuracy. Therefore, when considering the selection of an amplifier, its power supply part cannot be ignored. Therefore, for amplifiers that require higher accuracy, it is recommended to use MORNSU's IA_KS-1W/2W series products, such as IA0512KS-1W/2W. Due to its extremely low ripple noise and high-precision output voltage, it is widely used in various op amp circuits, A/D, and D/A converters. The power supply part. And it can be used at full load in harsh working environments.

The following provides some model references for DC/DC power supply modules used in amplifiers, A/D, D/A and other analog circuits:

Reference address：Common Problems and Analysis in DC/DC Applications (Figure)

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