Sinrace Power Supply Technology (Shenzhen) Co., Ltd.

Analog circuits are often designed as low frequency or RF as a result that the switching power supply is rarely used. but switching power supply must be selected in several cases , in order to meet the system performance!

1. The input supply voltage is lower than that the low voltage system need, in this case ,the system needs to boost chip to increase the input voltage. For this circuit, if the power supply circuit is sensitive analog signal or RF signal, then advised by LC network filtering, or re-use of an LDO to buck for the characteristics of low output ripple .

2. System voltage required negative pressure, in this case, the system needs to switch the power to transform negative pressure .If the power supply circuit is sensitive analog signal or RF signal, then advised by LC network filtering, or re-use of an LDO to buck for the characteristics of low output ripple .

3. The system input voltage is much higher than that the system required, and the system needs a large current at this time ,in this case , chip power consumption will be great if use the LDO or three-terminal LDO voltage , not only reduces the efficiency of the system and cause problems about the system cooling. At this point firstly down SMPS voltage to a more suitable voltage, then use the LDO.

Some problems that need attention in the use process:

One. Recently, when we used the transformer chip of positive to negative power, we found the negative-voltage output is insufficient , but the voltage recovery when the load off, we firstly suspect that there is a problem of the stage circuit, but when using regulated power supply, no negative voltage current limiting, and the current file using the multimeter test, found that current is only 50mA, later found out when I put the chip in the positive line to remove large inductor in series, the output is normal. Therefore, about switching power supply, the input voltage supply lines added to the large inductor, although to some extent, separated out the role of DC component, but also affect the SMPS to work properly.

II. Although the switching power supply with high efficiency, but after all not 100%, and switching power supply chip thermal resistance is relatively small, heat dissipation is relatively poor , so be sure to calculate the system voltage and current required to calculate the power consumption of the system , and then calculate the efficiency curve in switching power consumption on chip power consumption. Thermal resistance calculated by the temperature of the chip over the chip can withstand the temperature. Then leave a margin case, select chip.