How to use series and parallel of dcdc power modules?

1. dcdc power module - how to use the power module in series

The isolated module power supply of DC output allows several power modules to be applied in series with their "positive" and another "negative", so that some conventional or higher voltage values can be obtained.

As shown in Figure 1 below:

dcdc power modules connected in series

The power module 1 is 5V output, the module 2 is 12V output, the series connection obtains 17V conventional high voltage, the total output current, that is, the power consumption of the load, cannot exceed the output rated current.

The nominal value of the power supply module, the output voltage cannot be output synchronously because the power supply of each module in series can not be output synchronously, and the reverse polarity output protection of Schottky diodes with small voltage drop is used.

The output ripple cannot be canceled, the superposition becomes larger, and the impact frequency (noise) generated at the output also becomes larger accordingly, and more filters are required in the application.

2. How to use dcdc power modules in parallel

If the power of the current dcdc power supply module cannot meet the existing actual needs, it is necessary to connect several identical module power supplies in parallel to achieve the required output power; a warm reminder is that

The modules connected in parallel require very similar characteristics, otherwise the power supply with high output voltage may provide the full load current, resulting in unbalanced load current of each module power supply, even if the output voltage is high.

The output voltage is very similar, because the difference of the output load with time and temperature change also makes the balance of the load power extremely unstable, so try to avoid parallel use.

As shown in Figure 2 below:

dcdc power module.jpg

Parallel connection of dcdc power modules

When it needs to be used in parallel, it should be reminded that the use of redundancy technology is a better solution (two power module output ends are connected in parallel through diodes, and the diodes allow at least one

When it fails, it does not affect another power supply module to continue to supply power to the load. This method is often used in key places where failure of the power supply module is not allowed); however, consider the voltage drop of its diodes to prevent

This kind of method not only causes a regular frequency impact and strong interference, so that the ripple is much larger than the ripple of its two dcdc power modules. At this time, an external capacitor is needed to reduce the ripple.

The better method is to connect the inductance in series at the output, which is not only smaller than the diode voltage drop, but also selects the inductance and capacitance very appropriately, which can effectively reduce the impact frequency and the respective ripples.

Article tags: dc-dc power module ac-dc power module custom power module