# Filters and DC/DC Converters in parallel

• Runei
In summary, the conversation discusses the need for galvanic isolation between the primary power input and loads in a power distribution unit. The individual is designing a unit and is considering using a DC/DC converter with a built-in EMI filter, but also needs a separate 28V to 28V converter for a stepper motor. The individual has concerns about the interaction between the two filters and seeks input from others on a forum.

#### Runei

Hello there people.

Hopefully someone will have a bit of insight into how a possible solution to my problem could look.

Im designing a power distribution unit for a piece of equipment, and there has to be galvanic isolation between the primary power input and the loads.

I have a DC/DC Converter with a built in EMI Filter that converts from 28Vdc, to 5V,+12V and -12V. These voltages will be used to run various electronics such as microcontrollers, op-amps, sensors and the like.

However, there is also a stepper-motor involved that needs to run on 28V. And since we need galvanic isolation and I am not interested in building a separation transformer (neither is my boss), we need a 28V to 28V DC/DC Converter. I found one, but now the problem arises at the EMI filter. Since the 28/28 converter has no built in filter, I am thinking I will need an external one.

But since both converters will run from the same 28V power source, I am thinking that the filter coefficients will be changed when they are connected thus in parallel.

Here's a picture of the setup. Any thoughts?

https://www.physicsforums.com/attachment.php?attachmentid=61188&stc=1&d=1377603320

#### Attachments

• untitled.bmp
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If the source of your 28V power is low impedance (most likely it is), then the two parallel filters will not interact much with each other.

1 person
Thank you very much for your response berkeman :)

## 1. What is the purpose of using filters and DC/DC converters in parallel?

The purpose of using filters and DC/DC converters in parallel is to improve the overall efficiency and stability of a power supply system. Filters are used to reduce noise and ripple in the output voltage, while DC/DC converters are used to step up or step down the voltage level as needed. By using them together, the output voltage can be regulated more accurately and the system can handle a wider range of input voltages.

## 2. Can any type of filter be used in parallel with a DC/DC converter?

No, not all types of filters are suitable for use in parallel with a DC/DC converter. The filter must have a high enough impedance at the switching frequency of the converter to prevent interference. Generally, only low-pass or band-pass filters are recommended for use in parallel with DC/DC converters.

## 3. Are there any risks associated with using filters and DC/DC converters in parallel?

Yes, there are some potential risks to consider when using filters and DC/DC converters in parallel. One risk is the possibility of instability caused by interactions between the two components. Additionally, if the filter is not properly designed, it may introduce additional losses or affect the converter's regulation. It is important to carefully select and design both the filter and converter to avoid these risks.

## 4. How do I calculate the values of the filter components for use in parallel with a DC/DC converter?

The values of the filter components can be calculated using the specifications of the DC/DC converter and the desired filtering characteristics. It is important to consider the converter's switching frequency, output current, and desired ripple and noise levels when selecting the values of the filter components. Simulation tools or design guides can also be helpful in determining the appropriate values for the filter components.

## 5. Can multiple DC/DC converters be used in parallel with a single filter?

Yes, multiple DC/DC converters can be used in parallel with a single filter. This can be useful in applications where a high output current or multiple voltage levels are required. However, proper design and coordination of the converters is necessary to avoid issues such as current sharing imbalances or voltage differences between the converters.