Regarding the application report slaa391, I am implementing the capacitor supply from page 3, figure 2.My question to you is what is the purpose of the inductances (ferrite) and the potentiometers connected between each phase and the neutral point.
I'm quite confused because I couldn't find reference to any of these components in related application reports or in the forum.
Thanks in advance,
This circuit is explained in much more detail in this app note: http://www.ti.com/lit/an/slaa024/slaa024.pdf
I will move this post to the isolated forum, where these types of supplies are more common. The ferrite is likely for EMI/EMC reasons.
The SLAA391 doesn't appear in my search of TIs documents. Can you send a copy of the document?
I received a copy of SLAA391 and have taken a look at it. I am not familiar with the design. My best guess is that it is to prevent high frequency transients form entering the system.
Sorry I really can't help here.
Thanks for replying, indeed the inductances together with the potentiometers stand as a low-pass filter to high-frequencies. But I'm new to this area and I thought it would be best to ask someone before connecting each phase voltage to the neutral point through a resistance. This is where it gets tricky, I must have the frequencies of the signal up to 3kHz, and in order to have that the potentiometers must be of 10 to 100 ohm (assuming a value of few mH in each ferrite), this would likely lead to a short-circuit between the phase voltages and the neutral voltage... the obvious solution is to increase the values of the ferrite, but I know what consequences come from that, hence my question.
Thank you for replying, I've read through slaa024 but unfortunately it makes no reference to the potentiometers or ferrite.
*correction* ...I don't know what consequences come from that, hence my question.
Since I am unfamiliar with the design and would only be guessing I have forwarded your question to someone who might be able to answer. Unfortunately he is in Europe so I don't expect an immediate answer.
The "potentiometers" are incorrectly drawn. They are actually surge suppressors (VDRs). The ferrite inductors in the the three phases are bead inductors. These and the larger inductor in the neutral are for EMI and RF suppression purposes. In particular they are needed to avoid destabilising the MCU during the kind of EMI attack simulated in the standard fast pulse transient tests. The one in the neutral lead could probably be a lot small.
I hope the helps.
I does help a lot, thank you very much.
Do you happen to know what are the typical values for the ferrite inductors and the VDRs?
All content and materials on this site are provided "as is". TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with regard to these materials, including but not limited to all implied warranties and conditions of merchantability, fitness for a particular purpose, title and non-infringement of any third party intellectual property right. TI and its respective suppliers and providers of content make no representations about the suitability of these materials for any purpose and disclaim all warranties and conditions with respect to these materials. No license, either express or implied, by estoppel or otherwise, is granted by TI. Use of the information on this site may require a license from a third party, or a license from TI.
TI is a global semiconductor design and manufacturing company. Innovate with 100,000+ analog ICs andembedded processors, along with software, tools and the industry’s largest sales/support staff.