Should You Connect Grounds in a Power Supply?

Technical Consultant Zach Peterson is talking power and ground supplies today. How do you connect ground regions in a power supply, what's the difference between isolated and non-isolated power supplies, and how do Y-Capacitors come into play? Zach covers all this and more.
0:00 Intro
1:09 Non-Isolated Power Supply
3:08 Isolated Power Supply
5:25 Linking Grounds
9:26 Y-Capacitors
11:45 Connecting the Grounds
How to Connect Grounds in an Isolated Power Supply PCB Layout: resources.altium.com/p/how-co...
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[@andrasparanici5491]

I think these videos are a must for PCB Designers.

[@JohnScherer]

Thanks for all these videos you do and have done Zach! As a hobbyist doing PCB design mostly for the Amateur Radio community, its tough to find good information on best practices with regards to board layout, grounding, etc so most of the time I just wing it. That practice can lead to bad habits and your videos help correct some of that for me. Your videos are first rate and a big help for someone like me with little practical knowledge on the subject, they provide the answers to question that I wouldn't even know who to ask.. I wish you had a video series where we could submit a board layout to you and have you review it and provide feedback. That would really be a huge help!

[@leeslevin7602]

Awesome 👌, thank you, my colleague and I were having a debate on this very topic, discussing if we should bond the chassis ground to 0V, Star configuration etc. Your explanation will put our minds to rest 😁.

[@FailCommando]

Thank you very much for that video. I have actually asked myself that question a vew weeks ago. Also thank you very much for your great supportof students with the student license. It was a great help during my undergrad!

[@x1kianx1.]

Thanks because of you, I solved my problem

[@nishadrangnekar6933]

Thank you zach. This is the exact information i was seeking after for my Induction board design. I had faced issues with floating grounds earlier which i had used a y1 cap from my control ground to the PE. It had solved mostly my ground lift problems.

[@AltiumAcademy]

Glad it helped!

[@pouyaabdoollahy9218]

Very nice It was great, this amount of knowledge and information conveyed was unparalleled. I love your channel❤️❤️❤️❤️❤️

[@AltiumAcademy]

Thank you so much 😀

[@muhammadkamran9152]

Nice and easy explanation, Thanks

[@AltiumAcademy]

Glad it was helpful!

[@shahzaibzahid665]

Great Video Man. Thanks a lot

[@mrechbreger]

I know this is pretty old but how would you classify the leakage current to eg. old applications like DVD players or VCRs? I usually measured like 80-90V on the enclosure with very low current of course. Enclosures are usually not grounded of those applications. The voltage will collapse as soon as it's properly grounded of course. Examples who made such applications are Sony, Panasonic, etc.

[@jluke6861]

great video. Thank you.

[@AltiumAcademy]

You are welcome!

[@gbengaakeredolu7440]

hii, very insightful video indeed. How about if your system is purely battery powered, and there is no other power source around. There are analog inputs from field device. Does this require isolation?

[@beeslikehoney123]

Thank you, Zach! Super clear and helpful info. Just wondering though - is there ever a scenario to put a resistor in series or parallel to the capacitor that is connected between Secondary GND and Chassis GND? I seem to recall that being done on designs that I've come across. Thanks again.

[@crimpers5543]

Yes. A resistor will actual dissipate the charge. Otherwise a capacitor will simply hold the ESD charge.

[@crimpers5543]

an ESD event on the DC side ground will simply charge the capacitor. It's not going to "discharge" the ESD thru ground. You should use a resistor if you want to actually get rid of the excessive charge.

[@philiptong4978]

may be an inductor in series with the resistor to reduce that primary ground noise from getting in

[@yetanotherPC]

It will dissipate through the capacitor as leakage current over time

[@uricohen5463]

you are amazing , i love your videos

[@Zachariah-Peterson]

Thank you very much!

[@Dragonmastur24]

Is there a recomended equation for capacitor sizing to guard against esd in these various situations? Any rules of thumb to follow? For an ideal design do you want a large inductor and a resistor in parallel with an esd cap?

[@Zachariah-Peterson]

There is not really a good rule of thumb other than to look at the capacitor and its ESL/ESR values as well as its parallel resistor (if present). Those will limit the rate at which the capacitor can charge/discharge given an input edge rate. If the expected transient you need to shunt is faster, then the time constant needs to be smaller to provide effective protection. Transients can be pretty slow but with high voltage, so the edge rate is still large. If you are connecting across two grounds (primary and secondary) in a power supply, then the cap just needs to be much larger than the leakage/winding capacitance in the transformer. However be careful with this because there is leakage current that can cross that boundary, and leakage current can reach the user at the output side of the power supply. Some industry EMC standards, particularly medical, limit the amount of current that can pass to a user via leakage.

[@sudheerkumar5966]

Very good sir

[@AltiumAcademy]

Thanks and welcome

[@atluntadimanthoni]

Hi Zach...Learning a lot from your videos...How to calculate the capacitors value....?

[@Zachariah-Peterson]

You just need to make sure the capacitance is larger than the copupling capacitance between the coils in the transformer. If you are using an isolated power regulator chip, then you need to know the capacitance across the isolation barrier in the internal portion of the chip, which can be quite small. When the capacitor is larger, the impedance for higher frequency noise will be lower, so it can more easily travel back across the isolation gap through the capacitor rather than the transformer.

[@setia2258]

Hi Zak, we have an internal power supply and connect the earth to the chassis. Then we have an MCU and a motor driver. Should we connect the mounting hole (GND DC) to the chassis that is already connected to Earth?

[@Zachariah-Peterson]

If the mounting hole is connected to the system ground then you should not do this. You may allow some return current to flow in the chassis, which could then create a shock to the user. Earth connections are also not intended to be used to carry return current, it is intended for safety only. Since you are bringing in earth I might assume you are also bringing in AC and you have an isolated switching converter, in that case the primary side ground must not connect to earth. There are exceptions to this, for example if you did not have an AC connection with earth, you would want to connect a metal chassis to your system ground to eliminate any floating conductor. I have seen this connection made with a small resistor (milliOhms value) between system ground and chassis ground via the mounting hole.

[@setia2258]

@@Zachariah-Peterson Thank you

[@alvarodemontes3818]

thanks, how do you calculate the value of the capacitor ?

[@Zachariah-Peterson]

The standard guideline is to use a cap that has a larger value than the leakage capacitance of the transformer. The idea is to have higher frequency noise propagate back to the power supply return, rather than radiating or passing to an exposed connector where it could pass through the user to ground, so it is up to you to determine what the lowest frequency in the noise spectrum is and size the capacitor accordingly to provide low impedance across that isolation gap. The capacitor is typically a Y-type capacitor (that's the most commonly recommended I have seen), but the DC leakage current across the cap can also be important as this could create an annoying ESD shock if the user touches any plugs or connectors exposed in the system. This might also cause your design to fail some higher-end EMC requirements, such as in medical equipment.