Overvoltage Protection for Low Power SMPS

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Lately, I needed to extend the upper voltage rating of an SMPS (24V, 1A) from 250 to 380Vrms. So I added to it a circuit in series to act as an active high-voltage zener.

 

I tested the circuit on LTspice. But since I am not sure how to model the input of the AC-DC supply, I replaced it, on the schematic, with a resistive load. The simulation result shows, above a certain instantaneous mains voltage, a drop of about 200V and, below it, the drop reduces to a few volts. Both the voltage drop and the level at which the active zener is activated could be adjusted by varying 3 resistance values.

 

Then, I built the circuit and tested it with the SMPS in question (loaded from 0mA to 1A).

The overvoltage protection acted differently when the SMPS is used instead of the resistive load (in the simulation). I mean; although the protective circuit is added in series, the voltage on the SMPS input looks as if there were a high-voltage zener in parallel with it which lets its top voltage be rather constant/flat (say at 300V) while the input mains voltage is increased up to 400Vrms.

 

Do you think it will be a good idea to upload this small project in the project forum?

 

I asked this because the circuit has no AVR MCU (or alike; no programming). On the other hand, just a few engineers in the world may be interested in such sort of protection. And perhaps it is done already by someone.

 

Kerim

 

This topic has a solution.

Last Edited: Fri. Feb 7, 2020 - 03:46 PM
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indeed not much high voltage enthusiasts here, but it seems that with a changed zener the circuit could also be used for lower voltages, so sharing it here as common knowledge could be interesting. I am for one interested in what the schematic actually looks like, hahahahaha.

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I did something that is probably very similar - i used a mosfet in series and a handful of other bits that would effectively chop the top off the rectified dc waveform. Fairchild has an ic that does the same with the high voltage mosfet built in.

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"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Feb 6, 2020 - 09:09 PM
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KerimF wrote:
I asked this because the circuit has no AVR MCU (or alike; no programming).
Bleed to shunt bootstrap AVR VCC then switch by ZCD your preferred pass transistor?

AN_2508 : AVR182: Zero Cross Detector

 

edit : wild hair

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Feb 6, 2020 - 09:24 PM
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As long as it is a completed project, I see no harm in posting it to projects, you never know who may need it in the future.

Jim

 

 

(Possum Lodge oath) Quando omni flunkus, moritati.

"I thought growing old would take longer"

 

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Thank you, gchapman, for your references but I am afraid that Microchip has no right to open its door for me since more than 16 years. sad

After all, I doubt that protecting a standard AC-DC SMPS (100W and below for DC 5V, 12V or 24V) was needed in any market lately (excluding the one here where I live smiley ).

 

As Jim suggested, I will prepare the circuit files (Kicad and LTspice schematics) in order to upload them in the project forum.

 

But, as I noted earlier, the shape of the voltage waveform at the protected device input depends on the load characteristics.

In case the load is an SMPS (24V/1A; the one that I tested and use in a few sets I produce), the input sinewave voltage (as seen on a scope) is clipped as if there is a parallel zener (having high breakdown voltage and high dissipating power) though the added limiting circuit is actually connected in series with the load!

 

 

 

 

 

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You're welcome

KerimF wrote:
... but I am afraid that Microchip has no right to open its door for me since more than 16 years.
The SR086/SR087 datasheet has block diagrams; seems do-able with jellybean parts other than the IGBT.

FSAR001 is likewise and may be of interest.

KerimF wrote:
After all, I doubt that protecting a standard AC-DC SMPS (100W and below for DC 5V, 12V or 24V) was needed in any market lately (excluding the one here where I live smiley ).
Been stated that necessity is the mother of invention.

You're doing well ... may you stay that way.

Take care!

 


SR086/SR087 Adjustable Offline Inductorless Switching Regulators Data Sheet (page 2)

alternative avenue?

SR087SG-G Microchip Technology | Mouser

Distributors may copy datasheets unless the manufacturer requires distributors to link to home.

Distributors may also copy change notices, application notes, simulator files, etc.

 

"Dare to be naïve." - Buckminster Fuller

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 I replaced it, on the schematic, with a resistive load.

Hopefully you used a negative resistance, as a SMPS looks like a negative resistance loading value 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Salaam Kerim.

 

Might I also suggest that you include a pdf of your work. Some people do not have/use Kicad, but EVERYONE ( cheeky ) can read pdf files.

 

Shukran.

 

Ross

Ross McKenzie ValuSoft Melbourne Australia

This reply has been marked as the solution. 
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Last Edited: Fri. Feb 7, 2020 - 03:05 PM
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Why did you post that as a whole separate thread?!?

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Sorry awneil, it seems you didn't read all the posts of this thread.

 

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indeed not.

 

blush

 

Time to mark this thread as resolved, then.

Top Tips:

  1. How to properly post source code - see: https://www.avrfreaks.net/comment... - also how to properly include images/pictures
  2. "Garbage" characters on a serial terminal are (almost?) invariably due to wrong baud rate - see: https://learn.sparkfun.com/tutorials/serial-communication
  3. Wrong baud rate is usually due to not running at the speed you thought; check by blinking a LED to see if you get the speed you expected
  4. Difference between a crystal, and a crystal oscillatorhttps://www.avrfreaks.net/comment...
  5. When your question is resolved, mark the solution: https://www.avrfreaks.net/comment...
  6. Beginner's "Getting Started" tips: https://www.avrfreaks.net/comment...