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How to protect a flyback SMPS's output for misconnection of 230VAC mains

Former Member

It is easy and clear to understand from the title,

 

I have a SMPS for an device, it works good but traders say in usage people allways misconnect such things without reading our asking anything even they are educated for that kind of jobs. So we need to protect our SMPS's output from misconnection of 230VA or anything?

 

SMPS is made with PI's TNY275GN, there is a MUR115 Diode looking to output and a parallal 150uF Al. electrolic Capacitor as usual. After that we have a DC/DC converter made with LM25011MY/NOPBLM25011MY/NOPB to limit current on a specifik value (we put that to control output's rise times and fall times in normal mode and current limit mode). After this LM25011MY/NOPBLM25011MY/NOPB converter circuit we connect our devices but we need to protect this output for 220/230VAC 50/60Hz mains with large tolerances. LM25011 circuit is the circuit when you write TI's main page 23-25V input and 17,5V/0,22 output select LM25011 with adjustable current limit from selections then you can see the circuit which needs to be protected from mains connection.

 

Is there any easy way anyone already know basicly?

 

Best Regards,

 

Tolga,

  • 0

    Hello Tolga,

     

    If I understand correctly you are concerned that a user might connect the AC mains to the DC output of your power supply. As far as I am aware there is no reliable low cost way to do this but there is normally no requirement in regulations to offer such protection. Consumer devices are protected by using completely different connectors for AC mains and DC outputs. OEM modules have no such protection and it is assumed that the customer will read the instructions.

     

    If you MUST provide the protection then you could consider a series connected fast acting fuse, some kind of current limiting device and a transorb or similar to clamp the voltage.

     

    Michael Kellett

  • 0 in reply to michaelkellett

    Yes, In standart we do not have to protect DC output from AC mains connection. But in lighting and automation industry, they say it is a big problem in factories and most devices are already protected from mains. That's why we want to add this feature. Our PSU works great on normal mode but have no any protection from AC mains misconnection. And it would be better without changing any item from circuit. For Ex. if a circuit which opens the line and do not allows to pass anything over 24V will be great. Any idea for selecting zener? TVS? and MOSFET or Transistor to open and close the line depends on connected voltage? It should work when we connect our SMPS 17V but circuit should be closed when we connect something over 20V or 24V(adjustable what requires)? This should also should not differ the circuit's normal operation.

     

    Here a basic paint description to understand better our need. There is enough place to add some circuit to output of our SMPS PCB. What can we add and protect that device? And it should keep working after disconnect the cables and connect true device?

    image

  • 0 in reply to Former Member

    I've done  a good deal of work in automation (and other fields) which use a large number of 24V DC powered devices and I've NEVER been asked to provide protection from mains applied in this way.

     

    Your problem is that when the mains is applied and your voltage clamp operates there is nothing to limit the current except for any series resistance you add for that purpose. If you used  a PTC device like Farnell 1345914 you must limit the maximum current to 20A which means the series R would need to be at least 12R which would seriously compromise the way your supply works.

     

    You could put  a diode in the ouput path so that your supply can only source current, that will deal with the positive half cycle of mains and a P channel MOSFET able to take 400V or more which you must arrange to switch off as soon as the output voltage of your supply drops below zero. It's going to be difficult and expensive - but rather fun ! (You may need to take the feedback from after the diode and MOSFET if you need an accurate output voltage and then you will need to use components that can take mains voltage and protect the regulator from the huge feedback signals.)

     

    Michael Kellett

  • 0 in reply to michaelkellett

    Yes the funny way you advised is looking like my ideas also. I had thought a diode looking to smps's output to block positive cyle of mains and a zener , transistor, mosfet circuit to block positive voltage from notr to line?

     

    Or a circuit like picture can also protect the circuit enough? Need to not work when mains is connected and can work normally after correcting the connection?

    Diode and MOSFETs should be able to stand against 220VAC,

     

    I think i also need to add a zener between - to + connector to open base of the transistor.

    Anyway i am gonna handle this from fun way if PTC thing does not work. Ordered some PTC will come tomorrow i hope. But i don't know much what they are really.

     

    image