2kW Full Bridge Converter

Discussion in 'General Electronics Chat' started by Fethiyeli, Feb 15, 2014.

  1. Fethiyeli

    Thread Starter Member

    Mar 16, 2013
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    Hi everyone, i have designed 2kW full bridge for my friend. He wanted me to design 2kW full bridge having +- 70V output. I have some issues as below;

    1) How can i bypass NTC thermistor via optocoupler and triac with timing circuit. For example, it needs to bypass thermistor after couple of seconds due to power dissipation problem.

    2) I need to add undervoltage inhibit for my UC3825 but i dont know how to do it. For example, i need to shut output down in case of low AC input voltage like 180VAC.

    3) Do i really need to add speed controlled fan for cooling ?

    If you can check my circuit completely and say my faults, it will be very helpful for me =)

    Thnx.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    For timing just built a bistable using 555. It's simple.

    Speed controller is your opinion. You can very the speed with heatsink temperature.

    What does ur circuit do besides consuming power.

    Does it use DC to AC conversion ?
     
    Last edited: Feb 15, 2014
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  3. Fethiyeli

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    Mar 16, 2013
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    Yea it converts AC to DC. I thought using 555 but in simulator, proteus, i couldnt get any proper result. Also, i have found some speed controller via NTC thermistor. What else should i take into account ?
     
  4. R!f@@

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    Apr 2, 2009
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    Why do you go into trouble of using H-bridge to convert AC to DC..? :confused:

    I thought H bridge are used to convert DC to AC as in Inverters.

    If it's AC to DC why not use a 2KW Transformer ?
    You can get ± 70VDC quite easily.

    Besides, a thermistor is not appropriate for tht diagram. I would use a resistor and a relay to bypass the surge limiter
     
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  5. Fethiyeli

    Thread Starter Member

    Mar 16, 2013
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    No, H bridge can be used for AC to DC as well.

    2kW 50Hz transformer would be pretty large and my friend has a thesis that includes 2kW SMPS design. Therefore, he wanted me to design that SMPS.

    Maybe it will be funny, but i have never used relay before. I have no experience with relays =) and I have no examples of how to use them. I have heard that strategy though.
     
    Last edited: Feb 15, 2014
  6. R!f@@

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    Apr 2, 2009
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    You are doing ur friends thesis.?

    So u are doing an SMPS.
    An SMPS is simple than a H Bridge one, I think.

    But I will address ur issue.
    U want the thermistor to limit surge current, right ?
    You can use a power resistor or a thermistor for this.
    By passing is best done with a relay as it simple bypasses the surge limiting component through the relay contact thus eliminating that component from the circuit.
    All you need is a Transistor, a relay (properly rated for) and some resistors and a capacitor.
    You simple wire the circuit to charge the capacitor which is wired to the base of the transistor. As the cap charges to the pre determined voltage the transistor will switch on the relay.
     
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  7. Fethiyeli

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    Mar 16, 2013
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    Yeah, i am doing an SMPS for his thesis =) I need to limit surge current as you said but i am in stuck how to do it efficiently but i will do your solution. Unfortunately, i have no component to implement. Thnx.

    Do you know anything about how to shut my UC3825 down for low AC input like 180VAC ?
     
  8. R!f@@

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    Apr 2, 2009
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    Check the pdf. This something I made but it has evolved into something else.
    It's just to show you the basic idea.
    Ckt in question is labelled Inrush Current limiter.

    The Tr T5 and it's components forms the delay circuit.
    The cap C12 charges as the power is applied. After around 2 seconds the transistor turns on and switches the relay K2 on.
    The relay contacts are wired across the Power resistor R13 which is between bridge and smoothing caps.

    The idea is to limit the inrush charging current as the caps are pretty big. The current is limited by the value determined by R13. And after around a second or two the relay bypasses the resistor applying full voltage to caps and it stays tht way until the power is cutoff.

    This is the basic idea and you can use it too.
    But you need to calculate the Surge resistor value or use the thermistor you have in mind.
    The issue you would get is the Supply you would use as this will determine the timing ( mainly C12 & R22 Value too ) which the relay will switch on.
     
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  9. R!f@@

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    To shut off AC is simple.
    But need to check ur diagram though
     
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  10. Fethiyeli

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    Mar 16, 2013
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  11. takao21203

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    Apr 28, 2012
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    http://failblog.cheezburger.com/

    Sure, 2kW, never used a relay, get a paper from the thesis + crimp some wire terminals for 2kW and hope for the best.

    3) Do i really need to add speed controlled fan for cooling ?

    I made a 300 Watts SMPS and just left the fan blowing all the time. Main reason it was used for a purpose all the time.

    A paper from a thesis should certify that person in question is highly qualified to provide solutions to technical problems.

    At first, you or your friend need to learn how to proceed using professional approach.

    - Write a specification
    - Research existing products, schematics, components
    - Build prototypes + test them + create doumentation
    - Compare results to specification
    - Design the solution
    - Do a field testing for at least some months

    For instance 2kW is called a "power class". you need to collect information about the aspects dealing with a "power class".

    with professional approach method, you can build, design or repair about anything you wanted to.
     
  12. Fethiyeli

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    Mar 16, 2013
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    I dont need ur help =) Thnx anyway. No need to be arrogant =)
     
  13. takao21203

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    Apr 28, 2012
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    Sorry for being arrogant and Thnx for your reply. I won't write additional replies to your thread + hope it works out anyway.
     
  14. Fethiyeli

    Thread Starter Member

    Mar 16, 2013
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    I have completed cut off circuit which shuts down to circuit when AC line is 180VAC or 23.11VDC and 242VAC or 31.11VDC. I have simulated in proteus and it works nice. I have also added hysterisis so that circuit activates itself above 24VDC and below 30.5VDC.

    [​IMG]
     
  15. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    First I have to ask, why 2000W? That is a pretty tough job to do without any experience.
    Second thing, to pull this off you will at least need an isolation transformer, so that you lower the risk of accidentally electrocuting yourself in the process. Another thing will be a test load that can handle the 2000W.

    But the most important thing will be the transformer. You will have to design it yourself, and you would want it to be made by someone who knows how to wind it properly, and overall it won´t be cheap.
    When do you need to have this working?
     
  16. Fethiyeli

    Thread Starter Member

    Mar 16, 2013
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    Actually i do not know why it is 2kW. His teacher just wanted it as 2kW. Actually i have designed 1kW push pull SMPS but ı couldnt test it completely. I have designed all of things according to pressman's book and power supply cookbook. I think we have about 3 months for final implementation.
     
  17. Fethiyeli

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    Mar 16, 2013
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    Last edited: Feb 24, 2014
  18. R!f@@

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    Please resize the image to 800X600 before posting.
    Some of has does not have the luxury of not running out of Monthly data limit.

    You can always post the link to high res images for those who need to.
     
  19. R!f@@

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    You use a 24V voltage relay and drive from the 20V relay.
    Will be cheaper and efficient.
     
  20. Fethiyeli

    Thread Starter Member

    Mar 16, 2013
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    oh yea i will fix it.

    what about negative rail feedback ? :D

    Is that correct ?
     
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