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Thread: sg3525/ir2110 half bridge

  1. #1

    sg3525/ir2110 half bridge

    hi everyone
    i use this schematic to build a half bridge power supply.
    but i have some problems and need some helps.
    first problem is feedback.i think this feedback is not good beacause whit this feedback transformer produce a noisy sound like"tik-tik-tik"about twice every second.
    i read some where this feed back dosn't control duty cycle and it just turn pwm on or off but i need a feedback that control duty cycle
    without feedback there is no noisy sound.
    help me to change feedback.what should i do?

    ----
    is there any problem or worng parts or circuits in this schematic?which part?and what is the correct part?
    ----
    i change this schematic a little bit.
    my primary winding turns is 19 and secondary is 8*2
    i use a etd 39 core
    target output voltage is 45*2
    i change frequncy to 80 KHz
    Schematic.jpg

  2. #2
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    @ Yoosef

    Welcome to DIY smps.

    Yoosef. I see some things that are not right in what you just said.
    1) Where did you conclude that the core you are using ETD39 needs 19 turns for the primary?
    2) What is your input voltage?
    3) Does your smps work with the feedback disconnected?

    Give me some answers and I may help you.

  3. #3
    Quote Originally Posted by Silvio View Post
    @ Yoosef

    Welcome to DIY smps.

    Yoosef. I see some things that are not right in what you just said.
    1) Where did you conclude that the core you are using ETD39 needs 19 turns for the primary?
    2) What is your input voltage?
    3) Does your smps work with the feedback disconnected?

    Give me some answers and I may help you.
    hi
    1-I calculate primary by "V=4NFBA" formula
    2-my input voltage is 220VAC
    3-my smps works fine without feedback and i connect a 300 watt load and voltage droped about 20 volt which is normal.
    but now by this feedback transformer has a noise(like turning on/off) and output voltage change continuously beetwen 40-45 each rail

  4. #4
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    Quote Originally Posted by yoosefheidar View Post
    hi
    1-I calculate primary by "V=4NFBA" formula
    2-my input voltage is 220VAC
    3-my smps works fine without feedback and i connect a 300 watt load and voltage droped about 20 volt which is normal.
    but now by this feedback transformer has a noise(like turning on/off) and output voltage change continuously beetwen 40-45 each rail
    1) I think you made a mistake with the number of turns for the primary winding. Usually an ETD39 core takes around 28 to 30 turns for the primary winding. Are you sure it is an ETD39 not something else? DO you know the core material?

    2) if you have few turns the core may saturate and heat up quickly. At 80Khz we do not usually go more than 1600 guass (0.16 tesla)

    That circuit I tried it also and I experienced the same thing.

    1) I suggest you put a 10K multi turn preset in line with the zener diodes to find the right value of the resistor. The balance here is not good and it is opening and shutting suddenly the pulse width

    2) Put a small capacitor across like 0.47uf entering the diode for the opto coupler for start and see if it tames down a little bit.

    3) You must have a small load at the output.

    4) You should use an output inductor with each rail I guess 20 to 30uH each. I hope you fitted these.

    Try these for now and come back with your findings

  5. #5
    Quote Originally Posted by Silvio View Post
    1) I think you made a mistake with the number of turns for the primary winding. Usually an ETD39 core takes around 28 to 30 turns for the primary winding. Are you sure it is an ETD39 not something else? DO you know the core material?

    2) if you have few turns the core may saturate and heat up quickly. At 80Khz we do not usually go more than 1600 guass (0.16 tesla)

    That circuit I tried it also and I experienced the same thing.

    1) I suggest you put a 10K multi turn preset in line with the zener diodes to find the right value of the resistor. The balance here is not good and it is opening and shutting suddenly the pulse width

    2) Put a small capacitor across like 0.47uf entering the diode for the opto coupler for start and see if it tames down a little bit.

    3) You must have a small load at the output.

    4) You should use an output inductor with each rail I guess 20 to 30uH each. I hope you fitted these.

    Try these for now and come back with your findings
    1-there is no problem with core saturation or primary winding.the core works at 2000 guass and even can work at 5000 guass without saturation(pc40 material)core didn't get warm and transfer power without problem
    the only problem is feedback and i should redesign it.
    this feed back just work at positive output(above target voltage)and i need a feedback to control output voltage continuously by decrease/increase duty cycle(for example using TL431 but how??)
    2-i have a small load in output / i use a 28uh inductor in output for each rail

    just should change this crude feedback and need help for new feedback design

  6. #6
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    Quote Originally Posted by yoosefheidar View Post
    1-there is no problem with core saturation or primary winding.the core works at 2000 guass and even can work at 5000 guass without saturation(pc40 material)core didn't get warm and transfer power without problem
    the only problem is feedback and i should redesign it.
    this feed back just work at positive output(above target voltage)and i need a feedback to control output voltage continuously by decrease/increase duty cycle(for example using TL431 but how??)
    2-i have a small load in output / i use a 28uh inductor in output for each rail

    just should change this crude feedback and need help for new feedback design
    I am posting a pdf file for you to take an idea for the feed back circuit. This I tried and works. The schematic is from a DIYsmps member Carlos Bettecher.

    Bettecher_1Kw_Smps correction.pdf

    The only mistake I can see here is that R14 should be tied to pin 6 of the IR2110 instead of ground

    Regards Silvio

  7. #7
    Quote Originally Posted by Silvio View Post
    I am posting a pdf file for you to take an idea for the feed back circuit. This I tried and works. The schematic is from a DIYsmps member Carlos Bettecher.

    Bettecher_1Kw_Smps correction.pdf

    The only mistake I can see here is that R14 should be tied to pin 6 of the IR2110 instead of ground

    Regards Silvio
    thank you very much Silvio
    this pdf helps me very much and now i should calculate feedback resistors and capacitors and compensation parts based my circuit parts

    about R14 i think that is correct such as R12

  8. #8
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    Quote Originally Posted by yoosefheidar View Post
    thank you very much Silvio
    this pdf helps me very much and now i should calculate feedback resistors and capacitors and compensation parts based my circuit parts

    about R14 i think that is correct such as R12
    About R14 that is the gate source dumping resistor. This is fitted to the high side gate. the source of the high side gate is at pin 6 not ground. On the other hand the low side switch source is to ground so the dumping gate resistor is to ground. I hope this explains it.

    The 33v zener is fitted so that the TL431 does not see more voltage than it can handle.

    Cheers and good luck

  9. #9
    Quote Originally Posted by Silvio View Post
    About R14 that is the gate source dumping resistor. This is fitted to the high side gate. the source of the high side gate is at pin 6 not ground. On the other hand the low side switch source is to ground so the dumping gate resistor is to ground. I hope this explains it.

    The 33v zener is fitted so that the TL431 does not see more voltage than it can handle.

    Cheers and good luck
    i have a question
    can you explain how exactly this feed back work when output voltage is under or over target voltage?i need part by part(feedback) explanation at opto diode side and transistor side

  10. #10
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    Quote Originally Posted by yoosefheidar View Post
    i have a question
    can you explain how exactly this feed back work when output voltage is under or over target voltage?i need part by part(feedback) explanation at opto diode side and transistor side
    Well when I first tried this feedback circuit I asked myself the same question. What I found out was that the resistor before the zener has to be tailored in such a way to the point where the zener starts to conduct when it hits the target voltage. and feeding the reference, The circuit values shown are for 50v I needed 60v the resistor on the circuit shows a 33K resistor in my case I ended up using a 47K instead and got a 60v output.

    In your case I guess you have to go somewhat lower with the resistor. I suggest you insert a preset at first until you get the right resistor value than you can put a fixed one when the value is known. One other thing that I added was a 200nF cap across the zener and it helped a lot with a stable regulation. One other thing that I noticed was when giving the smps an continuous load at full power the output inductor started heating a bit and as the core changes the value due to heat the output voltage did drift a little.

    This I did not try but worth considering

    You can insert a voltage divider network with the output feeding an opamp input, the TL431 will be used as a reference for the opamp other input. A comparison is made with the reference and the output of the opamp will feed the opto directly. The supply rail for the opamp must be isolated from the one feeding the SG circuitry otherwise there will be no isolation on the ground point from high and low voltages

    Regards Silvio

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