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Thread: Audio smps 700w (IR2153)

  1. #61
    .... Silvio's Avatar
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    @ Steppler

    Some more considerations

    1) input soft start missing+ bridging triac or relay missing
    2) input fuse missing
    3) safety ground capacitors missing 2 X 2.2nF X1KV
    4) grounding of the negative output terminal missing
    5) 1uF capacitor in parallel with output capacitor missing
    6) Grounding of the SMPS is non existent.

    If something happens and the primary of the transformer shorts out with the secondary you will see God prematurely.

    Regards Silvio

  2. #62
    @ Silvio

    This is input power board:

    ipw.jpg

    Among other things include softstart. 2s delay relay bridged resistors 40ohm 20W.

    Fuse to rear panel.

  3. #63
    .... Silvio's Avatar
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    @Steppler
    That is much better. You showed a very basic schematic at first with a lot of things missing in it. By the way the pcbs you are making are very nice and looking professional.

    One other thing you should add is a 4.7nF capacitor from the high voltage ground to the negative ground of the secondary plus another capacitor 4.7nF from the negative of the secondary side to earth ground, this will protect both for EMI and also in the event of a short in the transformer windings (primary to secondary) it will find a path to earth ground and will trip the earth leak circuit breaker in the grid. One other choice is to ground the secondary negative terminal to chassis. If you have a double winding of say 30-0-30 then ground the center ground to earth ground. Take a look at my PDF file it can be downloaded on page 2 post #13. There I have a ground path which connects to chassis via the stand off pillars. Taking a general look you will see these capacitors I am mentioning, they are ceramic caps rated at 1kv.

    Did you get rid of the stray voltage?

    Regards Silvio

  4. #64
    I changed the transistors to IRF740, I added the snubber. Result? .... 90V !!!!

    I disconnected experimentally output coils and 2 capacitors ..... increase to 95V.

    And transformer is very hot.

    I will try to add ground capacitors.

    The experiment continues ........ my name is Don Quijote ......

  5. #65
    .... Silvio's Avatar
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    @ Steppler
    Did you wind the transformer yourself?

    This is very odd Iwound a lot of transformers and this issue never happened to me. As I said before without a scope you are blindfolded.

    The transformer getting very hot is not a good sign and it could be that something may be wrong with it. (There should be no gap in the center leg of the core for this topology (Half bridge) Try to change the IR2153 and see that it is genuine.
    Please check if the output diodes are in the right orientation as I am suspecting that you are having a voltage doubler effect.
    It could be also the case that the windings are in series aiding and doubling the voltage somehow. I am trying to figure out what may be wrong and these are only assumptions. The circuit is very basic and has been built by a lot of people but these mishaps have not been encountered before apart of a faulty chip or something that I mentioned before.

    Put a series 100w Lamp with your input wiring. You can attach it instead of the fuse. This will help in the event of something is wrong. The bulb should light up briefly and extinguish again on start up due to charging the main bulk and secondary caps. The filament should show no signs of glowing during operation of the smps without load.

    I suggest that you take a look at my Youtube video ( Winding small transformers for SMPS) This will help you out for a good safety transformer build Don Quijote LOL.

    Link https://www.youtube.com/watch?v=_K3ixhcTYFg&t=1s

    regards Silvio.

  6. #66
    I've just been glancing over this thread, but here is my thought.

    I'm assuming your input voltage is 220-240VAC. Rectified and filtered this would be around 340VDC, give or take a little bit. You are running a half-bridge topology, so the voltage being switched across the primary of your transformer will only be half of your input bus voltage, so about 170VDC. Now, given the details of your transformer, your turns ratio is 3.54:1, the maximum peak voltage coming from your transformer absolutely cannot be higher than 48 or so volts.

    Now, having said that, I can only think of two possibilities of what is going on here.

    1.) The primaries of your transformer accidentally got connected in parallel instead of in series. This would cause the output voltage to be doubled, but also would most likely cause the transformer core to saturate (or get really close to it) which would cause the output voltage to drop significantly under load and cause the transformer itself to get quite hot. This would also cause heating in the mosfets and could also cause them to fail.

    2.) The transformer is being driven as a flyback transformer. For example, if one of your mosfets isn't switching properly. These IR2153 chips tend to be quite fragile and I've seen many examples of the high-side driver just completely not working at all. If you've ever had a mosfet fail on this circuit, you should replace the IR2153 at the same time you replace the mosfets, because it is most likely failed also. In this case, if only your low-side mosfet is working, this could cause your transformer to saturate, run very hot, and due to the inductive flyback effect, cause a very high output voltage under no load conditions with a severe drop in voltage with any significant load applied.

    Your transformer only has a single secondary winding, so I'm not at all worried about the connections on that side. If the output diodes were reversed, it would either dead short the output (quickly killing the output diodes) or cause no output voltage at all.
    Without a scope you're just shooting off in the dark here, but those are my two ideas. Good luck and I like the professional board design.

    - Brad

  7. #67
    Hello I'm back.

    I measured transformer primary frequency ..... 92kHz !!!! That's weird !!! Rt=15k Ct=1n This is cca 50kHz. Puzzle ?????

  8. #68
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    Quote Originally Posted by steppler View Post
    Hello I'm back.

    I measured transformer primary frequency ..... 92kHz !!!! That's weird !!! Rt=15k Ct=1n This is cca 50kHz. Puzzle ?????
    Try to change the IR2153 and see if you have the same result, You can also change the timing resistor or capacitor until you get the right frequency

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