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Do you think this will work? My PI Circuit.

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  • Do you think this will work? My PI Circuit.

    I got an idea a few weeks ago and I wanted to make up a schematic,I got a program called gschem and it works pretty good.I made the schematic,I am still learning,I think this circuit will work.What do you think?If I have to use a voltage doubler to get above b+ for the reference voltage I'm ok with that,but I was going for minimum parts count.I figure the coil voltage at flyback Vin,will rise above the b+ supplied voltage divider Vref. Give me a lesson Carl.
    Attached Files

  • #2
    Hi
    Keep up the good work, im sure one of the lads like simon will put it on spice for you , why not build it and see what happens

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    • #3
      Originally posted by Brian Deese View Post
      I think this circuit will work.What do you think?
      It would depend upon a comparator type. With 393 it can't work - there is no biasing at output.

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      • #4
        Originally posted by Davor View Post
        It would depend upon a comparator type. With 393 it can't work - there is no biasing at output.
        Can you explain,I only understand the basics of comarator operation.I read the 393 datasheet,and did not see much difference from the 339.The 339 is the device used in the educational books I have.I have not chosen the device yet.

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        • #5
          Originally posted by Davor View Post
          It would depend upon a comparator type. With 393 it can't work - there is no biasing at output.
          Originally posted by Brian Deese View Post
          Can you explain,I only understand the basics of comarator operation.I read the 393 datasheet,and did not see much difference from the 339.The 339 is the device used in the educational books I have.I have not chosen the device yet.
          I think Davor is referring to the missing pullup resistor on the comparator output. Have a look at the datasheets for the LM393 and LM339. They both have open-collector outputs, and require a pullup resistor, usually 3k.

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          • #6
            Hysteresis,yes I left those out to simplify the schematic.I can insert those resistors no problem.I was most curious if the voltage divider schem is going to work.I will build it and see.

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            • #7
              Originally posted by Brian Deese View Post
              Hysteresis,yes I left those out to simplify the schematic.I can insert those resistors no problem.I was most curious if the voltage divider schem is going to work.I will build it and see.


              Hystereses, and adding pull-ups where there are open collectors, are two totally different animals. Not even close.

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              • #8
                I misunderstood,I think I have it now.

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                • #9
                  I see what I have done wrong here,the comparator is intended to sink current being an open collector.I intended for the comparator to source the current/voltage to drive the scr and npn. That is what the pullup is for right? so the 3k resistor sources most of the current to the load at output high.Correct me if I am wrong,I will mod the schematic right now.
                  Attached Files

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                  • #10
                    Circuitry around U1B is wrong. There is no time base and inverting input is too high.
                    I am used to PSpice/LTspice variants, and a bit less some other flavours. Most of the spice designs here are done in LTspice, and they are easily shared.

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                    • #11
                      Originally posted by Davor View Post
                      Circuitry around U1B is wrong. There is no time base and inverting input is too high.
                      I am used to PSpice/LTspice variants, and a bit less some other flavours. Most of the spice designs here are done in LTspice, and they are easily shared.
                      Sorry,hows this?
                      Attached Files

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                      • #12
                        Now many of the parts look familiar, but does it really work? I'd have to translate it to LTspice first to analise what's going on.

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                        • #13
                          This gschem program I am using has a simulator,but I just got it and I havent got that far yet. I plan to just put it on a breadboard and try it.

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