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Misc Electronic Questions

Discussion in 'General Electronics Chat' started by Billy Mayo, Apr 4, 2013.

  1. Billy Mayo

    Billy Mayo Member

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    I thought it was ringing also , but it's a switching power supply they call it ripple

    The waveform decays like a damping effect

    Does this waveform look normal to you for a switching power supply?

    This is the main waveform that will be converted to DC by using a cap.
     
  2. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Generally, you would like to minimize ringing. There usually is some. That much may be excessive, but as you say it's converted to DC, so it may not matter.

    You EZ-hook is too close to other interference sources. Not sure if they are EMI or RFI. In any event, you always want to cross the magnetic field lines perpendicular and not have any loops in your wire.
     
  3. Billy Mayo

    Billy Mayo Member

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    yes it looks like dc with noise ripple ripple on top, but its very small signal

    I'm not sure what those IC chips do, can you explain what is going on in this circuit

    There is two diodes D117, D119 that are feedback to change the PWM modulation signal to the U113 chip to regulate the output so the output is regulated

    I'm not sure how this work

    Switching Power supply pic#1.jpg
    Switching Power Supply pic#2.jpg
    Switching power supply pic#3.jpg
    Switching power supply pic#4.jpg
    Switching power supply pic#5.jpg
     
  4. dave

    Dave New Member

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  5. Billy Mayo

    Billy Mayo Member

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    Here is a 555 time with a FET on the output, what is the FET used for? i see this a lot when used with a 555 timer, they use a MosFET on the output of the 555 timer but why?

    555 time with FET output.jpg

    RC network on the ground buss going to the Earth , this RC network is a common mode rejection RC network for the whole circuits ground , the RC network is on the ground buss connect with Earth

    Have you seen this or heard of this?

    RC on the ground buss of whole circuit.jpg

    Zener Diodes to protect over voltage for both positive and negative cycles, The zener diodes keeps the positive and negative cycles amplitude at a set limit

    My manager said that the zener diodes are cancelling each other out, I'm not sure what he means by that

    If the feedback resistor that is controlling the gain gets open or shorted it's still going to saturate the op amp with those zener diodes right?

    zener diodes to protect from over volage.jpg

    Why did they use this PNP transistor? and not a NPN transistor? and will the base to emitter measure 0.7 volts?

    PNP pic#1.jpg

    Here is a couple more NPN transistor, will the base to emitter measure 0.7 volts?

    NPN pic#1.jpg
    NPN pic#2.jpg
     
  6. Billy Mayo

    Billy Mayo Member

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    Is this ground Impedance, my manager called it common mode reject the RC network of the whole circuits ground to earth

    He says that it helps out with the potential difference and that the whole circuit is not floating

    What does he mean by this?
     
  7. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The first 3. Need more time for the next 2.

    1. Easy to interface. It's probably a logic FET. I can't see what the other end is connected to.
    2. The Far end is a good AC ground, but poor DC ground. It's a decoupling circuit. That covers post #85, I think. manager is correct.
    3. The zener diodes are bidirectional clamps at +-(Vz+0.6). They are better put in the feedback loop.
     
  8. Billy Mayo

    Billy Mayo Member

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    Interface, do u mean the FET match the impedance or interfaces with the circuit and 555 timers output together better?

    How would u do the DC ground better?

    How do you tell what's an AC ground and what's an DC ground? the ground symbols look the same

    Mostly I would see a parallel cap to ground , that's when I know it's an AC ground

    Vz means the zeners voltage

    Zeners voltage + 0.6 volts = what?

    There bidirectional clamps , protect the op amp from what? if the feedback resistor opens or shorts the bidirectional clamps can't do much right? so what are they there for?
     
  9. Billy Mayo

    Billy Mayo Member

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    555 output with FET pictures
    555 with FET output pic#5.jpg
    555 with FET output pic#6.jpg


    AND gates used as a Flip flop circuit, I don't know why the designer didn't use a Flip flop chip instead he used AND gates and wired them up like a flip flop IC chip

    AND gate flip flop pic#1.jpg
    AND gate flip flop pic#2.jpg
     
  10. kubeek

    kubeek Well-Known Member

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    It is called ringing. If you measuerd this with those foot long probes, then no wonder it looks like that. The ground of the probe needs to be as short as possible to minimize the inductance and get good high frequency response. Try measuring the same thing without the hook clip, only putting the pin on the probe to the signal and using the spring ground lead attached to the nearest ground point.
     
  11. Billy Mayo

    Billy Mayo Member

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    Actually for that measurement I didn't use the Yellow Ez hook , so that is the waveform that goes to T100 and T102 and the output of T100 and T102 are that ringing waveform

    The Cap 117, C118, C119, converts that High Frequency ringing waveform into a 25VDC
     
  12. Billy Mayo

    Billy Mayo Member

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    What state or mode is this transistor in? since it needs an input signal to turn it on and forward bias the base - emitter?

    The transistor is off , not active , zero volts across base to emitter, no .7 volts

    The input AC voltage will make the transistor active and turn on but it will still measure zero volts across the base to emitter right?

    for Q2, it's less easy to determine whether other transistors have a permanent bias or not.

    If a transistor is not permanent bias , it gets forward biased , active, turns on, energized from an input signal

    Is the transistor a switch? or amplifier?
     
  13. kubeek

    kubeek Well-Known Member

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    Cap 117, C118, C119 in which picture?
    Too many pictures, too many questions.
     
  14. Billy Mayo

    Billy Mayo Member

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    Permanent bias
    0.7 volts from base to emitter as an amplifier
    0.7 volts from base to emitter as a transistor switch?

    Not Permanent bias
    0 volts from base to emitter as a transistor amplifier
    0 volts from base to emitter as a transistor switch
    ** Only gets forward biased 0.7 volts, active, turns on, energized the transistor from an input signal?

    What is this called when the transistor is not forward bias except when the input signal is applied?
     
  15. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    No, just do a search for "LOGIC FETS". The Vgs turn-on voltage is compatable with TTL and they require little current to tun on. Also some CMOS IC's require levels very close to Vss and Vdd. Adding a diode drop is too much.


    Chassis and Earth have two different symbols. Generally, in most systems, Earth and protective ground and some internal grounds are tied together at one place. There are times, however where one might want a clean low-current ground. Usually inductors and a resistor are used.

    What MIGHT be happening in your case, is that any AC transients are coupled through the capacitor. The resistor makes the other side a cleaner ground.

    Ground is a very mysterious concept to many people. In a hospital and other sensitive facilities, you may have a green for ground and also a green with yellow stripe for ground. There are ORANGE receptacles that are used for devices that need an "isolated ground".
    This is analogous to signal ground and Protective ground (Earth).

    It really is the right way to do things, but imagine every outlet in your house having a separate breaker, just to have the proper ground. What happens now, if a parallel circuit of outlets gets hit, it may take out devices in that circuit. If every outlet had their own ground, the devices would be safer.



    OK, this might be harder to explain. Lets go simpler. The unity gain OP amp. The input is applied to (+) and there is a wire from the output to (-). Maybe simple to understand. Maybe not. In any event, the OP amp tries to make the (-) input the same as the (+) input because of feedback. Easy enough.

    Now let's only apply a (+) signal, but put a reversed biased (4V Zener diode) in the loop. So, instead of a wire from out to (-) we have this diode. When the output gets bigger than 4V, the zener will start to conduct. Any voltage below that will effectively pass through. So, the Op amp could see a +12 V signal and clamp it at 4V to be compatible with say the input to TTL logic.

    The Back to Back zener diodes are clamps. Almost like a bidirectional TVS diode. Because the diodes are in series, there is an extra diode drop.
     
  16. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    They didn't cost anything. Extra parts re-used.

    PS: "The OP" is "The Original Poster"
     
  17. Billy Mayo

    Billy Mayo Member

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    So there is a difference between FET's and Logic FETS? they are two different things right?

    so if the input signal is +12 volts and the back to back zener diodes are clamps at 4 volts
    The input signal will only go up to 4 volts right?

    Is the back to back zener diodes clamping the input voltage or output voltage?

    How do you set the clamps voltage points?
     
  18. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Logic FETS just have lower full turn on voltages.

    ---

    Here is a simple example: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar3.html

    The clamps are crude. Basically set by Vz. Back to back 4v zener diodes would clamp at + and - 4.6 V approximately. They clamp the fed back voltage. If they were on the output, they would dissipate power. Same for the input. These are in the feedback path. Hardly no current.

    This is a very interesting part I ran across: http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar3.html

    I've considered getting one to play with.
     
  19. Billy Mayo

    Billy Mayo Member

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    You mean the FETS gate input threshold voltage is lower to turn on the FET?

    So Q3 FET is on the output of the 555 timer, but what does it do, why use a Logic FET on the output of a 555 timer?

    Does it Clean up the square waveform or sharpen the edges?

    oh ok , So the voltage rating of the zener Diodes sets the clamp voltage

    My manager said that since the diodes are in series but bi-directional is that they are cancelling each other out or they will cancel each other out because of the bi-directional configuration
     
  20. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    555: I can't see where the side goes.

    The Zener rating + 1 diode drop sets the clamp. You can even set them asymmetrical if you want.
     
  21. Billy Mayo

    Billy Mayo Member

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    Logic FET on the output of 555 pictures
    555 with FET output pic#5.jpg
    555 with FET output pic#6.jpg
     

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