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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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    Why do you like CHOP mode and not ALT mode?



    The power supply is a PWM power supply or a high frequency pulse power supply

    The power supply uses a UC3844N chip to Pulse a high frequency AC signals to an AC to AC transformer.

    UC3844N datasheet:
    http://www.alldatasheet.com/datasheet-pdf/pdf/25573/STMICROELECTRONICS/UC3844N.html
    http://pdf1.alldatasheet.com/datasheet-pdf/view/25573/STMICROELECTRONICS/UC3844N.html

    I'm using a Fluke 87 meter, I was trying to measure the AC voltages on the transformers primary and secondary windings

    There was no AC voltage on the secondary windings

    My Manager said it's because the Fluke DVM meter can't measure High Frequency AC , only very low AC frequency's to measure an AC voltage

    The Fluke DVM meter only measure AC voltages at low frequency

    Is this true and what kind of DVM meter measures High frequency AC voltages?
     
  2. Billy Mayo

    Billy Mayo Member

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    Another than was brought up today was that i noticed 2.0 ohm resistors only on 4 channels out of 10 channels

    It's like an audio mixer that has the same circuit just multiple channels

    The output transformer has 10 isolated outputs, 25 volts per isolated output with it's own ground per isolated channel

    Some of the circuits that get hooked up to the isolated output has 2.0 ohm resistors before it goes to the +VCC circuit where the other circuits are direct nothing in between the isolated transformer isolated output direct to the +Vcc to the circuit

    All the circuits are identical, the only difference is that some have a 2.0 ohm resistor inbetween the isolated power supply going to the circuit

    My manager said that the 2.0 ohm resistor make it high impedance for the power supply , which keeps it isolated more from the power supply

    2.0 ohm resistor is high impedance? i don't get it
     
  3. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    CHOP vs ALT: Older analog scopes when they did dual trace, ALT means that CH1 is swept and then channel 2. Used for high sweep speeds. In CHOP, a little piece of each channel is displayed alternately.

    87: True about 5 khz max. A meter to read high frequency AC: http://www.ballantinelabs.com/323meter.htm
    Try duty cycle, then. I didnlt check the specs.

    2 ohm resistors: I think there may be better explanations: 1) It helps isolate capacitive loads or 2) It gives some wiggle room. The output can't follow exactly, so it's better to drop some voltage across a resistor.
     
  4. dave

    Dave New Member

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  5. Billy Mayo

    Billy Mayo Member

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    Fluke 87 specs:
    http://www.electro-tech-online.com/custompdfs/2013/04/2161164_6116_ENG_B_WPDF.pdf

    Seems like the highest is 5Khz for measure AC voltage

    Any reason why they want the power supply to be at a very high frequency?



    How would a Troubleshooting tech know if zero volts is an open component or a short component?

    Cause a short to ground can cause components to measure zero volts, but so can an open component cause components to measure zero volts

    So how would a troubleshooting rule out its an OPEN component? because of why


    What is it called when a diode is not open or shorted , but measures a voltage like .175 volts in reverse or forward biased? it's not called a short or an open, its called what?

    What is it called when a component is shorted or open in a network , stage or circuit that causes other components around it has altered it's voltage or/& resistance for there normal values when taking measurements?

    I see this a lot when I'm troubleshooting, when a component is shorted or open it alters the resistance values of resistors, capacitors values, voltages, but what is the name of this?
     
  6. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Better syntheses of a sine wave.


    measure both sides relative to another reference.

    Normal or leaky. Shockkey diodes will have a low voltage drop. So will germanium diodes.

    1. "You missed a component" - when a component is shorted or open in a network.
    2. Resistor changed value for a resistor that did. No name for a short changing the value of another element. You might get away with "Shunt" or "Open"
     
  7. Billy Mayo

    Billy Mayo Member

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    What you mean by this?

    another reference where at? what reference would you use?

    No, it's not normal because it's a zener diode , normal is .7 volts, this bad diode had .175 volts tested reverse biased and forward biased, it's not shorted or open its called something?
     
  8. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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  9. Billy Mayo

    Billy Mayo Member

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    No, I took the Bad zener diode out of the circuit, I'm measure it out of the circuit which is .175 volts for forward and reversed baised direction

    the Diode is " out of circuit " it measure .175 volts forward biased and reversed biased what is this called ? its not a short or an open

    Yes I know the junctions are broken down in side, but its not called a short, leakage or an open, its called what?

    Also, what is this called when you get these types of "In circuit" measurements? it this circuit impedance's?

    When A component is shorted or open, it changes the "in circuit" measurements, what is it changing? the "in circuit" resistances change but is this called impedance?
     
  10. Billy Mayo

    Billy Mayo Member

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    A Switching Power supply adjusts the Pulse width to do output voltage regulation? how does this work?

    I'm not sure how the Pulse Width works to adjust the output voltage regulation in a switch power supply
     
  11. Billy Mayo

    Billy Mayo Member

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    Fluctuating voltage from a bad transistor


    If a circuit is fluctuating voltage, how do you know which transistor or IC chip is fluctuating the voltage up and down or at random?

    How would a troubleshooting tech, test and pin which transistor or IC that is cause this kind of problem?

    What is this called when a transistor or IC is fluctuating the voltage? the transistor is not shorted or open , so what is this called? or what state is the transistor or IC chip in when it's fluctuating either it's input or output?

    Using Freeze or a Heat gun on the transistor won't help troubleshoot this problem, I have tried that

    How would you guys approach this issue?
     
  12. Billy Mayo

    Billy Mayo Member

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    some filter caps , filter out the ripple frequency and other filter caps storage the power supply voltage

    I'm not sure how to tell the different between a filter cap that filters out the ripple frequency VS filter caps that store the power supply voltage, how can you tell?
     
  13. Billy Mayo

    Billy Mayo Member

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    To get the turn ratio of a power supply

    The formula is the transformers secondary voltage and divided by the primary's voltage = turn ratio

    Secondary voltage is 25 volts
    Primary voltage is 150 volts

    25 divided by 150 = 6

    Turn ratio is = 1 to 6?
     
  14. Billy Mayo

    Billy Mayo Member

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    in DVM diode mode, but its measuring 0.175 in DVM diode mode in both direction

    A shorted diode means the continuity is 0.2 ohms , it's like a bare wire

    Open Diode, measures OL , overload on the DVM meter

    When the diode has its junctions broken and it is at .175 volts it's not a short or open its called something
     
  15. Billy Mayo

    Billy Mayo Member

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    A switching power supply has a stage where is converts DC into an High frequency pulse

    Is this Stage/section that does this called an inverter or switcher?

    How does it Convert DC into a high frequency Pulse?

    The high frequency pulse is at what frequency range mostly? and does it have a Ripple frequency also riding on top of the pulse?
     
  16. Billy Mayo

    Billy Mayo Member

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    if a transistor internally is causing fluctuating, what internally is wrong with the transistor? and what kind of state is the transistor in when it's fluctuating on the collectors output?

    The Transistor is Partially Intermittent I guess you can say

    1.) The transistor is either fluctuating voltage AC or DC at the repetitive pattern
    2.) The transistor is fluctuating voltage either AC or DC at a random pattern
     
  17. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Billy:

    You should take apart a TO-3 transistor like a 2N3055. Take a good and a bad one apart. You might learn something.
    You can squeeze the top off with a vise at the edge.

    I'd guess that a wire bond broke loose.

    For all practical purposes, it's shorted.

    I can't make any sense out of this:

    nor can I make much sense out of this:

    It's usually expressed as N1/N2=V1/V2 or Primary/Secondary

    The turns ratio would be 150/25 or 6/1 or 6:1
     
  18. Billy Mayo

    Billy Mayo Member

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    Once your got the ratio , That part I'm confused about is trying to know for 1 volt on the primary it's how many volts on the secondary?

    1 volt divided by 6?

    And a 6:1 is stepping the voltage down by 125 volts, because 150 - 25 volts = 125 volts it stepped down

    150 volts is the primary voltage
    25 volts is the secondary voltage
    125 volts is the stepped down voltage
    150 - 25 = 125 volts

    So 6:1 means 125 volts?
     
  19. kubeek

    kubeek Well-Known Member

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    Man, do you even maths? 6:1 is steping the voltage down by a FACTOR of 6. That is, 150 to 25 is the same as 6 is to 1.
    That means, a 6:1 transformer puts 1/6 of the input voltage on the output. So you put in 150V and get out 25V, or you put in 1V and get out 0.1667V.
     
  20. Billy Mayo

    Billy Mayo Member

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    So 6:1 means 1/6 now? i don't get it

    When is it ever 6:2 or 6:3 , or is the secondary always :1?
     
  21. kubeek

    kubeek Well-Known Member

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    Really, have you ever had like fractions and stuff at school? 6:1 means just that, 6 volts on input, one volt on output; or 24V input 4V output; or 1V input 0.1666V output. Or 6 gazillion volts input one gazillion volt output.
    6:1 is the same thing as 1:1/6
    6:2 is tha same as 3:1. You are free to call it anything you want as long as the ratio is the same.
    6:3 is the same as 2:1 or 100:50. ditto
     

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