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Simple pulsing supply that acts like a switching supply.

Discussion in 'Electronic Basics' started by Scott Wiper, May 23, 2004.

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  1. Scott Wiper

    Scott Wiper Guest

    I would like to know if this curcuit
    will work to the spec I have calculated.



    This is a simple pulsing power supply useing
    transistors set in darlington pairs with ZENER diodes as a referance voltage
    so I can shunt regulate voltage and sustain high currents when in
    use with minimal heating of the power transistors. Yes They will be fully
    mounted on a 4"* 8" piece of matel for heat sinking.

    A Breif expanation:

    (http://www.travel-net.com/~swiper/switch.gif)

    I will be useng a large step down transformer to reduce mains voltage
    to 16.0VAC at 80VA (Watts/5A) But I just got a 25.2VAC at 100VA (Watts/4A).
    This marked T1 on my schmatic.

    The filter will comprise of a large high current bridge rectifer and a
    10,000 uF cap C1 that will charge to 25.2*1.414=35.63VDC or
    16.0*1.414=22.62. This will be fed into Q1, Q2 and Q3 (2N3055). At 16.1
    referance it should have a emitter voltage of 14.0 volts with no load. D1 is
    th part of the curcuit protect Q3 from back voltage of the battery or
    batterys. If you use more AH of storage you should get a longer run times on
    the 5 volt section. B1's charge is controlled by R4 that useing the spec
    float of 13.5 -13.8VDC that is well with the specs of most lead acid
    batterys. D8 is to reduce B1 by .6volts so when it becomes fully gharged
    it's voltage will always be .6 volts less of the Vout from Q3. D8 will stop
    reverse voltage on Q3 as well.

    The perpose of C2 and C7,C8 is to smooth out voltage and reduce noise from
    the pulsing outputs from Q3 and Q5. The battery or batterys will the 5 volt
    part of the supply functioning with the constany frequency that is applied
    through U1(NE556) and U2(CD4013). U2 is a garrenteed 50% duty cycle at 1/2
    Frequency. The whole idea is to make a simple 5VDC UPS but with the features
    of a switching power supply. This one is going to power the swiper7000 light
    controller with ADC inputs.

    For better viewing and printing. http://www.expresspcb.com
    http://www.travel-net.com/~swiper/switch.sch
    Run you spyware utility because this one is loaded with it.

    Question 1.

    Will I have to place an inductor on both the 12 and 5 volt outputs as
    current tanks? (C1 C7 C8)


    Question 2.

    If inductors have to be used. Will they have to be placed in series with the
    output caps or in parrallel?
     
  2. First of all, you should review this tutorial on switching regulator
    fundamentals. It will answer most of your questions:
    http://www.national.com/appinfo/power/files/f5.pdf

    I see lots of other problems.

    Q1, with 35 volts on its emitter will never turn off with either the 0
    or +12 volt output of U2A. In fact, you are likely to turn U2 into an
    SCR that shorts its 12 volt supply by the current R7 will dump into
    its output.

    Any time you connect two capacitors together with a switch, there must
    be a waste of energy (in some combination of the switch's resistance
    and the capacitors' resistance) that equals the energy you transfer
    from one capacitor to the other. This is why inductors are put in
    series with such circuits.

    If Q3 really represents a good, low resistance switch, then when it
    turns on, the voltage on C2 will jump up to 9/10ths of the voltage on
    C1 when the switch closes. How do you imagine that the voltage will
    rise only to 14 volts?

    As to your note at the top about Q3, Q3 (or Q3 and C1 and C2) must
    dissipate about (35-14)*average current through Q3. Switching Q3 on
    and off doesn't help in this configuration (connecting two capacitors
    together with a switch).

    These same comments apply to the 12 volt to 5 volt reduction circuit,
    sdince it also connects two capacitors together with a switch.
     
  3. A shunt regulator is a regulator tha tis in PARALLEL with the output,
    yours is not.


    Pulsing will NOT cause less heat, as the heat is proportional
    to teh power dissipated, and the power = i x u x t, where, I is the current
    through the transistor, U the voltage across it, and t teh time it is on.
    For teh SAME amount of output current (average) after C2, you can for
    example have 3 A for 100% of the time, and 6 A for 50% of the time,
    So in the fist case power is 3 x U and in the secon example the same:
    3 x Iu * .5
    etc.
    So you 'switching' idea without the use of an inductor sucks, and brings
    no advantage whatsoever.
    JP
     
  4. errata:
    6 x I * .5 of cause
     
  5. Scott Wiper

    Scott Wiper Guest

    First of all, you should review this tutorial on switching regulator
    fundamentals. It will answer most of your questions:
    http://www.national.com/appinfo/power/files/f5.pdf

    I see lots of other problems.
    I see the mistake on Q1 I will have to add a reverse block diode before R7.
    This will be corrected.

    I have built a non pulsing proto type here
    http://www.travel-net.com/~swiper/5volt.gif. What I am attempting to do is
    turn the transitors on and on rapidly This enegy is dumped D4 that charges
    the battery or batterys. Transistor do funny things on their emitters. they
    have at tendency to drop .7 volts to what ever Base/Emitter drive voltage is
    applied. So if you Base/Emitter follow through two transistors it
    Vref-.7-.7=Vout. EG: Q2 and Q3. http://www.travel-net.com/~swiper/switch.gif

    This why audio amplifiers have their npn and pnp transistors set on common
    emitter with a no signal voltage of .65 volts to hold them off. There two
    ..5ohm resistors tying the emitters together to the speaker output from both
    + rail and the - rail.
    A reverse block will also will have to be placed on Q6 as well you will see
    the changes after this post. As for traansistor theory. I am dealing with
    mosfet types I am useing old fashioned plain bipolar types. These have a
    good charatoristic of limit emitter voltage that will allways be .7volts
    less then Vbe. What I am doing is useing a low frequency square wave at 50%
    duty cycle for short periods of time resulting in C2 will only charge to Vbe
    set Vref on Q2's base.

    So lets review bipolar transistors. Vc (Collector) this is the input is 35.6
    from the heavy stepdown transformer. Q2 and Q3 are in a base/emitter
    follower so the emitter voltage on Q3 will 16.1()Vref-1.4=14.7V this with Q3
    held on all the time. R2 to v+. What will happen when Q3 sees several amps
    on it's emittier it's going to heat up quite abit. By turning on and off Q3
    at 60 hutrz This will allow for up to 10Amps without the transistor getting
    so hot you can cook a "McDonalds Pork burger" (1.5A constant has been
    tested) on it like the other one put going "POOP" and with rotten small and
    white smoke.
     
  6. Scott Wiper

    Scott Wiper Guest

    The whole Idea Of my website is to keep it simple If I can achieve this
    simplistity I will reached the holely grail. I will be useing the spice
    simulator to test this theory out. If I can switch one voltage from a
    stepdown coil and to a logic voltage without inductors so be it. Bipolar
    transistor can have there tranfer of resistance set by Vbe even when they
    are set in darlington pairs. This when you have two Bipolar transistors with
    the base/emitter of QA following through QB. So Vref=16.1V set by zener
    diode. So Vc = 35.6VDC Where Q2 and Q3 are commoned. So here is the math.
    (Vref)16.1 - 1.4(VbeQ2/Q3)=14.1VDC(Ve Q3). This project is suppsed be a
    wanna be that acts like a switching supply, but it fact it's not. This why
    I will recommend that you put a large aluminum plate where you intend to
    mount the transistors oruse your case as a heat sink. They will get warm but
    not buring hot to cook Mcdonalds pork burgers on the caseing of the
    transistors. If they get to warm thats what 12VDC box fans are for.
     
  7. I had rather you follwed Mr John Popelish recommendation, and read a good
    book on switchmodes, or the link he gave you.
    In your circuit you can leave out the switching, and it would work better.
    At 3A your serial transistor dissipates 3 x 25 = 75 W.
    If you allow for 150 C degrees juncion temp in the transistor, and 40 C
    outside temp, you can rize 110 degrees.
    So your total thermal resistance is 110 / 75 or about 1.5 C / Watt.
    Substract the Rth for a 3055, the Rth for any isolation whasher,
    you are out of luck, the Rth for a 2n30055 is 1.5 and the Tmax = 200 (just
    looked it up), and the transistor will go kaput, because you ALSO need
    to add the Rth for the heatsink.
    In fact I think you CAN fry egs on a 75 W heater, think about it,
    how much is your soldering iron ;-)
    So pleae, yes it IS a good idea to use the LTspice, and feel free to ask more
    once you get indo switchmodes.
    JP
    y
     
  8. R.Legg

    R.Legg Guest

    I see no e4vidence of calculations.
    You are attempting to reduce circuit losses by passing all energy
    through a 'linear' regulator circuit only during phase angles that
    ensure a low voltage drop across the series elements. Capacitive
    storage is relied upon to control output droop during all other phase
    conditions.

    A large peak-to-average current waveform is required from the source
    and in all conducting elements of such a regulator. This produces
    agravated rms current values.

    Series elements that heat under the influence of average current will
    not be as severely effected by this method as those that heat up under
    the influence of rms current. Feel free to make your own estimation of
    the effect on simple square waves of equal 'average' value, but of
    reducing duty cycle.

    The last time I saw this miraculous technique demonstrated, you could
    smell the transformer varnish outgassing, due to straight copper
    losses and the resulting internal transformer rises. The effect has
    the same relative severity at all power levels.

    The only current proponents of this type of regulation (that I am
    aware of) is the 'Research and Development Centre for Hybrid
    Microelectronics and Resistors' - primarily for use in battery
    chargers, where ripple voltage and storage capacitance is not an
    issue.

    http://www.prz.rzeszow.pl/imaps2001/artykul/T_24.ZIP

    Note the number of taps and switches that are inevitably employed -
    effectively forming a multi-pulse system - all in an attempt to reduce
    the peak-to-average current and increase the useful phase angle of a
    power system. Note that no claim is made concerning input harmonic
    compliance, after the first order effects of series element
    overheating is adressed.

    http://www.cyf-kr.edu.pl/academic/OBRMHiR/imaps/data/txt/txt45.htm

    Power conversion expertise is not a noted strength of this
    institution.

    RL
     
  9. I have actually been thinking a bit, and in the old times (sixtioes)
    thyristors became very popular, and many a battery charger with these
    was designed.


    In such a case, you can probably leave out 90% of the comnponents,
    I remember Motorol had a nice application book for their thyristors,
    lets see how the web is:
    http://pemclab.cn.nctu.edu.tw/peclub/w3cnotes/cn06.電力電子簡介/html/cn06.htm
    Here you see the diagram, AND all the formula you asked for ;-)


    ac bridge thryristor resistor battery
    full wave in
    ______________________|\|_______________________\/\/\/\_________ +12
    | | | |/| | R2
    | | | \ |
    / | | | |
    \ <-- | ^^^^ pulse transformer 1:1
    / Uout | ^^^^
    \ 220k | | |
    | |-- | |
    |------| UJT | |
    | |-- | |
    | |____________| |
    === |
    | 220nF |
    | C1 |
    ------------------------------------------------------------------


    See, in this circuit the thrystor is turned on late in the AC cycle,
    so you can control the output voltage.
    You can replace the potmeter by a PNP current source, and control its
    input voltage.
    This way if you use an error amplifier and voltage reference, and filter,
    you have a switching in the sense that perhaps you wanted...
    R2 limits the peak current into the battery...
    UJT is an unijunction transistor, fro example 2n2646
    You will have to make sure the UJT does not get to much voltage, else use
    some divider, I think the 2n2646 is about 30V.
    http://www.americanmicrosemi.com/tutorials/unijunction.htm

    Anyways, the idea is that you trigger the thyrister when the half
    sinewave drops below the required output voltage (so after the zero
    crossing), always in the last 90 degrees...
    The potmeter with C1 forms the timeconstant.
    The UJT will conduct when the voltage on C1 reaches half the input here,
    and discharge C1 via the pulse transformer into the thyristor gate.
    A rather crude circuit, but it works up to 30 amps or so.
    JP
     
  10. Scott Wiper

    Scott Wiper Guest

    I used the formal that was supplied with the datasheet on the transistor
    selected I may have gotten it wrong. I am just begining to grasp the
    function and math.
    Your point is taken... I DID COOK a tranformer by over currenting the
    secondary winding it gave good white smoke and burnt varnish after the
    thermal fuse whent in the prinary. This is why I have placed a large ballast
    resistor on the positive terminal of the battery. My Prototype is working
    just fine even after I outgassed the varnish of a small 25.2 1A stepdown
    coil. I am surprised that the first transistor survived the smoking. The 2A
    transformer do even get warm with the ballast resistor on the battery
    positive terminal

    The only current proponents of this type of regulation (that I am
    aware of) is the 'Research and Development Centre for Hybrid
    Microelectronics and Resistors' - primarily for use in battery
    chargers, where ripple voltage and storage capacitance is not an
    issue.

    http://www.prz.rzeszow.pl/imaps2001/artykul/T_24.ZIP

    Note the number of taps and switches that are inevitably employed -
    effectively forming a multi-pulse system - all in an attempt to reduce
    the peak-to-average current and increase the useful phase angle of a
    power system. Note that no claim is made concerning input harmonic
    compliance, after the first order effects of series element
    overheating is adressed.

    http://www.cyf-kr.edu.pl/academic/OBRMHiR/imaps/data/txt/txt45.htm

    Power conversion expertise is not a noted strength of this
    institution.

    RL
     
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