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"Black" regulator

Discussion in 'Electronic Design' started by Mike Young, Nov 28, 2005.

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  1. Mike Young

    Mike Young Guest

    http://www.romanblack.com/smps.htm

    I have a few questions about the Black regulator described in the above
    article.

    -- What controls the switching frequency?
    -- What determines the relationship between the two capacitors?
    -- What transistor datasheet characteristics would indicate its
    applicability in that circuit? The article states that "hard turn-on" and
    "hard turn-off" are important. (Oddly, these aren't spec'ed as such.) Sure
    enough, playing around in SPICE, a 2N2222/2N2904 pair switches poorly, and
    works only under very light loads.

    Also, playing around in SPICE, the power dissipated in the load is off by
    almost a magnitude from the RMS power entering the circuit. For a 48V
    battery voltage source V1, RMS(I(V1))*RMS(V(V1)) gives about 16A, but the
    dissipated power in the dummy-load resistor is about 2.5A. The dissipated
    power in all other components seem suitably small, in the micro-, nano-, and
    milliamp ranges. I'm at a loss to find where the losses are. The PG() and
    PS() results are similarly non-sensical; less power enters the circuit than
    the load dissipates.
     
  2. Bob Monsen

    Bob Monsen Guest

    Sigh... the load current...
    There are 3 caps. The feedback cap should be 1/3 of the larger one, and
    the smoothing cap on the output shouldn't be much larger than 47uF, or the
    thing won't oscillate.
    The transistor needs to be able to pass the maximum current the inductor
    passes, which is dependent on the inductance, the load, the smoothing cap,
    and the frequency.
    My god, man, this thing is meant to be used with up to abou 100mA. Use a
    real SMPS controller chip. See the linear or maxim site. If you have
    ltspice (a free spice from www.linear.com), it has lots of example
    circuits for SMPS that you can study.

    The losses in a SMPS are usually in the pass transistor, the inductor
    (which has non-zero resistance and dissipates energy, despite what SPICE
    says) and the diode from ground. The pass transistor will dissipate huge
    amounts of energy unless it is turned completely off, or turned completely
    on. When it is partially on, the current is high, but the voltage across
    it is also high, leading to P = V*I being high. If you graph power in the
    transistor, you'll see what is happening. Your problem is probably due to
    the wimpy drive, causing the transistor to only partially turn on...

    ---
    Regards,
    Bob Monsen

    The chief aim of all investigations of the external world should be to
    discover the rational order and harmony which has been imposed on it by God
    and which He revealed to us in the language of mathematics.
    - Johannes Kepler
     
  3. Fred Bloggs

    Fred Bloggs Guest

    http://www.romanblack.com/smps.htm
    The way it is supposed to work is that the zener establishes a
    switching reference voltage at the NPN base. When Vout on the emitter
    discharges to a minimal Vbe~0.6V below NPN base due to the load, the NPN
    begins conducting, its collector current drives PNP base causing it to
    conduct, and the PNP collector current drives into the inductor, free
    wheeling diode, 2nF junction. It is assumed that this turn-on is fast
    enough so that most of that PNP current couples through the 2n into the
    junction of the zener, 6.8n, and NPN base. This is the bad part, that
    feedback current divides between 6.8n high frequency shunt and the low
    impedance of the zener, leaving just a fraction of the low frequency
    component of current to enter NPN base and regenerate the turn-on
    action. So it makes no sense to have things arranged this way.
    Continuing with the fantasy for the moment, what little feedback couples
    into NPN base, with gain greater than one BTW, causes more PNP
    conduction and more base drive until the PNP is saturated, and the full
    Vin is applied to the inductor, current continues through the 2n to
    sustain this conduction in some unknown way, and the current in the
    inductor builds up at (Vin-Vout)/L amperes per second. This is supposed
    to continue until Vout builds enough to back bias the NPN base, which is
    still receiving base current from God knows where, causing a negative
    regeneration of the NPN-PNP pair non-regenerative thingamajig, assisted
    by the diode clamp and inductor feedback pulling so much reverse current
    from base junction that the zener even loses bias, causing its voltage
    to fall so as to maximize the chance of Vout blowing through the NPN
    emitter-base junction in reverse mode. Maybe Roger Hamlett can explain
    things better, but the circuit is a hopeless kluge which in my
    estimation is probably working off parasitics due to sloppy construction
    practices along with misapplied component technology.
     
  4. Tim Williams

    Tim Williams Guest

    I agree with this, maybe an inductor in series with the zener, but then you
    need to account for that stored energy later in the cycle. I suppose the
    circuit works as-is because the output voltage doesn't change very fast so
    Vbe in series with Cout can have a lower dynamic impedance than the zener.
    from base junction that the zener even loses bias, causing its voltage
    Yeah, except for the peak is limited to the capacitive voltage divider
    ratio, and if it does pass ground level, the zener forward-biases and clamps
    the pulse. <G>

    Doesn't work for Vout > 12V or so, but you could add a zener across the EB
    junction to spare the transistor.
    LOL. You don't understand elegant circuits very well, do you? <G>

    Tim
     
  5. Terry Given

    Terry Given Guest

    apply a short to the output, and tell me again how "elegant" this POS is....

    Cheers
    Terry
     
  6. Tim Williams

    Tim Williams Guest

    A short circuit takes it out of the Standard operating region, thus this
    condition is invalid and can be ignored. <BG>

    Check the next page with the three-transistor model. It has current
    limiting.

    Tim
     
  7. Terry Given

    Terry Given Guest

    then simulate that, and laugh (I did).

    Cheers
    Terry

    PS ratshit gatedrive = ratshit power supply. QED.
     
  8. Ken Smith

    Ken Smith Guest

    Below is a LTSpice drawing for an even worse regulator. It has only one
    transistor. The total parts count is lower than the "black" regulator.


    Version 4
    SHEET 1 880 680
    WIRE -208 144 -208 112
    WIRE -208 240 -208 224
    WIRE -80 112 -208 112
    WIRE -80 144 -80 112
    WIRE -80 288 -80 224
    WIRE -80 320 -80 288
    WIRE -80 400 -80 384
    WIRE 0 288 -80 288
    WIRE 0 320 0 288
    WIRE 0 400 0 384
    WIRE 48 288 0 288
    WIRE 176 288 128 288
    WIRE 240 112 -80 112
    WIRE 240 208 240 192
    WIRE 240 240 240 208
    WIRE 240 400 240 336
    WIRE 288 208 240 208
    WIRE 384 208 352 208
    WIRE 384 320 384 288
    WIRE 432 208 384 208
    WIRE 528 208 496 208
    WIRE 528 368 528 208
    WIRE 528 400 240 400
    WIRE 528 400 528 368
    WIRE 528 480 528 464
    WIRE 672 368 528 368
    WIRE 672 384 672 368
    WIRE 672 480 672 464
    FLAG 384 320 0
    FLAG 528 480 0
    FLAG -80 400 0
    FLAG 672 480 0
    FLAG -208 240 0
    FLAG 0 400 0
    SYMBOL npn 176 240 R0
    SYMATTR InstName Q1
    SYMATTR Value 2N2222
    SYMBOL ind2 224 96 R0
    WINDOW 0 47 -15 Left 0
    WINDOW 3 42 13 Left 0
    SYMATTR InstName L1
    SYMATTR Value 220µ
    SYMATTR Type ind
    SYMATTR SpiceLine Rser=0.1
    SYMBOL ind2 144 272 R90
    WINDOW 0 4 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName L2
    SYMATTR Value 0.5µ
    SYMATTR Type ind
    SYMBOL zener -64 384 R180
    WINDOW 0 24 72 Left 0
    WINDOW 3 24 0 Left 0
    SYMATTR InstName D1
    SYMATTR Value BZX84C6V2L
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL res -96 128 R0
    SYMATTR InstName R1
    SYMATTR Value 680
    SYMBOL cap 512 400 R0
    SYMATTR InstName C2
    SYMATTR Value 33µ
    SYMBOL ind 368 192 R0
    SYMATTR InstName L3
    SYMATTR Value 220µ
    SYMATTR SpiceLine Rser=0.1
    SYMBOL schottky 432 224 R270
    WINDOW 0 32 32 VTop 0
    WINDOW 3 65 105 VBottom 0
    SYMATTR InstName D2
    SYMATTR Value 1N5818
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL cap 352 192 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C3
    SYMATTR Value 0.1µ
    SYMBOL res 656 368 R0
    SYMATTR InstName R2
    SYMATTR Value 50
    SYMBOL voltage -208 128 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 18
    SYMBOL cap -16 320 R0
    SYMATTR InstName C1
    SYMATTR Value 10µ
    TEXT 32 232 Left 0 !K1 L1 L2 0.7
    TEXT -254 506 Left 0 !.tran 0.1 startup
    TEXT 24 144 Left 0 ;A few turns of\nhookup wire\non L1
     
  9. Ken Smith said
    <snip>

    Just curious. How does one import this into LTSpice?
     
  10. Ken Smith wrote...
    If it's so simple, you can make an ASCII drawing so the rest of us
    can look at it and comment.
     
  11. Ken Smith

    Ken Smith Guest

    (1)
    Put the post into a file called "somethingorother.asc"

    (2)
    Use your text editor to snip off the stuff before and after the LTSpice
    stuff.

    (3)
    Tell LTSpice to open it.
     
  12. Ken Smith

    Ken Smith Guest

    Here it is:

    -----+------------------
    ! !
    \ )
    / )
    \ ) L1
    / 680R ) 220u
    ! ! 0.1u 1N5818
    ! +----!!----+-->!---
    ! ! ! !
    ! ! ) !
    ! ! )220u !
    ! K1 L1 L2 0.7 ! ) !
    ! L2 !/ ! !
    +----+----)))----! GND !
    ! ! 0.5u !\ e !
    /-/ --- --------+---------+---------- Vout
    ^ --- 10u 2N2222 !
    ! ! --- 33u
    GND GND ---
    !
    GND

    L2 is a few turns of hook-up wire on L1.
     
  13. Ken Smith said
    <steps snipped>

    Thanks!

    I'm finding LTSPICE on hell of an app.

    I've used Saber at work for years (ugh). Recently I was convinced to
    fire up PSPICE for a test drive. I immediately like it better and
    spent a few months coming up to speed. Then I stumbled across
    LTSPICE. Nice!

    I continue to be amazed at it's capability/cost/ease-of-use tradeoff.
     
  14. Ken Smith

    Ken Smith Guest

    It works quite well under "wine". It is very fast on my 64 Bit system.
     
  15. Ken Smith wrote...
    <shudder>
     
  16. Ken Smith

    Ken Smith Guest

    <shudder>[/QUOTE]

    I said it was worse didn't I. :)
     
  17. Terry Given

    Terry Given Guest


    I said it was worse didn't I. :)
    [/QUOTE]

    Yeah, but I didnt really believe you :)

    Cheers
    Terry
     
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