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New Improved +/-45V PSU

Discussion in 'Electronic Design' started by Harry D, Jul 18, 2013.

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  1. Harry D

    Harry D Guest

    Here is my 2W +/-45V PSU

    http://kvisit.com/S_KuKAw

    See the MSD7342-224ml for coupled inductor.
    The IRF9640 is overkill but only SC3 model available.
    The control loop should be pretty straight forward.
    What is the input voltage range desired?

    I would copy in that neat net + wiring list that you guys use but do not know how. Just learning LTSPICE.

    Cheers, Harry
     
  2. John K

    John K Guest

    Harry, thanks for posting. You are doing great.

    To post your ASC file, you can put it on the web site as you have done.

    There is also an option on the web site to provide a direct download
    link. For example, your ASC file is at

    http://www.keepandshare.com/doc/6460924/fly-hob-hd-asc-2k?da=y

    You can also load the ASC file into an ascii editor and paste it into
    your newsgroup client. This creates the problem of line wrap when you
    have anything that extends past column 70 or so. It also creates havoc
    with some news clients that wish to change symbols to hex. For example,
    the equal sign, "=", becomes "=3D". This creates problems in LTspice
    since it cannot deciper lines like

    SYMATTR SpiceLine Rser=3D0.02 Rpar=3D5000

    Some newsgroups allow you to post an ASC file as an attachment. This is
    convenient since the newsreader usually saves the attachment to a folder.
    This eliminates the problem of wrapping long lines in the newsreader.

    There are a number of ways of conveying your circuit to the newsgroup.
    Try to pick one that causes the least amount of problems for your
    readers.

    There is a bit of overshoot in your circuit on startup. You might
    consider lowering the on time of the IRF9640. You can set V2 to around
    50% duty cycle. Try

    PULSE(0 10 10N 10N 10N 5U 10U)

    It needs just a tad more on time to come up exactly on the target
    voltage. However, this will change with the load.

    JK
     
  3. Ok, so here is my *.asc file:

    Version 4
    SHEET 1 1108 900
    WIRE -816 -256 -1200 -256
    WIRE -576 -256 -816 -256
    WIRE -80 -256 -576 -256
    WIRE -1632 -240 -1680 -240
    WIRE -1504 -240 -1552 -240
    WIRE -1488 -240 -1504 -240
    WIRE -576 -192 -576 -256
    WIRE -816 -176 -816 -256
    WIRE -864 -160 -944 -160
    WIRE -1856 -128 -1952 -128
    WIRE -1680 -128 -1680 -240
    WIRE -1456 -128 -1680 -128
    WIRE -80 -128 -80 -256
    WIRE -944 -112 -944 -160
    WIRE -256 -112 -288 -112
    WIRE -128 -112 -176 -112
    WIRE -1200 -80 -1200 -256
    WIRE -1952 -64 -1952 -128
    WIRE -576 -48 -576 -112
    WIRE -1456 -16 -1456 -128
    WIRE -1360 -16 -1456 -16
    WIRE -992 16 -1040 16
    WIRE -864 16 -864 -112
    WIRE -864 16 -992 16
    WIRE -816 16 -816 -96
    WIRE -688 16 -816 16
    WIRE -288 16 -288 -112
    WIRE -288 16 -688 16
    WIRE -1680 48 -1680 -128
    WIRE -1632 48 -1680 48
    WIRE -1520 48 -1568 48
    WIRE -1408 48 -1440 48
    WIRE -1360 48 -1408 48
    WIRE -1680 80 -1680 48
    WIRE -768 96 -816 96
    WIRE -752 96 -768 96
    WIRE -432 96 -464 96
    WIRE -320 96 -368 96
    WIRE -192 96 -240 96
    WIRE -1440 112 -1472 112
    WIRE -1376 112 -1440 112
    WIRE -1360 112 -1376 112
    WIRE -80 112 -80 -32
    WIRE -1472 128 -1472 112
    WIRE -816 128 -816 96
    WIRE -1024 144 -1040 144
    WIRE -976 144 -1024 144
    WIRE -912 144 -976 144
    WIRE -864 144 -864 16
    WIRE -1360 176 -1392 176
    WIRE -464 208 -464 96
    WIRE -464 208 -576 208
    WIRE -352 208 -464 208
    WIRE -192 208 -192 96
    WIRE -192 208 -288 208
    WIRE -80 208 -80 112
    WIRE 32 208 -80 208
    WIRE 192 208 96 208
    WIRE 288 208 192 208
    WIRE -1472 224 -1472 208
    WIRE -1392 224 -1392 176
    WIRE -1392 224 -1472 224
    WIRE -1472 240 -1472 224
    WIRE -576 240 -576 208
    WIRE -192 240 -192 208
    WIRE -80 240 -80 208
    WIRE 288 240 288 208
    WIRE -464 256 -464 208
    WIRE 192 256 192 208
    WIRE -912 272 -912 144
    WIRE -1200 288 -1200 240
    WIRE -816 288 -816 224
    WIRE -736 288 -816 288
    WIRE -816 352 -816 288
    WIRE -816 352 -864 352
    WIRE -576 368 -576 320
    WIRE -464 368 -464 320
    WIRE -192 368 -192 320
    WIRE -80 368 -80 320
    WIRE 192 368 192 320
    WIRE 288 368 288 320
    WIRE -1376 384 -1376 112
    WIRE -1312 384 -1376 384
    WIRE -1024 384 -1024 144
    WIRE -1024 384 -1232 384
    WIRE -1024 400 -1024 384
    FLAG -576 -48 0
    FLAG -80 368 0
    FLAG 192 368 0
    FLAG -192 368 0
    FLAG -464 368 0
    FLAG -576 368 0
    FLAG 288 368 0
    FLAG -80 112 VS
    FLAG 288 208 NO
    FLAG -576 208 PO
    FLAG -1200 288 0
    FLAG -992 16 DV
    FLAG -688 16 DN
    FLAG -1472 304 0
    FLAG -1472 224 FR
    FLAG -736 368 0
    FLAG -1024 464 0
    FLAG -912 368 0
    FLAG -1440 112 VR
    FLAG -768 96 VR
    FLAG -976 144 IS
    FLAG -944 -112 0
    FLAG -1680 160 0
    FLAG -1504 -240 PO
    FLAG -1408 48 CP
    FLAG -1952 16 0
    FLAG -1792 -128 CP
    SYMBOL ind2 -96 224 R0
    WINDOW 0 50 51 Left 2
    WINDOW 3 60 86 Left 2
    SYMATTR InstName L1
    SYMATTR Value 220µ
    SYMATTR Type ind
    SYMATTR SpiceLine Rser=1.72
    SYMBOL cap -480 256 R0
    SYMATTR InstName C1
    SYMATTR Value 1µ
    SYMBOL schottky 96 224 M270
    WINDOW 0 32 32 VTop 2
    WINDOW 3 -3 -7 VBottom 2
    SYMATTR InstName D1
    SYMATTR Value MBRS1100
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL voltage -576 -208 R0
    WINDOW 123 0 0 Left 2
    WINDOW 39 0 0 Left 2
    SYMATTR InstName V1
    SYMATTR Value 16
    SYMBOL schottky -288 224 M270
    WINDOW 0 32 32 VTop 2
    WINDOW 3 0 32 VBottom 2
    SYMATTR InstName D3
    SYMATTR Value MBRS1100
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL cap 208 320 R180
    WINDOW 0 24 56 Left 2
    WINDOW 3 24 8 Left 2
    SYMATTR InstName C6
    SYMATTR Value 1µ
    SYMBOL res -592 224 R0
    WINDOW 3 25 4 Left 2
    SYMATTR Value 2.2K
    SYMATTR InstName R2
    SYMBOL res 272 224 R0
    SYMATTR InstName R4
    SYMATTR Value 2.2K
    SYMBOL res -160 -128 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R1
    SYMATTR Value 20
    SYMBOL ind2 -208 336 M180
    WINDOW 0 36 80 Left 2
    WINDOW 3 36 40 Left 2
    SYMATTR InstName L2
    SYMATTR Value 220µ
    SYMATTR Type ind
    SYMATTR SpiceLine Rser=1.72
    SYMBOL pmos -128 -32 M180
    SYMATTR InstName M2
    SYMATTR Value IRF9640
    SYMBOL e -816 -192 R0
    SYMATTR InstName E1
    SYMATTR Value -1
    SYMBOL res -1488 112 R0
    SYMATTR InstName R3
    SYMATTR Value 30K
    SYMBOL cap -1488 240 R0
    SYMATTR InstName C2
    SYMATTR Value 470p
    SYMBOL res -1216 368 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R6
    SYMATTR Value 30K
    SYMBOL cap -1040 400 R0
    SYMATTR InstName C3
    SYMATTR Value 1n
    SYMBOL pmos -864 224 M180
    SYMATTR InstName M1
    SYMATTR Value BSS84
    SYMBOL nmos -864 272 M0
    SYMATTR InstName M3
    SYMATTR Value 2N7002
    SYMBOL res -752 272 R0
    SYMATTR InstName R5
    SYMATTR Value 2K
    SYMBOL res -1696 64 R0
    SYMATTR InstName R7
    SYMATTR Value 10K
    SYMBOL res -1536 -256 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R8
    SYMATTR Value 170K
    SYMBOL cap -1568 32 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName C4
    SYMATTR Value 100n
    SYMBOL res -1424 32 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R9
    SYMATTR Value 68K
    SYMBOL PowerProducts\\LT1242 -1200 80 R0
    SYMATTR InstName U1
    SYMBOL voltage -1952 -80 R0
    WINDOW 3 -49 325 Left 2
    WINDOW 123 0 0 Left 2
    WINDOW 39 0 0 Left 2
    SYMATTR Value PULSE(-1.0 5 10N 5M 10M 10M 30M)
    SYMATTR InstName V2
    SYMBOL diode -1792 -144 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName D2
    SYMBOL res -224 80 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 37 48 VTop 2
    SYMATTR InstName R11
    SYMATTR Value 220
    SYMBOL cap -368 80 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName C5
    SYMATTR Value 120p
    TEXT -912 -352 Left 2 !.tran 0 4MU 0 100N
    TEXT -216 424 Left 2 !K L1 L2 0.9965
    TEXT -216 472 Left 2 ;MSD7342-224


    Aah, will that work for everyone?

    Thanks, harry
     
  4. [snip]

    Very nice indeed. I just plugged it into PSpice, reduced the output caps to 100nF and induced a step response. It seems quite stable, allthough I have not dug very deep

    Increasing the value of the inductor L1 to 150uH does introduce ringing with C4 and C7 which makes is unstable during startup and transients due to the ringing sense current in R1.

    Regards

    Klaus
     
  5. That is, increasing the inductor to 150uH keeping all other components the same values as from the ASC posted by Larkin makes it unstable...

    Cheers

    Klaus
     
  6. Phil Hobbs

    Phil Hobbs Guest

    No, mine was a buck-boost, whereas John has posted a few capacitively
    coupled boosts, of which this is one.

    The nice thing about doing it his way is that you get some
    cross-regulation, because one polarity adjusts the voltage swing on the
    inductor, whereas I get the full input voltage variation impressed on
    the HV and have to get rid of it afterwards.

    The efficiency is comparatively poor for some reason that I haven't
    looked into very deeply--if you filter the current draw from V1 using a
    100 milliohm/1 millifarad RC lowpass to get rid of the spikes, and compute

    (V(VP)*I(R5)+V(VN)*I(R6))/(-16*I(V1)), it never gets above about 0.3.

    The nice thing about doing it my way is that you only need one switching
    regulator instead of two (one inverter and one AC-coupled boost), and
    that it's simpler and more efficient.

    The OP's circuit also has the nice cross-regulation feature, but needs a
    lot of parts, including a $2.50 regulator chip, and a transformer that
    would need to be a toroid to make me happy, at least at this stage of my
    education in how to combine SMPSes with ultrasensitive instruments.

    Defeating the current-sense like that seems a bit counterproductive as well.

    Cheers

    Phil Hobbs

    --
    Dr Philip C D Hobbs
    Principal Consultant
    ElectroOptical Innovations LLC
    Optics, Electro-optics, Photonics, Analog Electronics

    160 North State Road #203
    Briarcliff Manor NY 10510

    hobbs at electrooptical dot net
    http://electrooptical.net
     
  7. Here is Jl's PSU suitable for production. Note the rise and fall times have
    been soften.


    Version 4
    SHEET 1 1180 680
    WIRE 368 -272 320 -272
    WIRE 496 -272 432 -272
    WIRE 560 -272 496 -272
    WIRE 832 -272 624 -272
    WIRE 928 -272 832 -272
    WIRE 992 -272 928 -272
    WIRE 992 -240 992 -272
    WIRE 832 -224 832 -272
    WIRE 496 -208 496 -272
    WIRE 16 -160 -80 -160
    WIRE 128 -160 16 -160
    WIRE 272 -160 208 -160
    WIRE 320 -160 320 -272
    WIRE 320 -160 272 -160
    WIRE 16 -128 16 -160
    WIRE 496 -112 496 -144
    WIRE 832 -112 832 -160
    WIRE 992 -112 992 -160
    WIRE 320 -32 320 -160
    WIRE 368 -32 320 -32
    WIRE 496 -32 432 -32
    WIRE 576 -32 496 -32
    WIRE 832 -32 640 -32
    WIRE 928 -32 832 -32
    WIRE 992 -32 928 -32
    WIRE 16 -16 16 -48
    WIRE 496 0 496 -32
    WIRE 992 0 992 -32
    WIRE -528 16 -544 16
    WIRE -512 16 -528 16
    WIRE 832 16 832 -32
    WIRE -544 48 -544 16
    WIRE -80 80 -80 -160
    WIRE 320 96 320 -32
    WIRE 496 112 496 64
    WIRE 832 128 832 80
    WIRE 992 128 992 80
    WIRE -240 144 -480 144
    WIRE 112 176 80 176
    WIRE 160 176 112 176
    WIRE 272 176 240 176
    WIRE -544 208 -544 128
    WIRE -480 208 -480 144
    WIRE -480 208 -544 208
    WIRE -384 208 -416 208
    WIRE -272 208 -304 208
    WIRE -240 208 -272 208
    WIRE -544 272 -544 208
    WIRE -240 272 -400 272
    WIRE -400 288 -400 272
    WIRE 176 304 80 304
    WIRE 224 304 176 304
    WIRE 320 304 320 192
    WIRE 320 304 304 304
    WIRE 368 304 320 304
    WIRE 528 304 448 304
    WIRE -240 336 -272 336
    WIRE -400 384 -400 368
    WIRE -304 384 -400 384
    WIRE -272 384 -272 336
    WIRE -272 384 -304 384
    WIRE 176 384 176 304
    WIRE 528 384 528 304
    WIRE -400 400 -400 384
    WIRE -272 432 -272 384
    WIRE 112 496 112 176
    WIRE 112 496 -208 496
    WIRE -208 512 -208 496
    WIRE -208 512 -224 512
    FLAG 528 384 0
    FLAG -80 400 0
    FLAG 832 128 0
    FLAG 16 -16 0
    FLAG 496 112 0
    FLAG 832 -112 0
    FLAG 496 -112 0
    FLAG 992 -112 0
    FLAG 992 128 0
    FLAG 928 -32 VP
    FLAG 928 -272 VN
    FLAG 272 -160 D
    FLAG -544 352 0
    FLAG -528 16 VP
    FLAG 176 448 0
    FLAG -400 464 0
    FLAG -272 528 0
    FLAG 112 176 VG
    FLAG 320 304 IS
    FLAG -304 384 RT
    FLAG -272 208 CP
    SYMBOL nmos 272 96 R0
    WINDOW 0 101 34 Left 2
    WINDOW 3 76 70 Left 2
    SYMATTR InstName M1
    SYMATTR Value FDS3570
    SYMBOL res 352 320 R270
    WINDOW 0 32 56 VTop 2
    WINDOW 3 0 56 VBottom 2
    SYMATTR InstName R1
    SYMATTR Value 0.7
    SYMBOL schottky 576 -16 R270
    WINDOW 0 -40 31 VTop 2
    WINDOW 3 -41 34 VBottom 2
    SYMATTR InstName D1
    SYMATTR Value BAT46WJ
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL ind2 112 -144 R270
    WINDOW 0 94 58 VTop 2
    WINDOW 3 81 58 VBottom 2
    SYMATTR InstName L1
    SYMATTR Value 500µ
    SYMATTR Type ind
    SYMBOL cap 816 16 R0
    WINDOW 0 59 31 Left 2
    WINDOW 3 55 65 Left 2
    SYMATTR InstName C1
    SYMATTR Value 1µ
    SYMBOL res 320 288 R90
    WINDOW 0 0 78 VBottom 2
    WINDOW 3 38 62 VTop 2
    SYMATTR InstName R2
    SYMATTR Value 1K
    SYMBOL voltage 16 -144 R0
    WINDOW 0 51 45 Left 2
    WINDOW 3 54 81 Left 2
    WINDOW 123 0 0 Left 2
    WINDOW 39 0 0 Left 2
    SYMATTR InstName V1
    SYMATTR Value 16
    SYMBOL schottky 512 64 R180
    WINDOW 0 66 33 Left 2
    WINDOW 3 41 -7 Left 2
    SYMATTR InstName D4
    SYMATTR Value BAT46WJ
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL cap 432 -48 R90
    WINDOW 0 -52 29 VBottom 2
    WINDOW 3 -42 27 VTop 2
    SYMATTR InstName C4
    SYMATTR Value 10µ
    SYMBOL schottky 624 -288 R90
    WINDOW 0 65 -24 VBottom 2
    WINDOW 3 67 -26 VTop 2
    SYMATTR InstName D6
    SYMATTR Value BAT46WJ
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL cap 816 -224 R0
    WINDOW 0 62 24 Left 2
    WINDOW 3 58 57 Left 2
    SYMATTR InstName C6
    SYMATTR Value 1µ
    SYMBOL cap 432 -288 R90
    WINDOW 0 72 32 VBottom 2
    WINDOW 3 81 32 VTop 2
    SYMATTR InstName C7
    SYMATTR Value 10µ
    SYMBOL schottky 480 -208 R0
    WINDOW 0 84 51 Left 2
    WINDOW 3 59 85 Left 2
    SYMATTR InstName D7
    SYMATTR Value BAT46WJ
    SYMATTR Description Diode
    SYMATTR Type diode
    SYMBOL res 976 -256 R0
    WINDOW 0 62 50 Left 2
    WINDOW 3 62 81 Left 2
    SYMATTR InstName R5
    SYMATTR Value 2K
    SYMBOL res 976 -16 R0
    WINDOW 0 61 41 Left 2
    WINDOW 3 61 75 Left 2
    SYMATTR InstName R6
    SYMATTR Value 2K
    SYMBOL res 256 160 R90
    WINDOW 0 -44 55 VBottom 2
    WINDOW 3 -38 56 VTop 2
    SYMATTR InstName R7
    SYMATTR Value 22
    SYMBOL PowerProducts\\LT1242 -80 240 R0
    SYMATTR InstName U1
    SYMBOL res -288 192 R90
    WINDOW 0 0 56 VBottom 2
    WINDOW 3 32 56 VTop 2
    SYMATTR InstName R4
    SYMATTR Value 68K
    SYMBOL cap -416 192 R90
    WINDOW 0 0 32 VBottom 2
    WINDOW 3 32 32 VTop 2
    SYMATTR InstName C3
    SYMATTR Value 10n
    SYMBOL res -560 256 R0
    SYMATTR InstName R8
    SYMATTR Value 10K
    SYMBOL res -560 32 R0
    SYMATTR InstName R9
    SYMATTR Value 170K
    SYMBOL cap 160 384 R0
    WINDOW 3 46 44 Left 2
    SYMATTR InstName C5
    SYMATTR Value 1n
    SYMBOL cap -416 400 R0
    SYMATTR InstName C8
    SYMATTR Value 510p
    SYMBOL res -416 272 R0
    SYMATTR InstName R10
    SYMATTR Value 10K
    SYMBOL nmos -224 432 M0
    SYMATTR InstName M2
    SYMATTR Value 2N7002
    TEXT 792 320 Left 2 !.tran 2m uic
    TEXT 696 384 Left 2 ;Bipolar Boost JL July 2013
    TEXT 696 416 Left 2 ;SOFT SWITCHED HD 22/JLY/13

    Cheers, Harry
     
  8. That is Ok for a bench top tweak but will not make it in the production
    world.
    Your efficiency is poor due to 750KHz operation.
    C4 can be replaced with a short and D4 removed. C1,6 need be <1.0uF
    M1 can be your pilot light!

    Cheers, Harry
     
  9. So what magic Smitt-Trigger IC do you use that operates in this unit over
    temp and lot to lot?
    I admit that I use lots of ST but not in apps. like this. Looks like
    something JF would use with his 555s.

    Harry
     
  10. Glenn

    Glenn Guest

    On 23/07/13 02.53, Harry Dellamano wrote:
    ....
    This series replaced UC384x "long" ago:

    ucc3802 til 100% 0,5mA
    http://focus.ti.com/docs/prod/folders/print/ucc3802.html
    2,1 eu
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=296-11464-5-ND
    ->ucc3803 til 100% 0,5mA 2,1 eu
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=296-11466-5-ND
    ->ucc3800 til 100% 0,5mA 2,1 eu
    http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=296-11457-5-ND

    Also these - but they are also outdated:
    (
    UCC38C43
    MIC38HC43
    MIC38HC43-1
    MIC38C44
    SG3843
    KA3843
    ISL8843
    TL3843
    ISL8843
    )

    /Glenn
     
  11. Glenn

    Glenn Guest

    ....
    Quote: "...
    Features
    100µA Typical Starting Supply Current
    500µA Typical Operating Supply Current
    Operation to 1 MHz
    Internal Soft Start
    Internal Fault Soft Start
    Internal Leading-Edge Blanking of the Current Sense Signal
    1 Amp Totem-Pole Output
    70ns Typical Response from Current-Sense to Gate Drive Output
    1.5% Tolerance Voltage Reference
    Same Pinout as UC3842 and UC3842A
    ...."

    You can not ask for more?

    Glenn
     
  12. Ah... how about "not being 5x the price?" :)
     
  13. You folks are correct, it is not the cost of the parts but design time,
    risk, heat and EMI just to name a few. I believe that you are taking a risk
    in your design without protection features that are normally needed. Such as
    under voltage shutdown and poor short circuit protection. If the 16V supply
    come up low or if the output is shorted you have a good chance of letting
    the smoke out. In normal operation your design has a large charge dumping
    spike at R1 at turn on. This screams for a 1nF cap at Q1-B to ground to
    mitigate the spike but will greatly effect short circuit protection. Needs
    lots of tweaking.
    I used the LT1242 only because it was the only model available in LTSpice.
    You are correct about LT controllers. They have too many hooks and features,
    to allow easy integration. Designers using LT parts normally copy the
    published designs to the letter and not think on their own. LT never
    learned that a great IC controller has less than 10 pins.
    If I were task with this design I would probably look at the LM3475
    Hysteretic controller from TI. Your design works because this is a simple
    requirement but most PSU are not this simple and you need to be conformable
    with IC controllers.

    Highest regards, Harry
     
  14. Your sketch is a good case on point. If you replace the LM5112 with a
    LTC3801 (6 pins) with your feedback scheme, you now have a solid PSU and
    not a kludge. I have used that topology often, with an "off the shelf"
    coupled shielded inductor, to get tracking +/-V outputs.
    Safeway?? Have you ever eaten at "Brown Sugar" in Oakland. We should meet
    there some time an have grits an eggs.

    Cheers, Harry
     
  15. We should all meet at some time. I actually have met Joerg, great guy with his heart the right place (give my regards to your wife, if you read this)

    But, we would need bouncers, to keep JT and JL apart, although it seems to be better the last couple of days ;-)

    Cheers

    Klaus
     
  16. Bill Sloman

    Bill Sloman Guest

    A curiously quantitative assessment from somebody who can write dozens of lines on electronics without getting closer to numbers than saying that something didn't include a $3 part.

    Also a bit silly. Jim Thompson's net social worth may well be negative - anybody who publicly speculates about shooting his neighbours after the country falls apart can't be considered as an asset to his neighbourhood - and if John Larkin's wife worth was a 100 times more negative than Jim Thompson's it would be a very negative assessment.
     
  17. Guest

    Maybe I am extremely confused, but I don't understand why Q1 is
    connected the way it is.

    I think R1/R2/C1/U1 makes an oscillator when you turn on the juice.
    That turns Q2 on and off through R3. OK.

    When Q2 is on, a magnetic field builds up in L1. When Q2 turns off, the
    field collapses, inducing a voltage in L1. This is rectified by D1 and
    filtered by the capacitor that must not be named to become the -12 V
    out. OK.

    C2 is a power supply bypass capacitor, probably to deal with the
    current peaks when Q2 is on. OK.

    R4/R5/Q1 seem to be part of the feedback. I think the idea is that when
    the -12 V goes too far away from ground, you want the oscillator to have
    Q2 turned on for shorter amounts of time. I further think that the idea
    is to "steal" some of the current that would normally charge C1 and dump
    that current to ground instead, which changes how fast C1 charges.

    If that is true, I would sort of think that the base of Q1 would be
    towards the R4/R5 junction, the emitter would be grounded, and the
    collector would go to the R1/R2 junction.

    I'm not saying it doesn't work (it *is* in production); I am just
    trying to understand how it works.

    Matt Roberds
     
  18. Guest

    What if I put a bypass cap on the clove of garlic before wearing? Will
    that keep twice as many vampires away? (Or a clove of garlic across the
    bypass cap in a circuit. Hmm.)
    If it was hooked up like I said, as the base goes more and more
    negative, the transistor conducts less and less, and steals less current
    from C1? That isn't what you want, yeah.
    Aha. That, and the fact that negative voltages are involved, makes it
    make sense to me.

    I am used to seeing either common-emitter or common-collector circuits
    with a single supply, where the signal into the base tells the
    transistor what to do. From that perspective, having a grounded base
    seemed weird at first - "it's never gonna do anything". The fact
    that it isn't one of those topologies, plus the fact that there is a
    negative supply, means the emitter can get down to a voltage where the
    transistor will start turning on.

    I have seen common-base circuits before, but drawn with the whole
    transistor symbol rotated 90 degrees counterclockwise, mostly to
    emphasise that something different is happening.
    The current "stolen" from C1 via Q1 ends up in the -12 V out, right?
    Along with the < 1 mA from the +5 V reference that comes through R4 and
    R5?
    If you needed more accuracy, and as long as the opamps need between a
    few and few dozen mA or less, maybe you could follow your circuit with
    a 79L12 and be happy. On the other hand, if the opamps only need a
    couple of mA total, the current that the 79L12 needs to run becomes a
    big part of the load. If you're running on a watch battery or
    something, you're counting every mA.
    PIC, AVR or equal with a software PID loop. :)

    Matt Roberds
     
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