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upgrading stardard pwm to more power

Discussion in 'General Electronics Discussion' started by hydrogenpower, Nov 7, 2012.

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  1. hydrogenpower

    hydrogenpower

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    Nov 7, 2012
    I have this pwm in the picture
    and I want to controle more current with it so
    does somebody know how to put a transistor like BUZ350 behind it and controle a bigger load with it

    [​IMG]
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    More information would help.

    What is the load (what is it *exactly*)?

    How do you intend to change it (what's the new load *exactly*)?

    What is the current required by the current load?

    What is the total current required by the new load?

    Do you know the frequency the PWM operated at?

    What is T2 as shown on that diagram? (part number and package) (photo might help)

    Is T2 on a heatsink? How large? (photo might help)

    What are the values of R8 R9 and R10? (read them, don't measure them)

    What is the value of R2, C4, and C5?

    Please try to answer all the questions (that are not already answered).

    edit: It's best if you don't post a large image with a small diagram in the middle. Clip off the edges next time.
     
    Last edited: Nov 8, 2012
  3. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I don't particularly like having to put it in a photo editor to rotate it either.

    Chris
     
  4. CocaCola

    CocaCola

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    Apr 7, 2012
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I used the twisty thing my head is mounted on, but yeah.
     
  6. CocaCola

    CocaCola

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    Darn fast responses there the darn datasheet was larger than the forum would accept :D so I had to link instead...

    That gets us a lot further...
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    OK, still need answers for some the questions I asked (but only about the load you actually want to drive).

    But in general:

    R8, 9, and 10 should be reduced to 0.07 ohms 5W or therabouts. These may be hard to get, so you might be able to parallel up 9 0.22 ohm 2W resistors.

    The heatsink should be larger or perhaps forced air cooled.

    The traces on the board carrying the current should have wires capable of carrying the current soldered along them.

    D4 should be upgraded to a something with a higher current carrying capacity. There are a number of high current diodes in TO-220 packages (with 2 leads) that may be an almost droop-in replacement.

    The BUK9535-55 is probably OK for 20A

    R1 is the biggest problem. Turning the mosfet off this way is slow and will contribute most to the dissipation of the device.

    Changing the circuit to use something that will actively pull it low would be better.
     
  8. CocaCola

    CocaCola

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    I was just giving the OP a head start :p now they have a lot smaller list of questions to actually answer...
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Referring to the PDF schematic... It was drawn by someone or something that doesn't clearly dot nodes that are connected when conductors cross. I think I'm having a Rosana Rosana Danna day.

    Chris
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Fortunately it's unambiguous in this case.
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes, but not to a nube. What bugs me,... actually a lot of things bug me ..where was I? Oh yeah, they bothered to dot connections that couldn't be anything else but connected, like C2 and R4.

    I'm forming an alliance. Anyone who wants to join please PM me. I'm going to call it ...

    IAFMUONDIS. 'Interplanetary Alliance For Mandatory Use Of Node Dots In Schematics'. :D

    Chris
     
  12. hydrogenpower

    hydrogenpower

    4
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    Nov 7, 2012
    I thought it was a litle more simple like this
    is this posible ?
    [​IMG]

    its for a project involving hydrogen ,its for around 30 amps (buz350)
    the 2e transystor comes on a separate board
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    The problem with your circuit is that you lose the soft start and current limit and you gain the features of having mark and space inverted, and it will turn hard on if it ever shuts down.

    That would be bad.

    I had to ask... :(

    for all the good it's going to do, I would recommend that you do what I suggest. You can remove the current sense resistors if you want, but it provides valuable protection.

    Everything else is less work.
     
  14. hydrogenpower

    hydrogenpower

    4
    0
    Nov 7, 2012
    else

    cant i simply replace the existing transyster by the buz350 and change the resistor and diode

    or are the features off curent and so also specialy made for this transystor

    if so I am gonna have to change all that and recalculate what it would be for the buz350

    and thats a big difference I suggest
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I don't think you need to change the transistor. (as I said earlier)

    You will need to change the current sense resistors (as I said earlier). For three times the current, you should have 1/3 the resistance and a power rating three times as large (they're overspecced at the moment, so the ratings I gave earlier are marginal but OK) Dissipation will be around 15W.

    It may be better to use 9 of the 5W resistors to be extra safe.

    And yes, I would recommend that you change the diode too (as I said earlier)

    The only other thing (as I said earlier) is to solder wires to the PCB traces carrying the heavy current. It's almost certain that they've not been designed for the current you require, so simply solder some solid core wire along them.

    edit: I wouldn't replace the existing transistor with the one you are suggesting because you've selected a part that can handle about half the current and has an Rds(on) about 4 times higher than the part that's there. It would be like replacing a Porsche with a Volkswagen beetle.
     
    Last edited: Nov 8, 2012
  16. hydrogenpower

    hydrogenpower

    4
    0
    Nov 7, 2012
    try

    thank gonna try that
    will have to wait till I have the chip beceause i broke off one off its 14 leag's
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Since you're wisely not going to attempt the modifications that you posted on your schematic this is just for the record. It wouldn't work at all as drawn because there's no Drain resistor, thus no DC path from Vdd to the Drain.

    Chris

    Edit: I'm referring to T2.
     
    Last edited: Nov 8, 2012
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Do you mean the lack of a resistor pulling the gate up?

    I decided not to mention the resistor that would actually enable some function (that function most likely being the destruction of the mosfet)
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yup. I probably shouldn't have said anything.

    Chris
     
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