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PWM circuit

Discussion in 'General Electronics Discussion' started by Edwin Fitzpatrick, Jan 8, 2013.

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  1. Edwin Fitzpatrick

    Edwin Fitzpatrick

    Dec 26, 2012
    I built the Electric Scooter,E-Bike PWM speed controller circuit. I can not get the oscillator to work. I checked the pc bd and is ok All resistors are correct and in place.Replaced the LM339 and 4093 Checked all parts and their values.Don't know what to do, need help.Is ther some thing that I need to look for? I have been building circuits and pc board for years.
    [email protected]
  2. BobK


    Jan 5, 2010
    How about a link to the schematic?

  3. Edwin Fitzpatrick

    Edwin Fitzpatrick

    Dec 26, 2012
    To Bob K
    The web site is in my message.
  4. davenn

    davenn Moderator

    Sep 5, 2009
    no it isnt !!

  5. davenn

    davenn Moderator

    Sep 5, 2009

    he even PM'ed saying it was there lol
    but there isnt any clickable link in his post and you and I have commented on

    he may have intended making a clickable link but it hasnt shown as such

  6. JimW


    Oct 22, 2010
    Googling "Electric Scooter,E-Bike PWM speed controller" takes you to it. The link is here:

    OP, did you use the PCB design shown? Or did you wire it yourself? The circuit looks pretty straight forward for oscillating. But if you wired it yourself, you may have made a mistake on what was and what was not a connection in the schematic.

  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    For everyone's reference, here's the schematic.
    And here's the parts list.

    R1 = 1k
    R2 = 47k trimmer
    R3 = 10k
    R4 = 33k
    R5 = 270k
    R6 = 1M trimmer
    R7 = 330k
    R8 = 2M2
    R9 = 2k2
    R10 = 39k
    R11 = 100k
    R12 = 470k
    R13 = 100k
    R14 = 5k6
    R15 = 390k
    R16,17 = 100k
    R18 = 4k7
    R19 = 33k
    R20 = 10R
    R21 = 470R 2W
    R22 = 330R 2W

    P1 = 2k2 pot. flax. [Kris: I have no idea what flax means here!]

    C1 = 100n MLCC
    C2 = 10u 16V electrolytic
    C3 = 22n polyester
    C4 = 47n polyester
    C5 = 470u 16V electrolytic
    C6 = 100n MLCC
    C7 = 100n MLCC
    C8 = 1n ceramic
    C9 = 470u 63V electrolytic

    D1,2 = 1N4148
    D3 = BYW80-200

    T1 = BC547B
    T2 = BC557B

    U1 = LM339N
    U2 = CD4093B
    U3 = 7812

    MOS1 = RFG75N06
    RL1 = 24V 2 RT 10A [Kris: huh?]
    CH1 = Inter. Key
    P1 Pusher NF =
    M = Motor 180W 36V DC

    Attached Files:

    Last edited: Jan 9, 2013
  8. Edwin Fitzpatrick

    Edwin Fitzpatrick

    Dec 26, 2012
    Hi Krisblue NZ,Checked every thing All ok,When I move the speed pot thes schmitt triger will toogle ,But will not oscillate,Can you describe the circuit operation.?
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    Nov 28, 2011
    Probably, but I don't think that's a very good design.

    There are much better options available. Linear Technology makes the LTC6992, a versatile device that includes the oscillator and open-loop pulse-width modulator, that would be perfect for this application. Digikey have an evaluation board for USD 25 which I would suggest you use, since the device itself is a little 6-pin surface-mounted thing. See

    Other manufacturers make PWM devices too, but these are generally closed-loop devices for use in power supplies. The LTC6992 accepts a control voltage from 0V~1V to set the duty cycle. It can be powered from 3.3V or 5V. You would need a regulator to power it, a few small components, a MOSFET driver and a MOSFET with it, but not much else.
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I think you'd almost be better off replacing the entire left hand 2/3 of that with a variable duty cycle 555 oscillator.

    (I say "almost" because getting down to 0% duty cycle would not actually be achievable)
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