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PWM controller

Discussion in 'Electronic Projects' started by Dr.EM, Jun 3, 2006.

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  1. AirWalker83

    AirWalker83 New Member

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    hi everybody.......
    I had saw the datasheet of L298N which the current limit can be raised up by parellel the 2 H-Bridge in the IC. Actually it raised up to how many ampere?
    i hear that u all sugest to use power MOSFET, but i actually still dun understand how it can become motor driver???can somebody help?
    Or is ther any motor in the market have the same torque as power window motor but will draw less current?
    thanks...........
     
  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A Mosfet can switch many amps of current without much waste (heating).
    The IRF3205 mentioned can conduct 30A and heat only 7.2W.

    If you reduce the current for a motor then its torque becomes less.
    A gearbox allows a low-current motor to have more torque but its action is slower.
     
  3. AirWalker83

    AirWalker83 New Member

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    thanks for your explaination. Then u have any circuit uisng IRF3205 to build dc motor driver???
     
  4. dave

    Dave New Member

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  5. Sceadwian

    Sceadwian Banned

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    Take any of the thousands of readily available mosfet motor driver circuits and just replace the FET used with an IRF3205 (makeing sure the drive voltages are still acceptable)
     
  6. AirWalker83

    AirWalker83 New Member

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    hi, i just buy a motor driver kit for my power window motor.
    It can suipport up to 10A. I think it got 2 relays in the circuit.
    i had sucessfull testing for the motor to run.
    But for the PWM speed control, i didn't manage to do it.
    At the spec, it say it can be used for speed control.
    is it that is different way for PWM control using relay?
    So, did anyboy have any idea regarding this problem?
    Thanks
     
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The relays are probably for the motor to run forwards with one relay and run in reverse with the other relay.
    The PWM circuit switches on and off the power to the motor much faster than a relay can to control the duty-cycle of the power to control the speed of the motor.
     
  8. AirWalker83

    AirWalker83 New Member

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    sorry, i still not quite understand about the PWM circuit and the relay?
    is it PWM cannot use in relay?
    Can sulution to control speed using relay?
    Can u explain somemore?
    thanks....
     
  9. dknguyen

    dknguyen Well-Known Member

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    Relays can only go on or off. They cannot PWM. Relays wear out every time they switch. So if a relay can only handle 100,000 switches and you are switching them at 20kHz PWM...it wears out very very fast.

    Transistors can switch on and off very fast.

    So you might use relays to control direction since you aren't changing direction thousands of times per second, but then the current would have to pass through a transistor being switched with PWM to control the speed.
     
  10. Sceadwian

    Sceadwian Banned

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    PWM is almost never used for motor speed control when you're using a relay, the relay has to switch too fast and it will reduce it's lifetime by a factor of 10-100 makeing the relay burn out unuseably fast.
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Not strictly true, in fact it's very commonly done - you use the relay (DPDT) to reverse direction, and a single transistor or FET to provide the PWM - a lot cheaper and simpler (and more reliable) than an H-Bridge.
     
  12. cadstarsucks

    cadstarsucks Banned

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    True. We do it on a couple of units... though most units that do reverse direction are for relatively low power actuators as opposed to the 3HP main motors.

    D.
     
  13. boardinsnowman

    boardinsnowman New Member

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    a PWM with a regenerative brake

    Hello,
    I am doing an electronics project and I am completely stumped. I am trying to design a PWM speed controller for a 24v 300-500w DC motor. I've found a few circuit designs online but since my understanding is limited I'm afraid I'll build it wrong or pick the wrong one. So, could anyone point me in the right direction in designing the proper circuit for what it must do.

    Ideally, this is what I want it to do--
    -regulate the speed from 0-100%
    -have a regenerative brake
    -handle up to 50 amps (just in case)
    -not make noise -although after reading this thread though it seems I'll have to stick to around 3khz
    -be able to input 24-48v and still output 24v--I don't know if this is possible, but please let me know.

    Some of what I've found-
    http://www.4qdtec.com/pwm-01.html --pretty much what I'm looking for, scroll down to "A slightly more sophisticated controller" - but this one only goes from 0-90%
    http://www.aaroncake.net/circuits/motorcon.asp --less like what im looking for
    http://www.4qd.co.uk/fea/regen.html --how regenerative braking works
    http://www.educypedia.be/electronics/powermotor.htm --lots of info

    Any help at all would be greatly appreciated for I'm at quite an impasse.

    Thanks again,
    -Ed

    email address deleted - moderator.
    Again, I'm a beginner so hopefully the specs I want are even possible....
     
    Last edited by a moderator: Jan 19, 2011
  14. diaeldeen

    diaeldeen New Member

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    goooooooood
     
  15. Refusalspam

    Refusalspam New Member

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    I guess I'm very late to this discussion, but there are some points I'd like to bring up in case anyone is still reading. I'm not an expert, I've

    1) FET swapping in a circuit diagram
    I don't think you can just swap out one FET for another one in a PWM schematic. For N-channel MOSFETs you need the gate to source voltage to be around 8v to get max current (ie lowest resistance). Most of the time the supply voltage is the highest voltage and it will be tied to the source pin of the FET. Typically, you will want to use an N-channel MOSFET because of the lower resistance compared to the P-channel.

    2) Reversed biased Diodes across the motor terminal
    They is for both efficiency and protection as somebody said. This configuration is called a 'free-wheeling' diode and the diode must be able to switch faster than the pwm frequency. Its true that most FETs have a zener diode that will allow the kickback to be shorted to ground, but you would be wasting that power and heating up your FET even more.

    3) Ideal PWM frequency
    This tends to be a function of the motor speed. You only want to use as low of a frequency that will still give you smooth motor control at the highest rpm the motor is likely to go at under load. The reason for this is simple, no matter how fast a FET can switch, its still not instantaneous. During this time when the FET is half-on/half-off its resistance and current are fairly high meaning power dissipation is much higher than normal. The faster the pwm cycle the more time you spend heating up your FET (and diode). If you don't believe me, take a queue from competition level RC speed controllers like this one: http://www.teamnovak.com/products/esc/gtx/index.html
    The "drive frequency" can be adjusted from 1-11Khz. If higher was better then why bother with making it adjustable?

    4) Lack of current limiting for "stall currents"
    Most motors will consume a lot more current when stalled (rotor is locked). This is because the inductance of commutating coils in the motor keeps the current down when running, but a stalled motor will stop commutating leaving only the resistance in the motor windings to control the current. I get about .1 Ohm across the motor terminals of my cordless drill motor. At 10v that would be a 100 amp stall current! This doesn't just burn out your motor, but also the FET and possibly the diode.
     
  16. h.d

    h.d New Member

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    what we need to apply PWM controlling for 20A 2hp dc-motor using the PIC microcontroller?
     
  17. indulis

    indulis New Member

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    I know this thread is old, but for those that are interested, the circuit could be used to to make a SMPS. You just need to add an error amp and reference and you have a voltage mode PWM.
     
  18. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Hi Indulis,
    Welcome to this forum.
     
  19. bunghole

    bunghole New Member

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    what are the values of q2 and q3 in the schematic at the start of this thread, or do i have to make them something? and is there something that can takr the place of the bs170?
     
    Last edited: Jan 14, 2008
  20. RAKS

    RAKS New Member

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    I'm currently looking at PWM controller circuits because I need to design a DC-DC converter which I've never done as part of a home project before. I'll take a look at your circuit - thanks.
     
  21. Hero999

    Hero999 Banned

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    True but which is better and cheaper depends on the application, for a low powered motor, it's probably cheaper to use a full transistor h-bridge than a relay.
     
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