Page 1 of 2 12 LastLast
Results 1 to 10 of 20

Thread: GM-20 Driver

  1. #1
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Red face GM-20 Driver

    Im building a driver for GM-20s
    using a BTS412B2 highside power switch

    now my problem
    the bounce back makes the flag resonate
    how do i prevent it from bouncing around?

  2. #2
    Join Date
    Aug 2009
    Location
    Bristol, England
    Posts
    333

    Default

    If you need speed, use current mode drive by sensing the current with a low value resistor and feeding it back into the (linear) drive amp.
    The circuit of the original GS driver card is around on the net and will demonstrate the trick (But I would probably use a L165 or similar power opamp these days).

    If the basic speed is OK and you just want to kill the mechanical resonance, try putting a short across the galvo once the drive is removed. You might think about a zenner diode in anti parallel series with a 4001 or something if you are using unipolar drive.

    Regards, Dan.

  3. #3
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Default

    what is "anti parallel series"

    should i do like this
    Click image for larger version. 

Name:	GM20.GIF 
Views:	208 
Size:	2.4 KB 
ID:	18098


  4. #4
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Default

    wouldn't a diac in parallel with the gm20 work?

  5. #5
    Join Date
    Aug 2009
    Location
    Bristol, England
    Posts
    333

    Default

    Quote Originally Posted by teknofon View Post
    wouldn't a diac in parallel with the gm20 work?
    You have the diodes the wrong way around, the idea is that the back EMF is limited by the zenner (while the zenner drops a few volts to absorb the energy from the magnetic field) and the 4001 prevents the zenner acting as a normal doide in the forward direction.

    You probably already have a clamp diode in your circuit? This should replace it.

    Regards, Dan.

  6. #6
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Default

    what zener do you suggest?

  7. #7
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Default

    can i put a capacitor in parallel to the gm20
    to filter out its self resonation?

  8. #8
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Default

    something like this?
    Click image for larger version. 

Name:	GM20 FILTER CAP.GIF 
Views:	206 
Size:	2.8 KB 
ID:	18099

  9. #9
    mixedgas's Avatar
    mixedgas is online now Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    8,954

    Default

    Dmills is right, these are current driven, and they store copious amounts of energy.


    Put 20 ohms resistive in parallel across the coils if they are in series, damps nicely.

    Otherwise build something like a102 drivers with derived damping.


    http://www.camtech.com/archive/A102_AX200.pdf

    most people just put a hefty reverse diode across the coils.

    Steve
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

  10. #10
    Join Date
    Oct 2009
    Location
    sweden
    Posts
    116

    Default

    there is already a freewheel diode in the BTS412B2
    but it doesnt help

    should i put the resistor like this in parallel?
    is 1w resistor ok or should i go for 10w?

    Click image for larger version. 

Name:	gm20 res.GIF 
Views:	195 
Size:	2.8 KB 
ID:	18102
    Last edited by teknofon; 07-02-2010 at 23:26.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •