Build the Banshee

Those who can do!


          After selling several Banshee Booklets, a few people actually built the circuit and got it working. Then they started having problems with the Fets blowing. One guy had the Fets blow in a few minutes while others had them blow after one hour.  I had several people send me their boards. After replacing a blown Fet I ran the board to the cows came home. I have yet to blow a Fet here! This became very frustrating. Heat seemed to be tied to the problem in some way. My cellar is very cold and the Fets ran cool and without problem here!
          The circuit was nothing more than an update of the French circuit. I eliminated the 7409 with some transistors while driving the Fets a little harder. So what the hell was going on?  I did lots of reading.  When you drive a Fet at 24 volts on one winding of the stepper,  48 volts appears on the second winding due to a transformer effect. This blew my mind!!! I would expect 24 volts since the windings are one to one. So the Fet that is off is getting hit with 48 volts caused by the Fet that is working. No big deal I used 60 volt Fets. The Fets have built in diodes that protect them from spikes, Right? Wrong!  They only protect the Fets from spikes going in one direction. So the Fet is sitting there being hit with 48 volts along with some 90 volt or higher spikes. A 60 volt Fet being hit with 90 volt spikes will work for awhile. The Fet seems to handle the 90 volt spikes until it warms up. Then all the breakdown voltages start to go lower. The avalanche voltage of the 60 volt Fet is no longer 60 volts when it gets hot. Even 100 volt Fets are no match for the spikes. So we added some 48 volt snubber diodes to the outputs. This cured the problem. I found adding a .022uf and 10ohm 2watt  to each output also kills the unwanted spikes.

                                                             (End of UPDATE)

          The last four years in between projects I have been trying to come up with a simple and easy to build UniPolar chopper circuit. I wanted the circuit to use cheap easy to find off the shelf parts that don't require a minimum order. I bought some L297 and L298 chips along with some FETS and other parts in order to run some tests. I tried every chopper circuit I could find. As I started closing in on my goal, Dave at HobbyCNC came out with a single chip solution. As more and more of my cutomers bought Dave's board to use with my machines, I dropped out of the motor driver part of the business in order to do projects like the Jester and Woodturtle.

          On the Internet there is a company that uses a L297 with a 7409 to drive some FETs. The 7409 is needed to make up for the gates that are found in the L298. I thought they had come up with something really special until I found the idea inside the L297 data sheet. I tried the circuit and so did a few others. The FETs run hot because the 7409 can't supply the correct driving parameters for the FETs or the Logic Level FETs are not ment for this application. They show a giant heatsink on one of their webpages. The Logic Level FETs they use are hard to find and they are listed as obsolete. The 7409 use is an old rarely used TTL chip that can also be hard to find. Still the idea was interesting and it kept bouncing around in my head. One day while walking I got the idea to use a L297 with a L298. My idea was to use the L298 to power the FETs. Now I had the needed gates along with the necessary drivers. I called this circuit KleinChopper. I posted the circuit on the Internet with a message to only ask me questions in that conference. Then my mailbox loaded up so I pulled the schematic down. A year later I put the circuit back up only to have the same knuckleheads contacted me again even though I warned them again only to post questions in that conference. None of them tried the circuit. Gee what a surprise! If you can't read you can't build!!!

          A few weeks go by and during a long four hour walk my brain starts going back through the circuits I have built. It starts trying to find a replacement for the L298. Instead of using the L298 to drive the FETs my brain starts down the path of using some cheaper discrete components. In the past I did try using some diodes to make the Gates found in the L298. This resulted in a nightmare of parts. Suddenly I got a vision!!! The solution was to think in reverse!!! The solution was so simple! I now had a simple easy to build chopper that uses cheap easy to find parts. Instead of turning out a board and competing with Dave I decided to write a booklet showing how to wire this circuit on perfboard and to show a layout for a printed circuit board. I won't be coming out with a circuit board. If you want a cheap UniPolar driver on a circuit board see Dave!

       This project is not for beginners. The circuit is very simple but it requires wiring and soldering skill most people only think they have. I will only supply a little help with this project. The booklet is 16 pages printed on single sheets so you can lay out the ones you need while wiring.  The booklet shows how to wire the project on PerfBoard.  It also has traces superimposed on PerfBoard for those who want to enter the data into Eagle or other program using a .1 grid.

          The Booklet is $25 and only sold to the US and Canada!

Email: John a quick question

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