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Another Stepper Driver Question

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davidbear

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Dear All,

Thanks in advance for your patience, I'm still a newbe. I recently purchased on the cheep a Vexta PK244-01AA Stepper motor that I want to use in bipolar mode. Since the current for the ultimate bipolar stepper that I want to purchase requires 4 Amps per phase, I decided that a L298 or L293D would be inadequate for my needs and decided to design a discreet driver for use with a Arduino uC board with 5V/100mA outputs. I am particularly concerned with my component choices since I have never done this before. I chose the ILQ2 (pdf) opto-isolator to bring my logic levels to 24V so that I could control the H-bridge. I chose the FJAF4x10YTU PNP/NPN transistors because of their cost/current handling ability. I chose the 1N4148TA diodes because of their low t(RR). Would someone be kind enough to look at my schematic and let me know if it all makes sense or if there are other choices that should be made instead or if there are out-in-out errors.

Thanks,

DavidBear
 

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davidbear

New Member
Thanks for the solution, the price certainly can't be beat. Do you have anything that comes in a DIP? Also, what MOSFET/Diodes would you recommend? The data sheet only specifies an N-Chanel MOSFET and a diode with no further comment. For Pedagogical reasons I would still appreciate comments on the original circuit.

Thanks,

DavidBear
 

Ubergeek63

Well-Known Member
well i do like the allegro prices :) you can check the rest of their products. they do have some dips and more basic drivers.

that one is a current source driver with syncronous rectification and translator (direction/step control).

There is no further comment becuase that depends on your motor, a bigger motor requires bigger more expensive drive FETs. With synchronous rectification external rectifiers are not critical and can be left off with out problem if you have a FET with a switching rating on the parasytic diode. It also has the ability to microstep...

Well your low side does not need the optos, and will in fact blow out the ones there as shown. The chances are you are not going to be going very fast, but if you are the optos would likely be a failing point since most optos are very slow. The 10K resistors would ensure the system ran to slow as well as not supplying enough base drive to the transistors. Is that enough background?

Dan
 

davidbear

New Member
Sorry to be so daft. My understanding of the opto-isolator input side is that takes 1.1-1.4V at 20 mA, thus there will be 3.9V leftover through the 220 ohm resistor to give 18 mA. On the output side, I now see that I had a logic problem. Now, the 300 ohm resistor should allow a 80 mA current to control a 4A current (assuming an hfe of 50 at saturation). Am I on the right track?
 

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Ubergeek63

Well-Known Member
Sorry to be so daft. My understanding of the opto-isolator input side is that takes 1.1-1.4V at 20 mA, thus there will be 3.9V leftover through the 220 ohm resistor to give 18 mA. On the output side, I now see that I had a logic problem. Now, the 300 ohm resistor should allow a 80 mA current to control a 4A current (assuming an hfe of 50 at saturation). Am I on the right track?
well 80mA would be hard on the optos, they are still likely to be slow if you are switching at a reasonable rate, and while the opto is trying to pull to 24V the lower base emitter junction will hold it at 0.6V
 
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