help needed on UCN5804B

Discussion in 'The Projects Forum' started by thavamaran, Mar 16, 2009.

  1. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    Hi guys, im currently working with ucn5804b for my stepper motors, but the problem is from what i understand through the datasheet, it only supports 4 phase steppers, im planning to use 2 phase steppers, is it possible that ucn5804b can support 2 phase motors? and another thing, there is some problem with the quality of IC whereby me and few of my frens roast our UCN5804b by just connecting them according to the given schematic in datasheet.

    I think that might be the problem with the output line where the current from stepper motor strike back the IC, can i get any suggestion on the circuit design, as what i thought was may be i could fix a diode on the output line and a resistor for current limiting.

    I know the resistor value can be calculated out with ohms law, but then how about the power rating of the resistor? please guide me on this particular resistor part.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Where is the datasheet for the stepper motors that you are planning on using?

    The Allegro datasheet for the UCN5804 shows connections for a unipolar stepper motor.

    It won't support bipolar (4-wire) stepper motors. Those type stepper motors require an H-bridge for each lead.
    Some stepper motors are supplied with eight leads; those can be wired for use as either bipolar or unipolar stepper motors.

    Did you use the reverse-EMF protection diodes? Attach the datasheet for the UCN5804b that you are using.
    [eta] If your stepper motors are bipolar, you could not have wired them according to the datasheet.

    The Allegro datasheet for the UCN5804 shows two "Typical Applications" circuits. I prefer the lower scheme, because the reverse-EMF protection diodes only carry current for short periods of time.

     
    Last edited: Mar 17, 2009
  3. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    Hey sgt wokie, i have attached the datasheet, thanks for the quick reply, anyway im not using any bipolar stepper motors, im using unipolar but 2 phase stepper motor, but if you look at the datasheet, its written as 4 phase, thats why im wondering. and about the circuit design, can you go more brief about it.

    thank you mate!
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I already have the datasheet for the 5804.
    I need the datasheet for the stepper motors that you are planning on using.
     
  5. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    Oh im sorry, i misunderstood, here i attach my stepper motor datasheet. Thank you again.

    The model is PX243-01AA. Thank you again.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    OK, that's good.

    Where is your schematic of how you have it connected up?

    You're using +4v for the stepper motor supply, connected to both the white and yellow wires, right?
    [eta]
    If you don't have a schematic drawn, go by this:
    [​IMG]

    You may have to swap the black and green and/or red and blue wire connections to get the motor to rotate.

    Note that inputs on pins 9 through 15 MUST be connected to either +5V or ground.
    The STEP input must alternate between +5v and ground.
    If you leave any input "floating" (ie: not connected to +5V or ground), you will experience very erratic operation (if at all), and probably overheating.
     
    Last edited: Mar 17, 2009
  7. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    hi wookie, dun mind calling u wookie. its a great job mate, seriously great job, by the way i understand fixing a diode at the output line is apparently to block current from motor to strike back the IC, but then i understand why diode is fixed with respect to ground? do you mind explaining? sorry for the inconvience cause.

    Another thing is, if you look back at the motor datasheet, the torque vs speed graph, its written there that supplied with 24V, but according to the table, its only 4V DC. really confusing there.

    Another thing is, the other day when my frens was testing it, they fixed LED across the output line with respect to ground, still the IC got roasted.

    So how actually i can calculate out resistor for the output line?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    When the output of the 5804 turns off, the current in the motor's winding will still try to flow for a time. The diodes on the output, along with the IC's internal protection diodes, provide a path for that current. Otherwise, there would be a very high voltage spike (perhaps hundreds of volts) that would destroy the IC.

    That's if you're using a "chopper driver" IC. The 5804 is not a chopper driver, nor can it be easily made into one. If you want to look at chopper drivers, look at using a pair of L297/L298 IC's. They are harder to understand, though.

    LEDs are not designed for power rectification; most typical LEDs are rated for a maximum current of 30mA or less. Your friend probably roasted the LED along with the 5804 IC.
    If you use a 4v supply for the stepper motor, you don't need a resistor.

    If for some reason you need to use a 5v supply, you will need to use 1 Ohm resistors rated for at least 2 Watts in series with both the white and yellow wire connections.

    The stepper motors will generate a great deal of electrical noise. It would be a good idea to use a separate power supply for the motors and the logic circuits.
     
  9. thavamaran

    Thread Starter Active Member

    Feb 21, 2008
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    0
    Hey wokie, you did a great job mate, thanks a lot, my stepper actually working. Thanks again mate.

    Another thing is, i have a question, why is that step input pin is actually needed. because you see, from the recorded data i have now, the no matter the step input is low or high, there is still movement in stepper when i shift high and low at direction. another thing is, im just simply using DC supply and shifting the direction pin. so im using 2 supply, one for the IC and the other one for the Stepper, as u advised.

    So when just say when the direction pin is low, and i fix the white and yellow wire from stepper motor which is the common input to high, then i plug in each wire to its output, lets blue to output to B, Red to D, Green to C and Black to A, so when just say the direction is low, i put in each of the stepper wires into their output pin, when its show short in DC supply, there is a movement in stepper, but when there is no short, the stepper is not moving. its working the opposite way, may be i dont understand the principal.

    Like just say,step input low, my direction is low at one point, and at this point, just say i put the Green in, no short, no movement, then Red, got movement, then Black no movement, then Green got movement, so i assume its the rotor is moving from D to A point.

    And just say i keep my direction low and switch step input to high, and direction stick to low, the output is same, but when i change direction's input, the output changes. then what is the purpose of step input, cause as i understand step input should make the motor move during On timer and off during Off timer, but here its low or high, the motor still moves. really confusing me. And why the motor only moves when output shorted?

    And seriously thanks again for your in detail guidance. and as u said i didnt fix resistor at the output.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    That's good news.

    The datasheet indicates that the STEP input must be at a logic low level when changing the state of the DIRECTION, ONE-PHASE or HALF-STEP pins to prevent erroneous stepping. See page 4, paragraph 2 of the datasheet.

    The DIRECTION, ONE-PHASE and HALF-STEP pins set up the conditions for stepping. The STEP input is what tells the logic to perform the stepping.

    You have the grounds connected between the supplies, right?

    You shouldn't be connecting/disconnecting wires to the IC when power is applied.

    The IC works by completing the current path through the various windings of the stepper motor. Power is always available on the winding's center taps; the white and yellow wires. When the output transistors connect the motor's other wires to ground, the motor's winding is energized.

    Keep the STEP input low when changing the other inputs.

    That's how it works. Try studying the 5804 datasheet several times before you experiment more.
     
    Last edited: Mar 18, 2009
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