Diode equal

Discussion in 'The Projects Forum' started by Redstone2, Jan 11, 2011.

  1. Redstone2

    Thread Starter Member

    Oct 21, 2010
    20
    0
    Hello,
    I need help finding an equal to a “BYW98” diode. The application is for a 24 volt, 4 ampere (maximum) dc motor controller. Attached is the circuit diagram.
    Would a Schottky diode work in this application?
    Thanks for any ideas.
    Sincerely,
    Tom
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Redstone2 likes this.
  3. Redstone2

    Thread Starter Member

    Oct 21, 2010
    20
    0
    Hello,

    Finally got everything together, assembled, the motor controller and the microprocessor, and tested last night. There was no joy but no smoke, so not so bad. The code was checked = ok, the microcontroller checked: PWM=OK, logic flip-flop for bi-direction=OK, voltage=OK.

    I think the diodes purchased are no good. I'm complete novice, so I tried the test with battery found here http://www.allaboutcircuits.com/vol_3/chpt_3/2.html . The readings, with a 9 volt battery, are: test set-up as shown = 0.5 volts; text has another test "Connecting the diode backwards to this testing circuit will simply result in the voltmeter indicating the full voltage of the battery" this version of the test = 8.3 volts.

    I also did a simple test with a multimeter: Measure the voltage through the diode with a 9-volt battery. No matter the orientation of the diode the meter read battery voltage. This confuses me, should the voltage be 0 in one of the two directions?

    Attached are two images. One across the diode, the other at motor terminals.

    Thanks for any pointers and/or ideas on the problem.

    Kind Regards,
    Tom
     
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    The 1N5822 is a Schottky diode with a relatively high leakage current, specified at 2mA at 25C. See datasheet: http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00001626.pdf

    This may result in the reverse connection tests showing such results, which do not necessarily indicate a problem.

    Ordinary silicon PN diodes might have leakage currents around a thousand times less - and for some smaller devices the leakage would be lower still. The simple diode tests should give clearer indications with devices like these.
     
  5. Redstone2

    Thread Starter Member

    Oct 21, 2010
    20
    0
    Thank you. Makes sense now; the meter was measuring the voltage with the 2mA leakage.
    Using the test from volume 3, the diode tests good; V(f) is on target.
    Now to find the problem.

    Thanks for your reply.

    Tom
     
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