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I have been working on it for two weeks in this project. Last day I have built a circuit to control the DC Motor speed that is shown in the image here. I have seen some questions like this in this forum and take those as references to build a circuit. But My circuit is not working at all. Here is the measurement I have given as input to the circuit and some voltage measurements.

I/P for optocoupler 5V from Arduino, VGS of MOSFET is 3.9V. VDS of MOSFET is 24V.

According to the datasheet, input voltages are enough for this circuit. But I don't know which causes the problem in this circuit. The motor is 24V DC and it is not running when connected with this circuit. What must be the problem here? Help, please! enter image description here

Links for DATASHEET:

MOSFET STB55NF06L: http://www.st.com/content/ccc/resource/technical/document/datasheet/49/c5/a8/71/93/60/4f/86/CD00002690.pdf/files/CD00002690.pdf/jcr:content/translations/en.CD00002690.pdf

OptoCoupler PC817: http://www.sharp-world.com/products/device-china/lineup/data/pdf/datasheet/pc817xnnsz_e.pdf

Schottky Diode 1N5819 : https://www.vishay.com/docs/88525/1n5817.pdf

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  • \$\begingroup\$ Show gate-emotter oscilligram or even just a multimeter DC voltage measurement of the same when you apply 100% duty-cycle. \$\endgroup\$
    – winny
    Commented Sep 22, 2017 at 7:28
  • \$\begingroup\$ That gate-emitter voltage is 3.9V. \$\endgroup\$
    – CNA
    Commented Sep 22, 2017 at 9:07
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    \$\begingroup\$ Measure the supply voltage and drain-source voltage when "on". And test the motor runs connected straight to the supply. Is the supply rated for the motor's stall current, or is the starting current making the supply shutdown? \$\endgroup\$
    – user16324
    Commented Sep 22, 2017 at 9:45
  • \$\begingroup\$ Replace resistors with R2=1k, R3=680, ZD=10V or remove it. \$\endgroup\$
    – Marko Buršič
    Commented Sep 22, 2017 at 11:37
  • \$\begingroup\$ 3.9 V is enough for substantial current according to the datasheet. Is the transistor genuine? Is it heating up? Also, listen to Marko. \$\endgroup\$
    – winny
    Commented Sep 22, 2017 at 12:35

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