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I want to be able to control an RGB LED with common cathode and I've used the circuit below for each colour. For some reason there is 12V on the output all the time and I can't control the LED as it's switched on all the time.

Circuit

Any help will be greatly appreciated.

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    \$\begingroup\$ What are the voltages you apply to O1? \$\endgroup\$ Sep 28, 2020 at 18:09
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    \$\begingroup\$ also, your circuit is direly missing a series resistor for your LED. \$\endgroup\$ Sep 28, 2020 at 18:10
  • \$\begingroup\$ The voltage on O1 is 5V. The series resistor is already in the LED (it's a button with RGB LED inside) \$\endgroup\$
    – Cezerb
    Sep 28, 2020 at 18:13
  • \$\begingroup\$ then please add the resistor to your schematic – otherwise, the schematic is incomplete (you're using a "diode" symbol, not an "LED with series resistor" symbol, which afaik doesn't exist). \$\endgroup\$ Sep 28, 2020 at 18:15
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    \$\begingroup\$ @MarcusMüller I've checked the datasheet and there is indeed a body diode going from drain to source. Correct me if I'm wrong but as I understand the current goes through this diode and thus the MOSFET is kind of useless and does nothing. \$\endgroup\$
    – Cezerb
    Sep 28, 2020 at 19:03

2 Answers 2

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Body diode of Q12 is conducting permanently in your circuit. To avoid such mistakes use schematic symbol with diode drawn inside the mosfet. Link to datasheet of the mosfet.

enter image description here

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P_chanel mosfet should be connected source to "+ ", drain to resistor r14.turn it over

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