Can I use ULN2303 as input to Mosfet gate?

(I'm newbie) I have an Arduino Uno connected to a ULN2803(5V) which lights up an array of LEDS. I would like to take one of the outputs from the ULN2803 and use it as input to the GATE of a MOSFET(P30N06LE) to light another LED(or motor etc). I can get the MOSFET to light the LED without the ULN2803 but it does not work when the ULN2803 pin is connected to the MOSFET gate. What am I doing wrong?

by sheonbanks
December 01, 2020

VGS(TH) of the P30N06LE is between 1 and 2 V. At 1.6 V, you can probably light on a red LED with a reasonable 20mA through it, but 1.6V may be not enough to fully open the MOSFET. Note that generally, the VGS(TH) is defined when the current reaches 1mA, so you need more that this bare minimum. Typically, that MOSFET can let a current up to 20A with 3 V at the gate (figure 7 of RFP30N06LE), so, the Arduino should be able to supply enough voltage without using the ULN (the number in your title differs to the number in your text). Can you measure the VGS at your MOSFET with a multimeter?

Oh, and to protect it, if you use an inductive load, such as a motor, add a diode in reverse, in parallel to your inductive load, to provide a path to back EMF.

Final note, the "load" should be between the drain of the MOSFET and the + side of the DC power supply, while the source pin of your NMOS should be connected to the - side of the DC power supply. And avoid using a USB power supply, they may be unable to handle back EMF.

by vanderghast
December 02, 2020

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