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Author Topic: P-Channel Mosfet for switching  (Read 744 times)
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I'm using a P-Channel Mosfet as a switch to send 24vdc to my output all controlled through an ATMEGA.

Looking for any input on my schematic.

and

I have a question about my grounds. I am using two different voltages. 9v battery will provide pwr for Arduino and separate 24v battery will provide power to output. Do I have to be concerned with sharing grounds between these? If GND1-GND3 were all connected with this cause issues?

Is it safe to say that GND1 and GND2 would need to be shared for T1 to function properly?

Thoughts?

Tks

M


* PCHANNEL.bmp (892.14 KB, 811x375 - viewed 29 times.)
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Yes, in your configuration you will need all grounds connected together.

You're also going to apply a bit too much gate-to-source voltage when the P-channel MOSFET is turned on. A 24V difference may even damage it. I'd recommend adding another resistor in series with the BJT collector terminal to form a voltage divider with the 10k resistor and get the gate-to-source voltage to be about 12V (so another 10k resistor should do it).

Otherwise it's looking reasonable.

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Like this?


* PCHANNELrev1_1.bmp (913.55 KB, 811x384 - viewed 29 times.)
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Looks right.

I'd hook up AVCC and AGND too even if you don't need them.

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You definitely need to hook up AVcc and AGnd - in particular, the chip won't work if you don't hook up AVcc.

I'd reduce R1 and R3 to 1K each to help the mosfet switch faster, because it has quite a high gate charge. This is especially important if you are switching the output frequently, e.g. using PWM.
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The Avcc and Agnd will be hooked in the completed design I put the MC in there just as reference to show what the MOSFET was being controlled by and to identify the gnds for my question.

Thanks for the help.

Does anyone have any thoughts on using opto-isolators on my MC outputs?

M
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Does anyone have any thoughts on using opto-isolators on my MC outputs?

If commoning the Arduino and 24v grounds is OK, you don't need to use an opto isolator. If you can't or don't want to common the grounds then you do need one.
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