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My aim is to automatically power off the ESP by turning off the pinout.

When I test the circuit I get the out voltage 1.6 V when I assume to get 3.3 V.

What I'm doing wrong?

enter image description here

Vellu
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  • Yeah, we are done. The circuit work as expected. My R2 resistor value had a typo, I was meaning value 100 not 100k. My circuit started to work after I changed the Q2 fet.

    @andy-aka you are making a great work, thank you!

     – Vellu Jan 13 '22 at 08:12

1 Answers1

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The IRF4905 is no-way suitable for such low voltage supplies. The \$V_{GS(THRESHOLD)}\$ value is typically about -3 volts and could be as high as -4 volts. At this sort of drive level, the MOSFET can only really supply about 250 μA and this sounds like it is too low for any reasonable load you are trying to switch on or off. If you read the data sheet you'll see that at about -4.5 volts, you might be able to supply a load with a current of around 2 amps with a volt-drop of about 0.1 volts: -

enter image description here

You need to find a P channel MOSFET with a \$V_{GS(THRESHOLD)}\$ voltage closer to 0 volts. Maybe something like -1.5 volts. Maybe try Alpha and Omega Semiconductor. Maybe this one but it's still not that great on heavy currents with a 3 volt gate drive.

Regarding the ESP32 I'd take a look at the data sheet to see what they recommend: -

enter image description here

Andy aka
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  • So Vgs(th) max should be more than 3.3 V and min should be less than 3.3 V, right? – Vellu Jan 05 '22 at 16:01
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    Vgs(threshold) needs to be significantly closer to 0 volts than -3.3 volts. – Andy aka Jan 05 '22 at 16:03
  • Ok, thanks. I think I'll give a try for this one: https://datasheet.lcsc.com/lcsc/1808272021_Vishay-Intertech-SI2301CDS-T1-GE3_C10487.pdf – Vellu Jan 05 '22 at 16:11
  • If you are OK with a load of about 5 amps causing about 0.5 volts to be dropped across the MOSFET ----> your output voltage won't be 3.3 volts but more like 2.8 volts with 5 amps flowing. With 2 amps flowing the output will be more like 3.1 volts. Can you live with this I wonder? – Andy aka Jan 05 '22 at 16:15
  • Max current would be about 0.2 A. 0.2 V voltage drop would not be a problem but 0.5 would be. – Vellu Jan 05 '22 at 16:36
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    @Vellu if we're done here maybe you'd like to understand why folk give their time for free. Please take the 2 minute tour to understand this vexing question LOL. Look for this bit The person who asked can mark one answer as "accepted". Accepting doesn't mean it's the best answer, it just means that it worked for the person who asked. – Andy aka Jan 05 '22 at 16:49
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    @Vellu with 0.2A current the voltage drop will be very low. I.e. that MOSFET will work for your case. – NStorm Jan 05 '22 at 17:17
  • Nice. What you think are these resistor values 10k and 100k reasonables? – Vellu Jan 05 '22 at 17:44
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    @Vellu to whom are you addressing your comment. If me @andy aka then I would make R2 much lower, maybe 4k7. If you want Q2 to turn off real quickly then I'd make R1 possibly 1 kohm but, 10k is probably all right. Are we done here? – Andy aka Jan 05 '22 at 17:49
  • @Vellu you can drive Si2301CDS directly from ESP actually. With only single gate resistor of ~330-470 ohms. There is no real need for a BJT to drive it. – NStorm Jan 05 '22 at 18:01
  • @Vellu: regarding resistor R2's value, I recommend you take a look at this post: https://electronics.stackexchange.com/a/488355/79842. – Jim Fischer Jan 05 '22 at 21:22