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I am confused on whether this is a depletion or enchantment MOSFET and I am wondering if anyone could figure it out. I need a depletion MOSFET for my circuit and can't figure out if this MOSFET is one.

Here is the link to the MOSFET:

https://lcsc.com/product-detail/MOSFET_ROHM-Semicon-RTQ025P02TR_C79602.html

user29946
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3 Answers3

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No.

It is P-channel enhancement MOSFET, not depletion. You will probably not find one as depletion mode MOSFETs are exceedingly rare and I have never seen a P-channel one. You would be recommended to not require them in your design.

I agree it can be confusing with a P-channel as the voltages are negative and datasheets are not consistent in the way they present the negative gate voltage.

You can see from the datasheet that the drain current at zero Vgs is about zero so it is not a depletion mode.

enter image description here

Kevin White
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  • Thanks for the response! What would you recommend I use as an alternative to a depletion MOSFET? – user29946 Apr 02 '21 at 20:16
  • It depends upon the circuit. If you describe the circuit problem in the question we may be able to help provide a solution. It is unusual to need a depletion-mode MOSFET but they can be useful in some situations. – Kevin White Apr 02 '21 at 20:42
  • I am trying to use some sort of depletion transistor to close the battery from the circuit when I get a USB power supply. I am trying to pass 3.3V at about 300ma through the transistor. – user29946 Apr 02 '21 at 21:07
  • @user29946 - a depletion mode FET is not necessary. One way is to use a p-channel FET in reverse configuration where you drive the gate to ground to enable the FET to pass current from the battery with negligible voltage drop. When USB power is available drive the gate to 3.3V(or even directly from the USB Vbus) to turn it off and allow the circuitry to be powered from USB. – Kevin White Apr 02 '21 at 23:26
  • Can you send an example of this circuit because I am lost sorry. – user29946 Apr 03 '21 at 00:13
  • For example: https://electronics.stackexchange.com/questions/96059/switch-between-battery-and-usb-power-no-microcontroller-circuit – Kevin White Apr 03 '21 at 00:25
  • If I am understanding correctly by grounding it we are creating a drain current and therefore allowing current to pass through from the drain to source right? – user29946 Apr 03 '21 at 00:43
  • @user29946 - yes. The FET will have a -3.3V gate to source bias turning it on. – Kevin White Apr 03 '21 at 00:56
  • Sorry I keep asking, but I will have to account for a forward voltage drop when I use a Schottky Barrier Diode right? – user29946 Apr 03 '21 at 01:19
  • @user29946 - what is the battery voltage? do you have regulator for the 3.3V. Why not put this information in the question? The real question should be about this, not about getting an depletion MOSFET. – Kevin White Apr 03 '21 at 17:16
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Mouser says it is enhancement type, but datasheet does not say anything about that.

By googling "RTQ025P02TR depletion" google says there are no good matches for my search. So this must be the case. It is enhancement type

If I were you, I would choose another part, which would have a more complete datasheet. Not all datasheets are good/detailed datasheets

Christianidis Vasileios
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No it isn't. Just the symbol is (usually) enough to distinguish it.

Enhancement mode (from the datasheet):

enter image description here

Depletion mode (from an Ixys dataheet):

(you will note that the gaps are missing on the depletion mode symbol).

enter image description here

Too bad, there are many N-channel depletion mode MOSFETs but no P-channel that I know of. Depletion mode MOSFETs can come in very handy in some situations.

Spehro Pefhany
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