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P channel Power MOSFET - RF Cafe Forums
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lna
Post subject: P channel Power MOSFET Posted: Wed Jun 10,
2009 12:32 am
Captain
Joined: Mon May 04, 2009 6:47 pm
Posts: 22
Hi, there. Can someone suggest a p channel power mosfet
I need such one to switch +28VDC rail max current of 2A. The MOSFET
is controlled by a open drain output comparator, which is 5VDC powered.
As I can see, the max IGS of the MOSFET needs to be larger than +/-
25VDC. I have checked onsemi and found nothing meet my requirement.
Thanks!
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Mike_From_Plano
Post subject:
Re: P channel Power MOSFETPosted: Fri Jun 12, 2009 2:20 pm
Captain
Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14
Hello,
I don't think you'll find a MOSFET with such a high gate punch through,
but that's not the end of the world, you just need to modify the circuit
slightly.
I'd send you a picture, but I don't know how to get it
across... SO, here goes a way to describe what you need:
BOM:
1. (1) Q1, MMBT3906 (or other NPN)
2. (1) Q2, FDD8685 (or similar
P-MOSFET)
3. (1) R1, 2.2K, 1/10W, 5%
4. (1) R2, 2.7K, 1/10W, 5%
Netlist:
R1, Comparitor_out, NPN_Emitter
Q1, (E)NPN_Emitter,
(B)+5V, (C)MOSFET_Gate
R2, MOSFET_Gate, +28V
Q2, (S) +28V, (G)
MOSFET_Gate, (D) Switched_28V
I hope this isn't too much a mess,
communicating it by net list. Also, this circuit is only valid for slow
switching. If you need something in the kHz, this won't get it because
the MOSFET turns on & off very slowly.
If you need something
fast, post it, and I'll give you something a little more complicated
+ faster.
- Mike
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Mike_From_Plano
Post
subject: Re: P channel Power MOSFETPosted: Fri Jun 12, 2009 6:27 pm
Captain
Joined: Mon Apr 20, 2009 2:04 pm
Posts: 14
Oops,
Q1 should be MMBT 3904 (the NPN version!)
and
R2
should be 4.7K
I plead old age....
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lna
Post subject: Re: P channel Power MOSFETPosted: Tue Jun 16, 2009
9:39 pm
Captain
Joined: Mon May 04, 2009 6:47 pm
Posts:
22
Thanks a lot, Mike. This is a good solution but the logic is
reversed to my application so a NOT gate is needed to fix the logic,
or maybe connect comparator output to base and emitter to GND.
Is it possible to control P-channel MOSFET gate by a N-channel FET?
I found some N-channel FEt with 30VDC VDS however max VDG is not specified
. I wonder why VDG is not important.
Posted 11/12/2012
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