N-channel vs P-channel MOSFETs

[VinceC]

I was wondering if there is any particular reason why some PI designs are based on P-channel MOSFETs rather than N-channel. From what I have been reading N-channel MOSFETs are available in much higher voltages, can handle much higher currents, and are available with much lower ON resistance. And it appears that the circuit design changes to switch from one to the other are almost trivial.

What am I missing? Thanks!

[geoscash1]

I have often found myself wondering the same thing.. I hope to see some good replies from the gurus.

[kt315]

surfmaster pi was projected with TIP32C pnp transistor. Eric Foster's mod is to change it on p-channel MOS-FET directly. no another reason.
what schematic you did still mean?

[VinceC]

That is the general PI design that I was thinking about, and I ended up building silverdog's Surf PI kit which uses a IRF9640 (p-channel) also. The schematic for that kit is here (http://www.silverdog.co.uk/shop/imag...ematic1_2A.JPG).

[Jose]

I thought I heard that the advantage of using a P-channel power mos simplifies the power supply. I'm not sure, I hope someone can dispel the doubts.
Jose

[Davor]

Precisely. You pick a MOSFET polarity according to the power supply and where your reference is. You may observe MOSFET as a kind of Darlington transistor, but with some interesting features, and with awful capacitances.

[Qiaozhi]

That is the general PI design that I was thinking about, and I ended up building silverdog's Surf PI kit which uses a IRF9640 (p-channel) also. The schematic for that kit is here (http://www.silverdog.co.uk/shop/imag...ematic1_2A.JPG).

The Minipulse Plus uses an n-channel mosfet -> Minipulse Plus REV-C, and so does Hammerhead.

[VinceC]

The Minipulse Plus uses an n-channel mosfet -> Minipulse Plus REV-C, and so does Hammerhead.

But is there an advantage of one type over the other? I see n-channel as having many advantages (as I listed in the OP) but have yet to find one for p-channel. Am I mistaken?

[kt315]

That is the general PI design that I was thinking about, and I ended up building silverdog's Surf PI kit which uses a IRF9640 (p-channel) also. The schematic for that kit is here (http://www.silverdog.co.uk/shop/imag...ematic1_2A.JPG).

IRF9640 has Vds 200V max rating voltage while IRF740 has 400V. do you feel something difference between both?
you can not simply increase PULSE WIDTH using the p-channel because that limitation.

[VinceC]

IRF9640 has Vds 200V max rating voltage while IRF740 has 400V. do you feel something difference between both?
you can not simply increase PULSE WIDTH using the p-channel because that limitation.

Can I ask you to explain what you mean? I do not understand (I am not an electrical engineer, so there is something that is probably obvious to one, but not to me).

[Thomas]

it is difficult to make an n-channel device that is off at zero gate voltage, PMOS devices are more immune to noise than NMOS devices.

[VinceC]

it is difficult to make an n-channel device that is off at zero gate voltage, PMOS devices are more immune to noise than NMOS devices.

Thanks! That would make the choice of p-channel more logical. Are there n-channel devices that do shut off at zero voltage and have the noise immunity of standard p-channel devices?

[kt315]

Can I ask you to explain what you mean? I do not understand (I am not an electrical engineer, so there is something that is probably obvious to one, but not to me).

1 point. N-cnannel MOS-FET has more hight max raiting drain-source voltage than P-channel. in regarding to PI method that gives the tuning PULSE WIDTH to more hight value - more TX power in coil.
2 point. P-channel has more less resistance drain-source in open state than N-channel. in regarding to PI metod that decreases a loss of TX energy.

[daverave]

i think the P channel mosfet used on the surf pi is very limiting and restricts the pulse width that can be used !!!! i scoped the back emf and it clamps at around 200 volts !!! i feel a N channel mosfet like irf 840 is better cause we can increase the tx pulse current and get better depth...thats my personal opinion.

[kt315]

I am not an electrical engineer

sorry I am not able to tell you in terminology of a kitchen wife. my english is simplest. maybe speaking english gurus will give you more clear picture.
yes, Daverave you are right. but Surf PI, Surfmaster PI are UNDERWATER SPECIFIC detectors with ABSOLIUTELY MINIMAL POTS AT FALSE PANEL - SIC PLEASE
AT THIS FACT. NO there a possibility to turn THE TX POWER because PULSE WIDTH is fixed at 50 microsecond value. that is due enought for those
detectors and enought for P-channel with 200V max on the DRAIN.

3 point. a point where to connect the shield of schematic and a coil. with P-channel the point is a ground of the schematic. with N-channel the point is +E of the schematic, the PLUS of batteries.