MOSFET: N- or P-, enhance or deplete?

[Ian Field]

"rickman" <gnuarm@gmail.com> wrote in message
newsi3lfj$sco$1@dont-email.me...

Bob Engelhardt wrote on 6/17/2017 10:10 AM:
On 6/17/2017 3:25 AM, jurb6006@gmail.com wrote:
"So it would
be like this (P-channel, enhancement mode)? : "

It has to be enhancement mode ...

Thanks.

Furturlec has a bunch of P-channel MOSFETs & I picked IRFL9110 more or
less
randomly. Looking at the IR spec sheet for it, it doesn't say
"enhancement":
http://www.futurlec.com/Transistors/IRFL9110pr.shtml
The Mouser listing for it does say it's enhancement, but why isn't it on
the
spec sheet? Is it because enhancement is the default mode & it "goes
without saying"?

Look at the threshold voltage. That is what you care about. Make sure
your gate drive is significantly more than that wrt the source. This part
has a threshold of -4 volts max,

Motherboard MOSFETs switch well with Vgs slightly under 2V, they typically
go up to about 80A, but the voltage rating is usually 30V - sometimes only
20V.

You probably won't find any P-channel.

 

[Ian Field]

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:d4sakc9hdtt73kpgq6l9jbis0uhteep0pe@4ax.com...

On Sat, 17 Jun 2017 10:10:24 -0400, Bob Engelhardt
BobEngelhardt@comcast.net> wrote:

On 6/17/2017 3:25 AM, jurb6006@gmail.com wrote:
"So it would
be like this (P-channel, enhancement mode)? : "

It has to be enhancement mode ...

Thanks.

Furturlec has a bunch of P-channel MOSFETs & I picked IRFL9110 more or
less randomly. Looking at the IR spec sheet for it, it doesn't say
"enhancement":
http://www.futurlec.com/Transistors/IRFL9110pr.shtml
The Mouser listing for it does say it's enhancement, but why isn't it on
the spec sheet? Is it because enhancement is the default mode & it
"goes without saying"?

Bob



Yes; depletion mosfets are rare and they make a point about it.

Maybe its Supertex (or similar) that does depletion mode high voltage power
types.

A few years ago; Elektor magazine published a high voltage psu project with
the option of triode or MOSFET series pass.

 

[Ian Field]

"Bob Engelhardt" <BobEngelhardt@comcast.net> wrote in message
newsi4fbb11ssn@news6.newsguy.com...

On 6/17/2017 2:14 PM, John Larkin wrote:
Yes; depletion mosfets are rare and they make a point about it.

Look at the transfer curves and gate threshold specs to see what sorts
of gate voltages make what kind of drain currents.

I don't think I've ever seen a p-channel depletion mosfet. Well, not
in 30 years or so.

They were very common on late VGA monitors to regulate the line stage HT for
the various scan rates.

The buck converters were notorious for failing short circuit and wrecking
the horizontal output.

They switched to using lower secondary voltage on the main psu, and a step
up with N-channel MOSFET.

A short time after that development - CRT displays were history.

 

[John Larkin]

On Mon, 19 Jun 2017 20:08:33 +0100, "Ian Field"
<gangprobing.alien1@virginmedia.com> wrote:

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:d4sakc9hdtt73kpgq6l9jbis0uhteep0pe@4ax.com...
On Sat, 17 Jun 2017 10:10:24 -0400, Bob Engelhardt
BobEngelhardt@comcast.net> wrote:

On 6/17/2017 3:25 AM, jurb6006@gmail.com wrote:
"So it would
be like this (P-channel, enhancement mode)? : "

It has to be enhancement mode ...

Thanks.

Furturlec has a bunch of P-channel MOSFETs & I picked IRFL9110 more or
less randomly. Looking at the IR spec sheet for it, it doesn't say
"enhancement":
http://www.futurlec.com/Transistors/IRFL9110pr.shtml
The Mouser listing for it does say it's enhancement, but why isn't it on
the spec sheet? Is it because enhancement is the default mode & it
"goes without saying"?

Bob



Yes; depletion mosfets are rare and they make a point about it.

Maybe its Supertex (or similar) that does depletion mode high voltage power
types.

Supertex and Ixys (and maybe NXP?) make depletion fets, but I haven't
see a p-type.

A few years ago; Elektor magazine published a high voltage psu project with
the option of triode or MOSFET series pass.

A depletion fet can be handy as a series regulstor.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/HV/Depl_Reg.jpg


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Jim Thompson]

On Mon, 19 Jun 2017 12:31:00 -0700, John Larkin
<jjlarkin@highland_snip_technology.com> wrote:

[snip]

A depletion fet can be handy as a series regulstor.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/HV/Depl_Reg.jpg

Nice idea, no kick-start required from the "raw" side.

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

Thinking outside the box... producing elegant solutions.

"It is not in doing what you like, but in liking what you do that
is the secret of happiness." -James Barrie

 

[John Larkin]

On Mon, 19 Jun 2017 14:44:28 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

On Mon, 19 Jun 2017 12:31:00 -0700, John Larkin
jjlarkin@highland_snip_technology.com> wrote:

[snip]

A depletion fet can be handy as a series regulstor.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/HV/Depl_Reg.jpg

Nice idea, no kick-start required from the "raw" side.

...Jim Thompson

It current limits, too.

It's actually an old tube circuit.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Classic_Voltage_Regulators.JPG


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

"Eh?!!! - depletion mode needs the gate *LOWER* than the source to pinch it
off. "

You are ot catching this right. Maybe you are young and didn't know about this depletion mode shit. First of all it was first of all, JFETs were all there were for some time. Now there are depletion mode MOSFETs WHICH ARE NOT THE SAME THING.

Now, let's just consider an N channel depletion mode MOSFET or JFET, at this point it does not matter. I will let you know when it matters. You have the source at or near ground and are using a single ended positive supply. You NEED a negative voltage to turn the FET off. I the gate voltage is the same as the source voltage the device is turned on, somewhat like a tube/valve.

Unike tubes there is a complementary device, a P channel FET. I it is enhancement mode that means it is shut off when the gate voltage is at or near the source voltage. Like the N channel depletion mode, you must reverse bias the gate>source junction to turn the device off, or else it is always conducting.

It is like a tube. If you have too much trouble understanding this I suggest you study tubes, and hw to design with them. How to bias them so they don't burn up was always the first problem.

As is such with depletion mode FETs of JFETs.

And brother, in most cases that bias better be there before or right when that main power comes on.

 

[Ian Field]

<jurb6006@gmail.com> wrote in message
news:08eff453-58bb-483a-a032-21b2b6e55b49@googlegroups.com...

"Eh?!!! - depletion mode needs the gate *LOWER* than the source to pinch
it
off. "

You are ot catching this right. Maybe you are young and didn't know about
this depletion mode shit. First of all it was first of all, JFETs were all
there were for some time. Now there are depletion mode MOSFETs WHICH ARE
NOT THE SAME THING.

They seemed to work well enough when Elektor magazine published a HV PSU
with tube/SS options.

 

"They seemed to work well enough when Elektor magazine published a HV PSU
with tube/SS options."

Try attenuating high fidelity audio and let me know how that goes.

 

[Ian Field]

<jurb6006@gmail.com> wrote in message
news:7c8074c5-a192-4156-9ddb-9037be5a9613@googlegroups.com...

"They seemed to work well enough when Elektor magazine published a HV PSU
with tube/SS options."

Try attenuating high fidelity audio and let me know how that goes.

Eh?!!!!

 

On Sunday, June 25, 2017 at 1:47:01 PM UTC-5, Ian Field wrote:

jurb6006> wrote in message
news:7c8074c5-a192-4156-9ddb-9037be5a9613@googlegroups.com...
"They seemed to work well enough when Elektor magazine published a HV PSU
with tube/SS options."

Try attenuating high fidelity audio and let me know how that goes.

Eh?!!!!

JFETs have properties not available in any other device. Those Cds opto things come close. Actually they are better but it takes more tertiary circuitry to run them.

Fifty year old technology, you can't expect people to remember it. But some of it is not replaceable without great pains in the design.

To draw an analogy, take your dim bulb tester. Try putting a CCFL or LED in it instead of an old style incandescent light bulb. It will not work correctly.

Sometimes, there is no replacement for the old fashioned. Don't get e wrong, there are some really great devices on the market these days, but they cannot replace certain old devices. Among them are JFETs and those opto things.

They still do make and sell some JFETs. Few. But admittedly, the times you really need them are rare.

At least they are rare enough in the market that they are not as misused. Like Sony with those VFET amps. The things would fry if you used a variac or DBT on them. They would also fry out in a brownout. What, you need to run them on a UPS ? Buncha shit if you ask me.

But the old JFET, you know the feedback loop in an amp ? Well you can take a JFET to the bottom end of that and have it biased on all the tie, except when you need to bring the gain down, like an anti-clip type of circuit. This would be about the lowest distortion option, except for using digital.

The Cds cell offers even more options, like some degree of isolation. It opens up options, such as AC drive. Try that with your modern optocoupler.

 

[Phil Hobbs]

On 07/03/2017 10:04 AM, jurb6006@gmail.com wrote:

On Sunday, June 25, 2017 at 1:47:01 PM UTC-5, Ian Field wrote:
jurb6006> wrote in message
news:7c8074c5-a192-4156-9ddb-9037be5a9613@googlegroups.com...
"They seemed to work well enough when Elektor magazine
published a HV PSU
with tube/SS options."

Try attenuating high fidelity audio and let me know how that
goes.

Eh?!!!!

JFETs have properties not available in any other device.

Yup, such as low-frequency noise temperatures on the order of 10 mK
while running at room temperature. That's based on 1-Hz flatband noise
of 0.8 nV and the shot noise of a 1-pA gate leakage current, typical
behaviour for a BF862 or CPH3901.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

>"Yup, such as low-f" snip

That is not what I was talking about.

 

[Phil Hobbs]

On 07/07/2017 01:08 PM, jurb6006@gmail.com wrote:

"Yup, such as low-f" snip

That is not what I was talking about.

Well, they're not the greatest attenuators, but good ones make excellent
preamps.

A BJT diff pair makes a much better attenuator, if you bias it
correctly. You might need a couple of stages to get a wide enough range.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[John Larkin]

On Fri, 7 Jul 2017 13:54:05 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 07/07/2017 01:08 PM, jurb6006@gmail.com wrote:
"Yup, such as low-f" snip

That is not what I was talking about.

Well, they're not the greatest attenuators, but good ones make excellent
preamps.

A BJT diff pair makes a much better attenuator, if you bias it
correctly. You might need a couple of stages to get a wide enough range.

Cheers

Phil Hobbs

May as well buy an Analog Devices multiplier, like the AD835.

Nobody else seems to make multipliers any more.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Jim Thompson]

On Fri, 07 Jul 2017 19:12:13 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 7 Jul 2017 13:54:05 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 07/07/2017 01:08 PM, jurb6006@gmail.com wrote:
"Yup, such as low-f" snip

That is not what I was talking about.

Well, they're not the greatest attenuators, but good ones make excellent
preamps.

A BJT diff pair makes a much better attenuator, if you bias it
correctly. You might need a couple of stages to get a wide enough range.

Cheers

Phil Hobbs

May as well buy an Analog Devices multiplier, like the AD835.

Nobody else seems to make multipliers any more.

The "new math" defines as "analog multiplier": A-to-D each input, use
a uP or gate-array to calculate the product, then D-to-A back :-(

...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I'm looking for work... see my website.

Thinking outside the box... producing elegant solutions.