MOSFET Needed...

[rhor...@gmail.com]

I am looking for an inexpensive P-Channel enhancement node SOT-23 case MOSFET that will suit my design. See http://siliconventures.net/images/P%20Channel%20MOSFET.PNG

The M9 transistor will have a source voltage of between 18 and 28 volts maximum. Getting a MOSFET whose Source - Drain voltage (when off, in this case) is greater than 28 volts is no issue. I can easily get them for under $0.10. Getting one capable of handling a measly 1/2 milliamp or so is also no big deal. The problem I am having is finding one rated for more than 20 volts Soource - Gate voltage, which will be the case when the gate of M7 is high, turning the circuit on. At this point the source voltage of M9 may be as high as 28 volts, and the gate voltage will be near zero. I am doing it this way, because the source voltage of M9 is the power input voltage of the circuit, and I need the drain voltage of M9 to be as close to the power input as possible, so I can accurately measure it at the junction of R6 and R11 using an ADC.

 

[Jan Panteltje]

On a sunny day (Wed, 8 Mar 2023 01:41:21 -0800 (PST)) it happened
\"rhor...@gmail.com\" <rhorerles@gmail.com> wrote in
<b0fa0548-1a56-4a90-ac31-93138ec6ca69n@googlegroups.com>:

I am looking for an inexpensive P-Channel enhancement node SOT-23 case MOSFET
that will suit my design. See http://siliconventures.net/images/P%20Channel%20MOSFET.PNG

The
M9 transistor will have a source voltage of between 18 and 28 volts maximum.
Getting a MOSFET whose Source - Drain voltage (when off, in this case)
is greater than 28 volts is no issue. I can easily get them for under $0.10.
Getting one capable of handling a measly 1/2 milliamp or so is also no
big deal. The problem I am having is finding one rated for more than 20
volts Soource - Gate voltage, which will be the case when the gate of M7 is
high, turning the circuit on. At this point the source voltage of M9 may
be as high as 28 volts, and the gate voltage will be near zero. I am doing
it this way, because the source voltage of M9 is the power input voltage of
the circuit, and I need the drain voltage of M9 to be as close to the power
input as possible, so I can accurately measure it at the junction of R6
and R11 using an ADC.

Add a resistor in the drain of M7 so it forms a voltage divider with R17.
That will limit the source-gate voltage of M9.
I do not like this cicruit, resistor values are too high and high
values make external sensitivity and any leakage a problem.
Moisture.
Some decoupling caps may be a good idea too.

 

[Phil Hobbs]

On 2023-03-08 04:41, rhor...@gmail.com wrote:

I am looking for an inexpensive P-Channel enhancement node SOT-23 case MOSFET that will suit my design. See http://siliconventures.net/images/P%20Channel%20MOSFET.PNG

The M9 transistor will have a source voltage of between 18 and 28 volts maximum. Getting a MOSFET whose Source - Drain voltage (when off, in this case) is greater than 28 volts is no issue. I can easily get them for under $0.10. Getting one capable of handling a measly 1/2 milliamp or so is also no big deal. The problem I am having is finding one rated for more than 20 volts Soource - Gate voltage, which will be the case when the gate of M7 is high, turning the circuit on. At this point the source voltage of M9 may be as high as 28 volts, and the gate voltage will be near zero. I am doing it this way, because the source voltage of M9 is the power input voltage of the circuit, and I need the drain voltage of M9 to be as close to the power input as possible, so I can accurately measure it at the junction of R6 and R11 using an ADC.

There are a few, e.g. DMP3056L.

As Jan said, an extra resistor would help, and your impedance levels are
on the high side, if you want the FET to turn off rapidly.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Wed, 8 Mar 2023 01:41:21 -0800 (PST), \"rhor...@gmail.com\"
<rhorerles@gmail.com> wrote:

I am looking for an inexpensive P-Channel enhancement node SOT-23 case MOSFET that will suit my design. See http://siliconventures.net/images/P%20Channel%20MOSFET.PNG

The M9 transistor will have a source voltage of between 18 and 28 volts maximum. Getting a MOSFET whose Source - Drain voltage (when off, in this case) is greater than 28 volts is no issue. I can easily get them for under $0.10. Getting one capable of handling a measly 1/2 milliamp or so is also no big deal. The problem I am having is finding one rated for more than 20 volts Soource - Gate voltage, which will be the case when the gate of M7 is high, turning the circuit on. At this point the source voltage of M9 may be as high as 28 volts, and the gate voltage will be near zero. I am doing it this way, because the source voltage of M9 is the power input voltage of the circuit, and I need the drain voltage of M9 to be as close to the power input as possible, so I can accurately measure it at the junction of R6 and R11 using an ADC.

Add a resistor, as Jan says, if you want to stay within the abs-max of
the pfet. In real life, most pfets would survive 28 g-s; they usually
die around 60 or so.

You can also buy protected-gate mosfets, which actually have a s-g
zener, usually around 40 volts, but spec survival when the gate is
over-driven.

 

[Jan Panteltje]

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

 

[Fred Bloggs]

On Wednesday, March 8, 2023 at 12:00:58 PM UTC-5, John Larkin wrote:

On Wed, 8 Mar 2023 01:41:21 -0800 (PST), \"rhor...@gmail.com\"
rhor...@gmail.com> wrote:

I am looking for an inexpensive P-Channel enhancement node SOT-23 case MOSFET that will suit my design. See http://siliconventures.net/images/P%20Channel%20MOSFET.PNG

The M9 transistor will have a source voltage of between 18 and 28 volts maximum. Getting a MOSFET whose Source - Drain voltage (when off, in this case) is greater than 28 volts is no issue. I can easily get them for under $0.10. Getting one capable of handling a measly 1/2 milliamp or so is also no big deal. The problem I am having is finding one rated for more than 20 volts Soource - Gate voltage, which will be the case when the gate of M7 is high, turning the circuit on. At this point the source voltage of M9 may be as high as 28 volts, and the gate voltage will be near zero. I am doing it this way, because the source voltage of M9 is the power input voltage of the circuit, and I need the drain voltage of M9 to be as close to the power input as possible, so I can accurately measure it at the junction of R6 and R11 using an ADC.
Add a resistor, as Jan says, if you want to stay within the abs-max of
the pfet. In real life, most pfets would survive 28 g-s; they usually
die around 60 or so.

You can also buy protected-gate mosfets, which actually have a s-g
zener, usually around 40 volts, but spec survival when the gate is
over-driven.

Guess it\'s too much to ask what the sample rate might be. It surely not a high science instrumentation project. Higher voltages that vary over such large range are likely susceptible to large coupled transients. There are plenty of ways to use a single N-FET with bootstrapped gate to circumvent the special \"MOSFET needed\" non-requirement. That will get around the zero quiescent and minimum operating current requirement.

 

[Fred Bloggs]

On Thursday, March 9, 2023 at 2:03:30 AM UTC-5, Jan Panteltje wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

If he drops it in a coffee cup, unexpected things will happen too.

 

[Jan Panteltje]

On a sunny day (Thu, 9 Mar 2023 05:07:24 -0800 (PST)) it happened Fred Bloggs
<bloggs.fredbloggs.fred@gmail.com> wrote in
<5b315f99-cc6e-4c4d-a43b-7277a29c455cn@googlegroups.com>:

On Thursday, March 9, 2023 at 2:03:30=E2=80=AFAM UTC-5, Jan Panteltje wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:

try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,

if the signal is big enough unexpected things may happen.

If he drops it in a coffee cup, unexpected things will happen too.

You clealy have no RF experience.
So shut up.

 

[Fred Bloggs]

On Thursday, March 9, 2023 at 10:07:46 AM UTC-5, Jan Panteltje wrote:

On a sunny day (Thu, 9 Mar 2023 05:07:24 -0800 (PST)) it happened Fred Bloggs
bloggs.fred...@gmail.com> wrote in
5b315f99-cc6e-4c4d...@googlegroups.com>:
On Thursday, March 9, 2023 at 2:03:30=E2=80=AFAM UTC-5, Jan Panteltje wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:

try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,

if the signal is big enough unexpected things may happen.

If he drops it in a coffee cup, unexpected things will happen too.
You clealy have no RF experience.
So shut up.

I have way more than you\'re capable of even beginning to acquire, lightweight.

 

[John Larkin]

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

 

[Jan Panteltje]

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

 

[John Larkin]

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

 

[Phil Hobbs]

On 2023-03-10 10:12, John Larkin wrote:

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

Not to mention the Miller capacitance--the stage is running at maximum
voltage gain.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[John Larkin]

On Fri, 10 Mar 2023 10:18:51 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2023-03-10 10:12, John Larkin wrote:
On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.


Not to mention the Miller capacitance--the stage is running at maximum
voltage gain.

Cheers

Phil Hobbs

All our boards have a ground plane on layer 2. I can imagine a haywire
2-layer board with a grand-tour autorouted gate trace resonating at a
cell phone frequency. Don\'t do that.

 

[Jan Panteltje]

On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>:

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope?
Just call somebody...

 

[John Larkin]

On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>:

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope?
Just call somebody...

Of course a fast scope will see RF near a phone. But will the phone
turn on a mosfet on a PC board?

Lots of opamps are RF sensitive, so I\'d imagine that a phone close to
something sensitive, like a thermocouple front end, could cause
problems.

EMI-hardened opamps and diffamps are becoming common now.

Our fastest realtime scope is 7 GHz.

What frequencies are cell phones these days? I guess they send short
bursty packets. That would be cool on a scope.

 

[Lasse Langwadt Christensen]

fredag den 10. marts 2023 kl. 18.33.13 UTC+1 skrev John Larkin:

On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <al...@comet.invalid
wrote:

On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
90im0i1shrf91q085...@4ax.com>:

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <al...@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jla...@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6...@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <al...@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope?
Just call somebody...
Of course a fast scope will see RF near a phone. But will the phone
turn on a mosfet on a PC board?

Lots of opamps are RF sensitive, so I\'d imagine that a phone close to
something sensitive, like a thermocouple front end, could cause
problems.

EMI-hardened opamps and diffamps are becoming common now.

Our fastest realtime scope is 7 GHz.

What frequencies are cell phones these days?

depends on the service and where you are in the world, but roughly
700-800-900-1800-2100-2600MHz

I guess they send short
bursty packets.

not nearly as bad as old school GSM, https://www.youtube.com/shorts/nZ-gSKWr2RI

 

[Jan Panteltje]

On a sunny day (Fri, 10 Mar 2023 09:32:57 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<vjpm0i5gkh5q7d01oo0dha1m856f805p8c@4ax.com>:

On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>:

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope?
Just call somebody...

Of course a fast scope will see RF near a phone. But will the phone
turn on a mosfet on a PC board?

Lots of opamps are RF sensitive, so I\'d imagine that a phone close to
something sensitive, like a thermocouple front end, could cause
problems.

EMI-hardened opamps and diffamps are becoming common now.

Many transistor circuits exist that make great unexpected RF detectors (base emitter).
I have wondered why you do not RF decouple your walwart power input.. AT the connector.
When you are a radio-ham you will notice real fast what a few hunderd - or even tens of Watts can do.

Our fastest realtime scope is 7 GHz.
That should do.

What frequencies are cell phones these days? I guess they send short
bursty packets. That would be cool on a scope.

From google:

698-806 MHz 700 MHz Band
806- 849 / 851- 896 MHz 800 MHz Band
1850-1910 / 1930-1990 MHz PCS Band
1710-1755 / 2110-2155 MHz AWS Band

You can hear those on some FM radios too, I remeber in a train getting interference on my headplugs
on my mp3 player from the guy next to me phoning, you could hear those bursts.

 

[John Larkin]

On Sat, 11 Mar 2023 06:47:31 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

On a sunny day (Fri, 10 Mar 2023 09:32:57 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
vjpm0i5gkh5q7d01oo0dha1m856f805p8c@4ax.com>:

On Fri, 10 Mar 2023 16:01:23 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Fri, 10 Mar 2023 07:12:59 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
90im0i1shrf91q085uihf98ifps19e6m8l@4ax.com>:

On Fri, 10 Mar 2023 07:28:52 GMT, Jan Panteltje <alien@comet.invalid
wrote:

On a sunny day (Thu, 09 Mar 2023 09:56:12 -0800) it happened John Larkin
jlarkin@highlandSNIPMEtechnology.com> wrote in
ta7k0i5j95lqorlq6a41ushch2b3dss5fl@4ax.com>:

On Thu, 09 Mar 2023 06:54:56 GMT, Jan Panteltje <alien@comet.invalid
wrote:

PS
about that right side MOSFET with the high value series resistor in the gate:
try using your smartphone next to it...
It REALLY needs decoupling caps.

That gate input, when not in a 100% shielded housing, will react to any RF,
if the signal is big enough unexpected things may happen.

I doubt it. Fet capacitances will keep gate RF levels down to
millivolts.

That M7 MOSFET with the 1M or so gate resistor is a low power MOSFET I think,
or should be:
few pF

It forms a feeaking antenna in this circuit.

Well, try it. Put a small mosfet on a PC board with a 1M gate resistor
to ground, with a reasonable layout, and see if a cell phone will turn
it on. I\'m guessing it won\'t.

A 2N7002 is 20 pF typical Cin.

Maybe you can try with your few pF scope probe next to your smartphone and your gigglehertz scope?
Just call somebody...

Of course a fast scope will see RF near a phone. But will the phone
turn on a mosfet on a PC board?

Lots of opamps are RF sensitive, so I\'d imagine that a phone close to
something sensitive, like a thermocouple front end, could cause
problems.

EMI-hardened opamps and diffamps are becoming common now.

Many transistor circuits exist that make great unexpected RF detectors (base emitter).
I have wondered why you do not RF decouple your walwart power input.. AT the connector.

Our products generally have an EMI filter, a couple of caps and a
ferrite bead, and then a polyfuse, TVS, and more caps.

I don\'t bother to do all that on proto boards.

We do have an all-facility EMI test system:

https://www.dropbox.com/s/tmcpmvqp714c82o/Roof_West.JPG?raw=1

 

[Jan Panteltje]

On a sunny day (Sat, 11 Mar 2023 08:23:45 -0800) it happened John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote in
<kcap0i9kf0tuc35hnlirtoobkqj6u19fgu@4ax.com>:

We do have an all-facility EMI test system:

https://www.dropbox.com/s/tmcpmvqp714c82o/Roof_West.JPG?raw=1

?
All I see is a roof with some boxes?
Or are you referring to that antenna tower?
I remember a discussion about that here some time ago.
I have a similar source of RF power here, the radar station just a few km from here.
https://panteltje.nl/pub/radar_2kHz_spectrum_burst.gif
it works at about 1.35 GHz but sweeps over a wide band.
Signal is VERY strong and interferes with satellite reception on some channels
as the 1.35 GHz is in the middle of the signal from the LNB down converter.