unexpected negative voltage from JFETs...

[Gerhard Hoffmann]

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.


Cheers, Gerhard

 

[Jeroen Belleman]

On 2020-12-02 12:08, Gerhard Hoffmann wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.

Could your voltmeter be injecting pulses into the gates,
which then get rectified by the gate-source junction?
Some digital voltmeters do that.

Jeroen Belleman

 

[Gerhard Hoffmann]

Am 02.12.20 um 12:25 schrieb Jeroen Belleman:

On 2020-12-02 12:08, Gerhard Hoffmann wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.

Could your voltmeter be injecting pulses into the gates,
which then get rectified by the gate-source junction?
Some digital voltmeters do that.

Hi,

HP3478A multimeter, 10 GOhm for < 3V DC.
Voltcraft M8660 shows the same.
I just tried my analog Metrix MX225A, 100KOhm/V: also the same

Gerhard

 

[Arie de Muynck]

On 2020-12-02 12:08, Gerhard Hoffmann wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.


Cheers, Gerhard

Flash memory cells get erased by \'hot electron injection\' using a \'high\'
current through the FET. A mechanism like that might be present.

What is the voltage on the drain, are they conducting or cut-off?
Does it vary when measuring the gates?
What is the short-circuit current from the gates to GND?
Is the effect the same with an extra 100nF over the DMM inputs?

Arie

 

[Jeroen Belleman]

On 2020-12-02 12:35, Gerhard Hoffmann wrote:

Am 02.12.20 um 12:25 schrieb Jeroen Belleman:
On 2020-12-02 12:08, Gerhard Hoffmann wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.

Could your voltmeter be injecting pulses into the gates,
which then get rectified by the gate-source junction?
Some digital voltmeters do that.

Hi,

HP3478A multimeter, 10 GOhm for < 3V DC.
Voltcraft M8660 shows the same.
I just tried my analog Metrix MX225A, 100KOhm/V: also the same

Gerhard

I suppose you scoped the gates? I suppose the JFETs must be
completely pinched off. Are the drains at Vdd? Is there some
possible interference source nearby? Maybe you made an accidental
oscillator by connecting long instrument leads to the gates.

Jeroen Belleman

 

[server]

On Wed, 2 Dec 2020 12:08:04 +0100, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.


Cheers, Gerhard

Phil Hobbs has noted a \"venturi effect\" in depletion phemts, where
they bias themselves off.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[Mikko OH2HVJ]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:

On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity? The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

--
mikko

 

[Phil Hobbs]

On 12/3/20 1:45 PM, Mikko OH2HVJ wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity? The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

--
mikko

You could make a 2CV run backwards IIRC. There was a Car Talk puzzler
long ago that hinged on the ability to bump-start a two-stroke in
reverse while moving forwards, resulting in one forward and four reverse
speeds.

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 Thu, 3 Dec 2020 14:24:35 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/3/20 1:45 PM, Mikko OH2HVJ wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity? The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

--
mikko


You could make a 2CV run backwards IIRC. There was a Car Talk puzzler
long ago that hinged on the ability to bump-start a two-stroke in
reverse while moving forwards, resulting in one forward and four reverse
speeds.

Cheers

Phil Hobbs

Big ships have reversing diesels now. Reversing a steam turbine plant
was a little messy.

We can do things with fets and inductors that the mechanical boys can
only dream of.

Do hybrid cars have actual reverse gearing? Seems like it could be
done electronically.

 

[Tauno Voipio]

On 3.12.20 21.24, Phil Hobbs wrote:

On 12/3/20 1:45 PM, Mikko OH2HVJ wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity?  The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

--
mikko


You could make a 2CV run backwards IIRC.  There was a Car Talk puzzler
long ago that hinged on the ability to bump-start a two-stroke in
reverse while moving forwards, resulting in one forward and four reverse
speeds.

Cheers

Phil Hobbs

It cannot be the four-man overall (Citroen 2CV), as its
engine is four-stroke, with valves. The valve mechanism
does not allow backward gas exchange.

An example could be the national car of the DDR (East Germany),
the Trabant and its predecessor the IFA, whih were two-stroke,
as was also the Saab 92.

--

-TV

 

[Jasen Betts]

On 2020-12-03, Mikko OH2HVJ <mikko.syrjalahti@nospam.fi> wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity? The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

Sounds like bullshit, that won\'t crank the engine in reverse.
and if it did it would burn up the generator.



I had a Morris Minor and reversed the battery so I could install a new
radio. The only mod I did was put some red tape on the (now) positive
battery lead.

the the starter motor was a univeral motor (like almost all starter
motors) and the generator used a commutator and brushes for
rectification, so with the field polarity now reversed it adjusted
to the new supply polarity.

The heater fan and wiper motor were also wound field motors.

--
Jasen.

 

[Phil Hobbs]

On 12/4/20 4:00 AM, Tauno Voipio wrote:

On 3.12.20 21.24, Phil Hobbs wrote:
On 12/3/20 1:45 PM, Mikko OH2HVJ wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity?  The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

--
mikko


You could make a 2CV run backwards IIRC.  There was a Car Talk puzzler
long ago that hinged on the ability to bump-start a two-stroke in
reverse while moving forwards, resulting in one forward and four
reverse speeds.

Cheers

Phil Hobbs


It cannot be the four-man overall (Citroen 2CV), as its
engine is four-stroke, with valves. The valve mechanism
does not allow backward gas exchange.

An example could be the national car of the DDR (East Germany),
the Trabant and its predecessor the IFA, whih were two-stroke,
as was also the Saab 92.

<dim memory>
I think it was the Saab they were talking about.
</dim memory>

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

 

[server]

On Fri, 4 Dec 2020 09:38:46 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 12/4/20 4:00 AM, Tauno Voipio wrote:
On 3.12.20 21.24, Phil Hobbs wrote:
On 12/3/20 1:45 PM, Mikko OH2HVJ wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> writes:
On 12/3/20 10:47 AM, jlarkin@highlandsniptechnology.com wrote:
What happens in a p-fet?
When you reverse polarity?  The engines canna\' take it, Captain.

You\'ve not seen a two stroke UAZ. The rumour has it you just switch the
battery terminals and turn the ignition key.

--
mikko


You could make a 2CV run backwards IIRC.  There was a Car Talk puzzler
long ago that hinged on the ability to bump-start a two-stroke in
reverse while moving forwards, resulting in one forward and four
reverse speeds.

Cheers

Phil Hobbs


It cannot be the four-man overall (Citroen 2CV), as its
engine is four-stroke, with valves. The valve mechanism
does not allow backward gas exchange.

An example could be the national car of the DDR (East Germany),
the Trabant and its predecessor the IFA, whih were two-stroke,
as was also the Saab 92.

dim memory
I think it was the Saab they were talking about.
/dim memory

Cheers

Phil Hobbs

Saabs were great cars, between fires.



--

John Larkin Highland Technology, Inc

The best designs are necessarily accidental.

 

[ke...@kjwdesigns.com]

On Friday, 4 December 2020 at 03:30:53 UTC-8, Jasen Betts wrote:
....

I had a Morris Minor and reversed the battery so I could install a new
radio. The only mod I did was put some red tape on the (now) positive
battery lead.

You also needed to hold down the cut-out for a few seconds to polarize the field of the generator so the remanent magnetism matched the new battery polarity.
...

kw

 

[ke...@kjwdesigns.com]

On Thursday, 3 December 2020 at 12:20:50 UTC-8, John Larkin wrote:
....

Do hybrid cars have actual reverse gearing? Seems like it could be
done electronically.

That\'s what hybrids like the Prius or ones based on the same approach do.

However they can normally only use the battery for power when in reverse - any engine torque generated is still in the forward direction.

kw

 

[Tauno Voipio]

On 4.12.20 22.27, ke...@kjwdesigns.com wrote:

On Thursday, 3 December 2020 at 12:20:50 UTC-8, John Larkin wrote:
...
Do hybrid cars have actual reverse gearing? Seems like it could be
done electronically.

That\'s what hybrids like the Prius or ones based on the same approach do.

However they can normally only use the battery for power when in reverse - any engine torque generated is still in the forward direction.

kw

There are two permanent-magnet electrical motor/generators in the
Toyota (and Lexus) hybrid drive. They are connected with the engine
and drive train with a planetary drive functioning as a differential.

The effective gear ratios between the engine and the road are made
moving the electricity between the two electric machines and the
battery in a way the control electronics thinks best. The gearing
ratio range extends also to reverse, so both forward and reverse can
be driven by electricity only or combined engine and electricity.
The battery power is used when deemed suitable.

Slight braking is made by the electric drive, feeding the extra
energy into the battery. The disk brakes are used only to augment
the electrical braking.

--

-TV
A Lexus hybrid owner

 

[LM]

On Wed, 2 Dec 2020 12:08:04 +0100, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.


Cheers, Gerhard

A friend once wondered if an old Saab had positive ground. But no,
some true genius had charged and connected the battery wrong way.

But more on topic, I once saw old 7400 chips which had negative
voltages on their inputs if they were floating. Those chips were old,
old fashioned and from probably Soviet Union, so it is of no wonder. I
thought the chips were oscillating.

 

[ke...@kjwdesigns.com]

On Saturday, 5 December 2020 at 01:10:53 UTC-8, Tauno Voipio wrote:
....

The effective gear ratios between the engine and the road are made
moving the electricity between the two electric machines and the
battery in a way the control electronics thinks best. The gearing
ratio range extends also to reverse, so both forward and reverse can
be driven by electricity only or combined engine and electricity.
The battery power is used when deemed suitable.
...

I\'m not sure what point you are making.

In reverse the torque from MG2 can propel the car backwards -- however any torque from the engine will be in the opposite direction attempting to make the car go forward thus reducing the combined tractive effort.

In my Prius (gen4) reverse usually seems to be accompanied by the engine stopping, so MG2 with just battery power is doing the propulsion - so no torque from the engine/PSD.

If the battery had too low an SOC to provide the required power to MG2 the engine could be started so MG1 could generate power to feed MG2. In that case however the balancing torque through the PSD would tend to drive the car forwards - the available traction force would be less than if the engine was not running (of course there is potentially more torque available from MG2 because of the power generated by MG1).

When the engine is running I haven\'t noticed whether it is accompanied by using a high-rpm low torque operation to minimize the reverse torque.

kw

Prius and Tesla M3 owner.

 

[Bill Sloman]

On Wednesday, December 2, 2020 at 10:08:12 PM UTC+11, Gerhard Hoffmann wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.

It sounds odd. Sometimes, when circuits behave in an odd way, they turn out to be oscillating at frequency that you aren\'t set up to detect. It doesn\'t happen often, but it\'s a pest when it does.

--
Bill Sloman, Sydney

 

[Phil Hobbs]

On 12/2/20 6:08 AM, Gerhard Hoffmann wrote:

I have here an array of 16 On Semi CPH3910 JFETs, n-chan,
all in parallel. Sources are at GND, drains via 50 Ohm to +5.5V Vdd.

The gates are open and I measure there -2V, there is no negative supply.
Gate leakage seems also large, no way to use a 1 Meg gate resistor.

I would expect that from a 12AX7 array, but JFETs??

I remember Bob Pease\'s question about a negative voltage on an open
Collector when the BE junction Zeners.
That was photons from BE Zener glow into the BC junction.

Is that normal?

NSVJ5908 duals behave in the same way.


Cheers, Gerhard

ATF38143 depletion pHEMTs self-bias to about -0.3V if you leave the gate
open.

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