No more PolyZens :(

[Phil Hobbs]

All discontinued by those rotters at Littelfuse.

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

 

On Thu, 19 Mar 2020 13:40:07 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

All discontinued by those rotters at Littelfuse.

Cheers

Phil Hobbs

Pity. We need a really good resettable fuse. We tried the TI Efuse
things, and blew some up. The powerpad makes them really hard to
replace. No semiconductor should be connected to an external pin, much
less a power input.

One current design technique here is to thermally couple a thermistor
to a big DPAK power resistor and shut things down when it gets too
hot.





--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Phil Hobbs]

On 2020-03-19 14:01, jlarkin@highlandsniptechnology.com wrote:

On Thu, 19 Mar 2020 13:40:07 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

All discontinued by those rotters at Littelfuse.

Cheers

Phil Hobbs

Pity. We need a really good resettable fuse. We tried the TI Efuse
things, and blew some up. The powerpad makes them really hard to
replace. No semiconductor should be connected to an external pin, much
less a power input.

One current design technique here is to thermally couple a thermistor
to a big DPAK power resistor and shut things down when it gets too
hot.

Yeah, I'm doing something similar--back-to-back PFETs controlled by the
uC, which is powered by a bulletproof +3.3V supply. It measures the
voltage on the input supply and turns off if they're out of spec. This
can also be done with NFETs and a level shifter for negative supplies,
of course.

Irritating to have to do that though, when a PolyZen is about the same
price, much faster, and much easier to use.

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

 

[Chris Jones]

On 20/03/2020 04:40, Phil Hobbs wrote:

All discontinued by those rotters at Littelfuse.

Cheers

Phil Hobbs

At least from the distributors I was using, the range of PolyZens to
choose from was quite sparse anyway.

Perhaps someone could design a little board with a surface mount TVS and
surface mount polyswitch on it, maybe right next to each other or on
opposite sides of a thin board, with lots of vias in between. I wonder
whether this would work nearly as well as a PolyZen. This board could be
placed as a component on a bigger board, though I haven't thought much
about what would be the best way to do that.

 

On Fri, 20 Mar 2020 10:37:50 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

On 20/03/2020 04:40, Phil Hobbs wrote:
All discontinued by those rotters at Littelfuse.

Cheers

Phil Hobbs


At least from the distributors I was using, the range of PolyZens to
choose from was quite sparse anyway.

Perhaps someone could design a little board with a surface mount TVS and
surface mount polyswitch on it, maybe right next to each other or on
opposite sides of a thin board, with lots of vias in between. I wonder
whether this would work nearly as well as a PolyZen. This board could be
placed as a component on a bigger board, though I haven't thought much
about what would be the best way to do that.

We have considered doing that on a regular PCB, thermally coupling as
best we can. But we don't like the surface-mount polyfuses; we use the
radial leaded ones, which seem to work much better.

The usual combination of polyfuse and TVS, thermally uncoupled, can be
teased to fry the TVS. We standardize on 24 volt warts, on the theory
that some yahoo plugging in some higher voltage is unlikely.

My new pulse generator output stage is difficult, more like
impossible, to protect electronically, so I have a thermistor coupled
to the big DPAK 50 ohm output resistor, to shut things down if it gets
too hot.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

 

[Phil Hobbs]

On 2020-03-19 19:37, Chris Jones wrote:

On 20/03/2020 04:40, Phil Hobbs wrote:
All discontinued by those rotters at Littelfuse.

Cheers

Phil Hobbs


At least from the distributors I was using, the range of PolyZens to
choose from was quite sparse anyway.

Perhaps someone could design a little board with a surface mount TVS and
surface mount polyswitch on it, maybe right next to each other or on
opposite sides of a thin board, with lots of vias in between. I wonder
whether this would work nearly as well as a PolyZen. This board could be
placed as a component on a bigger board, though I haven't thought much
about what would be the best way to do that.

You'd probably be infringing the Tyco patents.

Thermal coupling between small SMT parts mounted close together on an
isolated pour is pretty good. We do high-performance temperature
controllers for detectors and diode lasers by putting 0603 thermistors
on the cold-plate board, with one end connected to a bottom-side pour in
intimate contact with a thermoelectric cooler, and a minimum-width trace
on the other end.

We routinely get thermal response times below 100 milliseconds that way,
which makes it easy to do fast control loops.

Thus I'd expect that for a positive supply a TVS with a thermal pour on
its cathode, shared with a SMT polyfuse, might do fine, especially if
there were some slots preventing lateral heat transfer in other
directions.

Getting that right is an awful lot of work compared with specifying a
75-cent PolyZen.

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

 

[George Herold]

On Thursday, March 19, 2020 at 1:40:15 PM UTC-4, Phil Hobbs wrote:

All discontinued by those rotters at Littelfuse.

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

I assume they are still making the polyfuse.
The polyzen is the resetable fuse and zener?
You'll just have to add your own zener.

George H.

 

[Phil Hobbs]

On 2020-03-20 11:24, George Herold wrote:

On Thursday, March 19, 2020 at 1:40:15 PM UTC-4, Phil Hobbs wrote:
All discontinued by those rotters at Littelfuse.


I assume they are still making the polyfuse.
The polyzen is the resetable fuse and zener?
You'll just have to add your own zener.

The genius of the PolyZen is that the polyfuse is tightly coupled
thermally with the TVS, so as the TVS heats up, it makes the polyfuse
switch much faster.

It's guaranteed to switch before the TVS melts or desolders itself,
which the separate approach is not. To be safe with the discrete
approach, you have to use a much bigger TVS and leave space for thermal
pours, etc. It's a pain.

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

 

[George Herold]

On Friday, March 20, 2020 at 12:51:54 PM UTC-4, Phil Hobbs wrote:

On 2020-03-20 11:24, George Herold wrote:
On Thursday, March 19, 2020 at 1:40:15 PM UTC-4, Phil Hobbs wrote:
All discontinued by those rotters at Littelfuse.


I assume they are still making the polyfuse.
The polyzen is the resetable fuse and zener?
You'll just have to add your own zener.

The genius of the PolyZen is that the polyfuse is tightly coupled
thermally with the TVS, so as the TVS heats up, it makes the polyfuse
switch much faster.

It's guaranteed to switch before the TVS melts or desolders itself,
which the separate approach is not. To be safe with the discrete
approach, you have to use a much bigger TVS and leave space for thermal
pours, etc. It's a pain.

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

OK.. I guess I just use big zeners, maybe it's a market opportunity
for someone?

George H.