audio recording on IC -help wanted

[Tam/WB2TT]

"gary s" <gary_s@REMexcite.com> wrote in message
news:k7qtn0lclsqhurcvlm0pnsa10jp5ov38hq@4ax.com...

Thanks for all the prompt replies I've seen so far.

I work for a reseller, and my company acts as the broker for large
batches of different types of microprocessors bought on the "gray"
market to meet production shortages. There is no longer any
manufacturer's warranty, therefore there is a desire to screen out
parts that are dead, slow, or counterfeit. It appears there are folks
out there who are making a living remarking slow parts, or assembling
parts that have been scrapped off the manufacturer's production
line...

I've been told that after a microprocessor leaves the manufacturer,
there is really no way to test it except on a motherboard/application
board (or some kind of evaluation board). My customers are doing this
after their assembly process. But it would be nice to have some kind
of meaningful acceptance testing at my end before they get the part.

I've received suggestions that (1) maybe there is a way to see if the
thing wiggles (the assumption is if you can wiggle it (maybe getting
it in and out of reset?), it's probably good - or there is a live chip
inside anyway), and (2) maybe there is a way to do something like
adding 2 and 2 (or loop on something) to see if the thing can perform
at the advertised speed.

Evidently I would need the services of an EE to attempt something like
this. And if this "generic microprocessor checker" can be built, I
suspect it's going to be a challenge mechanically, owing to all the
different pin-outs and package types. I just wanted to know from the
experts on here if this is something that is worth pursuing, or
proposing to my management.

Thanks again -

Gary

What I have done to test a new board is to write a simple program that

executes on power up:
1) write 55 to some memory location
2) write AA to same memory location
3) Read memory location
4 loop back to 1)

Hor an Intel type chip, I also did an IOR and IOW.

This obviously requires different hardware for each type of chip. I don't
see any way around that.

Tam

 

[Wim Ton]

"gary s" <gary_s@REMexcite.com> wrote in message
news:qfetn0tohn45q767g4okh70obnol7g9a1f@4ax.com...

I have a question that I hope someone on here can answer, or give me
an insight:

1. Is there any way to do a quick check on a microprocessor to
determine if it's "alive"? I realize manufacturers use million-dollar
testers for functional testing, but is there a way to "generically" do
a quick check on the bench using standard test equipment?

2. Ditto for speed? How can one determine if a microprocessor will run
at its marked speed on a bench?

3. If there is a "generic" feature set that is common to most
microprocessors, and what might that be?

4. How can one check for this - as far as hardware and software
requirements?

Elektor magazine had a suggestion way back: fill a memory with NOP's
suitable for the processor. If everything is working, you should see halving
the frequency on every higher address line. And you may use a variable clock
source to see when things start to go wrong.

Wim

 

[N. Thornton]

Joerg <notthisjoergsch@removethispacbell.net> wrote in message news:<YbAgd.15265$6q2.14318@newssvr14.news.prodigy.com>...

Hi MM,

Did you try through some of the obsolete part traders? If you just have
to stuff a limited number of boards that might be the ticket until you
can fix the layout. A good distributor might also be able to contact
some of their other clients to see if they can sell some back.

Regards, Joerg

http://www.analogconsultants.com

Another option is to make a tiny pcb. Slobber it to the main board,
and slobber the smaller ICs to it.

NT

 

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[Norm Dresner]

"Pooh Bear" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:4184574E.BE466FE0@hotmail.com...

Ken McDonald wrote:

Rail to Rail would be nice, but definitely want the output to go to
ground.

No op-amp that I know of has an output that actually goes to *ground*. For
the
simple reason that there will be an active device between the output
terminal
and the ground ( V- ) terminal.

CMOS types may typically get within a few tens of millivolts.

If we knew more about what you're doing it would help. Of course the
output can
go to ground if you're working with split supplies.


Graham

The output can go to ground if you're willing to use a pull-down resistor on
the output. There's at least one IC OpAmp that was made with an on-chip
resistor that way.

Norm

 

[Bill Sloman]

"Ken McDonald" <sorry.no@email.com> wrote in message news:<lGRgd.77085$5v2.32081@fe2.columbus.rr.com>...

"Repzak" <repzak@GEDhotmail.com> wrote in message
news:4183e595$0$33733$14726298@news.sunsite.dk...

"Ken McDonald" <sorry.no@email.com> skrev i en meddelelse
news:lhPgd.1977$vH5.1958@fe1.columbus.rr.com...
Can someone recommend a single supply op-amp with better specs than an
LM358?

What are you needs ?

I guess I'm looking for a single supply dual general purpose op-amp that has
higher gain and higher slew rate than an LM358. Something newer I guess.


which application ?

I'm working on an infrared receiver right now, but am always throwing some
kind of amplifier circuit together.


Rail to Rail ?

Rail to Rail would be nice, but definitely want the output to go to ground.

Ken

There are lots of parts around that satisfy that constraint, and more
every year.

The Linear Technology LT1006 (single), LT1013 (dual) and LT1014 (quad)
parts were introduced early on to satisfy the demand for something
slightly better than the LM324/LM358. Go to

http://www.linear.com/

and dig up the data sheets - I've checked that they exist, but I
suspect that the URL's that got me to them might not work the same way
for a second enquiry.

Farnell stocked the LT1013 and LT1014 the last time I looked, but the
LT1006 was a bit harder to get hold of.

-------
Bill Sloman, Nijmegen

 

[John Crighton]

On 2 Nov 2004 05:38:01 -0800, Winfield Hill
<whill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

* "At the input, the driving signal can fall below 0V— inadvertently
or on a transient basis. If the input is more than a few hundred
millivolts below ground, two distinct problems can occur on previous
single supply designs, such as the LM124, LM158, OP-20, OP-21, OP-220,
OP-221, OP-420:
a) When the input is more than a diode drop below ground, unlimited
current will flow from the substrate (V – terminal) to the input.
This can destroy the unit. On the LT1013/LT1014, the 400W resistors,
in series with the input (see Schematic Diagram), protect the devices
even when the input is 5V below ground.
b) When the input is more than 400mV below ground (at 25°C), the input
stage saturates (transistors Q3 and Q4) and phase reversal occurs at
the output. This can cause lock-up in servo systems.

Thank you for that explanation.

Years ago, I struggled trying to fix a problem in a Benmar
model 210 small ship auto-pilot.

A 50 foot luxury pleasure craft was sold to the third owner at
the same marina and the auto-pilot on board this vessel, from
new, had never worked, according to the boat yard workers.
Many people over the years had a go at trying to fix it for
the previous owners.
As soon as the auto-pilot was engaged the boat would
just skew off to starboard. The boatyard workers were
having a laugh at me as one of the many head scratching,
technicians to look at this auto-pilot.

After struggling a while, I was getting a bit fed-up with the
derogatory remarks and continual "Have you fixed it yet?"
from one particular shipwright at the yard, so to get back
at my tormentor I decided to take the whole auto-pilot
and interconnecting cables back to the workshop.
That really pissed off the boatyard shipwrights because
they had to remove the beautifully polished wood panels
that the cables were hidden behind. That was a big job
to do without damaging the polished woodwork too much.

Back at the workshop where I could have the two control units,
compass and motor drive unit in front of me I went through the
auto-pilot, stage by stage, from compass unit to motor power unit.
One op amp in an LM324 (quad) was the culprit.
The output was phase reversed.
I could hardly believe it!
The output level was normal but just swinging the wrong way
when the compass/binnacle unit was turned by hand.
No wonder that fault was never picked up on board the vessel,
it was just too hard to find when the units that make up the auto-
pilot are spaced well apart on board the vessel.

A new chip was fitted and the auto pilot worked fine,
after all the preset pots had been re-trimed to somewhere
near where they should be. Funny how pots must be
tweaked when something doesn't work.

I told my work mates about the phase reversal fault and
they didn't believe me. I kept that faulty LM324 chip
because I could hardly believe it my self.

I made the mistake of telling the owner about the faulty
part. He wasn't impressed about paying hundreds of
dollars for a $2 dollar culprit. He coughed up the money
OK after he had some fun playing with the auto pilot on
his boat out in the estuary. I showed the owner how to
adjust the feedback pots so that a steady course with
mimimal hunting could be obtained. That eased his
wallet open also.

Thanks again for that explanation on the op amp phase
reversal problem.

Regards,
John Crighton
Sydney

 

[Tim Shoppa]

Winfield Hill <whill_a@t_rowland-dotties-harvard-dot.s-edu> wrote in message news:<cm7vqe0lg9@drn.newsguy.com>...

Bill Sloman wrote...

Farnell stocked the LT1013 and LT1014 the last time I looked,
but the LT1006 was a bit harder to get hold of.

DigiKey stocks them. The Linear Technology version is expensive,
e.g. LT1013CN8 at $4.25 each, but the TI LT1013CP version is more
reasonably priced, at $1.40. Both feature a nice low 300uV max
offset voltage. As far as the LT1006 single opamp is concerned,
DigiKey has this LTC-only part, $2.88 each. It's getting scarce.

TI has some interesting parts if you know that you'll be working with
< 5V Vcc:

cheaper than the LT1013 is the LMV358

more expensive than the LT1013 is the TLV2472

I don't understand what in their manufacture limits these parts to
5V operation.

Tim.

 

[budgie]

On Wed, 03 Nov 2004 15:32:34 -0600, geneguy <gene@nothx.biz> wrote:

Good reason to stay away from "independent" distributors - No
warranty, suspicious circumstances re how they get their product.
Stick with the "franchised" distributors. They get their parts
directly from manufacturers.

Not always the case. Here in down-under-land, Maxim (as one example, also
LinearTechnology) are officially distibuted by Arrow Electronics Australia,
AFAIK a wholly owned subsidiary of Arrow Electronics in the U.S. Arrow Aus
order through Arrow in U.S. who in turn order from the factory. While that
distinction may sound minor, the US-based parent won't move until it has factory
MOQ orders in hand from its downstream. That means we can wait an indefinite
time for parts through "our" franchised distributor simply because of their
organisational structure. We had to wait 14 weeks for a Maxim eval kit that
was ex-stock Maxim throughout the entire waiting period because of this "food
chain". We also have to order factory MOQ as this sytem does not warehouse or
break down factory MOQ at any point.

As an alternative, there is a Maxim distributor next door (in N.Z.) who doesn't
seem to have the same hangups. His delivery is typically a couple of weeks vs
many months via the "official" chain - AND we get to order 20 chips instead of
500. So when we needed 20 chips for a pre-production run, guess which small
distributor got the business.

They also receive full technical support
from manufacturers (as opposed to having to ask questions on Usenet)

Not with Arrow Aust. If it isn't on the chip manufacturer's website then you
may as well forget it - or ask on usenet. Maybe they aren't representative of
authorised/franchised distributors elsewhere, but they certainly don't support
your model.

 

[Michael Kr?mer]

1. Is there any way to do a quick check on a microprocessor to
determine if it's "alive"? I realize manufacturers use million-dollar
testers for functional testing, but is there a way to "generically" do
a quick check on the bench using standard test equipment?

What you have in mind is a real challenge! A semiconductor
manufacturer is happy, if the test coverage exceeds 95% of all the
nodes inside the chip. That means that roundabout 5% of the chip
remains untested. And that is done with very sophisticated and
expensive test equipment, which can access the internal test logic. In
addition to the very fundamental IDDq test (measuring the qiescent
current), this results in a failure rate of a few ppm at the customer.

Without access to the test structures inside the device and without
thorough understanding of its design, you will hardly ever test more
than a third of the device with any test software. The other simple
tests which have been proposed here in other posts, will probably not
cover more than just 5 to 10% of the device.

One can find about 70% of all possible failures by means of dedicated
test software. We have done that for a 32-bit RISC CPU. It requires
the RTL description of the device and many days of simulation time per
iteration on expensive machines with even more expensive software.

The most simple test that you could do is the IDDq test (assuming the
device is CMOS and fully static). Measure the current consumption of
the device during Reset and then clock the device slowly. Measure the
static current after each clock edge. If it is more than the specified
leakage current, then discard the device. This test can find more than
50% of all possible bugs and therefore it is better than most test
software (which would still increase the coverage though). The idea
behind the IDDq test is that a failure will probably be caused by a
gate that is stuck at high or stuck at low, i.e. a transistor that is
constantly switched on or off. If the other transistor switches on,
then a short circuit exists and the leakage current is increased. Note
that such a short doesn't draw amps, but microamps...

2. Ditto for speed? How can one determine if a microprocessor will run
at its marked speed on a bench?

Run the device at nominal conditions (specified voltage and room
temperature) and use 1.5 times the specified clock frequency. That
should assure that the device works at minimum voltage and maximum
temperature at the specified speed.

I hope that helps.

Michael

 

[geneguy]

On Thu, 04 Nov 2004 09:35:17 +0800, budgie <me@privacy.net> wrote:

On Wed, 03 Nov 2004 15:32:34 -0600, geneguy <gene@nothx.biz> wrote:

Good reason to stay away from "independent" distributors - No
warranty, suspicious circumstances re how they get their product.
Stick with the "franchised" distributors. They get their parts
directly from manufacturers.

Not always the case. Here in down-under-land, Maxim (as one example, also
LinearTechnology) are officially distibuted by Arrow Electronics Australia,
AFAIK a wholly owned subsidiary of Arrow Electronics in the U.S. Arrow Aus
order through Arrow in U.S. who in turn order from the factory. While that
distinction may sound minor, the US-based parent won't move until it has factory
MOQ orders in hand from its downstream. That means we can wait an indefinite
time for parts through "our" franchised distributor simply because of their
organisational structure. We had to wait 14 weeks for a Maxim eval kit that
was ex-stock Maxim throughout the entire waiting period because of this "food
chain". We also have to order factory MOQ as this sytem does not warehouse or
break down factory MOQ at any point.

As an alternative, there is a Maxim distributor next door (in N.Z.) who doesn't
seem to have the same hangups. His delivery is typically a couple of weeks vs
many months via the "official" chain - AND we get to order 20 chips instead of
500. So when we needed 20 chips for a pre-production run, guess which small
distributor got the business.

I myself have used independent distributors to cover small-quantity
shortages as the original poster mentioned. Other OEMs do the same -
their buyers do this "under the table" so to speak (off the approved
vendor list). If the material is in original boxes then you can safely
say it's ok. All bets are off if the seal has been broken. I had one
batch with dead parts once. Failure analysis showed wrong die inside -
the outside marking was bogus.

They also receive full technical support
from manufacturers (as opposed to having to ask questions on Usenet)

Not with Arrow Aust. If it isn't on the chip manufacturer's website then you
may as well forget it - or ask on usenet. Maybe they aren't representative of
authorised/franchised distributors elsewhere, but they certainly don't support
your model.

By contractual agreement franchised distributors can refer their
customers to manufacturers for technical support (because the
questions tend to be application-specific and distributors are just
basically warehouses), and manufacturers are pretty supportive about
it in my experience. Independent distributors are not recognized by
manufacturers. As a matter of fact independent distributors are often
considered the cowboys of the industry, peddling parts of unknown
origin. Having said that, there is a place for them in the food chain.
You just have to be really careful.

 

[budgie]

On Thu, 04 Nov 2004 15:41:37 -0600, geneguy <gene@nothx.biz> wrote:

On Thu, 04 Nov 2004 09:35:17 +0800, budgie <me@privacy.net> wrote:

On Wed, 03 Nov 2004 15:32:34 -0600, geneguy <gene@nothx.biz> wrote:

Good reason to stay away from "independent" distributors - No
warranty, suspicious circumstances re how they get their product.
Stick with the "franchised" distributors. They get their parts
directly from manufacturers.

Not always the case. Here in down-under-land, Maxim (as one example, also
LinearTechnology) are officially distibuted by Arrow Electronics Australia,
AFAIK a wholly owned subsidiary of Arrow Electronics in the U.S. Arrow Aus
order through Arrow in U.S. who in turn order from the factory. While that
distinction may sound minor, the US-based parent won't move until it has factory
MOQ orders in hand from its downstream. That means we can wait an indefinite
time for parts through "our" franchised distributor simply because of their
organisational structure. We had to wait 14 weeks for a Maxim eval kit that
was ex-stock Maxim throughout the entire waiting period because of this "food
chain". We also have to order factory MOQ as this sytem does not warehouse or
break down factory MOQ at any point.

As an alternative, there is a Maxim distributor next door (in N.Z.) who doesn't
seem to have the same hangups. His delivery is typically a couple of weeks vs
many months via the "official" chain - AND we get to order 20 chips instead of
500. So when we needed 20 chips for a pre-production run, guess which small
distributor got the business.

I myself have used independent distributors to cover small-quantity
shortages as the original poster mentioned. Other OEMs do the same -
their buyers do this "under the table" so to speak (off the approved
vendor list). If the material is in original boxes then you can safely
say it's ok. All bets are off if the seal has been broken. I had one
batch with dead parts once. Failure analysis showed wrong die inside -
the outside marking was bogus.

They also receive full technical support
from manufacturers (as opposed to having to ask questions on Usenet)

Not with Arrow Aust. If it isn't on the chip manufacturer's website then you
may as well forget it - or ask on usenet. Maybe they aren't representative of
authorised/franchised distributors elsewhere, but they certainly don't support
your model.

By contractual agreement franchised distributors can refer their
customers to manufacturers for technical support (because the
questions tend to be application-specific and distributors are just
basically warehouses), and manufacturers are pretty supportive about
it in my experience. Independent distributors are not recognized by
manufacturers. As a matter of fact independent distributors are often
considered the cowboys of the industry, peddling parts of unknown
origin. Having said that, there is a place for them in the food chain.
You just have to be really careful.

Our experiences certainly differ. After waiting over three months for the "ex
stock" Maxim eval-kit, we commenced our product design in parallel with
evaluating the eval-kit. (Normally these would have been sequential but we had
lost 12 weeks).

A couple of complex design questions arose. I wasn't about to waste more time
dealing with/through the franchised distributor. I just fired emails into Maxim
tech support. They neither asked nor presumably cared where the parts were
sourced. I got exceptional one-to-one tech/design support.

We don't go down dark alleys seeking cheaper sources. We use known (and
long-standing) suppliers but don't get hung up on where they stand in the
official food chain. And we DON'T go anywhere near Arrow Aust any more.

 

[Winfield Hill]

I have taken the liberty of crossposting this to alt.ham-radio.hf,
rec.radio.amateur.homebrew, and alt.ham-radio.vhf-uhf

Joerg wrote...

On 3 Nov 2004 06:08:32 -0800, Winfield Hill
<whill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

I need a few 40W 40MHz RF power amplifiers and can think of a
half-dozen ways to do it, from RF transistors to commercial
modules, but I'm not that happy with any of my ideas; there has
to be something better out there. The load is tuned, but I'd like
a Q of no more than 40. Suggestions for easy-to-get transistors
or modules, etc.?

If it has to be quick and easy you could look at ham radio solutions.
There are plenty of transistor amps described in books such as the
ARRL Handbook that do 3MHz-30MHz at 100W or more. They may need a
little mod for 40MHz or will operate sluggishly there but should be
able to produce 40W.

This seemed a good idea, and I have an 18" bookshelf of ham books,
handbooks, and article compendiums. But looking through them I
was unable to find much of use - I'm not interested in using tubes.
The power amp chapter in the 2002 ARRL Handbook (unchanged in this
respect from the 1998 issue) suggested the MRF464 bipolar RF power
transistor for a 30MHz 80W amplifier, but this is an obsolete part,
no longer available at the distributors I checked. They also don't
present a detailed design to go with this suggestion.

It might even be possible at less cost to modify one of those 'not
so legal' CB booster amps.

Hmm.

Surplus VHF TV driver modules are another option.

Interesting, where does one get these?

If it's just a tuned circuit you want the best bet may be to take a
large enough FET, a tuned circuit at the drain and drive it hard
from a digital oscillator, buffer and resonant step-up transformer.

Checking the MRF464 reminded me to look at Motorola's other newer RF
MOSFET power transistors. They still offer some high-frequency parts,
but most of their RF power MOSFET line was sold to M/A-COM. The data
sheets and app notes are unchanged from the Motorola versions.

In the case of an RF MOSFET, where the device is "on" for only a small
part of each cycle, say 30 degrees (which is 2ns at 40MHz), it's not
possible to "hard drive" the FET and turn it on and off, in the sense
we are used to. Instead the gate is presented with a sine wave wave
from a tuned matching stage (the gate's high capacitance looks like a
low RF impedance), and it's DC biased to be on for a small time at the
tip of each cycle. Of course it's not going on and off, instead its
channel conductance is just increasing and decreasing for a few ns.

These RF FETs are not made with the VMOS groove construction we're used
to in common power MOSFETs. With high capacitance and poor high thermal
resistance, not to mention high gate spreading resistance, ordinary power
MOSFETs are badly suited for applications other than on/off switching.
Instead the RF types are lateral FETs, sort of large versions of the old
small enhancement-mode FETs such as the 2n4351 we talked about in AoE.
This means that despite the RF power MOSFET's large die area, it has a
comparatively low-capacitance, which is well suited for RF work.

The M/A-COM parts are stocked by Richardson, and three of them look
interesting for my inventory. Does anyone recognize any of these FETs?

. type Vdss Pd Ciss Crss cost ea
------- ---- ---- ---- ---- -------
MRF134 65V 18W 7pF 4.5pF $21.42
MRF171A 65 115 80 8 (at 28V) 37.40
MRF148A 120 115 50 8 (at 50V) 35.70

By comparison, a modern VMOS type power MOSFET rated at 100V and 127W
has Ciss = 1150pF and Crss = 62pF (at 25V), which is about 10x higher.
Of course, it's able to handle much higher DC currents when fully on.


--
Thanks,
- Win

 

[Joerg]

Hi Winfield,

For some reason I can't see my own post on this thread. Anyway, RF
transistors become obsolete quite quickly so a 2002 schematic may need
the transistor(s) to be substituted. Same for low noise preamp
transistors where my old Motorola favorite simply vanished. For bipolar
RF power transistors you might want to check BLX15 and things like that.
You probably have to settle for a transistor you can get easily and not
for the dream transistor, the market is so small that there may be no stock.

If the budget allows to simply buy the amps, their 6m amp might work:

http://www.mizuhoradio.com/personal/k7vo/thp/qpamps.html

Look on the web for "6m" amps since that is the newer 50MHz ham gear
which, if done broadband with toroid transformers, may work at 40MHz
without mods.

As for surplus TV driver amps the best bet would be to call the local
electronics surplus dealers and check EBay.

Regarding FETs, we did drive them hard a lot. Mainly in ultrasound where
frequencies were 15MHz or below but where we achieved very steep
transition times in the 25nsec range and could set power by controlling
the pulse width. But it does require very stiff drivers which are also
becoming scarce when you want a chip. Also, sometimes we just paralleled
a whole lot of smaller FETs for cost and performance reasons, and
because we didn't want a heat sink. For RF stuff you can also run four
or eight smaller amps with combiner toroids

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hi SioL,

What FET's did you use up to 15MHz? If garden variety,
how did you drive them (which chip/small fets). Just
applies to a small project of mine so I thought I might ask.


It is too long ago but I could find out if you really want to know. I

believe that the FETs we used as well as the drivers (from National's DS
Series) have to a large extent gone to lala-land, unobtainium.

Nowadays I'd use BSS123 or similar which are much cheaper than what we
used. ON-Semi also makes larger varities of these. BSS84 would be the
p-channel version. For driving I'd use paralleled bus drivers, and small
toroids for a zippier transistion. In the old days we couldn't as bus
drivers were either prohibitively expensive or too slow. You can usually
parallel stages from one chip for more drive but never between different
chips. A parallel configuration of four or eight bus driver pins results
in a whole lot of oompf.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hi SioL,

Nowadays I'd use BSS123 or similar which are much cheaper than what we used.
ON-Semi also makes larger varities of these. BSS84 would be the p-channel
version. For driving I'd use paralleled bus drivers, and small toroids for a
zippier transistion....



Hmm, this sounds interesting. How exactly did you do this toroid part?


Sometimes just by winding primary and secondary on top of each other,

with a ration of 1:2 or a bit higher. The best results require a
trifilar winding where you twist three wires, wind that bundle around a
core and wire it up so the secondary towards the FET has two in series.
But watch out that the FET gate can tolerate the resulting pulse
amplitude of four times the logic level with a healthy margin. You don't
want to pulse a FET with an abs max Vgs of 20V right smack at 20V. The
goal is to transit through the threshold region of the FET as fast as
possible but not run it 'into the red'. When it's all working as desired
measure carfully with a scope to make sure there are no spikes and other
adversities that could shorten the life of the FET or the driver.

Then there is the trick of running inverted and non-inverted into the
primary and get twice the logic level out of a secondary. This only
requires bifilar winding. You could take a CAT-5 pair, twist it a bit
more, about 2 twists every inch or so. But be careful, these drivers
must be in 100% transition time sync or they might blow out. That is
less easy than it seems to be.

Mostly I just used 43 material because I have lots in the lab. This is
also the material most popular for EMI remedies, the cores you slip over
offending cables. For pulsing a FET you only need a very small core 1/4"
or so. Nowadays I often need my glasses to wind these.

To try it out use a large ferrite bead that you find in the box, or one
of those six-holer 'VK200 style' cores. A really good source on how to
wind bifilar and trifilar is the ARRL Handbook. It's a good investment
anyway.

The bottomline is that 5V logic can't directly drive high speed pulser
FETs well enough, no matter what the marketing folks say about the FET.
With 3.3V logic there is not a chance. You need a higher gate drive.

Regards, Joerg

http://www.analogconsultants.com

 

[SioL]

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:m6xjd.18899$6q2.11092@newssvr14.news.prodigy.com...

Sometimes just by winding primary and secondary on top of each other, with a
ration of 1:2 or a bit higher. The best results require a trifilar winding
where you twist three wires, wind that bundle around a core and wire it up so
the secondary towards the FET has two in series. But watch out that the FET
gate can tolerate the resulting pulse amplitude of four times the logic level
with a healthy margin. You don't want to pulse a FET with an abs max Vgs of
20V right smack at 20V. The goal is to transit through the threshold region of
the FET as fast as possible but not run it 'into the red'. When it's all
working as desired measure carfully with a scope to make sure there are no
spikes and other adversities that could shorten the life of the FET or the
driver.

Then there is the trick of running inverted and non-inverted into the primary
and get twice the logic level out of a secondary. This only requires bifilar
winding. You could take a CAT-5 pair, twist it a bit more, about 2 twists
every inch or so. But be careful, these drivers must be in 100% transition
time sync or they might blow out. That is less easy than it seems to be.

Mostly I just used 43 material because I have lots in the lab. This is also
the material most popular for EMI remedies, the cores you slip over offending
cables. For pulsing a FET you only need a very small core 1/4" or so. Nowadays
I often need my glasses to wind these.

To try it out use a large ferrite bead that you find in the box, or one of
those six-holer 'VK200 style' cores. A really good source on how to wind
bifilar and trifilar is the ARRL Handbook. It's a good investment anyway.

The bottomline is that 5V logic can't directly drive high speed pulser FETs
well enough, no matter what the marketing folks say about the FET. With 3.3V
logic there is not a chance. You need a higher gate drive.

Regards, Joerg

Hey, this is really cool. I had that problem with 5V logic, never occured to me
to use toroid at that place. Thanks for a good idea.
I ended up using BS170 and BS250 at the time.

SioL

 

[Joerg]

Hi SioL,

Hey, this is really cool. I had that problem with 5V logic, never occured to me
to use toroid at that place. Thanks for a good idea.
I ended up using BS170 and BS250 at the time.


You are welcome. Just one word of caution. Since toroids do not transfer

DC these schemes are meant for short pulses. They are not very suitable
for longer pulse durations and large duty cycles.

I did use toroids for duty cycles up to 50%, like it almost would be
necessary in Winfield's application. But then you end up with 'half the
amplitude above GND, the other half below'. In some cases that is fine
and can actually help turning the FET off faster. When pulses are
significantly longer than 1usec you have to select other ferrite
materials. Amidon has a huge selection and guidelines. The longest
pulses I did with toroids were around a millisecond but that, of course,
was not with 43 material anymore.

Regards, Joerg

http://www.analogconsultants.com

 

[Joerg]

Hi Paul,

Mostly I just used 43 material because I have lots in the lab. This is
also the material most popular for EMI remedies, the cores you slip over
offending cables. For pulsing a FET you only need a very small core 1/4"
or so. Nowadays I often need my glasses to wind these.



Don't you find that stuff far too lossy for transformers?

Not really. Sure, it isn't ideal but very cheap and tons of sources. The
latter makes the purchasing folks happy. In the old days when
distributors brought chocolate boxes to the purchasing department around
Christmas that could place you high up the 'food chain'.

Some of the EMI material is more lossy but that is often not a clean 43
material. If the design needs tight specs I make sure that the ECO calls
for vendors where detailed data sheets are furnished, such as Amidon. In
Europe that would be larger companies such as Philips or smaller ones
like Vogt.

Regards, Joerg

http://www.analogconsultants.com

 

[Tim Wescott]

Joerg wrote:

Hi Paul,

Mostly I just used 43 material because I have lots in the lab. This
is also the material most popular for EMI remedies, the cores you
slip over offending cables. For pulsing a FET you only need a very
small core 1/4" or so. Nowadays I often need my glasses to wind these.



Don't you find that stuff far too lossy for transformers?



Not really. Sure, it isn't ideal but very cheap and tons of sources. The
latter makes the purchasing folks happy. In the old days when
distributors brought chocolate boxes to the purchasing department around
Christmas that could place you high up the 'food chain'.

Some of the EMI material is more lossy but that is often not a clean 43
material. If the design needs tight specs I make sure that the ECO calls
for vendors where detailed data sheets are furnished, such as Amidon. In
Europe that would be larger companies such as Philips or smaller ones
like Vogt.

Regards, Joerg

http://www.analogconsultants.com

It's interesting that you should cite Amidon -- to my knowledge they
just resell Fair-Rite ferrites and Micro Metals iron powder cores.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com