Driving common source MOSFets with OptoMosfet

[John Larkin]

On Sat, 09 Apr 2005 00:35:27 +0200, OBones
<obones_gfd_@_gds_altern.org> wrote:

John Larkin wrote:

Just buy a small solid-state relay or two. See cel.com for some
examples.

I wish I could simply buy 2 1-Form-C SSRs, but in France, they are
really hard to come by. And ordering from the US is just too costly (20$
S&H + Customs for two 4$ parts). Hence the desire to replace those with
what I get my hands on.

Bummer. How can a country have a high-tech infrastructure if they make
it hard for people to get parts? Do you have anything like Mouser or
Digikey, small-quantity distributors?

John

 

[OBones]

John Larkin wrote:

Bummer. How can a country have a high-tech infrastructure if they make
it hard for people to get parts? Do you have anything like Mouser or
Digikey, small-quantity distributors?

We do, but they don't have Opto Mosfets, or if they do, they don't have
the P types.
Well, one distributor has one of them, but sold 14.5 euros, it's way too
much when you know an equivalent one costs 4$ in the US...

 

[OBones]

Winfield Hill wrote:

Keep trying - I'm sure all SSR types are widely used in France,
so find out who's selling them industrially. Post the question
in sci.electronics.components

Yeah, industrial types, 20 euros each at least, able to commute 500V at
40Amps. Crazy and way too big. The telephony type ones are widely used
in the industry, they simply are not available in electronics store or
websites...

Hey, maybe you can get some free samples. :&gt

Well, I tried contacting the manufacturers, but they don't even answer
my requests. I guess the hobbyist market is of no interest to them (I
can understand that though)

 

[Winfield Hill]

OBones wrote...

John Larkin wrote:

Bummer. How can a country have a high-tech infrastructure if they
make it hard for people to get parts? Do you have anything like
Mouser or Digikey, small-quantity distributors?

We do, but they don't have Opto Mosfets, or if they do, they don't
have the P types. Well, one distributor has one of them, but sold
14.5 euros, it's way too much when you know an equivalent one costs
4$ in the US...

What? NOBODY has the "p-types," because n-channel FETs are more
suitable, and ac switches have no way to know if they're P or not.


--
Thanks,
- Win

 

[Wolfgang Mahringer]

Hi OBones,

OBones wrote:

Doing a mix of your proposition and Wolfgang's one, I came up with this:


In1
|
N |
.-----+-+ |
||-+ A A |
||<- | +---'
.-||-+ +-)---.
.---------. | | A A |
----. .-------+--------+ '--+--+-+ |
| | | | .-. | | |
| V -> A | |R| | Vss |
| - A | | | | +--- Out
| | | | '-' | |
----' '-------+ | |
'---------' | | .-----+-+ |
| | ||-+ A A |
Vss | ||-> | +---'
'-||-+ +-)---.
| A A |
P '--+--+-+ |
| |
Vss |
In2

Sorry, this will not work. By tieing both negative terminals
of the rectifiers to Vss, you short out parts of the rectifiers.
You can only use one of them, not two.
You can, however build 2 isolated circuits using two opto-mosfets.

HTH
Wolfgang

--
From-address is Spam trap
Use: wolfgang (dot) mahringer (at) sbg (dot) at

 

[OBones]

Winfield Hill wrote:

What? NOBODY has the "p-types," because n-channel FETs are more
suitable, and ac switches have no way to know if they're P or not.

But then, how do you create a Normally Closed relay ?

 

[OBones]

Wolfgang Mahringer wrote:

Sorry, this will not work. By tieing both negative terminals
of the rectifiers to Vss, you short out parts of the rectifiers.
You can only use one of them, not two.
You can, however build 2 isolated circuits using two opto-mosfets.

Bummer, that means I need 4 of those OptoIsolated drivers...
This is very annoying.

 

[Winfield Hill]

OBones wrote...

Wolfgang Mahringer wrote:

Sorry, this will not work. By tieing both negative terminals
of the rectifiers to Vss, you short out parts of the rectifiers.
You can only use one of them, not two.
You can, however build 2 isolated circuits using two opto-mosfets.

Bummer, that means I need 4 of those OptoIsolated drivers...
This is very annoying.

The simple part best suited for your use is available in France,
and the rest of Europe. At a reasonable price if you know where
to look, I'm sure. That's what you should pursue, in my opinion.


--
Thanks,
- Win

 

[OBones]

Winfield Hill wrote:

The simple part best suited for your use is available in France,
and the rest of Europe. At a reasonable price if you know where
to look, I'm sure. That's what you should pursue, in my opinion.

I keep looking, but I look at other options.
Thing is, we have Farnell, Radiospares and others, but either they don't
even have the part in their catalogue, or they have it but send it
directly from the US billing 25euros for S&H.
I even tried to call some of them, they sometimes don't even OptoMosfets
even exist...
That's a pity, I'll have to use a regular relay, less fun, much easier
to find.

 

[Winfield Hill]

OBones wrote...

Winfield Hill wrote:

What? NOBODY has the "p-types," because n-channel FETs are more
suitable, and ac switches have no way to know if they're P or not.

But then, how do you create a Normally Closed relay?

Didn't you read our elementary FET chapter? Or my detailed post
on the issue in the last thread? It's depletion mode rather than
enhancement mode that's required, and it has nothing to do with
whether it's n-channel or p-channel. The popular ones are n-type.


--
Thanks,
- Win

 

[Rich Grise]

On Sat, 09 Apr 2005 02:08:42 +0200, OBones wrote:

Winfield Hill wrote:

Keep trying - I'm sure all SSR types are widely used in France, so find
out who's selling them industrially. Post the question in
sci.electronics.components

Yeah, industrial types, 20 euros each at least, able to commute 500V at
40Amps. Crazy and way too big. The telephony type ones are widely used in
the industry, they simply are not available in electronics store or
websites...


Hey, maybe you can get some free samples. :&gt

Well, I tried contacting the manufacturers, but they don't even answer my
requests. I guess the hobbyist market is of no interest to them (I can
understand that though)

When you say, "Don't answer your requests" - that covers a lot of ground.
Are they not answering emails? Do you go to their web sites and fill out
information request forms? Have you tried calling a salesman or rep on
the telephone? Have you written a letter?

There's a way to get stuff - Don't listen to these weenies who are dissing
you just 'cuz you're French; but you are the man on the ground on-site,
and a little legwork, or even fingerwork ("let your fingers do the walking"
- Yellow Pages ad) can go a long way.

I've even told salesmen, "It's just for a hobby project, so I doubt if
I'll ever need more than a couple..." and they have sympathy and send me
a couple of parts. Usually it's stuff that costs like two bucks to send,
and he just puts that on his "dealing with prospects" budget. I even
once had a guy who was on a sales call at a company where I was a temp,
hand me two, 16-bit ADCs that were retailing at about $25.00 apiece back
in those days. He had a sample case full of them.

So, ask around - you never know!

Good Luck!
Rich

 

[Rich The Newsgropup Wacko]

On Fri, 08 Apr 2005 16:51:13 -0700, John Larkin wrote:

On Sat, 09 Apr 2005 00:35:27 +0200, OBones <obones_gfd_@_gds_altern.org
John Larkin wrote:

Just buy a small solid-state relay or two. See cel.com for some
examples.

I wish I could simply buy 2 1-Form-C SSRs, but in France, they are really
hard to come by. And ordering from the US is just too costly (20$ S&H +
Customs for two 4$ parts). Hence the desire to replace those with what I
get my hands on.

Bummer. How can a country have a high-tech infrastructure if they make it
hard for people to get parts? Do you have anything like Mouser or Digikey,
small-quantity distributors?

England has "Radio Spares" - why not just hitchhike over there and pick up
some parts? They finally got that tunnel finished, I hear. ;-P
--
Cheers!
Rich
------
HOW TO REMOVE STAINS -- #28 Semen stains can be removed from computer
terminals with Fantastik or the like. Use Windex on the glass however,
and be sure to turn the power off if you have to clean between the keys.

 

[John Larkin]

On Sat, 09 Apr 2005 19:58:07 GMT, Rich The Newsgropup Wacko
<wacko@example.com> wrote:

On Fri, 08 Apr 2005 16:51:13 -0700, John Larkin wrote:
On Sat, 09 Apr 2005 00:35:27 +0200, OBones <obones_gfd_@_gds_altern.org
John Larkin wrote:

Just buy a small solid-state relay or two. See cel.com for some
examples.

I wish I could simply buy 2 1-Form-C SSRs, but in France, they are really
hard to come by. And ordering from the US is just too costly (20$ S&H +
Customs for two 4$ parts). Hence the desire to replace those with what I
get my hands on.

Bummer. How can a country have a high-tech infrastructure if they make it
hard for people to get parts? Do you have anything like Mouser or Digikey,
small-quantity distributors?

England has "Radio Spares" - why not just hitchhike over there and pick up
some parts? They finally got that tunnel finished, I hear. ;-P

Yeah, I took the chunnel train from London to Paris, first class...
had my own steward who cooked breakfast for me. The thing that amazed
me was that, when I got to Paris, I just walked off the train out into
the street; no customs, no visible security. Cool. That's nice, being
able to step onto a train and spend the weekend in another country
with no hassles.

John

 

[Spehro Pefhany]

On Sat, 09 Apr 2005 13:47:23 -0700, the renowned John Larkin
<jjSNIPlarkin@highTHISlandPLEASEtechnology.XXX> wrote:

On Sat, 09 Apr 2005 19:58:07 GMT, Rich The Newsgropup Wacko
wacko@example.com> wrote:

On Fri, 08 Apr 2005 16:51:13 -0700, John Larkin wrote:
On Sat, 09 Apr 2005 00:35:27 +0200, OBones <obones_gfd_@_gds_altern.org
John Larkin wrote:

Just buy a small solid-state relay or two. See cel.com for some
examples.

I wish I could simply buy 2 1-Form-C SSRs, but in France, they are really
hard to come by. And ordering from the US is just too costly (20$ S&H +
Customs for two 4$ parts). Hence the desire to replace those with what I
get my hands on.

Bummer. How can a country have a high-tech infrastructure if they make it
hard for people to get parts? Do you have anything like Mouser or Digikey,
small-quantity distributors?

England has "Radio Spares" - why not just hitchhike over there and pick up
some parts? They finally got that tunnel finished, I hear. ;-P

Yeah, I took the chunnel train from London to Paris, first class...
had my own steward who cooked breakfast for me. The thing that amazed
me was that, when I got to Paris, I just walked off the train out into
the street; no customs, no visible security. Cool. That's nice, being
able to step onto a train and spend the weekend in another country
with no hassles.

John

Yup, and you can drive through a whole bunch of countries without ever
being asked to produce documents or a passport, and mostly keep using
the same currency. There's security for the train itself though. IIRC
they close the "departure" area 20 or 30 minutes before the train
actually leaves-- just like an airplane-- none of this dashing through
the station and jumping on the train as it begins to move, as I found
out to my chagrin. Stuck in Paris for a few extra hours- not such a
terrible thing. ;-)


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[OBones]

Rich Grise wrote:

On Sat, 09 Apr 2005 02:08:42 +0200, OBones wrote:

Well, I tried contacting the manufacturers, but they don't even answer my
requests. I guess the hobbyist market is of no interest to them (I can
understand that though)


When you say, "Don't answer your requests" - that covers a lot of ground.
Are they not answering emails? Do you go to their web sites and fill out
information request forms? Have you tried calling a salesman or rep on
the telephone? Have you written a letter?

I've mostly tried emails, filled request forms on the manufacturer
websites. Got one phone call, but the guy stopped as soon as I said I
was a hobbyist. I'd rather not lie to those guys, hence...

There's a way to get stuff - Don't listen to these weenies who are dissing
you just 'cuz you're French; but you are the man on the ground on-site,
and a little legwork, or even fingerwork ("let your fingers do the walking"
- Yellow Pages ad) can go a long way.
So, ask around - you never know!

I will, ask them about. But there is a "behaviour" within French
distributors of electronics component that makes them "despise"
hobbyist: They are not worthy of much. But a good hobbyist can convince
a company, or work for one and bring in his experience with these
components. Ah well, I'll keep those arguments for my next few days
phone calls.

Good Luck!

Thanks, I'll keep on trying.

Olivier

 

[OBones]

Winfield Hill wrote:

But then, how do you create a Normally Closed relay?

Didn't you read our elementary FET chapter?

I obviously has not, as you suppose. Fact is, I don't even know where it
would be located. Was that in one of the threads here?

Or my detailed post
on the issue in the last thread? It's depletion mode rather than
enhancement mode that's required, and it has nothing to do with
whether it's n-channel or p-channel. The popular ones are n-type.

Let me see... Yeah, I read that, but somehow must have "zapped" it.
Sorry about that, I'll look for depletion mode FETs

Once again, thanks a lot for your help.
Cheers
Olivier

 

[rex]

On Sun, 10 Apr 2005 01:14:18 +0200, OBones <obones_gfd_@_gds_altern.org>
wrote:

Rich Grise wrote:

On Sat, 09 Apr 2005 02:08:42 +0200, OBones wrote:

Well, I tried contacting the manufacturers, but they don't even answer my
requests. I guess the hobbyist market is of no interest to them (I can
understand that though)


When you say, "Don't answer your requests" - that covers a lot of ground.
Are they not answering emails? Do you go to their web sites and fill out
information request forms? Have you tried calling a salesman or rep on
the telephone? Have you written a letter?

I've mostly tried emails, filled request forms on the manufacturer
websites. Got one phone call, but the guy stopped as soon as I said I
was a hobbyist. I'd rather not lie to those guys, hence...

Bummer. I recently wanted to try a couple AD 2 axis accelerometer chips
for use in a tilt sensor project. I went online and asked for samples.
Not only did they give me a couple, they arrived at my door the next
morning. I could have waited if they had asked.

There's a way to get stuff - Don't listen to these weenies who are dissing
you just 'cuz you're French; but you are the man on the ground on-site,
and a little legwork, or even fingerwork ("let your fingers do the walking"
- Yellow Pages ad) can go a long way.
So, ask around - you never know!

I will, ask them about. But there is a "behaviour" within French
distributors of electronics component that makes them "despise"
hobbyist: They are not worthy of much. But a good hobbyist can convince
a company, or work for one and bring in his experience with these
components. Ah well, I'll keep those arguments for my next few days
phone calls.

I know one ham in France who is into high tech construction. You can
look at this page http://www.f1ehn.org/ . There is an email you can find
there. Mention that Rex sent you. Maybe he can give advice.

Good Luck!

Thanks, I'll keep on trying.

Olivier

 

[Winfield Hill]

OBones wrote...

How would I go about driving a common source MOSFet configuration
(Two N type) with the output of an Opto Mosfet (N type)

| D
||-+
.------------. ||<-
| --- -||-+
----- | | G | S
| | ||-+ | |
| V -> ||<- | |
| - -||-+ | G | S
| | | | -||-+
----- ---- ||<-
'------------' ||-+
| D

But I'm not sure as to how to connect the optically driven mosfet
to the two others.

You're missing an important element above, the stack of photodiodes
required to receive the light and create an isolated gate voltage.

Here are a bit more details:
What is connected to both D's is an AC signal, and that's the only
"power" source on that side. When the LED is on in the OptoMosfet,
the two Gates must be On so as to turn the two mosfets On.

Yes, so tie both gates together, and connect them to the output
of the PD stack, through a diode. The bottom end of the PD stack
goes to the sources.

When the LED is off in the OptoMosfet, the two Gates must be driven
to zero so as to stop the mosfets.

Yes, so add a high-value resistor across the PD stack, to pull it
down to zero, and add a PNP emitter follower in parallel with the
diode to pull down the FET gates following the high-value resistor.
You can edit the drawing for us (or you can find one I posted here).

And finally, if I replace the Two N type mosfets with two P type
mosfets, would that still work? Would the common source configuration
still be valid or would I need to go for a common drain configuration?

Yes of course, by reversing the polarities and using an NPN trannie.


--
Thanks,
- Win