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'FETs in OZ, was Re: Driving Relay'
2000\01\18@195105 by Des Bromilow

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OK,
hopefully someone from OZ can help me here.
I'm looking for a logic level MOSFET, or HEXFET, etc which is easily available in Australia (read from Jaycar, Tandy, Dick Smith or Dontronics) Small orders being no problem.
I typically will need it to be logically switched off normal TTL levels and I'll need it to switch 9-15V at several amps (2-5 for .25 of second).
Can someone direct me with part numbers of suitable components?

many many thanks,
Des Bromilow


 Use a "logic" MOSFET (turns on at about 3V on the gate) for this job.
If you want cheap, use a PNP transistor with emitter to 5V, collector to
relay to ground and base to logic gate via a resistor of about 10k.

 A corresponding logic FET would be a P-channel one, which are not as
readily available and therefore probably not as cheap.  With the FET
however, you do not need a resistor; the FET gate connects directly to
the CMOS output.

 For either FET or transistor, you need the diode across the relay in
the direction it doesn't conduct when the coil is energised by the
transistor.

 For any further suggestions, please specify the relay coil resistance.
--
 Cheers,
       Paul B.

2000\01\18@200554 by Tony Nixon

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Des Bromilow wrote:
>
> OK,
> hopefully someone from OZ can help me here.
> I'm looking for a logic level MOSFET, or HEXFET, etc which is easily available in Australia (read from Jaycar, Tandy, Dick Smith or Dontronics) Small orders being no problem.
> I typically will need it to be logically switched off normal TTL levels and I'll need it to switch 9-15V at several amps (2-5 for .25 of second).
> Can someone direct me with part numbers of suitable components?

A part like that is probably out those suppliers run of the mill product
line.

Farnell has plenty of T0-252 DPAK Logic Level types listed for as low as
$1.60ea.
(Feb '99 pg 1188)

It'll cost you $7.00 for next day delivery.

--
Best regards

Tony

http://www.picnpoke.com
spam_OUTsalesTakeThisOuTspampicnpoke.com

2000\01\18@214040 by quozl

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On Wed, Jan 19, 2000 at 10:49:05AM +1000, Des Bromilow wrote:
> I'm looking for a logic level MOSFET, or HEXFET, etc which is easily
> available in Australia (read from Jaycar, Tandy, Dick Smith or
> Dontronics) Small orders being no problem.

Jaycar: no.  Tandy: no.  Dick Smith: no.

Oatley Electronics had some surplus for a while.
http://www.oatleyelectronics.com/

Farnell, as has been mentioned.

I've mentioned this to Jaycar and Silicon Chip ... that logic level
MOSFETs are pretty essential for PIC projects but that they do not
stock any.  I'll remind Jaycar by e-mail.

Jaycar stock MTP3055E, BUZ71, BUK456-60 ... are any of these logic?

--
James Cameron   .....quozlKILLspamspam@spam@us.netrek.org   http://quozl.us.netrek.org/

2000\01\19@054006 by Russell McMahon

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-----Original Message-----
From: Des Bromilow <Des.BromilowspamKILLspamCITEC.COM.AU

I'm looking for a logic level MOSFET, or HEXFET, etc which is easily
available in Australia (read from Jaycar, Tandy, Dick Smith or Dontronics)
Small orders being no problem.



Possibly consider also SGS Thomson agents (Arrow?), Philips, REC (2 9638
1999 Sydney), Adilam? (2 9635v4500 Sydney)



     Russell McMahon
_____________________________

>From other worlds - http://www.easttimor.com
                               http://www.sudan.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

(* - or woman, child or internet enabled intelligent entity :-))

2000\01\19@114416 by Dennis Gearon

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If you're going to use 'real' TTL parts, make sure to use a pull up
resistor on the output, or you'll never  have enough voltage out
reliably.

--
________________________________________________________________
Real friends are those who, when you feel you've made a fool of
yourself, don't feel you've done a permanent job.
________________________________________________________________
Dennis K. Gearon (Kegley)
Scientific Instrument Technician, School of EIT
Oregon Institute of Technology - One of USA's 100 Best College Buys
3201 Campus Drive
Klamath Falls, OR 97601
Voice   1-541-885-1563
FAX     1-541-885-1689
email   .....gearondKILLspamspam.....oit.edu
________________________________________________________________

2000\01\19@190226 by paulb

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Dennis Gearon wrote:

> If you're going to use 'real' TTL parts,

 We *do* hope he's not that warped. ;-)

 I actually mentioned that (to him); "logic level" could be interpreted
as 3V, but if parts switch on reliably at 5V, (H)CMOS should drive this
fine.
--
 Cheers,
       Paul B.

2000\01\20@212635 by quozl

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Well, Jaycar responded with enthusiasm ... all uppercase, but they would
like to know a part number to look into.  MTP3055EL?

Perhaps a cheap asian part source?

Purpose: to make money from electronics enthusiasts by providing a
functional but cheap power MOSFET with logic level gate for switching
heavy DC loads.

--
James Cameron   EraseMEquozlspam_OUTspamTakeThisOuTus.netrek.org   http://quozl.us.netrek.org/

2000\01\21@025407 by Don McKenzie

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James Cameron wrote:
>
> Well, Jaycar responded with enthusiasm ... all uppercase, but they would
> like to know a part number to look into.  MTP3055EL?
>
> Perhaps a cheap asian part source?
>
> Purpose: to make money from electronics enthusiasts by providing a
> functional but cheap power MOSFET with logic level gate for switching
> heavy DC loads.

OK, I was sleeping during this thread, but the above sounds a bit like
me.
It is the MTP3055EL that is required?

Don McKenzie    donspamspam_OUTdontronics.com      http://www.dontronics.com

World's Largest Range of Atmel/AVR and  PICmicro Hardware and  Software.
Free Basic Compiler and Programmer http://www.dontronics.com/runavr.html

2000\01\23@181309 by Des Bromilow

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The specs on the MTP3055E offered by DSE show the following stats...
Vgs (min) = 2.1
Threshold (max) = 4v

I must display my ignorance and lack of understanding...... what does the threshold mean to me? The books say it's the voltage that guarantees a particular type of channel to saturate and be open. I do not understand the implications of this specification.

If the Vgs of 2.1v is adequate for our PIC/AVR/TTL/CMOS requirements, then DSE sell them for $1.95 (singles) $1.56 (10+)

Would someone like to explain what impact Threshold voltage of 4V will have on me?

Many thanks,
Des Bromilow


>>> Don McKenzie <@spam@donKILLspamspamDONTRONICS.COM> 1/21/00 5:50:12 pm >>>
James Cameron wrote:
>
> Well, Jaycar responded with enthusiasm ... all uppercase, but they would
> like to know a part number to look into.  MTP3055EL?
>
> Perhaps a cheap asian part source?
>
> Purpose: to make money from electronics enthusiasts by providing a
> functional but cheap power MOSFET with logic level gate for switching
> heavy DC loads.

OK, I was sleeping during this thread, but the above sounds a bit like
me.
It is the MTP3055EL that is required?

Don McKenzie    KILLspamdonKILLspamspamdontronics.com      http://www.dontronics.com

World's Largest Range of Atmel/AVR and  PICmicro Hardware and  Software.
Free Basic Compiler and Programmer http://www.dontronics.com/runavr.html

2000\01\23@184052 by Sean Breheny

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Hi Des,

First off, one important thing to keep in mind with MOSFETs is that the
term saturation has a totally different usage than it does with BJTs. In
BJTs, saturation means that the voltage from the collector to emitter is at
a minimum and the transistor is fully on. In MOSFETs, saturation means that
the FET is in constant-current mode (maximum drain-source resistance,
except for being off). This is the linear range of operation which you
would use for an amplifier,not a switch.

So, when a MOSFET is fully switched on (minimum drain-source resistance,
RDSon) it is in the triode region of operation. When the voltage from gate
to source exceeds the threshold voltage,the FET turns on. BUT, it won't be
fully on (triode region) unless the gate voltage minus the drain voltage is
ALSO bigger than the threshold voltage. The reason for this is that you
need to maintain an inversion condition all along the FET's drain-source
channel. Inversion requires that the voltage between the gate and the
channel at that point be greater than the threshold voltage. The highest
potential end of the channel is the drain, so if it is lower than the gate
by more than the threshold voltage, then the channel will be inverted all
the way across.

If you take a look at:

http://www.st.com/stonline/books/pdf/docs/3036.pdf

You should find a datasheet for this FET.

It looks to me like what they mean is that the threshold voltage can vary
between 2V and 4V. So, to be sure you are turning it on fully, we should
assume that it is 4V. This means that if you make the gate 5V, with the
source grounded, then the drain voltage cannot be higher than 1V to stay in
the fully-on state. It looks to me from the datasheet's characteristic
curves that the drain-source resistance is about 0.33 ohm when Vgs is 5V
and the FET is in the triode region. SO, you need to make sure that the
load you are driving (assuming it is connected between the drain and a 5V
supply) is more than 1.32 ohms to keep the FET fully on. It would need to
be even higher in resistance if the supply is a higher voltage.

I am not really familiar with logic-level FET typical characteristics, but
if I had to take a guess, I would say that this is not a logic-level FET,
considering that the curves mostly use the condition that Vgs=10V.

Sean


At 09:11 AM 1/24/00 +1000, you wrote:
>The specs on the MTP3055E offered by DSE show the following stats...
>Vgs (min) = 2.1
>Threshold (max) = 4v
>
>I must display my ignorance and lack of understanding...... what does the
threshold mean to me? The books say it's the voltage that guarantees a
particular type of channel to saturate and be open. I do not understand the
implications of this specification.
>
>If the Vgs of 2.1v is adequate for our PIC/AVR/TTL/CMOS requirements, then
DSE sell them for $1.95 (singles) $1.56 (10+)
>
>Would someone like to explain what impact Threshold voltage of 4V will
have on me?
>
>Many thanks,
>Des Bromilow
>
>

|
| Sean Breheny
| Amateur Radio Callsign: KA3YXM
| Electrical Engineering Student
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Save lives, please look at http://www.all.org
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2000\01\23@185756 by Thomas C. Sefranek

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Des Bromilow wrote:

> The specs on the MTP3055E offered by DSE show the following stats...
> Vgs (min) = 2.1
> Threshold (max) = 4v
>
> I must display my ignorance and lack of understanding...... what does the threshold mean to me? The books say it's the voltage that guarantees a particular type of channel to saturate and be open. I do not understand the implications of this specification.

It simply means it's REALLY turned on!
I some times drive Power FETs to 15 volts Vgs!
(The insulation breaks at 20!)

> If the Vgs of 2.1v is adequate for our PIC/AVR/TTL/CMOS requirements, then DSE sell them for $1.95 (singles) $1.56 (10+)
>
> Would someone like to explain what impact Threshold voltage of 4V will have on me?

I suspect it will not affect you in any way.  :)

> Many thanks,
> Des Bromilow

--
Thomas C. Sefranek  WA1RHP
ARRL Instructor, Technical Specialist, VE Contact.
http://www.harvardrepeater.org
http://hamradio.cmcorp.com/inventory/Inventory.html

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