Searching \ for '[EE] PC Parallel Port small footprint relay driver' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/io/motors.htm?key=relay
Search entire site for: 'PC Parallel Port small footprint relay driver'.

Exact match. Not showing close matches.
PICList Thread
'[EE] PC Parallel Port small footprint relay driver'
2007\07\02@180018 by James Newton, Host

face picon face
Short version: What is the absolute minimum footprint driver circuit (NOT
SMT) that will work from an Open Collector output with a 4.7K pull up to +5
(PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5 which has
a 5 volt, 63 Ohm coil?

Long version:

I have a PCB that I would like to squeeze a bit more functionality into, but
I have almost no real-estate available. I've managed to put a PCB mount
relay on the underside of the board (with other components on the top) by
fitting it's few through hole leads in between other stuff.

What remained was a drive circuit for the relay. Piclist.com has a great
page for PIC relay drivers at
http://www.piclist.com/techref/io/relays.htm and what I think is the best
page on the PC parallel port bar none at
http://www.piclist.com/techref/io/parallel/signals.htm  

However, the quick and dirty single transistor driver from the relays page
http://www.piclist.com/techref/io/relay5v.gif  will not work with the actual
PC parallel port outputs as specified on the parallel port page. It does
work with a PIC, I verified that, but the PIC has a lot more drive than a PC
parallel port pin... Especially the pin I want to use: nStrobe, which is an
open collector output with a 4.7k pull-up resistor.

There is another suggestion on the relay driver page that looks promising
for a very small footprint solution:

           +24
            |
        relay coil
            |
          drain
 +5  ---- gate      N Channel Hexfet
control   source
            |
           gnd


But there is no sample part number or other details. I spent some hours this
weekend searching the net for N Channel Hexfet examples circuits, hoping to
find something where one was used to drive a relay or used to drive
something like a relay from a PC parallel port and came up empty.

I would really like to avoid all the extra holes and space for a resistor,
diode, etc... In addition to the drive transistor.

If you are curious, the circuit is for the next version of this kit and PCB:
http://www.piclist.com/techref/io/stepper/linistep/4axis2build.htm which is
darn fine in most other respects... The first version (which I am now
selling) works nicely for the other functions (other than the relay driver).

---
James Newton: PICList webmaster/Admin
spam_OUTjamesnewtonTakeThisOuTspampiclist.com  1-619-652-0593 phone
http://www.piclist.com/member/JMN-EFP-786
PIC/PICList FAQ: http://www.piclist.com


2007\07\02@182900 by Mark Hanchey

flavicon
face

Some good info on parallel port driving relays :
http://www.epanorama.net/circuits/parallel_output.html#relaycontrol


I would probably use a optoisolator to drive the relay.
Get isolation and no problems driving a led from any parallel port.

Mark

At 06:00 PM 7/2/2007, you wrote:
>Short version: What is the absolute minimum footprint driver circuit (NOT
>SMT) that will work from an Open Collector output with a 4.7K pull up to +5
>(PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5 which has
>a 5 volt, 63 Ohm coil?

2007\07\02@183107 by Jon Chandler

picon face
OI'm partial to the ULN2001 - ULN2005 darlington driver chips. Seven sections
of darlington pairs with back-emf built in and with or without base resistors
built in (depending on the part number).  A number of chip makers build them.
Find TI's data sheet here:  

http://focus.ti.com/lit/ds/symlink/uln2003a.pdf

Jon

n Mon, 2 Jul 2007 15:00:14 -0700, James Newton, Host wrote
{Quote hidden}

> --

2007\07\02@183550 by alan smith

picon face
not smt? ok...was going to suggest
 
             NUD3112DMT1G
 
 Maybe it comes thru-hole...but ive used the smt part
 

"James Newton, Host" <jamesnewtonspamKILLspampiclist.com> wrote:
 Short version: What is the absolute minimum footprint driver circuit (NOT
SMT) that will work from an Open Collector output with a 4.7K pull up to +5
(PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5 which has
a 5 volt, 63 Ohm coil?

Long version:

I have a PCB that I would like to squeeze a bit more functionality into, but
I have almost no real-estate available. I've managed to put a PCB mount
relay on the underside of the board (with other components on the top) by
fitting it's few through hole leads in between other stuff.

What remained was a drive circuit for the relay. Piclist.com has a great
page for PIC relay drivers at
http://www.piclist.com/techref/io/relays.htm and what I think is the best
page on the PC parallel port bar none at
http://www.piclist.com/techref/io/parallel/signals.htm

However, the quick and dirty single transistor driver from the relays page
http://www.piclist.com/techref/io/relay5v.gif will not work with the actual
PC parallel port outputs as specified on the parallel port page. It does
work with a PIC, I verified that, but the PIC has a lot more drive than a PC
parallel port pin... Especially the pin I want to use: nStrobe, which is an
open collector output with a 4.7k pull-up resistor.

There is another suggestion on the relay driver page that looks promising
for a very small footprint solution:

+24
|
relay coil
|
drain
+5 ---- gate N Channel Hexfet
control source
|
gnd


But there is no sample part number or other details. I spent some hours this
weekend searching the net for N Channel Hexfet examples circuits, hoping to
find something where one was used to drive a relay or used to drive
something like a relay from a PC parallel port and came up empty.

I would really like to avoid all the extra holes and space for a resistor,
diode, etc... In addition to the drive transistor.

If you are curious, the circuit is for the next version of this kit and PCB:
http://www.piclist.com/techref/io/stepper/linistep/4axis2build.htm which is
darn fine in most other respects... The first version (which I am now
selling) works nicely for the other functions (other than the relay driver).

---
James Newton: PICList webmaster/Admin
.....jamesnewtonKILLspamspam.....piclist.com 1-619-652-0593 phone
http://www.piclist.com/member/JMN-EFP-786
PIC/PICList FAQ: http://www.piclist.com


2007\07\02@194554 by Gerhard Fiedler

picon face
James Newton, Host wrote:

> Short version: What is the absolute minimum footprint driver circuit (NOT
> SMT) that will work from an Open Collector output with a 4.7K pull up to +5
> (PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5 which has
> a 5 volt, 63 Ohm coil?

Any n-channel MOSFET that can carry the required 80mA (thermal
considerations)? The 2N7000 should do it, but there are others that do it
cooler albeit more expensively.

<http://www.fairchildsemi.com/ds/2N/2N7000.pdf>

{Quote hidden}

No need for a Hexfet, unless I'm missing something. A standard MOSFET
should do it, provided that its Idsmax is >80mA, and it can carry the 80mA
with 5V Vgs and not get too hot. The reverse diode in a MOSFET typically
can carry the same current as Idsmax, which is all you need.

Gerhard

2007\07\02@203340 by Gerhard Fiedler

picon face
Gerhard Fiedler wrote:

>>             +24
>>              |
>>          relay coil
>>              |
>>            drain
>>   +5  ---- gate      N Channel Hexfet
>>  control   source
>>              |
>>             gnd
>>
>> But there is no sample part number or other details.
>
> No need for a Hexfet, unless I'm missing something. A standard MOSFET
> should do it, provided that its Idsmax is >80mA, and it can carry the
> 80mA with 5V Vgs and not get too hot. The reverse diode in a MOSFET
> typically can carry the same current as Idsmax, which is all you need.

I forgot: of course the relay coil would be connected to +5V and not +24V,
but you knew this (that's why I'm writing this msg :)

Gerhard

2007\07\02@221726 by Kevin Timmerman

flavicon
face
The 2N7000 would probably be the best choice. A 2N2222/3904/4401/etc
could be directly driven by an OC output with pullup. Just connect it
to the base, emitter to ground, collector to relay. The pullup will
bias the trasistor on, and the OC output will shunt the pullup to
ground and turn it off. The danger with doing this is that some
parallel ports can change the OC outputs to totem pole for higher
speed operation.

For parallel port lines that are not OC (data lines), a FJN3305R can
be used. Lower cost than a 2N7000, and a bit more rugged.

http://www.fairchildsemi.com/ds/FJ/FJN3305R.pdf



At 06:00 PM 7/2/2007, you wrote:
>Short version: What is the absolute minimum footprint driver circuit (NOT
>SMT) that will work from an Open Collector output with a 4.7K pull up to +5
>(PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5 which has
>a 5 volt, 63 Ohm coil?

2007\07\03@064609 by Russell McMahon

face
flavicon
face
> Short version: What is the absolute minimum footprint driver circuit
> (NOT
> SMT) that will work from an Open Collector output with a 4.7K pull
> up to +5
> (PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5
> which has
> a 5 volt, 63 Ohm coil?
>
> Long version:
>
> I have a PCB that I would like to squeeze a bit more functionality
> into, but
> I have almost no real-estate available. I've managed to put a PCB
> mount
> relay on the underside of the board (with other components on the
> top) by
> fitting it's few through hole leads in between other stuff.

5V, 63 ohm = 80 mA.
Drive from the pullup will be (Vstrobe-1Vbe)/4k7 ~= (5-0.6)/4700 ~=
0.9 mA

With say 0.5 mA drive you need a transistor current gain (Beta) of
80/.5 = 160 which is  achievable with many of the more capable small
transistors. I'd use BC337 here but there are many others.

The 2N2222 is a bit low Beta as is at 100 min at 150 mA.
It would quite possibly work but ... .

An appropriate small N Channel MOSFET would work with ease as the
voltage gain is close to infinite for practical purposes.
You want Vgsmin comfortably more than the driver off (low) voltage and
the FET suitably enhanced (on) at Vgs = 5 V.
Not a hard spec to meet. Using a Digikey parametric search would
probably turn up many parts.

Either  a FET or bipolar could be added with NO other components and a
TO92 pkg probably meets your spec.

Using Digikey parametric search on MOSFET, N Channel, TO92, 12-100V,
200 - 1000 mA gave 4 pages of results.

________

2N7000FS $US0.26/1, $US0.13\52/100, $US0.0572/1000 is a typical
starter for 10 points.
Current rating a bit low but would work.
Rdson about <= 2.5 ohms at your load at 100C which sounds (and is)
terrible BUT at your load current that gives 0.2V drop which is fine.
Dissipation is minimal.

       http://www.fairchildsemi.com/ds/2N/2N7000.pdf

___________

BS170_D27ZTR-ND $US0.075/2000
Looks near ideal

       http://www.fairchildsemi.com/ds/BS/BS170.pdf

Watch the Vgsonmin which is too GOOD ie low at 0.8V min, 2.1V typical,
3V max. Need to be sure that driver pulls below 0.8V always.


Many more but that's an OK start.



       Russell










2007\07\03@065930 by Brent Brown

picon face
Russell McMahon wrote:
> An appropriate small N Channel MOSFET would work with ease as the
> voltage gain is close to infinite for practical purposes. You want...

I think you intended to say "current gain is close to infinite..."   :-)

MOSFET requires essentially a voltage at the Gate to turn it on, insignificant DC
input current causes significant DC output current flow (Drain - Source).
--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  EraseMEbrent.brownspam_OUTspamTakeThisOuTclear.net.nz


2007\07\03@074037 by Gerhard Fiedler

picon face
Russell McMahon wrote:

> With say 0.5 mA drive you need a transistor current gain (Beta) of
> 80/.5 = 160 which is  achievable with many of the more capable small
> transistors. I'd use BC337 here but there are many others.

Wouldn't you need an extra diode with a bipolar transistor that you don't
need with a MOSFET (built-in)? That's the reason I suggested a MOSFET.

Gerhard

2007\07\03@105137 by Spehro Pefhany

picon face

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


Quoting Gerhard Fiedler <@spam@listsKILLspamspamconnectionbrazil.com>:

{Quote hidden}

Unless the MOSFET is avalanche-rated for the coil energy you need a diode
anyway. The parasitic body diode should never conduct.

Best regards,



2007\07\03@121251 by Russell McMahon

face
flavicon
face
>> An appropriate small N Channel MOSFET would work with ease as the
>> voltage gain is close to infinite for practical purposes. You
>> want...

> I think you intended to say "current gain is close to infinite..."
> :-)

How about

        ... transconductance is extremely high ... :-)


           RM


2007\07\03@121252 by Russell McMahon

face
flavicon
face
>> With say 0.5 mA drive you need a transistor current gain (Beta) of
>> 80/.5 = 160 which is  achievable with many of the more capable
>> small
>> transistors. I'd use BC337 here but there are many others.

Pre-script: It's surprising how much needs to be thought about with
such a very very simple arrangement to actually get it right :-(.

I'd too would tend to use a MOSFET if doing this in volume, but more
for low effective Vsat and for the certainty of available drive
reasons and not because it has an internal diode. A MOSFET has some
dangers, such as needing to ensure that it's Vgsmin is not too GOOD so
that it is not turned on accidentally. This depends on how well the
parallel port driver saturates when low and this would need to be
checked as part of what starts out looking like a trivial design. A
MOSFET can also have very nasty leakage current at elevated
temperatures but that is not an issue here with a relay load.

> Wouldn't you need an extra diode with a bipolar transistor that you
> don't
> need with a MOSFET (built-in)? That's the reason I suggested a
> MOSFET.

Essentially, no, but you probably do :-).

ie         The MOSFET diode won't help spike suppression. The inherent
body diode of the MOSFET is in the wrong place and of the wrong
polarity to act as a spike suppressor in this application and will be
stressed by the spike just as a bipolar transistor will be. (The
bipolar and the FET proper are in forward blocking mode and the diode
is in its reverse blocking mode during the inductive spike). Without
an external diode or similar both would generate a reactive transient
on turn off which would quite probably require some form of
suppressor - typically either a reverse polarity diode *across the
relay coil* or a resistor.

One could use a MOSFET which is specified for avalanche breakdown (at
slightly above its maximum rated voltage) and thus remove the need for
an external suppression device.  This is more or less equivalent to
adding a zener diode as below.

Transient current is initially the relay current at turnoff time and
energy to be dissipated is 0.5 x Lrelay coil x i^2. A diode clamps the
turn off transient at 1 diode drop above supply and this can greatly
increase the turn off time as the energy stored in the relay coil is
dissipated at low voltage (typically 0.6 x Irelay decaying
exponentially as current drops). If turn off time considerations are
an issue then a series resistor will allow faster turnoff as it will
let the transient rise to V = I.R above rail but will lead to much
faster turnoff. IR + Vsupply must be no more than the transistor
rating if breakdown is not to occur. A zener diode may also be used,
with the advantage that it only dissipates power from the spike. Zener
will be collector (or drain) to ground for a grounded emitter/source
driver while a diode will always be across the relay and a resistor
may be in either location with advantages and disadvantages in each
case.

MOSFETs are generally more tolerant of breakdown than bipolar devices
BUT a power MOSFET which is not explicitly designed to spread
breakdown energy across it's multiple cells (and many aren't) may well
experience localised overloading and permanent punch through damage.
At this low power level the manufacturers probably haven't gone to
vast effort to optimise their devices for forward breakdown so a
midget power device may be more prone to damage than if the design
called for much higher power levels.

Due to the modest amount of energy involved in this case (small relay,
low voltage, lowish current) one MAY get away with no diode but the
secondary effect of interference with related circuitry will almost
certainly mean that a diode or similar should be used.

While the end result is a trivially simple circuit there is more to it
than meets the eye if it is actually to work as intended.



                   Russell.

2007\07\03@142458 by Dwayne Reid

flavicon
face
At 04:00 PM 7/2/2007, James Newton, Host wrote:
>Short version: What is the absolute minimum footprint driver circuit (NOT
>SMT) that will work from an Open Collector output with a 4.7K pull up to +5
>(PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5 which has
>a 5 volt, 63 Ohm coil?

N-channel MOSFET.  Suggest 47R resistor in series with the gate
(reduces / stops parasitic oscillation) and don't forget the back-EMF
diode across the relay.

You can omit the 47R gate resistor if you slide a ferrite bead over
the Gate lead before inserting into the PCB.

Part numbers:
2n7000, 2n7001, 2n7002 (maybe), vn2222, vn2105, vn2106

All of the above are logic-level MOSFETs in TO-92 package or similar.

I have 2 different versions of 2n7002: one is a TO-92 just like the
2n7000, the other is a sot23-6 package with 2 identical MOSFETs
inside.  Go figure . . .

One other question: why wouldn't you use a 24V relay if you have a
24V rail handy?  No need to cause extra heat dissipation on your 5V
regulator if you can avoid it.

dwayne

--
Dwayne Reid   <KILLspamdwaynerKILLspamspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

2007\07\03@180304 by Brent Brown

picon face
> > Wouldn't you need an extra diode with a bipolar transistor that you
> > don't need with a MOSFET (built-in)? That's the reason I suggested a
> > MOSFET.
>
> Unless the MOSFET is avalanche-rated for the coil energy you need a
> diode anyway. The parasitic body diode should never conduct.

True. In other words the MOSFETs parasitic body diode is in the wrong place to be
useful in this circuit. It won't become forward biased. It would be ok however if, as
Spehro says, the parasitic body diode is suitably avalanche rated (behaves like a
zener diode when reverse biased). Some power MOSFETs do have this feature.

--
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: 027 433 4069
eMail:  RemoveMEbrent.brownTakeThisOuTspamclear.net.nz


2007\07\03@182630 by James Newtons Massmind

face picon face
Jon Chandler Sent: 2007 Jul 02, Mon 15:31
> OI'm partial to the ULN2001 - ULN2005 darlington driver
> chips. Seven sections of darlington pairs with back-emf built
> in and with or without base resistors built in (depending on
> the part number).  A number of chip makers build them.
>  Find TI's data sheet here:  
>
> http://focus.ti.com/lit/ds/symlink/uln2003a.pdf
>

Nice, but way too big (physically) for this application. Very little space
left on the PCB.

---
James.



2007\07\03@182834 by James Newtons Massmind

face picon face
Mark Hanchey Sent: 2007 Jul 02, Mon 15:29
>
> Some good info on parallel port driving relays :
> http://www.epanorama.net/circuits/parallel_output.html#relaycontrol

One of the first places I looked, but they just have the standard stuff...

>
> I would probably use a optoisolator to drive the relay.
> Get isolation and no problems driving a led from any parallel port.

This is probably what I should do on the next version rather than messing
about with the TO92's. The little DIP is quite a lot larger, but I might be
able to fit it in...

---
James.


2007\07\03@193256 by James Newtons Massmind

face picon face
alan smith Sent: 2007 Jul 02, Mon 15:36
> not smt? ok...was going to suggest
>    
>               NUD3112DMT1G
>    
>   Maybe it comes thru-hole...but ive used the smt part
>  

Wow... That is a nice part. But I can't find it in a TO92 case, and it
appears to have limited availability, only available from 2 distributors
that I can find: Digikey and Mouser.

If anyone knows of such a think in a TO-92, it would be a real find.

---
James.


2007\07\04@003416 by Steve Smith

flavicon
face
Use the SMT version and put it on the back (ULN2801 has 8 sections)
Steve

-----Original Message-----
From: spamBeGonepiclist-bouncesspamBeGonespammit.edu [TakeThisOuTpiclist-bouncesEraseMEspamspam_OUTmit.edu] On Behalf Of
James Newtons Massmind
Sent: 03 July 2007 23:26
To: 'Microcontroller discussion list - Public.'
Subject: RE: [EE] PC Parallel Port small footprint relay driver

Jon Chandler Sent: 2007 Jul 02, Mon 15:31
> OI'm partial to the ULN2001 - ULN2005 darlington driver
> chips. Seven sections of darlington pairs with back-emf built
> in and with or without base resistors built in (depending on
> the part number).  A number of chip makers build them.
>  Find TI's data sheet here:  
>
> http://focus.ti.com/lit/ds/symlink/uln2003a.pdf
>

Nice, but way too big (physically) for this application. Very little space
left on the PCB.

---
James.



2007\07\04@040304 by Alan B. Pearce

face picon face
>You can omit the 47R gate resistor if you slide a ferrite
>bead over the Gate lead before inserting into the PCB.

Still looking for a supplier of beads to fit SOT-23 packages ;))))

2007\07\04@080026 by Spehro Pefhany

picon face
At 11:34 PM 7/3/2007, you wrote:
>Use the SMT version and put it on the back (ULN2801 has 8 sections)
>Steve

I like the ULN2003 and similar series (15 cents in 1K for 7 drivers),
but they are Darlingtons and are marginal driving a 5V relay under worst-case
conditions, though perhaps 'good enough' for hobby use-- voltage drop is
in the 1V range @ 80mA, which is 20% of the coil voltage, leaving not
much for 5V tolerance and temperature effects.

I don't think James will like it AT ALL.. but here is one way of
doing it, but NOT small footprint and SIX (count 'em) parts.
It IS cheap, through-hole, has a rugged input (no MOSFET gate brought out),
and is 'off' for disconnected input:

(View with fixed-width font such as Courier)


          o-----------------------------+------+
         +5V                            |      |
                                       .-.     |
                                       | |     |
                                  4K7  | |     |
                                       '-'     |
                                        |    |<  2N4403
                                        +----|
                                        |    |\
                                       .-.     |
                                    1K | |     |
                                       | |     |
                            2N4401     '-'     |
                                        |      |
                                 +------+      +----------+
     P. Port  4K7                |             |          |
              ___              |/              |          |
          o -|___|- ----+---- -|               |          |
                        |      |>              C|         |
                       .-.       |         63R C|         -
                       | |       |             C|         ^
                   10K | |       |             |   1N4148 |
                       '-'       |             |          |
                        |        |             |          |
          o-------------+--------+-------------+----------+
         0V

This is pretty much how I would do it for offshore hand assembly of
through hole parts (I'd use more appropriate Asian transistors). Total
parts cost would be around a nickel (plus relay) in moderate quantities.

The 1K can be lowered to get more base drive if desired. Nothing is
critical.


Best regards,

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



2007\07\04@093819 by Gerhard Fiedler

picon face
Spehro Pefhany wrote:

> I don't think James will like it AT ALL.. but here is one way of doing
> it, but NOT small footprint and SIX (count 'em) parts. It IS cheap,
> through-hole, has a rugged input (no MOSFET gate brought out), and is
> 'off' for disconnected input:

Why do you use two transistors instead of one? To be less dependent on a
high beta?

Gerhard

2007\07\04@110748 by Russell McMahon

face
flavicon
face
TO92's are fine here - especially if the solution is cheaper and
simpler :-). If not then by all means get more complex.


       Russell

> This is probably what I should do on the next version rather than
> messing
> about with the TO92's. The little DIP is quite a lot larger, but I
> might be
> able to fit it in...


2007\07\04@113347 by Russell McMahon

face
flavicon
face
> I don't think James will like it AT ALL.. but here is one way of
> doing it, but NOT small footprint and SIX (count 'em) parts.

Counts ...
SEVEN parts :-)

> It IS cheap, through-hole, has a rugged input (no MOSFET gate
> brought out),
> and is 'off' for disconnected input:

James specified an open collector gate drive with pullup.
That circuit works with minor input mods. Main advantages are ease of
enough gain with junk transistors and non inverting polarity - driver
high = relay on.

An "emitter follower" with a single bipolar transistor and no diode
should work if you redcue relay voltage to 3 volts and use a suitably
high beta transistor.
BC337-40 will work with the resistor that James specified and BC337-25
with a 2k2 pullup.

Despite the BC3xx transistors being arcane European parts eg Digikey
has them in stock and cheap! One of the nicest small bipolars for this
sort of task and often cheaper than inferior parts. PNP complement is
BC327. Buy 100 of each of them now for your parts box (< $US10 total.)

Gargoyle revealed that the Omron relay that James specified has a 3V
version with a 75% of Vnominal "must turn on" value = 2.25V = 100 mA
turn on current.
After the emitter follower Vbe drop that gives (5-0.6-2.25) = 2.15
drop across the pullup resistor. Base current then is 2.15/4k7 ~= 0.45
mA so the requird beta is 100/.45 or about 250 - preferably a bit
more. This would be OK with selected 337-25's abnd with all 337-40's.
As these are both under $US0.05 in 100's price is "good".

The turn off is interesting.
Relay is in emitter to ground and pulled high when on.
At turnoff the relay/emitter ring negative to BELOW ground.
The emitter is pulled negatively until the transistor with base
grounded by the low-on driver reaches -0.6V or so across Vbe. The on
transistor now sinks current into the inductor at a diminishing rate
and the inductor also sinks current via the base emitter diode. Most
interesting.  I haven't tried it or simulated it but it "must" work as
with base grounded the static off state is stable and the only thing
keeping the transistor on above is the 'ringing' inductor.

The 3V relay is the "enabling technology" as with a 5v part the "must
operate" spec is 5V x 75% = 3.75V. After the Vbe allowance that gives
about 0.65V drop across the pullup to bias the transistor on and the
requisite beta is vast or the pullup needs to be much smaller than
James specified.

FYI AFAIR "must turn off" is 0.1 x Vnominal or 0.3V for a 3V relay.
The off emitter follower has its base at or near ground from the
driver so the emitter is 1Vbe below that (if it can be) so meeting
this low must-turn-off spec is acceptable.

So that gives a 2 part solution :-) - a (very) cheap npn bipolar and a
pullup resistor.



       Russell

2007\07\04@154224 by Richard Prosser

picon face
On 05/07/07, Russell McMahon <apptechEraseMEspam.....paradise.net.nz> wrote:
> > I don't think James will like it AT ALL.. but here is one way of
> > doing it, but NOT small footprint and SIX (count 'em) parts.
>
........
{Quote hidden}

Hi Russell,
This circuit is a good one when trying to establish the level of
understanding of new recruits, managers, draughtsmen etc.
Several times I've used it and been told by people who I thought
should know better that a flyback diode is required.

RP

2007\07\04@165333 by Spehro Pefhany

picon face

> Hi Russell,
> This circuit is a good one when trying to establish the level of
> understanding of new recruits, managers, draughtsmen etc.
> Several times I've used it and been told by people who I thought
> should know better that a flyback diode is required.
>
> RP

A set of schematics just came across my desk in which the designer
used HC595 outputs to directly pull down the bases of MMBT2907s and thusly
drive a bunch 5V latching relay coils of similar resistance to the one in
question. No flyback diodes, no base resistors, and it looks like there
is plenty of margin since the HC outputs pull down quite smartly
(I figure within ~25mV of GND with a 0.5mA load, leaving 4.4V almost
for the coils). Further, the tempco is in the correct direction to
compensate for coil resistance.. but only ~1/10 the value, unfortunately.
I think it's a pretty good design, in this case. The coils run cold
since it's a latching relay and does not get switched very often.

Best regards,
SP



----- End forwarded message -----



2007\07\04@165614 by Spehro Pefhany

picon face


Quoting Russell McMahon <EraseMEapptechspamparadise.net.nz>:
>
> James specified an open collector gate drive with pullup.
> That circuit works with minor input mods. Main advantages are ease of
> enough gain with junk transistors and non inverting polarity - driver
> high = relay on.
>
> An "emitter follower" with a single bipolar transistor and no diode
> should work if you redcue relay voltage to 3 volts and use a suitably
> high beta transistor.
> BC337-40 will work with the resistor that James specified and BC337-25
> with a 2k2 pullup.

True, but if the port is disconnected with a pullup, the relay turns on.
That is often *not* a desirable thing (eg. spindle with razor-sharp cutter
unexpectedly starting, smelly coolant gushing all over the place etc.).

> Despite the BC3xx transistors being arcane European parts eg Digikey
> has them in stock and cheap!

Unfortuantely, the BC337-40 is not in stock at Digikey. It's cheap enough,
but MOQ is 16,000-30,000 pieces.

One of the nicest small bipolars for this
> sort of task and often cheaper than inferior parts. PNP complement is
> BC327. Buy 100 of each of them now for your parts box (< $US10 total.)
>
> Gargoyle revealed that the Omron relay that James specified has a 3V
> version with a 75% of Vnominal "must turn on" value = 2.25V = 100 mA
> turn on current.

At exactly what coil temperature is it guaranteed to turn on? ;-)
If you're going to bend the rules, and make the design reliable,
you have to know exactly. Also, the 3V version is not stocked by
Digikey. I made this mistake about 15 years ago and designed a whole
bunch of products with 9V relays. They were always long delivery and
never in stock, although the price was okay. Eventually we went to 12V
'standard' relays which were always stocked.

> After the emitter follower Vbe drop that gives (5-0.6-2.25) = 2.15
> drop across the pullup resistor. Base current then is 2.15/4k7 ~= 0.45
> mA so the requird beta is 100/.45 or about 250 - preferably a bit
> more. This would be OK with selected 337-25's abnd with all 337-40's.
> As these are both under $US0.05 in 100's price is "good".

It's going to run a bit warm with that dissipation. Oh well, that will help
with the voltage drop. ;-)

{Quote hidden}

Yes, it will work fine. I have used a similar circuit to drive inductive
loads (magnetic sound transducers) from a microcontroller output (actually
with a voltage divider (half a network, so 1.5 parts total) on the input
to get down to the rated 1.x volts).l

{Quote hidden}

But it turns on when the cable is disconnected.




2007\07\04@165736 by Spehro Pefhany

picon face

Quoting Russell McMahon <RemoveMEapptechEraseMEspamEraseMEparadise.net.nz>:

> TO92's are fine here - especially if the solution is cheaper and
> simpler :-). If not then by all means get more complex.
>
>         Russell

Almost no new parts are being introduced in TO-92, so anything using
that package tends to be "mature" (10, 20, or even 30+ years old).
There are still some parts being introduced in DIP packages, but not
that many.

Best regards,
SP


2007\07\04@204041 by Russell McMahon

face
flavicon
face
I answered this and went to send it when I noticed it had apparently
come to me offlist. As it's wholly technical and relevant to the
subject I'll reply on list with no reference to the writer. There may
be a parallel on list copy that isn't in my PICList folder for some
reason:
_______________


> James specified an open collector gate drive with pullup.

> An "emitter follower" with a single bipolar transistor and no diode
> should work ...

> True, but if the port is disconnected with a pullup, the relay turns
> on.

The customer is always right :-).
One can redefine what the customer says he wants in due course
(perhaps), but it's reasonable to assume that if he said he has an OC
driver then that's what you need to work with. This MAY be changeable.
but ... .


> Unfortuantely, the BC337-40 is not in stock at Digikey. It's cheap
> enough,
> but MOQ is 16,000-30,000 pieces.

They are however in stock at several other places on the FINDCHIPS.COM
part finder list (Newark, ...?)

>> Gargoyle revealed that the Omron relay that James specified has a
>> 3V
>> version with a 75% of Vnominal "must turn on" value = 2.25V = 100
>> mA
>> turn on current.

> At exactly what coil temperature is it guaranteed to turn on? ;-)

The spec sheet says "must operate voltage is 75% ...".
With a BC337-40 there will probably be a reasonable safety margin
running at midday at Badwater in August*. Final design MAY require the
4k7 to be reduced to say 2k2 (as I noted) if the driver can tolerate
this.
As one may expect, I haven't gone right through everything involved
for such a first cut approach but I'm confident that it can be made to
work properly when done properly. Odds are it will in fact work as
shown in all conditions with the BC337-40.

> If you're going to bend the rules,

No. No rule bending intended. Just "Here's a design starter that will
work when you finish designing it. Some component values shown  may
not be the final ones".

> Also, the 3V version is not stocked by Digikey.

Again. As long as it IS made / stocked by Omron it's liable to be
available from somewhere. If every design answer on PICList had to be
backed by a fully sourced priced and totally designed BOM we'd have a
far quieter electronic designs section :-). Omron make the relay,
Newark and others sell the transistor, there are other trasnsistors
available that will also work (with certainty)

I made this mistake about 15 years ago and designed a whole
bunch of products with 9V relays. They were always long delivery and
never in stock, although the price was okay. Eventually we went to 12V
'standard' relays which were always stocked.


> > So that gives a 2 part solution :-) - a (very) cheap npn bipolar
> > and a  pullup resistor.

> But it turns on when the cable is disconnected.

Cable?
James specd this as wedged onto an existing PCB in a "must be very
very small" space, electrically between the existing driver IC and a
relay. There may be a cable in there but it isn't obvious to me from
memory. Ideally one would take the whole circuit and design it from
scratch but this is a retrofit. In fact, I think from all I've heard
now in the course of things that what I've proposed is in fact what
he's done already, but that it didn't work with existing parts he had.
If so, all I've added is  showing that it can be made to work with a 3
V relay and high beta transistor. Also pointed out that a diode which
he didn't use isn't needed because of an unusual spike catching method
that "just happens".



       Russell

* How low can you go.
Lowest point in continental USA.
Bottom of Death Valley.
Hottest known place on earth less a few degrees on some days .
"Hottest place I've ever been."
Record location is in Algeria.






2007\07\05@175719 by James Newtons Massmind

face picon face
> > James specified an open collector gate drive with pullup.
>
> > An "emitter follower" with a single bipolar transistor and no diode
> > should work ...
>
> > True, but if the port is disconnected with a pullup, the
> relay turns
> > on.
>
> The customer is always right :-).

As if... This "customer" reserves the write to be spectacularly wrong. But
in this case it was asked as a "if I've already got these PCB's made, can
you see a way of solving the problem or do I have to redesign and wait this
feature for the next version."

> > But it turns on when the cable is disconnected.
>
> Cable?
> James specd this as wedged onto an existing PCB in a "must be
> very very small" space, electrically between the existing
> driver IC and a relay. There may be a cable in there but it
> isn't obvious to me from memory.

This is being driven from the nStrobe line of a PC parallel port. That is an
OC pin with a 4.7K pull up on standard PC Parallel Port boards. Some boards
MAY drive high and low, but the spec calls for OC. There is, therefore, a
cable and no drive IC on the PCB.

So, with the proposed "interim" design, the relay WOULD turn on if the cable
were disconnected, which would most likely fire up the spindle on the CNC
router that the relay is there for. On the other hand, the user has no
business unplugging the data cable while there is still power to the relay
drive or the spindle in the first place.


> Ideally one would take the
> whole circuit and design it from scratch but this is a
> retrofit. In fact, I think from all I've heard now in the
> course of things that what I've proposed is in fact what he's
> done already, but that it didn't work with existing parts he had.

Exactly. I made the mistake of trying to use a circuit from the archives
that DOES work nicely (and very simply with only 1 component) with a PIC
driving the transistor but will NOT work with the parallel port pin driving
it. Actually, on my PC the thing will work if I decrease the pull up to
about 1K, but that is pushing it.

> If so, all I've added is  showing that it can be made to work
> with a 3 V relay and high beta transistor. Also pointed out
> that a diode which he didn't use isn't needed because of an
> unusual spike catching method that "just happens".

Absolutely. It's a very nice workaround for the existing PCB's and I will be
ordering the parts (if I can find them :) ) today or tomorrow.

For the next board version, I will find a way to squeeze in the extra
resistor and protection diode for the more standard driver or a little DIP
optocoupler like a H11G2 or maybe that really cool little NUD3112DMT1G if I
can find a through hole version.

Many thanks to all who have helped and especially to Russ and Spef.

---
James.


2007\07\06@182913 by James Newtons Massmind

face picon face
> > Also, the 3V version is not stocked by Digikey.
>
> Again. As long as it IS made / stocked by Omron it's liable
> to be available from somewhere. If every design answer on
> PICList had to be backed by a fully sourced priced and
> totally designed BOM we'd have a far quieter electronic
> designs section :-). Omron make the relay, Newark and others
> sell the transistor, there are other trasnsistors available
> that will also work (with certainty)
>
> I made this mistake about 15 years ago and designed a whole
> bunch of products with 9V relays. They were always long
> delivery and never in stock, although the price was okay.
> Eventually we went to 12V 'standard' relays which were always stocked.

Yep, this G5LE-1-DC3 is not even stocked by the manufacturer: Omron. They
said that digikey can special order it (although digikey doesn't even list
that part) and they will make as few as 10 for me.  I've emailed Digikey and
can't wait to hear how much and how long.

For now, I'm going to call it a lost cause and work on the next version of
the PCB, with an opto driver like the H11G2 if I can figure out how to
squeeze it into the available space.

Has anyone used the FOD852? With only 4 pins, it has a nice little footprint
while also being available in a DIP for easy kit assembly.
http://www.fairchildsemi.com/pf/FO/FOD852.html

Is there an opto-isolated driver that already includes the resistor for the
LED?

---
James.


More... (looser matching)
- Last day of these posts
- In 2007 , 2008 only
- Today
- New search...