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'[EE]: Solid state relay difficulty'
2001\08\02@025014 by Nick Veys

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Hi all, I'm using an Omron G3MB-202P solid state relay, 5V flavor.  It's
a phototriac.  It's not behaving how I would expect though, hopefully
someone can clear this up..

Pin definitions:

1 - load
2 - load
3 - (+) input
4 - (-) input

Here's what I am seeing:

Connections:  to test this I just want to light an LED...

5V to Anode of 5V LED
pin 1 - cathode of LED
pin 2 - ground
pin 3 - ground
pin 4 - ground

This is how I start it up.

Now when I apply power to this, of course nothing happens as I expect.
I then switch over the pin 3 to +5V, the LED lights, as expected, I then
switch the pin 3 back to ground, the led stays lit.  In fact, no
arrangement of the input pins (3,4) will make the damn LED shut off, I
can't break the circuit once it's made...  Doesn't sound too useful of a
relay!

Hopefully I'm doing something obviously wrong!!

I've tried this with 3 different relays so I doubt they are defective...

Someone please smack me and tell me the simple solution! :)

Thanks all!

-- Nick

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2001\08\02@032723 by Vasile Surducan

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It seems you don't know how a thyristor or a triac works.
If you supply A-K ( thyristor ) or A1-A2 ( triac ) ( A = anode, K =
cathode ) in DC the AK or A1-A2 junction will stay on after a gate or opto
command until the currrent through this junction will go to zero ( in fact
must be less than sustain current) and this will never hapened in DC .
Use a bulb for test and supply it in AC. Will works.
Cheers, Vasile


On Thu, 2 Aug 2001, Nick Veys wrote:

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2001\08\02@045946 by Sergi Sanchez

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The opto-TRIAC is working well. :-D

And as Vasili said, when the triac is ON remains on as long as courrent
flows throug it.

This feature is very usefull when you works with AC courrents, in fact, you
can trigger the triac with a pulse, and when AC courrent cross the zero
level the triac shuts off.

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2001\08\02@052108 by Ned Seith

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Nick,

The phototriac is intended to switch high voltage AC currents from a low
voltage DC source and to provide dielectric isolation (7,500V insulation)
between the DC and AC sources.
As per the pin out that you provided:
Pin 3 is the anode of the phototriac's internal LED.
A DC current (+) of 10mA to 25 mA  should be applied to pin 3 to illuminate
the internal LED and to turn on the triac.
Pin 4 is the cathode of the phototriac's internal LED and is frequently
connected to the DC power supply's common (-).
Pin 1 is typically connected to the AC load. The other end of the AC load
is connected directly to the AC power source (excluding fuses/circuit
breakers).
Pin 2 is connected to the AC common.
A true test of the triac's performance requires an AC power source, an AC
load and a low voltage DC power source. However, a crude basic functional
test may be performed using DC.
While not intended, nor conventional, the triac may be used for certain DC
applications, however, generally there are more appropriate DC devices.

Vasile,

A triac will turn off or interrupt DC current, if the DC current is pulsed
energy and decreases in amplitude to near zero volts. As an example, a
triac will effectively control a half wave or full wave rectified DC signal.
However, an SCR would be a more appropriate control device.

Good Luck!
Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858




At 09:22 AM 8/2/01 +0300, you wrote:
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2001\08\02@052509 by Quentin

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Nick Veys wrote:

> Someone please smack me and tell me the simple solution! :)
>
WHACK!
Is the SSR output not rated for AC? Sounds like the triac switch on and
wait for zero crossing to switch off.
You do get DC load type from Omron. Can look up a number later.

Quentin

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2001\08\02@053126 by Sergi Sanchez

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> A triac will turn off or interrupt DC current, if the DC
> current is pulsed
> energy and decreases in amplitude to near zero volts. As an example, a
> triac will effectively control a half wave or full wave
> rectified DC signal.

Dear, formally a 'DC PULSE' is an AC signal plus a DC bias. And Vasili
explains CLEAR the physics of a triac. Tiacs CUT-OFF in absence of current,
not where DC voltage nears zero (remember inductive loads).

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2001\08\02@053343 by Vasile Surducan

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On Thu, 2 Aug 2001, Ned Seith wrote:

>
> Vasile,
>
> A triac will turn off or interrupt DC current, if the DC current is pulsed
> energy and decreases in amplitude to near zero volts.

 Do I said something else ? If the current flowing from A to K is less
than sustaining current then will shut off. This current may be near zero
or greatest, depends on device. Power devices have greatest sustaining
current. GTO are better for DC usage, they haven't this ill, but are
difficult to command.
 Cheers to you, too !
 Vasile


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2001\08\02@061807 by mike

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If it's a triac device it will only work on AC, as the triac will stay
conducting until the current crosses zero.

On Thu, 2 Aug 2001 01:47:31 -0500, you wrote:

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2001\08\02@062443 by Ned Seith

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Sergi,

Vasili's statement that "this will never hapened in DC" suggests that a
triac would not turn off while conducting DC current. When the DC current
of a half or full wave rectified DC signal diminishes below the holding
current of the triac, the triac will shut off, if a gate signal is not
present. The DC current of a half or full wave rectified DC signal is a
proportional by product of the DC voltage. If the load was purely
resistive, then the DC voltage and the DC current would reach zero at the
same moment. However, as you have "correctly" indicated, if the load is
inductive (or capacitive) there will be a phase shift between the DC
voltage and DC current. However, the fact remains that a triac will turn
off when conducting the DC current of a half or full wave rectified signal.
When I attended school nearly 40 years ago, half wave and full wave
rectified signals were referred to as "pulsed DC energy" and our fellow
classmates were never referred to as "dear". How times have changed

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858
.
At 11:32 AM 8/2/01 +0200, you wrote:
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2001\08\02@063103 by Spehro Pefhany

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At 11:18 AM 8/2/01 +0100, you wrote:
>If it's a triac device it will only work on AC, as the triac will stay
>conducting until the current crosses zero.

While this is correct there might be situations where you could use the
behavior to advantage on DC. Shorting the output with a momentary
switch (or interrupting the current) will turn it off ( assuming dv/dt isn't
too high). So, for a security alarm powered from a 12VDC battery, it might
be just what you want.

Another possible use on DC would be as a cheap isolated way to control
high voltage relatively low currents.. 10's of uA, say.  With a high value
series resistor between, say +300 and -300 VDC you could get an isolated
600V swing from your micro etc. with a very cheap little devices. This
works because the current is less than the holding current (confirm this
at maximum Ta).

Best regards,
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2001\08\02@092518 by Sergi Sanchez

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Mr. Steith,

When I attented school nerly 25 years ago, I was (I think) so applied to the
fellow lessons in order to
remember now if they referred us as 'dear' or not.

By the by, 15 years ago I was dessigning special needs triacs and srcs on
the National Microelectronics Center (Spain). So I think I know a little.

Sincerely,
Sergi Sanchez

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2001\08\02@101457 by Ned Seith

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Sergi,

I'm sure that you are quite knowledgeable and very capable.

Disrespect was never intended.

The way that I see it, is that anyone who posts to this list, has
significant knowledge and/or experience which has contributed to them
gravitating to this list. To the uninitiated, the contents of this list
with the hardware, firmware, software and other technical references would
be un-interpretable sending them off to the nearest prime time chat room.
It's amazing to me that we have this virtual space where those individuals
who are motivated by electronics, science and technology from around the
entire world can gather, listen, observe, talk, share, debate, argue and
occasionally throw rocks at each other.

Sincerely,
Ned Seith
Nedtronics
59 3rd Street
Gilroy, CA 95020
(408) 842-0858


At 03:25 PM 8/2/01 +0200, you wrote:
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2001\08\02@114010 by Nick Veys

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Ok, first I want to thank everyone who replied to this... The responses
make perfect sense, I picked the wrong part.  I guess the next time I
need to switch a light bulb, I'll be ready!

Here is what I am trying to do.

I have a shorting block I want to control from a PIC.  I picked a relay
since it's basically able to mimic a momentary pushbutton which is what
I am trying to do.  I assumed a "relay is a relay" so I thought a solid
state relay would behave like any other relay, I was wrong! :)

So basically I need some way to short a block momentarily, preferably
without any additional hardware between it and the PIC (which is why I
picked the previous relay, had 5V input, low low amperage to switch).

Speed isn't a big issue, it needs to be able to switch on/off within
~500ms.

If anyone can perhaps show me the "correct" solid state relay I would
really appreciate it, as I don't want to just try again and see if I
pick a DC one this time! :)

Thanks again for all the answers!

@spam@nickKILLspamspamveys.com | http://www.veys.com/nick


> {Original Message removed}

2001\08\02@121022 by Raymond Choat

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Are you using this "relay" for braking?


----- Original Message -----
From: "Nick Veys" <KILLspamnickKILLspamspamVEYS.COM>
To: <RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU>
Sent: Thursday, August 02, 2001 7:26 AM
Subject: Re: [EE]: Solid state relay difficulty


{Quote hidden}

> > {Original Message removed}

2001\08\02@134153 by Nick Veys

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Hmm, I don't know what you mean, like braking in a car?  If so, no.  All
it's doing is shorting two leads to turn a device on, just needs to be
momentary and logic level driveable.

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> {Original Message removed}

2001\08\02@134829 by Roman Black

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Nick Veys wrote:
>
> Hmm, I don't know what you mean, like braking in a car?  If so, no.  All
> it's doing is shorting two leads to turn a device on, just needs to be
> momentary and logic level driveable.


Hi Nick, this shouldn't be too hard!
What type of device? Is this switching AC mains?
-Roman

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2001\08\02@142124 by Nick Veys

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I know it should be hard, hence my difficulty! :)  Go figure!

It's simply shorting two pins on a little fan controller I have made
here, on the device it brings +5 to Ground to let it know to turn on but
really, I don't want it to matter... I simple want something that will
be switchable from: Open circuit -> Closed circuit -> Open circuit in
1/2 a second or so, nothing complex, nothing elaborate, simply like what
a relay would do, only no real significant current (uA) or anything will
flow though this so it doesn't need to be heavy duty at all!

I'm looking at some Optoisolators and some seem like they might work,
and I really like the idea of having 4 channels, that would simplify my
PCB...  But again I have no experience with those and don't know if they
would work either...

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> {Original Message removed}

2001\08\02@144812 by Roman Black

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Nick Veys wrote:
>
> I know it should be hard, hence my difficulty! :)  Go figure!
>
> It's simply shorting two pins on a little fan controller I have made
> here, on the device it brings +5 to Ground to let it know to turn on but
> really, I don't want it to matter... I simple want something that will
> be switchable from: Open circuit -> Closed circuit -> Open circuit in
> 1/2 a second or so, nothing complex, nothing elaborate, simply like what
> a relay would do, only no real significant current (uA) or anything will
> flow though this so it doesn't need to be heavy duty at all!
>
> I'm looking at some Optoisolators and some seem like they might work,
> and I really like the idea of having 4 channels, that would simplify my
> PCB...  But again I have no experience with those and don't know if they
> would work either...


Have you considered a relay? A "real" relay that
is! :o) Simple to drive with your PIC and should
work your AC fan load ok since you say it is low
power.
-Roman

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2001\08\02@151113 by Mike Mansheim

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> Have you considered a relay? A "real" relay that
> is! :o) Simple to drive with your PIC and should
> work your AC fan load ok since you say it is low
> power.

Last time I went looking for a relay to run with a pic,
I ended up using a solid state relay because the
mechanical relays needed more drive current than the
pic could do directly.  Of course, I limited my selection
to whatever was listed in Digikey.
So, does a solid state relay count as "real"?

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2001\08\02@151906 by Roman Black

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Mike Mansheim wrote:
>
> > Have you considered a relay? A "real" relay that
> > is! :o) Simple to drive with your PIC and should
> > work your AC fan load ok since you say it is low
> > power.
>
> Last time I went looking for a relay to run with a pic,
> I ended up using a solid state relay because the
> mechanical relays needed more drive current than the
> pic could do directly.  Of course, I limited my selection
> to whatever was listed in Digikey.
> So, does a solid state relay count as "real"?

No. :o)
Try using a real relay with the coil driven by
a cheap 10 cent transistor like a BC337 or equiv,
and a diode across the relay coil, this can give
advantages over a solid state relay because of
the total isolation of the relay contacts from
the coil and PIC.

Solid state relays are fine in many cases, but
"real" relays have their place, and are good
safe hardware for newbies.
-Roman

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2001\08\02@152529 by Heinz Czychun

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Hi Nick,

At 1:19 PM -0500 8/2/01, Nick Veys wrote:
>I know it should be hard, hence my difficulty! :)  Go figure!
>
>It's simply shorting two pins on a little fan controller I have made
>here, on the device it brings +5 to Ground to let it know to turn on

       If this is the case why not use a NPN transistor. Connect the
control line through a limiting resistor to the base, emitter to
ground and the pin to be switched to the collector ?


>but
>really, I don't want it to matter... I simple want something that will
>be switchable from: Open circuit -> Closed circuit -> Open circuit in
>1/2 a second or so, nothing complex, nothing elaborate, simply like what
>a relay would do, only no real significant current (uA) or anything will
>flow though this so it doesn't need to be heavy duty at all!
>
>I'm looking at some Optoisolators

       These are only necessary if you want to electrically isolate
the control line from the controlled circuit.

>and some seem like they might work,
>and I really like the idea of having 4 channels,


       Multiple transistors can be had in a multi-pin DIP package,
or since your switching 5v to gnd, with little current, you could use
CMOS switches (a.k.a. transmission gates) such as the 4066, 4
switches/package. This may be a better choice since the inputs are
logic compatible, so the limiting resistors can be eliminated.

>that would simplify my
>PCB...  But again I have no experience with those and don't know if they
>would work either...
>
>nickEraseMEspam.....veys.com | http://www.veys.com/nick
>

Heinz

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2001\08\02@152541 by Douglas Butler

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A reed relay (such as Digi-Key #HE101-ND) has a 5V 500 ohm coil.  That
is about the same as driving a LED.  It will turn on at 3.5V and even
has a built in snubber diode.  The price is about US$2.70.  It can
switch 200V at .5A.

Sherpa Doug

> {Original Message removed}

2001\08\02@170909 by Nick Veys

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I think everyone is missing my point... I was hesistant to say I was
connecting +5 to Gnd because then I would get the "use a transistor"
message.  And a real relay is great, but I don't like the extra hardware
involved, I'm looking for something simple, all I'm doing is shorting
leads!

I would think there would be some kind of solid state relay that can do
this but apparently not?

EraseMEnickspamveys.com | http://www.veys.com/nick

> {Original Message removed}

2001\08\02@171531 by Barry Gershenfeld

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Seems like your original idea would almost work, now if
you could put a capacitor in series with it you'd get
your "shorting" current briefly, then it would go
away.  Once it did the triac would reset.  Make sure
something bleeds the capacitor off between uses.

Barry

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2001\08\02@171922 by t F. Touchton

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part 1 3010 bytes content-type:text/plain; charset=us-ascii
You can do this with a mosfet if you can bias it correctly.  I have not
seen your circuit, so I can't suggest any biasing solutions.

You might be able to use something like a 4066 quad switch......

Scott F. Touchton
1550 Engineering Manager
JDS Uniphase



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I think everyone is missing my point... I was hesistant to say I was
connecting +5 to Gnd because then I would get the "use a transistor"
message.  And a real relay is great, but I don't like the extra hardware
involved, I'm looking for something simple, all I'm doing is shorting
leads!

I would think there would be some kind of solid state relay that can do
this but apparently not?

EraseMEnickspamspamspamBeGoneveys.com | http://www.veys.com/nick

> {Original Message removed}
part 2 4336 bytes content-type:application/octet-stream; (decode)

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2001\08\02@172959 by Nick Masluk

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Solid state relays will work, just as long as you get
the right one.  The relay you got used a triac, so
once it was activated, it will stay on as long as you
have current running through it.  Get a relay that
does not have an SCR or triac output an you should be
fine.

Also, I never saw solid state relays with this, but I
might as well add this in just in case; make sure it
is not a latching relay.  Latching relays act like
toggle switches, with an input for on, and an input
for off.  Once you activate the on/off state, it will
remain in that state.

--Nick


--- Nick Veys <RemoveMEnickKILLspamspamVEYS.COM> wrote:
{Quote hidden}

> > {Original Message removed}

2001\08\02@173014 by Douglas Butler

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The reed relay would not require any other components, no resistors, no
transistors, nothing but the relay from +5 to a PIC pin (the snubber
diode is built into the relay I mentioned (Digi-Key #HE101-ND)).  It
gives you a nice isolated mechanical switch for $2.70.  That is hard to
beat, but if you look around you might find a cheaper relay.

Sherpa Doug

> {Original Message removed}

2001\08\02@175015 by Nick Veys

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That looks great.  I think I'll give those a try, DIP package is always
handy...  Thanks a bunch!

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> {Original Message removed}

2001\08\02@200746 by Gennette, Bruce

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If it is truly low current (and you can afford loosing a little voltage) why
not use a 4066 quad analog switch chip?

Isolation, 4 switches per package, works at 5V and cheap!

Bye.

{Original Message removed}

2001\08\02@233758 by Gennette, Bruce

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It looks to me like you wish to switch an (isolated) external current loop.
If you are using a current loop because long lines make voltage sensing
chancy why don't you follow the tried-and-true method used by RS232?  Kick
the voltage up on the comm connection and slow the signaling rate until
comms become reliable.

Or if it is truly low current (and you can afford loosing a little voltage
in your current loop) why not use a 4066 quad analog switch chip?

Isolation, 4 switches per package, works at 5V and cheap!

Bye.

{Original Message removed}

2001\08\03@032056 by Vasile Surducan

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On Fri, 3 Aug 2001, Roman Black wrote:

> Have you considered a relay? A "real" relay that
> is! :o) Simple to drive with your PIC and should
> work your AC fan load ok since you say it is low
> power.
> -Roman

 Roman, Nick, what do you say about this:

One npn transistor driven in base through a resistence from pic,
transistor will short circuit ( when is on ) the +/- section of one
rectifying bridge, colector to +bridge pin, emiter to -bridge pin and
GND of pic supply. In series with ~ bridge pin, the fan , the other fan
pin and ~ pin of the bridge to AC.
( same configuration like those used for driving full AC load using
thyristors but with transistors )
I think will work ok and will be better than a relay.
Vasile

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2001\08\03@032112 by Vasile Surducan

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Yes Ned, you have right. Now I'm sure it was a language problem. There are
some diferences using technical terminology in different countries. This
make me seriously thinking that probably is better to keep my mouth shut
on this list.
BTW, when I said DC I was thinking exactly only to rectified and filtered
DC. And of course a full or half rectified wave is also DC.
It's important we both understood the problem ( me only 25 years ago...) I
hope Nick too.
Sincerely yours, Vasile

On Thu, 2 Aug 2001, Ned Seith wrote:

{Quote hidden}

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2001\08\03@035624 by jeethur

flavicon
face
Nick,
I've done something like this before. But I've used it
to control 230 Volts AC. I used MOC3041 Triac OptoCoupler
with a BTA610 Triac to make a Solid State Relay.

Triacs don't turn off even if you take the gate drive off.
That is one of the greatest features of SCRs and Triacs.
Sometimes this latching effect can come in quite handy.
On AC, this makes no difference, unless you want to play with
the AC waveform.

If you really want to test out the Triac, use an AC voltage.
If you turn on the triac and remove the drive, it will turn off
in the next Zero Crossing of the AC line.

SSRs are actually meant for switching AC. They are of little or
no use on DC.

To test the SSR, you may try connecting a small light bulb or something
in series with the SSR and AC Line.

Regards,

Jeethu Rao


> {Original Message removed}

2001\08\03@040948 by Peter L. Peres

picon face
> I would think there would be some kind of solid state relay that can do
> this but apparently not?

There are 'optofets' that do this. See MOC3xxx series and others. It's an
optocoupler whose target device is a FET transistor. It goes almost short
when the LED is on (<10 ohms). A opto-darlington will also likely work.

Peter

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2001\08\03@054121 by Peter L. Peres

picon face
Nick, for real low current, and if you take care of the inductive
kickback, you might be able to use a MOC3xxx series device directly.
Normally they fire triacs. They will run <30mA at 220Vac into a small load
if that's what you need. Read the data sheets carefully, there are some
gotchas when used like this.

For 5V several optoisolators will work. Look for a darlington type, it
will be more appropriate for a TTL level switch. Maybe take a DVM set it
on current scale and plug it in parallel with the switch. This will tell
you the current you really need to switch. I bet about 400 uA to 1 mA for
a LS TTL input with some internal pullup.

Peter

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2001\08\03@064504 by Roman Black

flavicon
face
Vasile Surducan wrote:
{Quote hidden}

Yep that would work for the AC load, someone mentioned
that old tape decks used that system for speed control.
BUT it doesn't give safe isolation. :o)
-roman

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2001\08\03@090734 by Olin Lathrop

face picon face
> if the load is
> inductive (or capacitive) there will be a phase shift between the DC
> voltage and DC current. However, the fact remains that a triac will turn
> off when conducting the DC current of a half or full wave rectified
signal.

It's more than just a phase shift issue.  Series inductance can cause the
current to never reach zero (or fall below the triac dropout current).


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2001\08\03@100930 by Spehro Pefhany
picon face
At 08:33 AM 8/3/01 -0400, you wrote:
>> if the load is
>> inductive (or capacitive) there will be a phase shift between the DC
>> voltage and DC current. However, the fact remains that a triac will turn
>> off when conducting the DC current of a half or full wave rectified
>signal.
>
>It's more than just a phase shift issue.  Series inductance can cause the
>current to never reach zero (or fall below the triac dropout current).

Well, it obviously *must* pass through zero twice per cycle. But the
problem with inductive loads is that excessive dv/dt during the time
period when the current is less than the holding current (passing
through zero), particularly for triacs, may prevent commutation
from reliably occuring.

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2001\08\04@115648 by Olin Lathrop

face picon face
>         If this is the case why not use a NPN transistor. Connect the
> control line through a limiting resistor to the base, emitter to
> ground and the pin to be switched to the collector ?

Don't forget the flyback diode!


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2001\08\04@115652 by Olin Lathrop

face picon face
> I think everyone is missing my point... I was hesistant to say I was
> connecting +5 to Gnd because then I would get the "use a transistor"
> message.  And a real relay is great, but I don't like the extra hardware
> involved, I'm looking for something simple, all I'm doing is shorting
> leads!

So I guess you are saying the most important concearn is that this be a
single part solution?  If that is truly the case, try a logic level FET.
However, if you are switching something with coils, like a fan, then you
still need a flyback diode backwards accross the load.  This is true no
matter what method you use to switch.


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2001\08\04@115712 by Olin Lathrop

face picon face
> >> if the load is
> >> inductive (or capacitive) there will be a phase shift between the DC
> >> voltage and DC current. However, the fact remains that a triac will
turn
> >> off when conducting the DC current of a half or full wave rectified
> >signal.
> >
> >It's more than just a phase shift issue.  Series inductance can cause the
> >current to never reach zero (or fall below the triac dropout current).
>
> Well, it obviously *must* pass through zero twice per cycle.

A full wave rectified sine wave with no DC is ABS(SINE()).  This goes to
zero twice per cycle for a short time (instantaneously with perfect
rectifiers).  Now imaging this signal connected to a sufficiently large
inductor and some resistance.  Since this signal has an average DC
component, there will be an average DC current thru the inductor, which will
be AVE(ABS(SINE()))/R.  The current in the inductor will lag the rectified
voltage, but will also "average" it.  With an inductance of 0 the current
will be ABS(SINE())/R.  With an infinite inductor in steady state, the
current will totally flat at AVE(ABS(SINE)))/R.  Real inductances will vary
it between these two extremes, but lowest point in the current waveform will
rise from 0 when the inductance is increased from 0.  For real world parts
some minimum inductance will be required to overcome the finite time the
voltage is 0 due to voltage drops in the rectifiers and to get past the SCR
holding current.


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