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'[EE:] Analog switches'
2004\04\22@153133 by Omer YALHI

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The analog switches that I have recently found, opened a new window for me.
Could I use the analog switches, like MAX323, like a relay?  To better
explain what I am thinking, if I have circuit that works with 3V, could I
use the switch to close and open a 24V line coming from outside world, thus
imititating the SPST relay?

Thanks in advance,

Omer

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2004\04\22@153759 by teven Kosmerchock

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Omer,

If you just want to switch high voltage ON or OFF I would use
a FET ckt to do that. I would only use the analog switches if you
have an analog signal that needs to be switched without loosing
too  much of the signal. I would check the specs closely, the current
draw of whatever you're switching too and the voltage level might be
too much.

Steve



>>> spam_OUToyalhiTakeThisOuTspamTEKSAN.COM.TR 4/22/2004 12:33:23 PM >>>
The analog switches that I have recently found, opened a new window for
me.
Could I use the analog switches, like MAX323, like a relay?  To better
explain what I am thinking, if I have circuit that works with 3V, could
I
use the switch to close and open a 24V line coming from outside world,
thus
imititating the SPST relay?

Thanks in advance,

Omer

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2004\04\22@171548 by Dave Dilatush

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Omer wrote...

>The analog switches that I have recently found, opened a new window for me.
>Could I use the analog switches, like MAX323, like a relay?  To better
>explain what I am thinking, if I have circuit that works with 3V, could I
>use the switch to close and open a 24V line coming from outside world, thus
>imititating the SPST relay?

Nearly all analog switches allow switching of analog signals ONLY
within the supply voltage boundaries; that is, the analog signal
must be "between the rails" at all times.

In the case of the MAX323, the data sheet gives a signal range of
-0.3V to (V+ +0.3V) in its ABSOLUTE MAXIMUM RATINGS section,
indicating that going outside this range may permanently damage
the device.

So, switching a 24 volt line with a MAX323 powered from 3 volts
would not work.

HTH...

Dave D.

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2004\04\22@173641 by David VanHorn

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You can connect N RS232 devices together in a ring topology, if the software supports it.

Basically:
Each message has the form of <dest><src><payload>

You send your message to a recipient, and mark yourself as the source.
You pass on any messages that aren't for you.
You receive any messages that are for you.

You swallow any messages you sent.
They've gone around the ring once. You might need to do something else as the recipient is apparently asleep or gone or ?

For bonus points, configure the hub so that unplugged devices are bypassed automatically (relay on CTS?)

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2004\04\22@185715 by Omer YALHI

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I have double checked the maximum ratings and you are right, I missed that.
So much for "opened windows".  :-(

Thank you.

{Original Message removed}

2004\04\23@013140 by Nate Duehr

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David VanHorn wrote:

> You can connect N RS232 devices together in a ring topology, if the software supports it.
>
> Basically:
> Each message has the form of <dest><src><payload>
>
> You send your message to a recipient, and mark yourself as the source.
> You pass on any messages that aren't for you.
> You receive any messages that are for you.
>
> You swallow any messages you sent.
> They've gone around the ring once. You might need to do something else as the recipient is apparently asleep or gone or ?
>
> For bonus points, configure the hub so that unplugged devices are bypassed automatically (relay on CTS?)

You're bringing back nightmares of a network that used MAU's that
weren't "smart" and really really big network connectors, Dave... and it
ran at 4Mb/s...

Nate Duehr, .....nateKILLspamspam@spam@natetech.com

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2004\04\23@021751 by William Chops Westfield

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On Thursday, Apr 22, 2004, at 15:59 US/Pacific, Omer YALHI wrote:
>
> I have double checked the maximum ratings and you are right, I missed
> that. So much for "opened windows".  :-(

There are small "solid-state relays" that might do the sort of thing
you are looking for (but they tend to be a bit on the expensive side.)
For instance, the Claire LCA110 switches up to 350V/120mA with a max
Ron of 35 ohms, and comes in a 6-pin DIP.  $3-4 at digikey...  Found a
lot in telco stuff like phone switches...

BillW

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2004\04\23@094151 by Mike Hord

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There are a couple of factors that affect this.

First, the ON resistance of most (inexpensive) analog switches is quite high
(hundreds of ohms).  The pricier units get that value down, but still don't
want to pass a lot of current.

Second, the cheaper ones (4061, 4066 etc) require control voltages in the
range of the signals to be switched.  Want to switch a signal that swings to
+10V?  You need 10V logic, and a 10V supply rail.  Maxim (and others, I'm
sure) make some that have dual supplies, one for analog and one for digital,
but those get pricey.

Your best bet is solid state relays.  Jameco (for example) has some in the
$2-$3 dollar range.  MUCH better than most of the analog switch chips.

Mike H.

>The analog switches that I have recently found, opened a new window for me.
>Could I use the analog switches, like MAX323, like a relay?  To better
>explain what I am thinking, if I have circuit that works with 3V, could I
>use the switch to close and open a 24V line coming from outside world, thus
>imititating the SPST relay?
>
>Thanks in advance,
>
>Omer

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2004\04\23@094604 by hael Rigby-Jones

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{Quote hidden}

I thought solid state relays were Triac/SCR based and therefore only
suitable for AC?  Or am I way off the mark?

Regards

Mike




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2004\04\23@100641 by Mike Hord

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Look at Jameco part numbers 172591CL, 175222CL, 176647CL, and
176655CL.  Solid state relays, 3-32V DC control, switching up to 120
V DC.  That said, I'm noticing that I was looking at the wrong prices
and the cost is in fact somewhat higher, and I don't know exactly
how they work.

Mike H.

>I thought solid state relays were Triac/SCR based and therefore only
>suitable for AC?  Or am I way off the mark?
>
>Regards
>
>Mike

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2004\04\23@102933 by Roy J. Gromlich

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Solid State Relays come in two forms (as far as I know) - there
are units using a BiPolar transistor as a switch, and others which
use a FET as a switch.  Both are optically coupled - a photoisolator
activated by a low voltage/low current signal (5v @ 15mA) drives the switch device. The bipolar devices are intended for DC and the FET
devices are often intended for AC loads.

These devices are intended for switching power loads - usually 60/150 volts at anything up to several Amps. They usually include reverse voltage and spike/surge protection, so they tend to be rather expensive.
Also, they are not intended for low level signal switching.

This is general information - I do not know exactly what configuration the Jameco devices use.

The MAXIM analog switches are just about the best units I have found
for switching low-level signals - I have used them for many years in
lots of different projects.

Roy J. Gromlich

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2004\04\23@103555 by Ehlers Riaan

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What about driving a transistor (or darlington pair) with an opto-isolator. If the transistor cost more than the opto, protect the transistor by calculating the gain so that the Opto will pop first under fault condition.

Like a relay the "output switch" will be completely isolated from the switching signal. Don't forget free weeling diode when switching inductive loads.

The same priciple can be used to switch ac. For ac you need to use a different Opto driving a Triac. Same principle different components.

See 4N25..4n36 for DC and MOC3041 for AC

Riaan

{Original Message removed}

2004\04\23@113754 by William Chops Westfield

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>
>> I thought solid state relays were Triac/SCR based and therefore only
>> suitable for AC?  Or am I way off the mark?
>>
"power" solid state relays are usually triac based, but there are also
"signal" style SSR like the LCA110 I mentioned, and they use
light-activated mosfets interally (according to the clare datasheet,
anyway.  Don't know offhand how 'logical' vs 'real' that is.)  The opto
link
isolates the Vgs sorts of issues, and of course you can use
arbitrarilly high voltage mosfets...

BillW

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