Change input voltage polarity based on control signal

Hi all I have 2 DC voltage inputs, Va and Vb. Va varies from 0V to 10V, while Vb has output of + or - 1V. I want to change the sign of Va depending on whether Vb is positive or negative. All this has to be done in analog, not dsp. Current through the circuit is 1A max. I've thought of using a Gilbert

2Q multiplier, but I was wondering if there was another way. Thanks Sid
Reply to
Siddharth
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1A ??

There was a thread a while back (IIRC on A.B.S.E) that used power fets to provide the right polarity to a load, irrespective of input polarity.

I can't seem to track it down now, but perhaps some other poster can recall it.

It would require a few additions to do what you want.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

There is a simple comparator-opamp circuit that might do what you want.

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R R Va-------------+----/\\/\\------+---/\\/\\--+ | | _ | | +--|- \\ | | R2 |Op >--+-->Vout +----/\\/\\------+--|+_/ _ | Vb-----------|- \\ + |Co >---+------->/Switch 0v--/\\/\\---+-|+_/ | + | | | +--/\\/\\---+ --+--0v

The comparator senses the zero-crossing of Va, and turns the Switch ON and OFF.

When Switch= ON, Vout = -Va, when OFF, Vout= +Va.

Operation is slightly improved if R2 and Switch are replaced by a SPCO switch, switching the +ve input between Va and 0v.

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Tony Williams.
Reply to
Tony Williams

How about an H-bridge chip, as long as you could get your +-1 volt signal to look like a 1/0 logic input to the "direction" input.

Reply to
blueflash

Thanks everyone for your help. Tony, I dont think your circuit would work. Notice when the switch is connected to Va, both inputs to the opamp would be the same. For the input impedance to the opamp to be the same, R2 = R. Thus, the voltage inputs to the terminals would be the same. Thanks though for your help, and please tell me if I'm wrong in my thinking. I think I'm going to out Va and -Va as inputs to a FET switch, with the gate being the comparator output. sid P.S: I'm wondering how to conceal my email address to prevent spam. I can't see a place to do that.

Reply to
Matrix

Double pole change-over relay....?

Ken

Reply to
Ken Taylor

Hello,

That won't flip the polarity of Va unless Va was coming in decoupled from ground.

Regards, Joerg

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Reply to
Joerg

Nope. Tonys circuit will work, but not with 1A output current. When the switch is open, Va is on the +in, -in and also the output. Va=Vout when the switch is closed, +in is on ground, so the output must invert to keep also -in on virtual ground. I think Matrix, you should read up on opamps again.

ciao Ban

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ciao Ban
Bordighera, Italy
Reply to
Ban

[snip]

Depends on newsreader. In Agent it's under "User and System Profile, User"... just type in a munged E-mail address there.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

The "professional" answer to that is, of course, use a real newsreader and ask your ISP for the name of their real newsserver, and avoid google groups like the plague. (It used to be OK, until the google minions found out that there's much more revenue to be had by underestimating the intelligence of the public.)

What I did was make up a new bogus email at yahoo: snipped-for-privacy@yahoo.com . When I want to expose my real email, I say "elide ard". I reckon that if someone wants to email me, they'll bother to figure out what that means. Of course, as soon as I used it for my googlegroups account, I went back to yahoo and redirected _everything_ to the bit bucket. Damn! Sometimes I'm so f***in' clever I even scare myself! ;-P

Cheers! Rich

Reply to
Rich Grise

JT, he's posting from googlegroups. They want a "real" email, so that they can send you a "yes, I really signed up, and this is my real email" autoresponse, and then they authorize you to post. At least, that's the way it worked a few years ago. IOW, he's not even using a newsreader - he's using a browser and google's atrocious chatroomoid interface.

Sigh.

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Thanks,
Rich
Reply to
Rich Grise

1) Never publish your primary email address on the Internet unless it's munged http://66.102.7.104/search?q=cache:R0u-koBQf6IJ:en.wikipedia.org/wiki/Mung+modify-an-e-mail-address or unless (if you're not running your own email server) your ISP's mail server has excellent anti-spam filtering. Once your primary email address has gotten out into the wild, set up a new email account and abandon the old one. 2) Before you give your primary email address to someone, have that someone explain the difference between CC and BCC.
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3) Never give your primary email address to someone whom you would not trust with your wallet.

Set up throw-away email accounts for contact with everyone else.

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Since you're already using hotmail, all you had to do was create another account and abandon it after 1 use. . . Rich already mentioned using a real newsreader:

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Reply to
JeffM

In article , Fred Bartoli

Ah yes. I can see that, now you have pointed it out.

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Tony Williams.
Reply to
Tony Williams

What do you suppose the OP expects to happen when Vb=0?

The intermediate values of resistance between open and short for the switch do not produce gradual intermediate values.of gain.

RL

Reply to
legg

There's the OP's original Q above.

I read it that he wants a switch of polarity at Vb=0. Note the allowance for a small amount of hysteresis (10mV?) around the comparator.

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Tony Williams.
Reply to
Tony Williams

"Tony Williams" a écrit dans le message de news: snipped-for-privacy@ledelec.demon.co.uk...

Tony,

the way I read it is that only 2 discrete values are possible for vb: + or -

1V.

In that case you can get rid of the comparator and just use a simple BJT.

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Thanks,
Fred.
Reply to
Fred Bartoli

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