The bridge drive alternates the polarity of voltage across the solenoid- so the current will attempt to reverse. If you put the solenoid inside a full-wave rectifier bridge with (+) and (-) terminals connected to solenoid and AC terminals connected to opamp outputs, then the voltage doubles and is rectified- but you lose two diode drops.
You can try this- assuming any other problems- there is no diode drop: View in a fixed-width font such as Courier.
. . 2V . --- . | | . | | . | | . V | | . --- -- -- . | | + - . | | >----|+\\ . -- -- | >-|>|---+-KKKKKK--+----+ . +-|-/ | | | . | | | | . +------------+---| -+ . +-|+/ . | . --- . gnd . . . .
Maybe we're taking about two different things- the differential voltage across the solenoid is 2x the voltage drive of the op-amp pair: one output goes to Vin and the other to -Vin, this makes a magnitude of
2xVin across the solenoid. A safe way to do this is: View in a fixed-width font such as Courier.. . 2V . --- . | | . | | . | | . V | | . --- -- -- . | | + - . | | >-+----|+\\ . -- -- | | >-|>|---+-KKKKKK--+----+ . | +-|-/ | | | . | | | | | . | +------------+---|--+ . +-|+/ . | . --- . gnd . . . .
Actually, your push-pull ( actually a bridge configuration ) is used quite specifically in order to be able to reverse current flow. It doesn't actually double the voltage available, merely offers a bi-directional output.
Single output gives a swing of 0 to Vsupply. Dual output gives 0 to +Vsupply or -Vsupply.
Tie one connection to the solenoid to ground or supply ( whichever makes most sense ). Drive it from one op-amp only.
I hope you have catch diodes on the op-amps output to deal with the inductive 'flyback' pulse when the solenoid is de-activated btw.
Graham
I suppose if he is just railing them out- this will work well too: View in a fixed-width font such as Courier.
. . 2V . --- . | | . | | . | | . V | | . --- -- -- . | | + - . | | >-+----|+\\ . -- -- | | >-|>|---+-KKKKKK--+----+ . | +-|-/ | | | . | | | | | . | | +---|--+ . - >----+---------------------|+/ . 2 . . . . . .
Make that : View in a fixed-width font such as Courier.
. . 2Vdd- some things . --- . | | . | | . | | . V Vdd | | . --- | -- -- . | | | + - . | | >-+----|+\\ . -- -- | | >-|>|---+-KKKKKK--+----+ . | +-|-/ | | | . | | | | | | . | | | +---|--+ . - >----+---------------------|+/ . 2 . . . . . .
I just noticed he said a *single* positive supply-"I have an app where I am driving a solenoid using a dual op amp in bridge configuration to double the effective voltage from a single positive supply." So he's sunk. I can't even understand them half the time- the basis for their question is so off-the-wall they are unintelligible.
The voltage *does not* double !
A single driver will product a drive voltage = Vsupply.
A bridge will produce a drive voltage of Vsupply or -Vsupply.
A bridge driver arrangeemnt with rectifier bridge will produce a drive voltage of Vsupply - 2*Vf. I.e. *less* than the single driver.
Graham
I canna repeal the laws of ffisiks..........
martin
Your circuit understood. I 'assumed' that the OP was driving the op-amps to rail ( which would make sense ).
In any event the gain can be simply increased - if that's what's needed - by adjusting the feedback but a newbie might indeed not realise that.
Usual problem - not enough detailed info from OP.
Regards, Graham
Exactly.
If we knew the relay voltage and the supply voltage it would make more sesne.
As you say, with a single supply there's a limit to what's do-able here.
Graham
Not as funny, now that James Doohan is dead. :(
I don't agree. For a public figure to be remembered with affection can't be bad.
I have an app where I am driving a solenoid using a dual op amp in bridge configuration to double the effective voltage from a single positive supply.
In terms of current flow, can someone please clarifiy how this is different from using a single amp?
I need the emiited field to be unidirectional and not reverse.
Is this possible with a push/pull driver?
Thank you,
Jeffery
"Jeffery Dean"
** HUH ???Scotty needs to hear about this.
.......... Phil
I disagree, Scotty, did one hell of a lot for getting youngsters interested in engineering. I hope that he would be happy for people to use his quotes.
martin
"John Woodgate" schreef in bericht news: snipped-for-privacy@jmwa.demon.co.uk...
Ditto for non-public figures ;)
We've been here before Fred, a year or so ago. A transient capacitive voltage doubler, generating 2xVs to pull the solenoid in, dropping back to 1xVs for holding.
Nice. I handed my technician a design for a box with ten small microwave relays -- except the crazy relays want tight connections I suppose, and each one takes 5W of coil power! That's 50W for the set, and it's got me worried about heat. I can't add a fan, because it's going on a quiet optics bench. My tech's waiting for parts, so I've got a few days to improve the coil-power scene.
Tony, did you come up with a slick circuit?
Yea Tony, let's see that X2 relay driver again. I can do it with a FET bridge, diode and 2*V storage cap but yours was much slicker. Regards, Harry
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