Analogue help needed

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,617
My expertise in analogue circuitry is a little lacking, so I would like help with a suggested starting point in order to solve a small problem.
It consists of a analogue 0-10vdc signal which requires to be changed to either 0 to +10 or 0 to -10v, either of which is decided by the status of 0v or 5v digital signal.
It would be preferable that when a change-over occurs, there is a small progressive ramp-over delay.
I could not really find anything out there that would do it, so any starting point would help.
Max.
 

crutschow

Joined Mar 14, 2008
34,281
Being from the USA I can only help with analog problems, but that's close enough. ;)
The inversion is easy enough to do with an opamp, a few resistors, and a transistor, but what exactly do you want it to do at the changeover?
Do you just want the change in voltage to have a slow rise/fall time, or do you want some delay also?
If so, what time-constant and/or time delay?
What is the maximum frequency of the analog signal?
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,617
The analog(ue):) input signal has a very slow variable rate, .5sec tops.
The output can follow the input with no delay, for a particular state of the 5v signal.
It is only when the 0-5v signal changes, an immediate switch from say -ve to +ve is not desired, IOW a ramp over on the output of at least 2 sec min. is desired, when the 5v signal transitions.
Thanks.
Max.
 

crutschow

Joined Mar 14, 2008
34,281
I'll have to think about how to slow the signal to a 2 sec ramp when you want a 0.5 sec signal rate change.
That complicates the circuit some.
Would it be okay if the signal is also slowed to a 2 sec ramp?
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,617
Yes, that would be OK.
Basically the input is set to a fixed level between 0 & 10vdc, the output will be the same setting, but polarity dependent on the 5v level.
Just that the output requires a delay when switching the 5v, IOW if the input is set to, say 10v and a 5v signal change occurs, it is not desirable for the output to go from a +10 to -10 without a gradual change over.
It wouldn't matter if there was a small delay when the input was adjusted or changed
Max.
 
Last edited:

Alec_t

Joined Sep 17, 2013
14,280
What dual-polarity power supplies do you have for this?
What is the approximate signal source impedance?
What % error can you tolerate?
 

Kermit2

Joined Feb 5, 2010
4,162
So you want a mirror image of you signal?
Plus ten changing to minus ten and zero stays zero at the change of the 5 volt control line?
Not a ten volt translation of the signal where 10 volts becomes zero and zero changes to minus ten?
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
28,617
What dual-polarity power supplies do you have for this?
What is the approximate signal source impedance?
What % error can you tolerate?
Dual supply is on design.
Unfortunately I do not have access to the source impedance but I believe it to be the output of a digital to analogue convertor.

So you want a mirror image of you signal?
Plus ten changing to minus ten and zero stays zero at the change of the 5 volt control line?
Not a ten volt translation of the signal where 10 volts becomes zero and zero changes to minus ten?
Zero reference stays the same for input and output, just the polarity of the input to output signal changes.
Max.
 

hp1729

Joined Nov 23, 2015
2,304
Design 932 p10 ot m10.PNG
My expertise in analogue circuitry is a little lacking, so I would like help with a suggested starting point in order to solve a small problem.
It consists of a analogue 0-10vdc signal which requires to be changed to either 0 to +10 or 0 to -10v, either of which is decided by the status of 0v or 5v digital signal.
It would be preferable that when a change-over occurs, there is a small progressive ramp-over delay.
I could not really find anything out there that would do it, so any starting point would help.
Max.
Okay here's a start. Most any op amp that would work on + and - 15 would work and be an improvement. DG301 is a CMOS switch that work + to - 15 V. "Choose" input is TTL or 5 V CMOS compatible.
 
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crutschow

Joined Mar 14, 2008
34,281
Here's my take on a circuit to do what (I think) you want.
It may look a little complicated but I couldn't think of a simpler circuit to perform both the invert and slew-rate limit functions.
The input opamp output polarity is controlled by the two back-to-back MOSFETs used as ±10V analog switch.
When the switch is OFF, the first opamp acts as a follower.
When the switch is ON, shorting the non-inverting input to ground, the opamp acts as an inverter.

U2 and U3 act as slew-rate limiters.
The slew-rate is determined by the U3 integrator R1C1 time-constant.

The N-MOSFETS can be just about any logic-level (Ron specified at a Vgs of ≤5V) with a low ON resistance.

The opamp is a CMOS low input offset, rail-rail device with very low input bias currents.

As the LTspice simulation shows the output is in phase with the input when the V(pol) signal is low and inverted when V(pol) =5V.
The slew rate is a little over 2s for a 10V change.

Edit: You could use the DG301 switch posted by hp1729 in place of the transistors if you prefer.
Edit 2: If you use the DG301, it has a 50 ohm ON resistance so you may want to increase the value of R4 to minimize the otherwise 0.5% error from that.

upload_2016-11-14_23-22-16.png
 

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AnalogKid

Joined Aug 1, 2013
10,986
The thing about the slow-ramp output is whether or not you want (or can tolerate) that same slew-rate limiting when the circuit is not operating near a transition event. If yes, then the slew rate limiter, either linear or logarithmic, becomes part of the output circuit. If no, then it has to be switched in and out of the circuit as required.

ak
 

crutschow

Joined Mar 14, 2008
34,281
The thing about the slow-ramp output is whether or not you want (or can tolerate) that same slew-rate limiting when the circuit is not operating near a transition event.
............
He answered my post #5 question about that in post #6, in the affirmative.
 
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