Need help on converting 0-5v signal to 0-10v signal

[davenn]

So I ended up going with a rail-to-rail op amp (OPA171AIDR) and for the most part it has been working great.

but you are not using it in a rail-to-rail setting ... you are showing just a single rail PSU

I also really don't like the use of a zener for this situation
regulation is going to be horrible. The supply voltage from the zener is going to fluctuate
as the Op-Amp 's output/load varies

I think it was Harald that suggested you use a 7812 V-reg some posts back

what is the load on the analog output ?

Dave

 

[Mahonroy]

but you are not using it in a rail-to-rail setting ... you are showing just a single rail PSU

I also really don't like the use of a zener for this situation
regulation is going to be horrible. The supply voltage from the zener is going to fluctuate
as the Op-Amp 's output/load varies

I think it was Harald that suggested you use a 7812 V-reg some posts back

what is the load on the analog output ?

Dave

I'm not sure what you mean by saying I am not using it in a rail-to-rail setting? The op-amp has ground and +15 volts, and it mentions that it can go up to within 2 volts of the supply voltage. I am using it to output between 0-10 volts.
I could probably update the design and use a regulator... and possibly a higher voltage wall wart.
I didn't think the supply voltage would matter that much? The zener is being used to clip the power supply if it becomes too high for some reason.

Part of the problem is I don't know the load on the analog output... this is a huge unknown. The analog output is being used to control another device. Because of this I was hoping to come up with something robust enough so that it can be as compatible as possible.

 

[Old Steve]

Part of the problem is I don't know the load on the analog output... this is a huge unknown. The analog output is being used to control another device. Because of this I was hoping to come up with something robust enough so that it can be as compatible as possible.

Can't you measure the current consumption of the load? Just put a very small-value resistor between the op-amp output and the 'unknown device' input and measure the voltage developed across it.

 

[davenn]

I'm not sure what you mean by saying I am not using it in a rail-to-rail setting? The op-amp has ground and +15 volts, and it mentions that it can go up to within 2 volts of the supply voltage. I am using it to output between 0-10 volts.

A rail to rail PSU is one with say -15v 0v + 15v yours is only 0V and +15V

Part of the problem is I don't know the load on the analog output... this is a huge unknown. The analog output is being used to control another device. Because of this I was hoping to come up with something robust enough so that it can be as compatible as possible.

you really need to work out that load if you want your Op-Amps to survive
is its a significant load then you may have to use the Op-Amp output to switch a power transistor that can handle the load

Dave

 

[Old Steve]

A rail to rail PSU is one with say -15v 0v + 15v yours is only 0V and +15V



you really need to work out that load if you want your Op-Amps to survive
is its a significant load then you may have to use the Op-Amp output to switch a power transistor that can handle the load

Dave

Yep. If a slight loss of accuracy is acceptable, due to temperature and load variations, the op-amp could be given an 0.6V offset, then an NPN transistor could be added in common-collector mode to follow the voltage.

Edit: If a diode was used on the op-amp input to provide the 0.6V offset, the variations due to temperature could be minimised, too, if the diodes temp characteristics matched those of the transistor's Vbe junction.
(About -2mV per degree Celsius for a BC548, I think, from memory.)

 

[Mahonroy]

Ok I was able to measure the amps by just cutting a spare cable and measuring it from there. The machine draws between 150uA and 10uA (0.15mA and 0.01mA)depending on the potentiometer position (my device is basically going in place of the potentiometer to control the machine). So this is basically nothing? So there is no chance that the machine is drawing too much current and overloading the op-amp then correct?

 

[davenn]

can you show us/tell us more about this "machine" and exactly how you were connecting the op-amp into its circuit

at the moment your description is very unclear

 

[eetech00]

Hi

With a 0-5v input, 0-10v output, 15v supply, I don't understand why you couldn't just use an LM324 or LM358(?), but anyway...

What type of load are you driving with the output? Is it inductive?
Could be an inductive spike damaging the opamp output. Might try
placing a diode from the opamp output to ground.