Single Supply OPAMP instead of 741

[tahoka]

Please can someone suggest me an alternative to IC 741 in the basic V to I converter and non inverting amplifier circuit as we require an opamp which uses only a single supply.
The input to V to I converter is 0 to 5 volts and output is 0 to 20 milliamperes.
the output of amplifier is 0 to 5 volts.

 

[Nigel Goodwin]

What's wrong with just using a 250 ohm resistor?.

 

[ericgibbs]

Please can someone suggest me an alternative to IC 741 in the basic V to I converter and non inverting amplifier circuit as we require an opamp which uses only a single supply.
The input to V to I converter is 0 to 5 volts and output is 0 to 20 milliamperes.
the output of amplifier is 0 to 5 volts.

hi,
You can buy V2I ic's, this is one example, single supply

 

[Hero999]

What's wrong with just using a 250 ohm resistor?.

Because it isn't a normal standard value?

Nevertheless it can easily made by connecting 240Ω and 10Ω in series or just use 249Ω which is a 2% value and is only 0.4% out in this case.

However it seems like a pretty common thing to do so it wouldn't surprise me if you can buy 250Ω resistors specifically made for the purpose

 

[ericgibbs]

Because it isn't a normal standard value?

Nevertheless it can easily made by connecting 240Ω and 10Ω in series or just use 249Ω which is a 2% value and is only 0.4% out in this case.

However it seems like a pretty common thing to do so it wouldn't surprise me if you can buy 250Ω resistors specifically made for the purpose

You can buy HS 250R's

**broken link removed**

 

[Willbe]

we require an opamp which uses only a single supply.

https://www.electro-tech-online.com/custompdfs/2008/09/LM324.pdf

 

[Roff]

What's wrong with just using a 250 ohm resistor?.

A resistor works well if the load is zero ohms. If he is trying to make a voltage-controlled current source, well, ....

 

[Nigel Goodwin]

A resistor works well if the load is zero ohms. If he is trying to make a voltage-controlled current source, well, ....

The load can't be zero ohms, it couldn't possibly work no matter what you did if it was

 

[Roff]

The load can't be zero ohms, it couldn't possibly work no matter what you did if it was

It could be virtual ground. But you just made my point. If the load is other than zero ohms, then the current won't be Vin/250.

 

[Hero999]

https://www.electro-tech-online.com/custompdfs/2008/09/LM324-1.pdf

Or LM358, if you just want an 8 pin DIP.

One problem with using a 250Ω resistor is that it drops 5V which might not be acceptable.

Just use a 10Ω resister and a non-inverting amplifier with a gain of 25 and it will drop just 200mV.

**broken link removed**
https://en.wikipedia.org/wiki/Operational_amplifier#Basic_non-inverting_amplifier_circuit
R2 = 240k
R1 = 10k

 

[ericgibbs]

There are a number of ways to use OPA's as V 2 I convertors.

https://en.wikipedia.org/wiki/Transimpedance_amplifier

 

[MrAl]

Please can someone suggest me an alternative to IC 741 in the basic V to I converter and non inverting amplifier circuit as we require an opamp which uses only a single supply.
The input to V to I converter is 0 to 5 volts and output is 0 to 20 milliamperes.
the output of amplifier is 0 to 5 volts.

Hello,


It would help if we knew if you need the load to connect to ground or
not. If the load has to connect to ground the circuit is a little more
complex than if it does not have to connect to ground.

There are also sometimes simplifications possible if the input voltage
generator does not have to connect to ground, so knowing this
would be good too...if the input voltage source is floating.

 

[bnfdvn]

I did a Google search of 'single supply op amp' and came upon this thread. The original post could have been written by me today as this is exactly my dilemma. I implemented a Voltage to Current converter using a 741 Op amp with a single 24 V supply and it is not working correctly. The lower the voltage input, the more incorrect the output current is. I am assuming this is related to the common mode voltage or the single supply operation. (I'm not an analog wizard by any means.) It is good at 4.7 volts on the input. (I only have two input voltages in this application, 1 volt and 4.7 volts).

Then I read the posts in this thread and realized that the load that I will be driving goes to ground so this won't work for me. So my question becomes, "How do I implement a voltage to current converter with a 24 VDC supply and 5 VDC supply that will drive a grounded load?" The XTR110 is looking better all the time but the cost is more than I had hoped for. Any suggestions will be greatly appreciated!!

 

[Willbe]

Howland Current Pump?

 

[Roff]

I did a Google search of 'single supply op amp' and came upon this thread. The original post could have been written by me today as this is exactly my dilemma. I implemented a Voltage to Current converter using a 741 Op amp with a single 24 V supply and it is not working correctly. The lower the voltage input, the more incorrect the output current is. I am assuming this is related to the common mode voltage or the single supply operation. (I'm not an analog wizard by any means.) It is good at 4.7 volts on the input. (I only have two input voltages in this application, 1 volt and 4.7 volts).

Then I read the posts in this thread and realized that the load that I will be driving goes to ground so this won't work for me. So my question becomes, "How do I implement a voltage to current converter with a 24 VDC supply and 5 VDC supply that will drive a grounded load?" The XTR110 is looking better all the time but the cost is more than I had hoped for. Any suggestions will be greatly appreciated!!

How much current do you want with 1V in? How much with 4.7V in?

 

[bnfdvn]

I would like a 4-20 mA output proportional to the 1 to 5 volt input.

 

[Roff]

I would like a 4-20 mA output proportional to the 1 to 5 volt input.

4-20mA into what load?

 

[bnfdvn]

500 Ohms maximum but probably more in the neighborhood of 50-100 Ohms. I would like the design to be good for 500 Ohms, though.

 

[Roff]

Sorry for the nitpicking questions, but what accuracy do you need? In other words, when the input is 5V, you want 20mA out. What percentage error can you tolerate?

 

[bnfdvn]

The circuit doesn't have to be super accurate. Within 2-3% would be okay.