Using TL051C in non-inverting mode - Page 1
Forum section: electronics / beginners

author: Memductor
author_rank: Newbie
timestamp: September 24, 2020, 08:15:57 pm
content: Hello everyoneI am trying to use a TL051C to amplify a positive voltage signal but I can't get it to work in non-inverting mode. I used this OpAmp before in inverting mode (with +/- 5V supplies) and it worked fine. Right now I use it with 0V/5V supplies but the output is at constant 5V independent of input signal.I'm not sure if I understand the datasheet correctly, but it mentions under recommended operating conditions VCC+/- = +/-5V to +/-15V. Does that mean I can't use this OpAmp with 0V/5V supplied?Thanks!

author: Benta
author_rank: Super Contributor
timestamp: September 24, 2020, 08:51:20 pm
content: The datasheet specifically says that this type of BiFET opamp is designed to work with dual supplies.Didn't you read this? What is unclear?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: September 24, 2020, 08:57:26 pm
content: the TL0x1 series are neither single supply nor rail-to-rail opamps; you have to take about +/-3V below/above of the supply rails into consideration, so with a 5V single supply is really not much headroom for a voltage swing.

author: Memductor
author_rank: Newbie
timestamp: September 24, 2020, 09:29:23 pm
content: Hello and thanks for your replies. So the datasheet states:Because BiFET operational amplifiers are designed for use with dual power supplies, care must be taken toobserve common-mode input voltage limits and output swing when operating from a single supply. DC biasingof the input signal is required, and loads should be terminated to a virtual-ground node at mid-supply. TexasInstruments TLE2426 integrated virtual ground generator is useful when operating BiFET amplifiers from singlesupplies.So I guess in this case I should better take another OpAmp which is single supply and rail-to-rail.

author: Benta
author_rank: Super Contributor
timestamp: September 24, 2020, 09:36:07 pm
content: That's the first realization.The second is, that a 0/5 V supply is not the same as +/-5 V. A 0/10 V supply would be more to the point if you really want to use this amp for something it's not designed for.

author: tkamiya
author_rank: Super Contributor
timestamp: September 25, 2020, 01:01:55 am
content: Answering to OP's original question....Is your circuit a comparator or an amplifier with some specific and reasonably low gain? If your power source is 5V and it is non-inverting, and you are seeing output to be 5V, there can be few possible scenarios. Remember, FET op amp has very high input impedance.If it is set up as a comparator, any input to positive above negative will swing it to rail. This includes noise or any stray voltage. (likely case)If it is set up as a high amplification amplifier, same will happen. (another likely case)If it is set up as unity gain gain = 1, then shorting positive input to ground should bring output to zero.I don't know what your circuit will look like, but you will need to put some kind of register between input and ground. Otherwise, high impedance op amp will be very susceptible to every little noise.

author: magic
author_rank: Super Contributor
timestamp: September 25, 2020, 07:44:28 am
content: I think I have used TL072 on 5V supply once as a comparator and it worked.You need to observe the allowed input common mode range. This opamp cannot work with its inputs close to VCC-, but it works with inputs anywhere else including at VCC+.The popular LM358 is opposite. And specified to work at 5V supply.Whether you really need rail to rail is another matter which depends on application, of which you have disclosed nothing.