# Single Supply in Op-amps

I am using in a project TL081 operational amplifiers and an INA118P instrumentation amplifier. Both need a ± 15 V Symmetric Power Supply, however I have seen some projects in which it uses single supply.

I intend to build a portable system that sends electrical signals to the body (sinusoidal voltage of 2 V pp with 100 kHz to 1 mA). And for this I will use the op amps TL081 to make a high pass filter, a current source and a voltage follower. With the INA118P I will amplify the signal.

My questions:

I'm going to use arduino, I intend to use a single 5 V supply and GND. What's the difference between a Symmetric Power Supply and Single Supply?

The TL081 does not have much information about Single Supply Operation. For the voltage that I intend to work, is 5 V enough?

Thanks!

• No, 5 V is not enough, the minimum recommended is +/-5 V (or 10 V if you dynamically split a single supply. since you only need 2 V p-p, it would be possible to use a single 5 V power supply, but you need to select different devices. – Jack Creasey Feb 11 '17 at 20:31
• What does the datasheet say the minimum recommended power supply rails are? – Lawrence NK1G Feb 11 '17 at 20:38
• Okay, For the TL081, 5V single supply is not enough. But for INA118 it's allowed, right? I found the AD8606, I looked at the datasheet, and it allows 5V single supply, besides it, does anyone know another device that allows 5V single supply? – VF35468 Feb 12 '17 at 14:10
• Just google single supply low voltage opamp The INA118 datasheet says: The INA118 can be used on single power supplies of 2.7 V to 36 V Remember sometimes need a "ground" plane at 2.5 V is needed. – skvery Feb 12 '17 at 16:39

The answer is in the datasheet. The absolute maximums don't list a minimum supply voltage, but there recommended operating conditions. +/-5V minimum is a 10V single supply, not out of the ordinary for a JFET op amp.

What's the difference between a Symmetric Power Supply and Single Supply?

None, absolutely none. the opamp will never know if the dual supply is symmetrical or not - and many times it is not; nor does it care if it is powered by a dual-rail supply or a single-rail supply.

The TL081 does not have much information about Single Supply Operation.

it is right there in the datasheet, for maximum Vcc+ - Vcc-. As the opamp isn't spec'd for single rail operations (due to its limited common mode voltage range).

For the voltage that I intend to work, is 5 V enough?

depending on the application. it cannot get too close to the rails - 1.5 - 2v headroom is needed typically. So at 5v, your "usable" range of output is quite limited.

• I beg to clarify something: although it is true the opamp doesn't know and/or care if the supply is a dual symmetric or a single supply, opamps can be specifically branded as "single-supply", and it actually means something very significant: it means their negative supply voltage is included in their common-mode input range (and, therefore, if the negative supply is gnd - which is the case for a single supply - you can still use gnd as a valid input voltage - which is forbidden for a regular opamp, whose common-mode input range typically starts a few volts away from both rails). – dim lost faith in SE Sep 17 '19 at 11:10

In single-supply operation "ground" can't be the negative rail. TL081 (and in general all op-amps for symmetric supply) need a minimun of negative supply (not necesarilly the same symmetrical value, but at least -5 or -6 volts). I repeat: Ground CAN'T be the negative rail.