Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Inverting Op Amp

Status
Not open for further replies.

Tykulcsar666

New Member
This may be pretty simple- but I’m a electronics newbie. Trying to power a UA741 op amp with 3V as VCC+ and -3V as VCC-. But not entirely sure how to get a negative voltage without a voltage generator (just using batteries). Any help would be much appreciated.
 
It's a very old chip and the newer ones will operate at lower voltages but I think the minimum is ±5V.

Mike.
 
Just wire them in series and use the middle connection as ground (0V) and each end as the ± supply. Two 9V batteries will give you ±9V.

Mike.
 
The 741 opamp was introduced 52 years ago. Its datasheet shows only a +15V/-15V power supply. Some of them might work poorly with a total of 10V. Any opamp can use a single positive supply if its + input is biased at about half the supply voltage and coupling capacitors are used. Kiss the old 741 opamp goodbye then bury it!
 
Got to agree, the 741 is a very bad choise for any current circuit.

Mike.
 
I have never seen that new datasheet. All its written spec's and most graphs are with +15V/-15V. A graph of voltage gain vs supply voltage shows how bad it is at a low supply voltage and the graphs are only for a typical one, a minimum one is worse. Modern opamps are much better and many work perfectly with a single 3V supply.
 
What are you actually doing with the op-amp?

Many textbook circuits (which are still often built around the 741) are shown using bipolar supplies to the op-amps. Many modern op-amps work fine with single rail supplies, but you may need to adjust your circuit to do that.

Please post your schematic and we can likely suggest a single supply alternate.
 
image.PNG



First two are just voltage buffers, third one is amplifying the signal. Any suggestions on better op amp models would be appreciated.
 
Your schematic shows "skin" and "Prof" so the circuit is an ECG or lie detector school circuit attempted 50 years ago. It needs a modern intrumentation amplifier IC. Use much higher supply voltages for the old 741 opamp.
 
Thanks for the schematic.

I haven't modeled it, but it looks like all of your signals are positive, so you should not need to change the basic circuit for use with a single supply op-amp.

The op-amp you want would be have rail-to-rail input and output capability, and voltage operation below 3 volts. There are many parts that meet those needs. Here is one that is already in LT-Spice, ADA4505. Tie it's negative supply pin to GND.

PS. It would be useful to include your LT-Spice .asc file in your posts when asking questions. That way other forum members can model your circuit without having to rebuild it.
 
I assume that you mean that you want a DIP package.

Look through this list to pick something out. My search criteria was: Rail to rail output, Vcc down to 1.8 Volts.
 
Thanks for the schematic.

I haven't modeled it, but it looks like all of your signals are positive, so you should not need to change the basic circuit for use with a single supply op-amp.

The op-amp you want would be have rail-to-rail input and output capability, and voltage operation below 3 volts. There are many parts that meet those needs. Here is one that is already in LT-Spice, ADA4505. Tie it's negative supply pin to GND.

PS. It would be useful to include your LT-Spice .asc file in your posts when asking questions. That way other forum members can model your circuit without having to rebuild it.

Havent seen an MC Escher in a long time.
 
I've tried replacing 741's with ADA4505 and tying negative supply to ground. Output voltage seems to be 0.
 

Attachments

  • project schematic 2.asc
    2.8 KB · Views: 109
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top