Oct 24, 2009 #1 F fruct0se Newbie level 4 Joined Oct 21, 2009 Messages 7 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,325 OP amp help I am using a 741 op amp to try and amplify a low dc voltage. + = 5vdc - = 0v + non inverting input = 0 to 0.8vdc - inverting input = 100k to 0v / 20k to Output No matter what I try I get around 4.2 to 4.6 on the output even if I use 0 feedback. I would like to amplify a range 0 to 0.8v to a 0 to 5v range, please help.
OP amp help I am using a 741 op amp to try and amplify a low dc voltage. + = 5vdc - = 0v + non inverting input = 0 to 0.8vdc - inverting input = 100k to 0v / 20k to Output No matter what I try I get around 4.2 to 4.6 on the output even if I use 0 feedback. I would like to amplify a range 0 to 0.8v to a 0 to 5v range, please help.
Oct 24, 2009 #2 snafflekid Full Member level 4 Joined May 9, 2007 Messages 211 Helped 31 Reputation 62 Reaction score 8 Trophy points 1,298 Location USA Activity points 2,644 your output should be 20% larger than your input. Double check your connections well my computer won't load a damn pdf now. I think you may be below the common mode voltage range of the 741
your output should be 20% larger than your input. Double check your connections well my computer won't load a damn pdf now. I think you may be below the common mode voltage range of the 741
Oct 24, 2009 #3 F fruct0se Newbie level 4 Joined Oct 21, 2009 Messages 7 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,325 Ah, the minimum supply is 10v... Would this explain why I was getting a constant 5v out though?
Oct 24, 2009 #4 snafflekid Full Member level 4 Joined May 9, 2007 Messages 211 Helped 31 Reputation 62 Reaction score 8 Trophy points 1,298 Location USA Activity points 2,644 That is probably part of the problem. Looks like it is spec'd for +/-15V although it might run on 0V/10V. I doubt 5V would work. Also the input will not amplify signals that close to ground. Looking at the schematic I think you would need at least 3V common mode input voltage.
That is probably part of the problem. Looks like it is spec'd for +/-15V although it might run on 0V/10V. I doubt 5V would work. Also the input will not amplify signals that close to ground. Looking at the schematic I think you would need at least 3V common mode input voltage.
Oct 24, 2009 #5 F fruct0se Newbie level 4 Joined Oct 21, 2009 Messages 7 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,325 Any ideas on how I could amplify 0-0.8 to 0-5?
Oct 24, 2009 #6 snafflekid Full Member level 4 Joined May 9, 2007 Messages 211 Helped 31 Reputation 62 Reaction score 8 Trophy points 1,298 Location USA Activity points 2,644 You need an opamp that is "ground sensing" and single supply. I'm looking at something like MAX4122. It operates at 5V
You need an opamp that is "ground sensing" and single supply. I'm looking at something like MAX4122. It operates at 5V
Oct 24, 2009 #7 F fruct0se Newbie level 4 Joined Oct 21, 2009 Messages 7 Helped 0 Reputation 0 Reaction score 0 Trophy points 1,281 Activity points 1,325 Thanks for the great responses, I am going to try that out.
Oct 25, 2009 #8 Audioguru Advanced Member level 7 Joined Jan 19, 2008 Messages 9,457 Helped 2,151 Reputation 4,302 Reaction score 2,008 Trophy points 1,393 Location Toronto area of Canada Activity points 59,719 An LM358 is a dual opamp with a minimum power supply voltage of 3V and inputs that work at 0V up to 3.5V when the supply is 5V. With a 5V supply its max unloaded output is 3.8V.
An LM358 is a dual opamp with a minimum power supply voltage of 3V and inputs that work at 0V up to 3.5V when the supply is 5V. With a 5V supply its max unloaded output is 3.8V.