Inverting OP-Amp

gramo

New Member

• Nov 11, 2006

• #1

Just trying to get a non-inverting op-amp to work, could someone give me a heads up on what I have done wrong please, heres whats happening;

**broken link removed**

The OP-Amp is a LM324, and I need a gain of -2

 

Last edited: Nov 12, 2006

P

penoy_balut

New Member

• Nov 12, 2006

• #2

you can't get more negative output from a single supply configuration

 

gramo

New Member

• Nov 12, 2006

• #3

can you explain that a little more please

 

P

penoy_balut

New Member

• Nov 12, 2006

• #4

try using a dual polarity supply and connect pin 11 to -12VDC, theoretically you should get -20V but since your supply is -12V this the maximum you can get

 

gramo

New Member

• Nov 12, 2006

• #5

ooooohhhh, thanks,

im using the 324 as i need one with a single power supply, but i was chasing a gain of 2 as i thought that would trim it to a 0 - 5V range... but thats not the gain I need, i need a gain of -.5 not -2!!

With a gain of -.5 my output will swing within 0-5V compared to a gain of -2 that would be -10 to +20 in this case. thanks for your help


/salute

 

gramo

New Member

• Nov 12, 2006

• #6

no, wait, i just figured it out for sure now, i dont need an inverting amp...

i need a non inverting amp with a gain of .5

how hard was that lol, ohh, the simple things

 

Roff

Well-Known Member

• Nov 12, 2006

• #7

For a gain of 0.5, all you need is a resistor divider. If your load impedance is low, you will need a unity gain non-inverting amplifier (voltage follower) after the divider to drive the load. If the source is high impedance, you might need to put the follower first, and then the divider. In the case where source and load are both high impedance, you could require two voltage followers, with a divider between them.
What are you trying to drive, and what is the signal source?

 

gramo

New Member

• Nov 12, 2006

• #8

Thanks for your help guys, heres the end result
**broken link removed**

**broken link removed**

 

audioguru

Well-Known Member

Most Helpful Member

• Nov 12, 2006

• #9

For the input to work with an input voltage up to 5.0V and for the output to go up to 5.0V then the supply voltage for the awful, old, noisy, distorted and narrow bandwidth LM324 opamp is a minimum of +6.5V. If it has a 1k resistor to ground at its output then the output will go as low as about +5mV.

 

gramo

New Member

• Nov 12, 2006

• #10

could someone reccommend a better single supply op-amp that can be powered at around 5-6v?

 

audioguru

Well-Known Member

Most Helpful Member

• Nov 12, 2006

• #11

An MC33171 single, MC33172 dual and MC33174 quad opamps are much better than a lousy old quad LM324 and its lousy old dual LM358 sister.

Their inputs and outputs work at ground, and their power supply can be as low as 3.0V like the others but they have a wider bandwidth and no crossover distortion. They have a low supply current.

An MC34071 single, MC34072 dual and MC34074 quad opamps are the same except have a much wider bandwidth and use more supply current.

These Motorola/ON Semi opamps also need a supply voltage that is 1.5V higher than their max input or output voltage.

 

Roff

Well-Known Member

• Nov 12, 2006

• #12

There are many rail-to-rail I/O op amps available that can be powered at 5 volts. If you need it in a DIP package, your selection range narrows considerably. Microchip has a dual RRIO op amp in a DIP, the MCP6002. There are almost certainly others available.

 

gramo

New Member

• Nov 12, 2006

• #13

thanks for the point in the right direction, the MC33174's are a little more expensive, but its worth it in the end i guess