"hello world" circuit with op42

Question

Hello guys, 
 Sorry for this post, I am guessing it is extreamly basic but I just cannot get around it. 
 I am using an op42, The connections are: 
 1 (NULL) -> Not connected 
 2 (-IN) -> through 10k to (6) and through 10k to signal 
 3 (+IN) -> GROUND 
 4 (V-) -> GROUND 
 5 (NULL) -> Not connected 
 6 (OUT) -> through 10k to (2) and output 
 7 (V+) -> ~5V 
 8 (N.C.) -> Not connected 
 This is the simplest inverting cicuit that I could make. I was just playing with the op to learn how to use it. The signal is a square function from 0 to 1.5V. 
 The output of that configuration, I was expecting to be the inverted signal, nevertheless, what I obtain is a square signal with really small pk to pk and with an offset of 1.5V. 
 I have also tried with other resistors pairs (100R and 100R) and what I get is a DC voltage with the input signal on top. 
 Searching the web, they recomended to use a compensating resitor (with resistance equal to the parallel equivalent of the other two resistors) between (3) and GROUND, but this did not change anything at all. 
 Do you have any idea of what I am doing wrong? 
 Thank you 
 JMGL

krisf · Accepted Answer

Hi Marcos, 
 The input voltage range of the OP42 looks like it can only accept voltages within 4V from the rails. Another thing is that since you're using an inverting configuration, you would expect your output to go from 0 to -1.5V. The output can't get there because your supplies are limited to ground. Can you possibly use dual supplies? This would solve both the input voltage range and the output problem. It should work with +/-5V supply. 
 If you can't provide a negative supply and you just want to learn how the op amp works, you could do a non-inverting configuration -- that is, have the same feedback circuit but tie one end of the 10k resistor to ground and apply the input to Vin+ instead, as in the figure below. You'll need to offset your input to about 3V for the amplifier to give you an output, and use a higher power supply, maybe about 10V. 
 
 Try this out and let me know if it works! 
 Kris)

krisf · Answer

Hi Marcos, 
 Harry's got it right, I stand corrected on the supply voltage. The minimum you can use is a +/-8V dual or a 16V single supply. Otherwise, it should work as you intended! 
 Thanks, Kris

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"hello world" circuit with op42