thanks for that... helped a bit, got my output at 5V now which is nominal TTL I need... will check on the oscilloscope again to see if I have frequency... I still cant read any, I am almost sure I am trying to read incorrect method and that the circuit is functioning...

 

hope this helps give an idea to the experts and maybe I can be helped... I am still not seeing any pulses on oscilloscope...

here are my values... I built the cct and used 15V for supply and -5V for input voltage... the ohmic resistance on pin3 of the LF was = 1 ohm...
Vb = 1.47V, Ve = 0.94V

LM pins
1. its like its oscillating, going up and down between certain voltage
2. 1.61
3. 5
4. GND
5. 0.099
6. 7.46
7. 0.734
8. 14.9

LF pins
1. -14.74
2. its like its oscillating, going up and down between certain voltage
3. close to zero
4. -15
5. -14.8
6. 0.75
7. 14.9
8. -

 

I think I see the problem. The data sheet seems to indicate that the full scale voltage is -10 volts (negative ten). However, the same data sheet list the maximum range of input voltages as -.2 volts to Vss (the voltage applied to power the IC).

It looks like a misprint as to the full scale voltage. It should be +10 volts.

We can all tell tales of time and money spent due to bad data on data sheets, schematics, or in manuals.

 

ok i will try this and see if there is a difference... thanks

 

ok, its still not functioning properly... here are results... also LF pin3 voltage I can change with the pot... what voltage should there be? is that not the offset voltage? cause I have adjusted it close to 0V... I am getting some sort of wave on the output... but it looks like AC sino wave so it cant be correct, also the frequency doesnt change if I increase the Vin... so its not correct...

LM pins
1. alternating
2. 1.42
3. 5, also I set this by using the voltage logic resistor
4. GND
5. 0.115
6. 7.4
7. alternating
8. 14.9

LF pins
1. -14.74
2. alternating
3. close to zero, this I adjust with the pot
4. -15
5. -14.8
6. alternating
7. 14.9
8. -

 

ok so I have inputted now rather +V to Vin and its oscillating voltage on many pins... also on pin3 of the LM which is what I want right? now the pull up resistor I supply with 5V... will this make my output pulses peak at 5V? or can I apply Vsupply also on that resistor? I am using 20V supply at moment...

 

The 20 volt supply is within the 40 maximum. The output does not seem to have a maximum, but take the 40 volts as a limit. The typical applications simply show Vlogic on the pull up resistor, so anything from 5 to 15 volts should be in that range.

At this point, having exceeded the negative maximum for input voltage with the original test, your IC may be damaged.

Do you have the data sheet? Do not place more than +10 volts on the voltage input.

 

what is the negative max? not -11V? but will both IC's maybe have been damaged?

 

We may be talking at cross-purposes. You must be trying to use the figure 4 circuit with the inverting op amp. Notice that the op amp inverts the -10 volt input, so the LM331 only has a positive-going input on pin 7. The diode between the 2.2K resistor and ground is there to clamp the output from the op amp so the LM331 will not get danaged but a negative voltage on its input pin.

The op amp has to have a negative supply on its pin 4 so the output can swing to 0. This was necessary for older op amps. The positive supply has to be symmetrical and enough above 10 volts so the op amp can swing its output to +10 volts. A +/- 15 volts supply would be reasonable in this circuit.

So, we have the Lm331 running on +20 VDC, and the op amp on +/- 15VDC. That leaves

what is the negative max? not -11V?

as a bit of a mystery. Where do you get -11 volts?

 

I saw that value on the pdf for LM331... no I was thinking of something else... I am running the LM 20V and the LF +-20V... should I change this?...

I get something like this on osc... am I not suppose to get square waves?

http://i531.photobucket.com/albums/dd351/Switch_639/SDC12444.jpg

 

Better check your connections. And your probe compensation.

 

so there is no need to replace IC's or the transistor? would you say it is working at least? apart from what is on the scope? I will build a pulse counter rather also...

 

Does the output vary linearly with a change in input voltage? Can you adjust things to vary the output frequency for a fixed input voltage?

 

I can not really see a difference... inaccurate osc? or think I should try with the counter? no need for replacing components? when I adjust Vin the amplitude changes, this I know shouldn't be...

 

With a constant, distorted output that does not change with the input voltage, you probably have either a bad IC or an improper hookup.

 

you said something about going beyond the max lowest voltage... what is this amount? -0.2V or something? I read on pdf something about max being -0.2V to +40V... so it would be the LM and LF that are damaged?

 

If you apply a voltage to a terminal of any device that exceeds the maximum stated on the data sheet, that device will almost certainly be damaged or destroyed.

 

so you are almost recommending me to get new ones... I will do it... and see if it improves... sure it will... thanks so far...

 

I replaced both the LM and LF in the circuit... I get the same kind of output pulse... its not square wave... I built a pulse counter cct to test the pulses coming from the converter... the counter works, tested it with function generator... but the frequency converter pulses do not work on the counter... what other ideas could you have in getting the converter to work?

 

Can you post an accurate schematic of your connections, and describe how you have physically constructed the circuit?