lm741 in power supply

[audioguru]

The output transistor doesn't have a protection diode so when it turns off a positive spike will be on its emitter which is also the input to the opamp.

 

[Hero999]

Since under static conditions in this circuit the +input voltage nearly equals the -input voltage so you can protect the inputs by connecting a silicon diode (e.g. 1N4001) across them.

 

[Gaston]

I made some changes to the schematic when i was trying to fix it. It was just a crude drawing to show the basics of how the transistors and the op amp was hooked up. here is a better drawing. not all of the values are correct and some of the part numbers are wrong because they don't have all of the part numbers in the multisim. i added some coils at the bottom to represent the stepper

 

[audioguru]

When a TIP142 turns off, its collector voltage spikes to +100V or more. The diodes built into it won't conduct because they will be reverse biased. The diodes would be protection diodes only if the TIP142 darlingtons are used as emitter-followers.

 

[Gaston]

so the spike could back up all of the way to the op amp? where would you recomend puting the suppression diodes. directly at the input to the stepper?

 

[Gaston]

or should i take the common leads to the stepper and put them to ground and feed the other end positive through the transistors?

 

[audioguru]

I don't know why you have a high current positive voltage on the common leads of the stepper motor. It complicates the circuit and is not needed if the supply voltage is correct for the pulses to the stepper's coils.

 

[Gaston]

thats the way we did it in microcontroller class, but with a small stepper and 2n2222's. so basically i have it hooked up wrong?

 

[Gaston]

all we were tought were common emmiter amps. we were told that the other configurations weren't common ( no pun intended ) and were beyond what we had time for. so i appreiciate you and everyone else helping me.your advice is invaluable to me.

 

[bananasiong]

one reverse diode for each coil. Last time I didn't know about that, then smoke coming out from the transistor and become very hot.

 

[kchriste]

so basically i have it hooked up wrong?

I've added the diodes that you need for the stepper coils:

 

[Gaston]

the specs on the back of the stepper are 4.0v/phase,1.6A/phase,2.5 ohm/ phase1.8 deg step. i can't believe that it only runs on 4 volts. the power to the control board of the equipment it came off of runs on 24 volts.so i thought it would run on 24 volts. i started out with zero volts and brought the voltage up until it started stepping and it was way over four volts before it started to step. unless i have too much load on it? i will have to try with a fresh motor. right now i have to stop and clean up my lab. i can't move around and my bench has too much stuff on it.