• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 60 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM334: Noise spikes with capacitive load

Glenn Kubota
Prodigy 50 points
Part Number: LM334

I am trying to use an LM334 to supply 2.1mA to a capacitive load and I get some large spikes in the voltage. I've reduced my circuit down to what is shown The signal acquired is AC coupled to eliminate the DC offset, but R1 has about 9VDC across it as it should. The acquired signal shows noise across R1 that is reduced when C1 is connected. However, it also introduces large spikes in the noise.  Is there some reason that I see this with a capacitive load? Is there any way of compensating the LM334 to eliminate these spikes?

  • 0
    TI__Expert 5890 points

    Hello Glenn,

    The spikes could be due to flicker or shot noise which is larger in amplitude at low frequencies. The spikes may have been hidden by the high frequency noise before adding C1. Have you tried larger C1 values?

    Best,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 50 points

    Hi Walter, I took the same measurement data and applied a low-pass filter to those two signals and, as you suspected, I see the same downward spikes in the noise without C1, although the spikes with C1 are higher in magnitude instead of lower. I can't use larger C1 values, because my circuit is just a simplification of the actual circuit. There's actually a sensor that is AC-coupled through C1. I just removed it and shorted to ground for the measurement.

    If this low-frequency noise is inherent in the part, then this may not be the part to use. Is there another part that would have a lower noise floor?

  • 0 in reply to Glenn Kubota
    TI__Expert 5890 points

    Can you measure the noise on the 24V power supply? The large spikes appear to be periodic about every 0.1ms or 10Hz and so might be caused by something else in the circuit. Does increasing C2 show any improvement? 

    Thanks,

    Walter