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PWM output using UC3824N Integrated circuit

Jordan Thorpe
Prodigy 80 points
Other Parts Discussed in Thread: UC3824

I am using the Texas Instrument UC3824 PWM chip to supply a signal for a Senior class lab PCB. We were troubleshooting the board and were having trouble making the chip supply the correct PWM output. We know that the board is connected correctly because when we apply the 12V Vcc, the PWM signal initially comes through perfectly (Oscilloscope probe at pin 11), but after 10-30 seconds, the signal flickers on the oscilloscope and disappears, leaving voltage spikes only at the points where the PWM signal goes from low to high. If we disconnect the power and reapply it, the signal comes back, but disappears again, usually quicker than before. What we can't explain is that when we probe Pin 4 (Clock), the signal from pin 11 comes back clearly and stays on, but disappears as soon as the probe on pin 4 is removed. Also, the inverting output (Pin 14) always works correctly unless we probe pin 11 and pin 14 simultaneously (both of the chip outputs). So, I am looking for more information on how the UC3824 chip works and perhaps why we are getting this output.

Thanks

Schematic:

  • 0
    Guru 25210 points

    You posted this in the wrong forum.

  • 0
    Guru 227245 points

    Unfortunately, your picture is barely readable. On schematics or fine text, one shouldn't use a lossy compression format. Even though PNG usually is much better than JPG, it's still meant for full-color pictures rather than high-contrast images like schematics. Usually, GIF gives the best results if you need color, or even PCX for B/W drawings.

    However, you wrote this in the MSP430 microcontroller forum, and the UC3824 isn't MSP430 related at all. You should probably try again in /etc_analog forum (I don't see a dedicated forum for signal generators). Or maybe in clocks and timers.

  • 0 in reply to Jens-Michael Gross
    Prodigy 80 points

    I posted this in the etc./other forum and it got moved here. I have posted it in a couple different forums with a better .gif image. Thanks for your help.

    Jordan

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