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IC 555

Discussion in 'Electronic Basics' started by ZhangLu, Mar 17, 2007.

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  1. ZhangLu

    ZhangLu Guest


    I was using 555 astable output and connect to a radio transformer
    ( 1:70), trying to step up the output voltage from pin 3. Somehow I
    could not measure any output from the secondary coil of the
    transformer. Is there anything wrong with this set up?

    I got my schematic for the 555 astable from:

    Your advice and suggestion is much appreciated.

    Newbie Zhang
  2. What values did you pick? IOW, at what frequency are you trying to get the
    555 to oscillate? Are you sure the 555 is outputting a signal now? Have
    you looked at it with a scope?
  3. Have you verified that the transformer is good and capable of working well
    at the frequency of interest?

    Have you scoped pin 3?
  4. kell

    kell Guest

    What is this "radio transformer," what frequency are you using and how
    are you driving the transformer -- did you attempt to drive it
    directly from pin 3, or did you use a switching element such as a
    transistor or a mosfet? You didn't say.
  5. ZhangLu

    ZhangLu Guest

    The frequency is set at 1K Hz, I use a mini transformer ( the input
    has two wires and out put with 3 wires, input is 1 ohm and output 72
    ohms, it appears like a cube measuring 1cmx1cmx1cm). As I need only
    high voltage and low current, I drive the transformer direct from pin
    3. I can measure output from pin 3 using a multitester, I connected a
    LED to the output after a resistor it lights up.

    Hope the above description helps....

  6. kell

    kell Guest

    Did you use a breadboard? If so, it's easier to troubleshoot. I'll
    assume you can swap components easily.
    At 1kHz you will not be able to see an LED turning on and off.
    When you need to build a timer circuit at some frequency that is too
    high for the naked eye to perceive, you have a couple of options.
    One of my favorite tricks is to take a radio and set it to a blank
    spot on the AM dial. If you hear a buzz on the radio when you turn
    the 555 on, that means it's working.
    Another way is to replace your timing cap with one that's big enough
    to give you a frequency of about 10 Hz or 1 Hz, or something on that
    order. If it makes an LED blink, you know it's working; then you can
    swap the timing cap back to the design value, for 1kHz. You can be
    pretty sure it will work with the new cap, since you didn't change
    anything else.
    Once you have made sure the timer is working, you can go on to the
    rest of the circuit.

    Possibly the one ohm primary of the transformer is too heavy a load
    for the timer. Bogging the 555 down with such a heavy load might be
    causing the output to malfunction. You may be able to improve
    performance by putting some resistance in series with the transformer
    primary. But I would be inclined to use a transistor to drive the
  7. ehsjr

    ehsjr Guest

    You need to add a resistor between pin 3 and the
    transformer primary. Divide whatever voltage you are
    using to power the 555 by .15. Use the standard value
    resistor closest to that number.

    You may get some pretty high voltage at the secondary.
    I would recommend you run the 555 at no more than 5
    or 6 volts. You don't know how much voltage the
    insulation on the wires on the secondary can withstand.

  8. Phil Allison

    Phil Allison Guest


    ** You MUST use a coupling capacitor to drive a transformer from pin 3 of
    a 555.

    Try a 10 uF electro with the + to pin 3.

    ....... Phil
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