2n6027 PUT help.

Discussion in 'General Electronics Chat' started by Enea, Sep 6, 2011.

  1. Enea

    Thread Starter New Member

    Sep 5, 2011
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    Hello :)

    I am new to all this stuff, i mean really new!! page 85 new :D

    I am starting to learn electronics as a hobby and as such have a book "Make: Electronics" that i am currently going through.

    I have a question about a circuit that is called Slow speed Oscillation using the 2N6027 PUT, a capacitor and a few resistors.. oh and a LED to flash :)

    But i am getting some unexpected results.. instead of the LED flashing it just turns on as soon as i connect the power and stays on. I am 100% sure that i have the correct wiring etc.. it should flash. i have tried everything in my knowledge to fix this but cannot understand what is happening to make it go wrong :-
    • swapped the pins on the PUT in case it is non standard Anode, gate and cathode
    • increased and decreased the resistors across the Gate
    • Checked, checked and checked again the layout, wires etc.
    • changed capacitor, and so on.

    The only thing i can think of is that the transistor is wrong but it definatley says 2N6027 on it. are there any checks i can do to see it if it a PUT?

    i did notice that if i out a negative charge on the "gate" pin the LED dims and the apposite for positive charge. is this usual behaviour for a PUT?

    Anyone can help me out here? the rest of the book depends on adding to this simple circuit :D

    Thanks
     
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Please post the circuit and maybe a photo of what you've built.
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Compare your ckt with one below. It is possible that C1 cannot discharge low enough with just a current limiting diode, R2, & LED, hence Rx, about 300 to 1k. Un labled R is 20k. C1 to suit flash rate.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    I've attached a schematic and simulation of a PUT LED driver I was experimenting with a few years ago. Note that if the input voltage (yellow trace) becomes too low, the voltage on the LED (green trace) indicates that the circuit is oscillating rapidly. This would make the LED appear to be lit constantly. In the simulation, I was using a blue LED with a Vf of 3.4v @ 20mA.

    You haven't mentioned specifications for any of your components other than the PUT itself. The best thing you could do is to post a schematic that documents not only all of your connections, but the values of all parts used, including your supply voltage.

    Complete, accurate schematics are very important tools; they convey almost all of the information needed and eliminate almost any question that could be asked in order to help us to help you solve problems you may be having.
     
    Last edited: Sep 7, 2011
  5. Enea

    Thread Starter New Member

    Sep 5, 2011
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    Thanks all.

    Attached the files.. I took apart my one to make it look nicer for the picture, plugged it all back in and still nothing.. ramped the volts up to 12 and i actually got a flashing LED! but it is very dim.

    i also had to use a different resistor than the original as i don't have them.. for the 470K resistor i used a 100k also tried an 812k in my messing to get it work.

    thanks for the other schematics i'm going to try them out too.

    I'm still not happy about why putting up the voltage has made it flash, and why it is not flashing bright?
     
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  6. Enea

    Thread Starter New Member

    Sep 5, 2011
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    I cant see any attachments.

    oh.. so the LED matters too.. mine just said use an LED not sure what mine are rated at :(
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry about forgetting the schematic; it's there now.


    I just simulated the schematic you're trying to use - it doesn't work @ 6v.
    Try the one I posted. If you don't have a Schottky diode, try a 1N914/1N4148.
     
    Last edited: Sep 7, 2011
  8. vsserafim

    New Member

    Jan 22, 2012
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    Enea, have the same problem here. Any solution working for you?
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    WOW!
    The PUT brings back memories because I used them about 36 years ago.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    PUT's are good pulse generators,[ as to drive SCR's] lousy LED flashers unless a darlington is used to couple the cap to LED. First used around 1968 & have two in present project.
     
  11. vsserafim

    New Member

    Jan 22, 2012
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    Ok, this stuff is older than me so! :) But this super simple circuit (the exact one posted by Enea) is driving me crazy. I have everything setup exactly as showed in the Enea's diagram and the result is the same: LED lit and no flashing.

    And just to be more annoying, there are people reporting this very circuit works perfectly. Take a look at this site: http://handsonelectronics.blogspot.com/2010/01/chapter-2-exercise-11-step-1.html

    Enea: what did you do? :)

    Thanks for your attention and patience.

    Vini
     
  12. cyberion

    New Member

    Apr 22, 2013
    1
    0
    Hello,

    This is for anybody else that might find this while searching online:

    I had this same problem and fixed it with a 100K resistor in place of the 470K resistor (R1 in the schematic). Not sure why the 470K resistor didn't work, but I'm still learning!
     
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