Which is the best 555 timer??

Discussion in 'The Projects Forum' started by Skfir, Dec 11, 2012.

  1. Skfir

    Thread Starter Active Member

    Aug 19, 2010
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    Hello again, guyz!
    I have been experimenting with a 555 timer and a flyback convertor based on it with a transistor regulation over the 6th pin. NE555 works very good, it is stable, it allows for good regulation, but it eats a lot of current. I tried TLC555, but it was quite unstable, now and then it started to oscillate and so on. Could you please advise me which is the best 555 chip? Something which is quite stable and does not eat much current.
     
  2. Jaguarjoe

    Active Member

    Apr 7, 2010
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    My Dad said that if you don't have anything nice to say about a 555 don't say anything at all.
     
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  3. Skfir

    Thread Starter Active Member

    Aug 19, 2010
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    But I said nice things. I said that ne555 worked very good, I just wanted to find some other 555 which is equally stable as ne555 but consumes less power.
     
  4. #12

    Expert

    Nov 30, 2010
    16,345
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    Your instability isn't caused by the timer. It's caused by the circuit you built around it. When you change to a different version you have to consider how that changes the design.
     
  5. Skfir

    Thread Starter Active Member

    Aug 19, 2010
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    Since I have everything on my breadboard and the wires are long and frequencies are high, potentially there are many spots which can generate. But the interesting thing is, I plug in NE555 - everything works, I take it away, plug in TLC555 and nothing works, just noise.
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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  7. Skfir

    Thread Starter Active Member

    Aug 19, 2010
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    100ma is fine, I use MOSFET driver, so should work. Thanks!!
     
  8. Audioguru

    New Member

    Dec 20, 2007
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    We can't help you fix it if you don't post the schematic.
     
  9. Skfir

    Thread Starter Active Member

    Aug 19, 2010
    135
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    It is an extremely simple one looks like that which is attached. The only difference is that I made a negative feedback to regulate the output voltage. So on the output I have a voltage divider, lower shoulder of which is connected to the gate of a MOSFET, which drain is connected to the 5th pin of the 555. Whether I pull drain up to Vss or not - makes no difference. If I use the 4th pin instead - nothing works, just noise on both ICs. With the 5th pin, ne555 works fine, LTC555 does not work. Or to be more precise works but only on very low frequencies. The funny thing though is a rather important difference between NE555 and TLC555. If NE555 is controlled through the 5th pin, it alters frequency, preserving the length of its ON state intact. TLC555 alter duty cycle. The frequency also changes, but just on the delta-length of the duty cycle.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    The output high current of an ordinary NE555 is 200mA. But the output high current of a Cmos 555 (TLC555, LMC555 or ICM87555) is only about 10mA. Then the Mosfet's high gate capacitance charges very slowly from a Cmos 555 which is why it works with a low frequency.
     
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  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I built an actual working boost power supply using an LMC555 to increase a 9V battery up to 30V for a calibrator circuit I built. It can be done, but as shown in the schematic, it takes some compensation and tweaking to make it stable. The "30V power" node is 9V from the battery. The op amp injects current back into the 555 circuit to regulate the voltage at 30V.
     
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  12. Skfir

    Thread Starter Active Member

    Aug 19, 2010
    135
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    Well.. I use IXDD604 mosfet driver. Just thought that those drivers should have very low capacitance, right for the cases of a "weak" signal generator. I will try the chip suggested above, since it can give 100ma, should be fine.
     
    Last edited: Dec 12, 2012
  13. Skfir

    Thread Starter Active Member

    Aug 19, 2010
    135
    4
    Thanks a lot! I will look at it very carefully, hope you will not mind to much should I have some questions since I am a newbie in electronics.
     
    Last edited: Dec 12, 2012
  14. Skfir

    Thread Starter Active Member

    Aug 19, 2010
    135
    4

    Could you please explain what is the purpose of the diode, which is right under 200k resistor (above the timing capacitor)?
     
  15. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    In my far memory, I recall those diodes are there to allow the duty cycle to go wider than 50%? Been a while since I designed it (more than ten years)
     
  16. Skfir

    Thread Starter Active Member

    Aug 19, 2010
    135
    4
    I just thought that the second diode shunts the resistor in any way...
     
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