Firing circuit with AVR

Discussion in 'General Electronics Chat' started by Far, May 12, 2009.

  1. Far

    Thread Starter Member

    May 11, 2009
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    Hi all:)
    I'm trying to design a Firing circuit to drive a simple Low voltage rectifier and inverter (1phase, 1A, ). now I need to know that I should design it in PWM mod?
    and can I use an AVR to generate 6 pulse out?
    it's my wonder if you could help me!
     
  2. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    please help me!:confused:
     
  3. hgmjr

    Moderator

    Jan 28, 2005
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    Can you provide us with more information?

    hgmjr
     
  4. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    dear all
    I want to design an evaluation set for Industrial Electronics laboratory.
    I need to design such a firing circuit to Excite thyristors in a low voltage(24 VAC, 12 VDC) rectifier & inverter circuits(in full bridge design).
    the Inverter output is a square wave. since these circuits work in low power mod, it doesn’t make any problem!
    now I want to know if I could design a digital firing circuit using AVR ?
    regards
     
  5. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    please Help me!:confused:
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    The problem is you are assuming we know what you are talking about. AVR? That and a schematic to base your question on would go a long ways.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    I think he wants to make an Inverter with an input of 24V DC
     
  8. Far

    Thread Starter Member

    May 11, 2009
    20
    0

    exactly:rolleyes:! I want to fire thyristors in such an inverter!
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    We still have no parameters on the device. The statement -
    - gives nothing to work with.
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Thyristors are used in really powerful inverters . they go in the range of KW.
    You should consider IGBJT's or MOSFET's
     
  11. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    24 VDC input/12 V-50 Hz sinusoidal wave in output/using Bridge 1phase design with 4 Thyristors or power MOSFET/ RL load(R=1 Ohm, L=10 mH)
    enough information? or u wanna know how does it work?!:D
     
  12. Far

    Thread Starter Member

    May 11, 2009
    20
    0
    Thanks for your constructive Help!:cool:
    I cope with my problem by explain it to the other:)
    if u found any problem in power electronics, I'm here to help you.
     
  13. DickCappels

    Moderator

    Aug 21, 2008
    2,653
    632
    I think you question would get a better reception on www.avrfreaks.net.

    To fire a thyristor (through a transformer?), you should do it by sending a "picket fence" series of firing pulses that start at the phase that you would like the thyristor to start firing. I really doubt you can get the PWM outputs in any of the AVRs to do this for you without tricky real time firmware intervention. Instead, I think you would be better off to use a timer interrupt to create the dealy from zero crossing, then either the same timer again, or a better yet, a different timer interrupt to time the firing interval. The pulses themselves can be only a couple or few us wide, depending on the thyristor, and that can be timed in firmware.

    Rather than timing directly from sensed zero crossings, I recommend using a timer in a free-running mode along with a zero crossing detector and some servo firmware (such as PID controller) to make a digital phase locked loop, locked to the power line zero crossings, and then time your thyristor firing from that. This way, you will greatly reduce the risk of accidentally firing from a glitch on the power line.

    And one more thing...while debugging, use an isolation transformer if at all possible, but most importantly, remember to keep one hand in your back pocket (seriously!)
     
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