wein bridge & darlington pari dc to ac inverter

Discussion in 'The Projects Forum' started by RickFC, Jun 27, 2012.

  1. RickFC

    Thread Starter New Member

    Jun 27, 2012
    3
    0
    Hello everyone, I am fairly new to electronics and I'm currently working on a dc to ac inverter (to power small electronics ex: camera, laptop) using a wein bridge oscillator and a darlington pair transistor. I want to accomplish the following:
    14vdc in
    22-24 vpp out
    60Hz pure sine wave
    4-5 A

    I can get the 24vpp and 60 Hz sine wave at the output of the op amp. I can also get 5 A at the collector of the transistors. However, I get no voltage at the collector. I'm puzzled by this. I can get the values I need, but at two different ends. Can someone shed some light on what I am doing wrong? what components I am missing?

    p.s I have attached my schematic along with sine wave and scopes measuring at the output of my op amp and the collector.
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,003
    745
    the transistor q3 is across the battery and will short it out as soon as its turned on, so your circuit wont work.
     
  3. RickFC

    Thread Starter New Member

    Jun 27, 2012
    3
    0
    Thanks for your reply Dave. How would you suggest connecting it? I may be wrong, but I thought the typical connection was to feed the signal to the base, connect the collector to vcc (14v) and emitter to ground (0v).
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    How do you expect to see voltage at the transistor collector when it's directly connected to the voltage source. You are missing one tiny detail -- the load. The collector needs a load in series with the voltage source to generate a signal voltage and limit the current. Otherwise what you have is likely a transistor zapper. :rolleyes:
     
  5. RickFC

    Thread Starter New Member

    Jun 27, 2012
    3
    0
    Thanks for your reply and help. I have added a resistor (1K) between the collector and voltage source as you suggested. I can now see some voltage and current values now. However, the voltage is not the same as my 24vpp from the output of my op amp. The current output is also down to a few mA. I am a bit confused about the load. Ill try my best to word this question. Is the load (my 1k resistor) consuming the 24vpp voltage and 4A and is the reason I am seeing lower values? or do I need a load there regardless of what I connect to it (ex: 75 W lightbulb)?
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    A single-ended driver such as you show, does not work well to provide a plus and minus output voltage as you want for your loads. You need a push-pull follower output to generate ±12vp into a load such as shown in Section 6 here.
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Your extremely simple wien bridge oscillator will have a square-wave output because the opamp clips. It clips because there is nothing to limit the output level.

    Your idea is not useful because you are simply amplifying a sine-wave then the amplifier is linear and gets extremely hot while wasting the battery power.

    A pure sine-wave inverter uses Pulse-Width-Modulation at a high frequency. The output Mosfets switch on (low voltage across them then low power loss) and switch off (no current so no power loss) then the high frequency switching is filtered out leaving the low frequency pure sine-wave that modulates the PWM.
     
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