Please help rectify this inverter circuit.

Discussion in 'The Projects Forum' started by livayahurd, Jun 10, 2010.

  1. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    I somehow recently made this circuit. The relays won't switch off ever. Even if i remove the op amp the relay still goes on. The inverter section works fine independently. its the control side which causes all troubles. Unfortunately i cant use any sort of micro controller help in any case.

    please check the attachment.
     
    Last edited: Jun 10, 2010
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The 4N25 mains sensing opto-coupler wiring looks wrong.

    Removing the op-amps probably meant that the 4011 NAND gates just went permanently high at their outputs - thereby forcing on the relay driver transistors.
     
  3. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    I tried grounding the input of the nand bypassing the opto coupler but still the same effect.

    And if the outputs are to go high by removing the opamp then the transistor used is PNP should receive +ve at their base.. they should not work and the relays should therefore be shut down.
     
  4. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    like this one.. recently I made a circuit for automatic water level controller with voltage protection for the pump and dry running preventer. When i made it first I used a PNP to drive the relay.. i faced the same issues.. but when i redraw the circuit for NPN it worked fine..
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    OK - sorry - I missed that they were PNP types and that the supply was opposite to what I thought. The opto-coupler looks OK as well. It's hard to get my head around the circuit when drawn this way!

    Then perhaps the LOCMOS 4011 NAND gates just can't pull the BSV10 bases high enough to turn them off.
     
    Last edited: Jun 10, 2010
  6. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    any idea what the problem is?

    Since its the nanad gate use the operation will be:-

    1. Inverter will be on iff :- Battery is above the Vmin (opamp low voltage sending gives out +ve signal) and No AC signal in the lines.

    Final output will be "0" from the Nand which powers the PNP of inverter relay supply

    all other cases the output will be "1" and hence the PNP wont conduct preveting the operation of the inverter.

    2. Charging will be on iff :- Battery charge is below Vmax (op amp high voltage sending give out +ve signal) and AC signal is present in the line.

    Here to the final output will be "0" from the Nand which powers the PNP of the Transformer relay supply.

    all other cases the output will be "1" and hence the PNP wont conduct preventing the operation of the charging.
     
  7. t_n_k

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    Mar 6, 2009
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    What's the supply voltage for the NAND gates - is that from the 7805 reg [IC2]? Is the relay supply rail also 5V? It seems to come from VCC which is presumably higher than 5V.
     
  8. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    nand gates do get the supply (5v) from the regulator IC 7805.
    But the relays get it from VCC.. arround 12V
     
  9. t_n_k

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    Mar 6, 2009
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    To turn off the transistors the 4011 gates would have to pull the BSV10 base up to 12V. They can't do that if they have a maximum output of 5V.
     
  10. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    Thats a point. So what should I do now.. The relay which i have wont go with 5v. Should i Change the nanad supply to 12v.
     
  11. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    That should work - the CMOS would run at up to 15V without any problems.

    I'd also be inclined to add some base resistance to reduce the current demand on the gate output circuit when they go low output. Though it may not matter, since they will effectively only sink about 20 uA before their output swing starts to limit. Anyway they appear to be "happily" switching the transistor on.
     
  12. livayahurd

    Thread Starter New Member

    Oct 12, 2009
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    Thanks a lot mate.. Let me try and will give you a feed back soon..

    Thanks again.
     
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