Constant Voltage and Current Circuit

Discussion in 'The Projects Forum' started by alyeomans, Jun 11, 2015.

  1. alyeomans

    Thread Starter Member

    Sep 13, 2010
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    I need a CV CC circuit with the load grounded. I had been using an LM317 circuit with success but that had the current sense resistor below the load causing problems with other parts of the project.

    So I have connected 2 simple circuits to make a CV and CC source as per the picture. I would like to combine the voltage ref and current feedback into one transistor but have had no luck locating some examples.

    Any advise on helping to temperature stabilize the zener (swap zener with TLC431?), rationalising the circuit to one transistor or examples would be most welcome.

    Thanks
    Al
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Two LM317s in series, the first for the current limit and the second to control the output voltage, are a simple way to go.

    What do you mean your LM317 circuit "had the current sense resistor below the load causing problems with other parts of the project"? :confused:
    The current sense resistor is in series with the output of the LM317.
     
  3. alyeomans

    Thread Starter Member

    Sep 13, 2010
    29
    2
    For reference regarding the single LM317 in CV CC see below the circuit. Note there is additional circuitry for current sensing.

    One of the first iterations of this circuit did have the 2 LM317s but was dropped due to space constraints in the enclosure.

    I'd like to peruse the single transistor CV CC for my understanding and the hopeful finesse it would provide. old cv cc.png
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Over what range do you need to adjust the voltage and current?
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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  6. alyeomans

    Thread Starter Member

    Sep 13, 2010
    29
    2
    Thanks AK most appreciated, I had seen some of those circuits but what I was after needs to be more simple.

    Crutshow I need a constant voltage at 8.4V and current limited at under 1 amp for a lithium ion battery charger and balancer. While most bench supply circuits will do this they also cater for more frills than is needed and take up precious board space.

    I found a circuit on this forum through google image search but cannot figure who uploaded it to give credit. It is a constant voltage using the TL431 shunt reference with current limit using a single LM317. See below - it simulates without flaw so the next step is to the breadboard.

    new lm317 cv cc.png
     
  7. alyeomans

    Thread Starter Member

    Sep 13, 2010
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  8. crutschow

    Expert

    Mar 14, 2008
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    If you can lower the input voltage to 12V or so you will minimize the power dissipated in the LM317.
    But it will still need a heatsink.
     
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