LM317 Variable Voltage + Variable Current

Discussion in 'The Projects Forum' started by ShayanFiroozi, May 4, 2016.

  1. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    Hi Guys
    i found a LM317 variable current and voltage regulator

    actually i need current from 100ma to 1.2 AMP with voltage between 13 to 14.5 volts

    any help and development for this circuit please to be an industrial circuit !!

    i really appreciate that
    thank you
     
  2. dannyf

    Well-Known Member

    Sep 13, 2015
    1,767
    357
    Put a variable load to shun the output current.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Do you need to regulate the voltage to a point between 13 and 14.5 or is that the acceptable range?

    Again, do you need to regulate the current between 0.1 and 1.2 amps or is that the range you need to supply?

    Also, toss your sketch, it does not regulate or control current.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    619
    As noted, the circuit will not work. The first LM317 isn't connected correctly. In addition to taking the output from the wrong point, you can't use a multi-turn pot as as shown. You won't find any that will dissipate a watt over a small portion of the range and you need to have a way to prevent the pot from shorting the regulator output.

    What is the intent of the transistor and fuse?

    A 14.5V output would be cutting it close. 16VAC would give you 22.6V minus rectifier drop, 2 dropout voltages, minus another 1.2V from the current set resistor.
     
  5. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    i need that voltages but if more or less regulation is acceptable

    thank you
     
  6. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    So any circuit or any correction ?

    thank you
     
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    The LM317 by itself can deliver up to 1.5 amps as your load requires. It needs to be on a good heat sink to accomplish this.

    Suitable circuits may be found on the data sheet.
     
  8. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I see what you are trying to do. You have combined two schematics, but have errors in both. If you break the connection between R4 and C945's emitter and insert a shunt resistor, that transistor can act as a current limiter and you need only one LM317. Here are two variations to get you started. In both, the battery would be replaced by your power supply load.
    http://www.tradeofic.com/Circuit/6714-CURRENT_LIMITED_6_V_CHARGER.html
    http://www.electronicecircuits.com/electronic-circuits/lm317-regulated-battery-charger-circuit

    ak
     
  9. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,281
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    The 100 ma. to 1.5 amp spec. will keep you from using the easy circuits. Do you really need that range? It's not like it can't be done, it just gets more complicated.
     
  10. crutschow

    Expert

    Mar 14, 2008
    12,977
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    Also, do you need that current limit into a short circuit?
    The simple current-limit circuits can only reduce the output voltage to about 1.2V, at which point the current is limited to about 1.5A by the intrinsic limit of the LM317.
     
  11. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    Your are so wise man !!! yes i did combine 2 circuit ;) but i'm not familiar with electronic at all ;)

    thanks for your links , but as my batteries are 1.1AH to 12AH i need a variable current limiter
    i don't wanna replace my current limiter resistor every time !

    thank you
     
    Last edited: May 5, 2016
  12. crutschow

    Expert

    Mar 14, 2008
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    What exactly are you doing with the batteries?
    Are you trying to charge them?
     
  13. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    Yes
     
  14. crutschow

    Expert

    Mar 14, 2008
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    Below is the LTspice simulation of an LM317 with an LM339 comparator that senses the voltage across shunt resistor R1 due to the load current.
    The comparator reduces the regulation pin control voltage for the LM317 when the current exceeds the threshold set by the voltage reference U5 and pot U2, thus performing the current limit function.
    The current limit can vary from 1.2A to essentially zero current by varying pot U2, as shown for pot positions of 0%, 50% and 100%.
    Pot U4 controls the maximum output charging voltage.

    upload_2016-5-5_0-30-8.png
     
    Last edited: May 5, 2016
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  15. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    Thank you very much,can I leave my battery permanently with this charger??? Also can I use multi turn ?? Also which component will get hot?? Just LM317??
     
  16. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    Besides this circuit
    http://www.electronicecircuits.com/electronic-circuits/lm317-regulated-battery-charger-circuit
    Uses transistor , all I know is it will reduce voltage and current when battery get fully charged and circuit will go in float charging or trickle mode
    Is you circuit do that ?? Because I need to leave my battery permanently
    My batteries are rated 12volts and their amperage are from 1Ah to 12 Ah,that's why I need to regulate my current to achieve 1/10 of a battery

    Thank you
     
  17. crutschow

    Expert

    Mar 14, 2008
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    That circuit doesn't have the wide current adjustment range that you wanted, while the circuit I posted does.
    That's why mine is more complex.

    You can use a multi-turn pot if you like. The only difference between a multi-turn pot and a single-turn pot is the number of turns. ;)

    Yes, the only device that will get warm is the LM317.

    Both circuits reduce to trickle charge when the battery voltage reaches the set voltage as long as its the proper voltage.
    Neither circuit reduces voltage at the end of charge.
    The current reduces because the battery voltage rises and becomes close to the charger set voltage.
    To adjust that point, monitor the charge current after the battery is charged and then set the output voltage to give the trickle charge current you want.
     
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  18. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1

    You are the man !!!

    thank you very much

    is it easy to add a battery full indicator to your circuit ?
     
  19. crutschow

    Expert

    Mar 14, 2008
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    How would you define a full battery?
    You likely would have to monitor the charge current to see when it drops below a certain current.
    You could use a LM339 comparator in the package to monitor the voltage across the shunt resistor R1 and light an LED when it drops below the desired value.
     
  20. ShayanFiroozi

    Thread Starter Member

    Nov 18, 2015
    41
    1
    crutschow , i'm pretty beginner in electronics , that's why i'm asking stupid questions ;)

    will R1 get hot during current limiting ? all in know LM317 is acting as a voltage regulator and of course will get hot , but which component is responsible for current limiting ?


    thank you
     
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