Voltage Regulator wih One amp regulator

Discussion in 'The Projects Forum' started by RodneyB, Aug 11, 2014.

  1. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I am wanting to build a voltage regulator with current limiting of 1 Amp.

    The output must be 1.2Amps at 13.8 Amps. The input voltage is the tricky one.

    Under normal conditions its input voltage is 26 Volts DC but can spike to around 60 Volts under certain conditions.

    I was considering the L200 but don't understand a few things.

    Firstly I don't want the voltage to ever go above 13.8 volts on the output or the 1.2 Amps.

    I also want to protect the input voltage so the unit is not going to be damaged. I was thinking of putting an MOV and a resettable fuse. On the input.

    I would value some guidance here.
     
    Last edited: Aug 11, 2014
  2. Ramussons

    Active Member

    May 3, 2013
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    You will be dissipating around 15 Watts as heat in the LM317, maybe more depending on the input voltage.

    I would suggest a Switching Regulator with a provision for a Current Limit; else usea 15 volt Switching Regulator at the front end of Dodgydave's idea.

    Ramesh
     
  3. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Sorry about the typo it is 1.2 amps 13.8 Volts. As the output. The current Has to be regulated. If I was to use the LM317 and the voltage went to 60 Volts this would blow the LM317. The datasheet shows a maximum of 40Volts. If my understanding is correct I would need 2x LM317 one for voltage regulation he second for current regulation.

    If my understanding is correct I will be able to achieve both current and voltage regulation using a single L200.

    I would happily use another component suggested.
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How long does the input voltage stay at 60V? Is that just an occasional transient?

    You might get some ideas from my posting here.
     
    Last edited: Aug 11, 2014
  5. RichardO

    Well-Known Member

    May 4, 2013
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    National Semiconductor (now TI) makes regulators specified to withstand voltage transients up to 60 volts. Check for ones intended for automotive applications.
     
  6. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    The output voltage at 60Volts is an occasional transient
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    You can't regulate current and voltage at the same time.. Its either constant current OR constant voltage.. Not both. not possible.
    What is this device you are trying to power?
     
  8. crutschow

    Expert

    Mar 14, 2008
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    First you say the current limit should be 1A, then you say the load is 1.2A. Which is it?

    What is the purpose of this current limit?
     
    Last edited: Aug 11, 2014
  9. MikeML

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    Then what is this thing on my workbench which has two knobs; one to set the open-circuit output voltage, and the other to set the maximum short-circuit current????

    Read the posting I linked to...
     
  10. wayneh

    Expert

    Sep 9, 2010
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    Perhaps you are joking but just for the benefit of any noob that might be following this, a hi cut-out is not simultaneous "regulation" of voltage and current in the sense that mcgyvr was referring to. You cannot control both at the same time without adjusting the load properties. Of course you CAN place limits on either, but this is not the same kind of "control".
     
  11. MikeML

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    Yes, I was joking.

    No, but, what I described is what the OP is requesting... He wasn't asking about theoretical voltage sources and current sources...
     
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  12. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    Ish! I am now totally confused. I have a tracking unit which is powered from a 12 Volt 7Ah battery. I want to charge it as recommended by the supplier o 13.8 volts. he charge current should not exceed 1.2 Amps.

    The source for charging is from a 24 volt battery bank which I believe charges to 28.8 Volts. I am advised periodically the incoming voltage can surge to 60 Volts but only for a short period of time.

    I need to therefore regulate the voltage from 28.8 volts to 13.8 volts, further if I do not have current limiting the battery will overcharge and he battery will pop.

    I wan to have a resettable fuse on the output to prevent overcurrent into the battery if the current limiting circuit develops a fault. I was asking about an MOV and resettable fuse on he input to prevent the instances of voltage spikes.

    So the circuit I am asking for advice for is one that limits he current to the battery and the voltage.
     
  13. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I agree with Ramusson's suggestion (post #2). If you can't get a switcher with adjustable built-in current-limiting then you could use an LM317 as an external current-limiter. The MOV and fuse would be useful additions.
     
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  14. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I have attached a diagam of my prposed current limiter. Assuming the output current is 1 Amp and the voltage is 13.8 Volts.

    I used a online calculator and the resistor calculated was 1R2Ω 3 Watt.

    is his correct
     
  15. crutschow

    Expert

    Mar 14, 2008
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    The resistor is in the wrong location in your posted circuit. It needs to be between the output of the LM317 and the load with the Adj pin also going to the load side of the resistor.

    Edit: Note that this circuit will drop more than a volt even when operating well below its current limit.
     
    Last edited: Aug 12, 2014
  16. MikeML

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    Even if you fix the current limiter, you cannot just put it between the output of your voltage regulated supply (switcher or linear), and the battery... The LM317 current limiter has a minimum voltage drop across it of about 3.3V, so if placed behind the voltage regulator would screw up the voltage regulation.

    You must connect the voltage sensing for the voltage regulator so that it senses the battery voltage on the output side of the current limiter. To say this another way, the current limiter must be inside the voltage sensing loop.

    The circuit I linked you to way back in post #4 has the current limiter properly integrated inside the voltage control loop.
    It is specifically for limiting the maximum charging current and limiting the final float voltage for a sealed lead acid battery...
    It is like the lab supply, which has independent control of voltage and current.
     
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  17. RodneyB

    Thread Starter Active Member

    Apr 28, 2012
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    I would appreciate comments regarding my attached voltage and current regulator circuit attached.
     
  18. MikeML

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    Oct 2, 2009
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    Why add the LM317 current limiter at all???

    The L200 already has one built in to it. It takes just one resistor to program the current limit. See R3 in Figure 3 of this app note.
     
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