voltage~current regulator 48V 2A

Discussion in 'The Projects Forum' started by podgymax, Feb 4, 2009.

  1. podgymax

    Thread Starter Member

    Oct 19, 2008
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    [​IMG]

    The output of this circuit is 53V. How to regulate this circuit to have a fixed voltage and current 2A? Do I need to add some chips? Any help or recommendations would be greatly appreciated!!!

    (the ele. cap on this circuit is 2200uF/100V, not 50V)
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What is the voltage on the capacitor ?
    What voltage do you want to regulate it to ?

    Greetings,
    Bertus
     
  3. podgymax

    Thread Starter Member

    Oct 19, 2008
    25
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    input: about 53V
    how can I regulate the output to fixed 48V 2A?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    And yes, you will likely have chips and/or transistors. Regulators are pretty simple however, both the voltage and current regulators sections. The voltage is a bit high, but this isn't insurmounable. Bertus is right though, need specs.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Just a suggestion, don't start a new thread for an existing problem that was asked about on the old thread. It is very confusing. I answered the previous thread just before getting to this one.

    What you want may be a little harder, because we only have 5 Voltage between the input voltage and the output voltage. The situation is made worse by the fact that when you draw 2 amps the unregulated voltage will drop, most likely below 48V!

    Have you built the basic circuit yet? If so, then load it with 2A and see what you have in the way of voltage. I know this is a pain, but I don't think it will work, and building electronics and finding it doesn't work due to something basic as this is even more so a pain. Figure a 100W total. You could throw together an electronic load, many of the parts would work in both, such as power transistors and large heat sinks.

    Don't forget, you wanted two separate regulators (or two in one), a voltage AND a current regulator.
     
  6. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    In an attempt to reduce confusion, I have merged the threads.
     
  7. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Well you need to be a little more explicit in your requirement. For the current specification do you mean you wish the circuit to have a current limit such that it can't exceed 2 amps output and will automatically start to cut the output voltage to limit it to 2 amps max?

    Or do you wish to have a adjustable current limit from 0-2amps such that you can set where the supply will start to cut output voltage to keep the current at or under the set current limit?

    Or do you wish the supply to have a constant current mode where it can raise or lower the output current to maintain it at the adjusted setpoint value?

    Or do you mean that there should be a max fixed current limit at 2amps, like a fuse that blows a 2amps or more?

    You see the load determines how much current will be drawn from the supply so there are several methods that are used to 'control' current in a power supply.

    Having adjustable output voltage is rather straight forward although one has to specifiy if they wish to be able to independently adjust the output voltage and also have an adjustable max current limit at the same time.

    It is not possible to have an adjustable output voltage while also having a constant current adjustment at the same time with a fixed load, it would kind of piss off Mr. OHM and his law. ;)

    Lefty
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    There is a high voltage version of the LM317.
    Try to find the datasheet of a TL783.
    It is a regulator for 1.2 to 125 Volts.
    Its maximum current is 0.7 A, but with an external transistor it can be made more.

    Greetings,
    Bertus
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    I still doubt he'll get 48V at 2A, probably more like 46 from the unregulated side.

    Generally power supplies can set the constant current at a number, and then output a regulated voltage until the current regulator takes over, as the max current has been reached. This is how most HP (now Agilent Technologies) power supplies work.
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    If he gets 53V at the capacitor, then the AC secondary RMS voltage is only 38V. (38V x 1.414 = 53V)

    Therefore, one can only get a possible of 36V 2A from the regulator afterwards.
     
  11. Wendy

    Moderator

    Mar 24, 2008
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    Uhh, don't think so. Your math is off somewhere. The loading will drop the transformer voltage, and will result in the reduced voltage.

    I've built my share of power supplies, experience says it may go as low as 45, but it is somewhat dependent on how his transformer responds to loading. The heavier duty it is, the less it will drop.
     
  12. podgymax

    Thread Starter Member

    Oct 19, 2008
    25
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    Is it possible to use LM317 to have a 48V output? And my teacher called me to regulate this circuit. And I don't know how to regulate it? I hope all of you can give more suggestions so I can make the circuit work ...Thanks a lot
     
  13. wattotech

    New Member

    Feb 2, 2009
    1
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    Ref your requirement to control output current and voltage: You can purchase a series regulator chip etc. to regulate voltage for your max current demand. You could also design your own current limit by using say a very low value series resistor (0.5 Ohm) in the ground return to shut down the series regulator for current limit. Sorry if this is a bit hazy but it's really quite simple.
     
  14. podgymax

    Thread Starter Member

    Oct 19, 2008
    25
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    The most difficult problem is I don't not know which chip can meet my requirement...

    Can I use LM317 to set the output become 48V?
    The max. current of TL783 is 0.7A, can I change it to 2A?
    Is it possible to use 2 chip in the same time to meet the requirement?
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    You are ignoring the root and most difficult problem, that if the 52V drops much more than 2 volts you won't be able to use it. Is this a real world design, or a design project?

    There are ways of boosting a LM317 or L783 current output. The LM317 drops 3V just doing it's job, less than that it is starved for power. I have yet to check the specs out for sure, but I believe the LM317 stops around 35V, which is why the TL783 was brought in. Before we get into regulation design, how are you going to address the basic low voltage of the power supply though?
     
  16. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    Before we can offer more suggestions, its time you tell us what is the secondary AC voltage of the 220V transformer you are using.

    This is an important piece of information for circuit design.
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    Actually, include both the secondary AC voltage and the current rating. Both count.

    We could start throwing out regulator designs, but if the unregulated power supply won't feed the regulators power requirments, you're spinning your wheels. When I get a chance I may do so anyhow, but understand, every stage of regulation, both current and voltage, take some of the juice away from the power supply, usually in the form of voltage drop.
     
  18. eblc1388

    Senior Member

    Nov 28, 2008
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    I waited a bit to see if anyone spotted the use of 1N4008 for the 2 Amps output current requirement.

    Apparently no. :eek:
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    That's about as bad as using a capacitor rated for 50v in a circuit that's measuring 53v! :eek:
     
  20. Wendy

    Moderator

    Mar 24, 2008
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    I can't find the datasheet for 1N4008. A 1N4007 is a 1000V PIV 1A unit.

    The OP did state the cap was 100VDC, as a note on the bottom. Right now we're waiting for them to get back with us.
     
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