More Current From Regulators

Discussion in 'General Electronics Chat' started by Overclocked2300, May 22, 2005.

  1. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0
    If I hooked Up Voltage Regulators in Parallel, would I get more current?

    The regulators I am using are LM338K, TO3 Package. They supply 5 to 8 amps each.

    I know there are circuits out there using transistors, and I still have the circuit (and transistor) around somewhere. Thing is I Dont want to use that. I want to use what I have instock. The transistor is BDW94C. It is able to pass a Max Of 12 Amps. But I think it would be easier to use regulators in parallel since I have TO3 heatsinks lying around.

    Ok Heres what Im building: A TEC Power Supply. 0-12 Volts @14 Amps. Its Just to experiment with TEC's. The TEC's I will be using are DT6-6 From BGmicro.

    1) Would I be Able to Get more Current if the regulators are in parallel?
    2) For TEC's How do I figure out how big of a heatsink I would need? Wouldnt I treat them as if I were solving for Semiconductors?
    3) And for the Powersupply How big of a Cap would I need? I assume atleast 10,000uf.(and sorry dont wanna use a cap multiplier)
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Yes, running regulators in parallel will let you pass more current. But they don't play well together, and one will hog current because it will pass a lower voltage and try to source the load and sink the other regualtor and get real hot. National should have an LM338 datasheet that shows how to operate two or more in parallel.

    Take the voltage dropped across the regulator - the difference between what's on the filter and the load - and multiply it by the load current. The figure is the wattage being dissipated by the regulators. One rule of thumb - if they are too hot to hold a finger on, they are about to fail.

    10,000 mikes may be enough filter. Check the AC voltage across the filter under load. If you see more than 2 VAC, you need more filter caps.
     
  3. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1

    hi

    here's the datasheet of the LM338 and the circuit diagram of 3 LM338 in parallel
     
  4. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0
    oor wait...what if I had the regulators in parallel, but all the regulators going to a seperate load.

    That would work better right?
     
  5. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1

    hi

    it's alright as long as you don't exceed the current rating capability of the system. with three in parallel you would have a maximum capability of 15A. drawing 15A would drive your regs very hot inspite of the heat sink. for safe and longer life usage draw only a maximum of 75% - 80% of the rated capability.
     
  6. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0

    yea i wont be using the full 14 Amps. At max i'll be using 11 Amps

    EDIT: Should I Use those insulator things for mounting them on heatsinks? The case happenes to be the output. If I do use them, Wont it effect the transfer of heat?

    And what Material should I use? I have this stuff called Silicone Heat Transfer Compound..would that work well? It says its for Diodes and transistors.
     
  7. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    "I have this stuff called Silicone Heat Transfer Compound..would that work well? It says its for Diodes and transistors."

    use it and spread it evenly. likewise use the insolators. :D
     
  8. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0

    What are they for any way? Wont they prohibit heat transfer?

    EDIT: Just thought of something..but what would happen if I were to put a clock on the ADJ pin of the regulator? Wouldnt I have a switching Regulator? And if so, i could also incorportate a feed back system using comprartors that have a reference voltage and adjust the freq of the signal accordingly..if appling a clock signal to the ADJ pin does that of course.
     
  9. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,583
    725
    Kind of reinventing the wheel, and perhaps, a slow one.

    Perhaps.
     
  10. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    that silicon grease will facilitate heat transfer so you will have a cooler device

    you idea of pulsing the adj pin will work if we tweak the internal guts of the regulator. :p :D :lol:
     
  11. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0

    Ill just open the thing up and move a couple resistors and bistors around. Maybe if I move the flux capacitor and the flux diode in series with the bobculator inductor it might work..

    lol :p
     
  12. Overclocked2300

    Thread Starter Senior Member

    Apr 24, 2005
    124
    0
    Then how come the 78xx series shows that you could use it as a switching regulator?

    EDIT: we are talking about the mica insulators correct?The little clear things the shape of the case.
     
  13. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    mica or polyrubber will do :p
     
Loading...