High volt options for 7805 voltage regulator?

Discussion in 'General Electronics Chat' started by Mad Professor, Mar 1, 2012.

  1. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    Good day all.

    As per the title I am trying to find out what are my options to find a suitable drop it replament for a 7805 voltage regulator, that will work with a 48volt battery pack. and could see as high as 55v to 60v.

    Can you please advice?

    Thanks for your time.

    Best Regards.
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
    Check your datasheet. it isn't really a good idea to run the differential higher than the limits specified......................unless a massive heatsink were involved....tho' that might not make much difference.
  3. Ron H

    AAC Fanatic!

    Apr 14, 2005
    How much current will your regulator see? Power dissipation might be a problem, even if you do find something that will withstand the voltage.
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    The numbers that are of most importance here are the maximum input voltage, the minimum input voltage, and the maximum load current. With those yuo couls start to make some informed choices for a regulator.

    As this is a battery powered device a switching supply may be in order.

    The best 7805 I can find maxes out at a 35V max input. If you put a 25V zener in series with the 7805 it will only see a max in of 35V for 65V in, and still be good for 48V (48-25=23V). Obviously a 25V zener is a razor thin margin, so use a 35V device.

    As mentioned, check the power ratings.
  5. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    Thanks for your replys.

    Here are the required specs.

    Min Voltage: 30v.
    Max Voltage: 55v.
    Current: 50ma.

    Best Regards.
  6. Potato Pudding

    Well-Known Member

    Jun 11, 2010
    You really need to consider a Switching supply for this application, even if just as a first stage regulator.

    It will clear up all of the uncertainty from that range of input voltages.

    It will eliminate most of the wasted power and avoid the need for the large heatsink on a fully linear regulator that would resemble a space heater. (Well maybe not at only 50mA which will keep you around 2 watts.)

    It will allow you to isolate your output which might not be important.

    You can find many different ICs that will take care of the switching regulation. Just connect them up with the capacitors and coils and let them go to work.
  7. crutschow


    Mar 14, 2008
    An LM317HV is a high voltage version of the LM317 adjustable regulator that can tolerate up to 60V and can be adjusted to give 5V out with two resistors. For reliability margin you might want to add a 10V zener diode in series with the input of the regulator.
  8. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Just use an NPN transistor and Zener diode to "pre regulate" the voltage down to maybe 30V and feed that to the 7805.
  9. assembler_C

    New Member

    Mar 19, 2008
    I like Bountyhunter's idea... (NPN + Zener). This circuit will continue to work even with input voltages lower than the Zener's threshold (NPN satuated).

    Also, to aid, use a power resistor between the NPN's collector and input voltage to distribute the dissipated power between the NPN and the resistor.
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
    I like the idea, too, but if the zener isn't conducting, the transistor isn't conducting.
  11. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Sure it does, you have a resistor from the base of the NPN up to V+. You can also use an NPN darlington so you don't have to have much resistor current to feed it.
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Ok, I understand where you're coming from. I was thinking of a "power zener", which has the zener from collector to base, and a resistor from base to emitter. The "power zener" has its cathode on the collector and its anode on the emitter, and would be in series with the LM7805 input.
  13. highvoltpower

    New Member

    Apr 5, 2016
    7805 ICs not require extra component to provide regulated source of power but input voltage always higher than output voltage normally 2.5 volts. It require specs min volt 30v and max volt 55.
  14. ScottWang


    Aug 23, 2012
    I only can find the input voltage : 7.0V≦VI≦25V, do you have the links page or datasheet to match what your said?
  15. hp1729

    Well-Known Member

    Nov 23, 2015
    Something like the VB408 maybe. Up to 400 V in, programmable output like an LM317, 40 mA output.. There are others similar used in old CRT TVs to generate initial VCC.
    Or LR-8
    Last edited: Apr 5, 2016
    ScottWang likes this.
  16. Bordodynov

    Active Member

    May 20, 2015
    Sensacell likes this.
  17. dannyf

    Well-Known Member

    Sep 13, 2015
    What's key is the max output voltage.

    It is easy to deal with high input voltage, a pre regulator, particularly a tracking prr regulator references to the 7805s output, can do that. You only need a transistor, a resistor and a zener or less.

    Expanding the output voltage range is a little more complicated.
  18. wayneh


    Sep 9, 2010
    4 year old thread, guys.