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Voltage regulators in series? — Parallax Forums

Voltage regulators in series?

ArchiverArchiver Posts: 46,084
edited 2000-07-16 22:23 in General Discussion
Hello all,
I've got a working radio control circuit for my electric
wheelchair platform. To step the voltage down from 24V to power my circuit
can use a 12V regulator (ie. 7812) and then a 5V regulator (ie.7805)? I
know the 7805 can handle 24V , but it gets pretty hot and I'm wondering if
I can have this dissipated by two devices...

Cheers, Duncan

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2000-07-16 05:39
    Duncan:

    No problem. Just be sure to use capacitors at each input/output to prevent
    oscillations.

    Ray McArthur

    > I've got a working radio control circuit for my electric
    > wheelchair platform. To step the voltage down from 24V to power my circuit
    > can use a 12V regulator (ie. 7812) and then a 5V regulator (ie.7805)? I
    > know the 7805 can handle 24V , but it gets pretty hot and I'm wondering if
    > I can have this dissipated by two devices...
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-16 09:54
    Hi,

    Another excellent choice is the LM2940CT (5V 1A LDO) regulator, made,
    amongst others, by National Semiconductor. It features extra protections
    that the 7805 doesn't have, and can handle up to 26V.

    Cheers,

    Mike

    >
    Mensaje original
    > De: rjmca [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=k4BRGBhCAYQ9yBlfrMriaVGhzaYMx7FOAnWaWAYDig5JvxQgIhJ-5wp6uNjOhxhle_Wp6pTB6mMMTYg]rjmca@w...[/url
    > Enviado el: domingo, 16 de julio de 2000 6:40
    > Para: basicstamps@egroups.com
    > Asunto: Re: [noparse][[/noparse]basicstamps] Voltage regulators in series?
    >
    >
    > Duncan:
    >
    > No problem. Just be sure to use capacitors at each input/output
    > to prevent
    > oscillations.
    >
    > Ray McArthur
    >
    > > I've got a working radio control circuit for my electric
    > > wheelchair platform. To step the voltage down from 24V to power
    > my circuit
    > > can use a 12V regulator (ie. 7812) and then a 5V regulator (ie.7805)? I
    > > know the 7805 can handle 24V , but it gets pretty hot and I'm
    > wondering if
    > > I can have this dissipated by two devices...
    >
    >
    >
    >
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-16 18:15
    At 10:54 AM 7/16/00 +0200, Ray wrote:
    > Duncan:
    >
    > No problem. Just be sure to use capacitors at each input/output
    > to prevent
    > oscillations.

    Thanks Ray and Miguel, I'll do that. I'm also going to heatsink them both
    right to the side of the case. I don't need the additional protection of
    the LM2940 as the control box circuitry (where I'm drawing power) is
    already well isolated from the two batteries.

    Duncan
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-16 22:23
    > Hello all,
    > I've got a working radio control circuit for my electric
    > wheelchair platform. To step the voltage down from 24V to power my
    > circuit can use a 12V regulator (ie. 7812) and then a 5V regulator
    > (ie.7805)?
    Yes this is one way, a better way would be one of National's
    switching regulators. These only require 2 caps and a coil and will
    not waste power as heat.
    > I know the 7805 can handle 24V , but it gets pretty hot and
    Some are spec'd up to 35V max in, but remember your have
    16.5V(24-5-2.5)*Iout worth of power to dissipate.
    > I'm wondering if I can have this dissipated by two devices...
    >
    > Cheers, Duncan
    >
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