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Putting the 5V and 3.3V regulator in parallel — Parallax Forums

Putting the 5V and 3.3V regulator in parallel

edlikestoboogieedlikestoboogie Posts: 71
edited 2010-05-04 09:18 in Propeller 1
I always wondered why the parallax propeller reference schematics and protoboard schematics have the voltage regulators in series from 5v to 3.3v? My application has some analog circuitry (12 op amps) all running off the 5v regulator, and a wiznet W5100 ethernet and propeller running of the 3.3v regulator. Both regulators get a bit hot. Will running the voltage regulators in parallel help? and what are the negatives for this? and why are all the reference designs using borth regulators in series?

Comments

  • Peter JakackiPeter Jakacki Posts: 10,193
    edited 2010-05-04 05:15
    "Independently" rather than "in parallel" would be more accurate, we would hardly want them in parallel.

    The series or independent configuration depends upon the input voltage, the current that is drawn from both rails, and the type of regulators used. If most of your current went to the 3.3V rail and the 5V only ran a few light loads then you might put these in series especially if the input voltage was a bit high. But if the 5V current drain would already make the regulator run hot then you would not do it. On the demo board the 5V is primarily used for PS/2 and the load on the 3.3V is relatively light so considering that the input comes from supply that could be up around 9V it makes sense to put them in series so the 3.3V regulator can run cooler otherwise it could get quite hot at over 1/2W and this way the dissipation is shared a bit.

    It is very rare for me to use linear regulators to 5V as I like to switch regulate to 5V and then use tiny LDO regulators as required for the 3.3V rail. The switch-mode regulator is very efficient and can handle much higher supply voltages at higher currents without raising too much of a sweat. So this combo is always a series configuration.

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    *Peter*
  • Toby SeckshundToby Seckshund Posts: 2,027
    edited 2010-05-04 09:18
    Some 3.3V regs have a very resticted input voltage, so check the data sheets.
    I have done it both ways, without any problems, chaining them can be a good way of sharing out the heat load. But if the 5V rail is liable to be hostile then separate would be best. I only throw 9V at them, either a SMPSU or a pair of Li-ions.

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    Style and grace : Nil point
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