Using a transformer to reduce 230VAC to 24DVC and 5VDC1

[drkidd22]

I'm building a little project using a transformer from 230VAC. I have found the transformer (14A-10R-24 from Signal) and (DF10M) Bridge Rectifier so far.

-I will need 24VDC to run an axial ball bearing Fan that draws 70mA.
(Can I just take the voltage out of the DF10M to run the fan? or would it be more practical to use a regulator, like LM317?)

-Will also need 5VDC to run a few other little things.
(Will need step down regulator, maybe a BUCK)

So what I was thinking was use two LM317 in "series" to accomplish this.
the first one would regulate the 24VDC to drive the FAn, and the second one would take the regulated 24VDC from the first LM317 to reduce down to 5V.

Any suggestions would be appreciated.
Thanks.

 

[Diver300]

You could probably run the fan directly from the bridge rectifier. The voltage may be quite a bit bigger than 24 V, and will have loads of ripple, but fans are tolerant of poor power supplies.

A capacitor of about 2200 uF or more would reduce the ripple a lot. The voltage will also go up.

You could use a regulator to hold the voltage at 24 V if you want. You could also adjust it to alter the fan speed.

It depends on how much current you want as to what sort of regulator is appropriate for the 5V.

A zener regulator is simplest, but is hardly any worse than a linear regulator if the current at 5V is fixed. The current taken by a zener regulator is the same whatever the load.

A linear regulator is still quite simple, and the input current is about the same as the output current.

A buck regulator is much more efficient at large loads, but a lot more complicated.

 

[MikeMl]

Here is how I would do it. Connect the two windings in series. Note that the RMS value of the un-filtered waveform at "FAN" is about 24Vdc. Take the other output from the center-tap "CT".

Size the filter cap to the 5V load current. The minimum value that still meets the drop-out requirement for the LM7805 minimizes the power dissipation in the regulator. At 0.25A drawn from the 5V, with a 470uF filter cap, the dissipation in the regulator is still over 2.2W, so you will need to heatsink it...