🚀 go-pugleaf

On Jun 9, 5:42 am, F Murtz <hagg...@hotmail.com> wrote:
> I would like to make an adjustable power supply using a transformer with
> a 24v 5a single wound secondary I would like the voltage to be
> adjustable from lowest to highest possible given transformer I would
> like to have regulated current
>
> There is another possibility I also have a larger transformer with two
> 32v 4.7a secondaries If anyone has a schematic for an adjustable power
> supply with adjustable current regulation making the most of the
> transformer specs I would be eternally grateful


How much current do you want?

Lets just assume you make DC from the AC and then regulate down.

Doing a couple of figures for making 4A into lets say zero volts:

24V * sqrt(2) = 34V

34V * 4A = 136W

The the regulator circuit needs to get rid of 136W.

To do this, you need something like 10 TO-220 packages transistors
screwed down to a quite large chunk of fins.

If you have enough fin area, about 5 to 7 TIP-35 or TIP-36 transistors
would work for you.

Another question is how fast the current limiting or regulation needs
to act.  A lot of very practical designs can make a large spike of
current when suddenly shorted.  The power supply will easily survive
this but if the short was you connecting it to a diode, the diode may
be damaged.

Do you need instant (or nearly so) action on the current limiting?

Take a look at the LT3080:
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1040,C1055,P38503

Notice how it lets you set the output voltage all the way down to
zero.  This sort of design is a good place to start your thinking.

You can also think of the circuit as just a non-inverting op-amp
amplifying the output of the pot you use to set the voltage.  This is
another good direction to go.