Power supply problems

[wiles1987]

Im currently in the design process of a 240vac to 0-24vdc adjustable power supply with 0-3.3amps adjustable current

i have a 240vac to 24vac transformer wired in series with output of 26.8-27.0vac that feeds a single full wave bridge rectifier that outputs 24.4vdc this is where the problem comes. i need it regulated but with vf of bridge rectifier being 2.4-2.6v and the average voltage drop out of 3-5amp regulators being 1.2 - 1.4 volts is the only option buying a 30vac transformer or is there another way around this? as i need top voltage of 24vdc

 

[Comcokid]

Diode drop and extra voltage for minimum regulation requirements are part of what needs to be considered in a linear supply. Another issue is ripple voltage minimums on your filter capacitors at full load and low AC line voltage. Sometimes there is a little extra room between the transformer core and bobbin and you can add a few wire turns connected the secondary to get the few extra volts you need. You could also add a 240-to-6.3VAC transformer. Otherwise, you need an new transformer. Other techniques like voltage-doubler circuits are impractical at your current. There are some newer ICs from companies like Linear Technology that will drive MOSFETS to create "ideal" diodes at 50/60 Hz which could get rid of your diode-bridge drops but this adds complexity and cost.

 

[IRstuff]

Why does it have to be linear? A step-up would seem to be an obvious option.

TTFN
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[VEBill]

Here is an example of a voltage boost module as hinted above. This particular example doesn't exactly meet your current spec, but there are many variations of the same theme available.

You'd probably follow it with additional circuitry to provide the variable voltage and current you want.

These functions could all be integrated into one design if you're ambitious.

Or you could just order an off-the-shelf adjustable PS if you're not...

 

[Noway2]

240vac to 0-24vdc adjustable power supply with 0-3.3amps adjustable current

Sounds pretty standard with respect to input (look for universal input) and output. I agree with VE1BLL in that you could probably purchase an off the shelf switch mode supply for less than you can make it.

 

[wiles1987]

ok thanks everyone it mainly due to curiosity and having to make everything from scratch so i understand the smallest part of a design that stops me buying off the shelf ps but i am going to go ahead and try it without any additioonal parts and then with each option and see benefits.
is there anyway i can cross over between parallel and series wiring on transformer to utilize some part of the transformer not being used already? as i understand each side has 6 pins and all i use is 4? if not what are these misc. pins for?

 

[VEBill]

We can't see your transformer from here. You'll have to provide a link to a data sheet, or a part number, or maybe a series of photos. Then maybe we can figure out the other connection points.

 

[IRstuff]

Assuming that your description is correct, then the "extra" pins are probably connected to center taps, i.e, a point on the transformer coil that's halfway between the extreme ends of the coil, which provides access to 1/2 of the voltage output.

TTFN
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[wiles1987]

i gathered as much just wishful thinking thanks all the same