how to voltage regulate


2008-03-08 2:11 pm
hi, i want to regulate voltage for my amp. its require _,+,Gnd 36volt dc. i want to step down from 56volt to 36volt with +,- and gnd.

is there any ic or transistor for it or easy way to do it? i need output should be 5 amp. because my transformer is 6amp 56volt dc out.

thank you.
Let me make sure I understand--you have 56V available and you want 36V. You expect to be using 5A. Your transformer is rated for 6A. Is that correct?
A few random things:
--Continuously using 5 out of 6A from a transformer will cause it to overheat. If you only expect to use 5A on peaks, that might be more feasible.
--Dropping 20V x 5A will require 100W of dissipation. There's no chip regulator that can take that kind of punishment. There are various ways that you can slave power transistors off of a chip regulator so that they take the brunt of the punishment, or you can build a discrete regulator. No matter how you look at it, dissipating 100W of heat is a non-trivial task.
--One way to knock off some volts is to use an inductor at the beginning of the power supply filter, but the amount of voltage it will drop will depend on the amount of current drawn.
I had a couple of other points, but it's taken me three hours to write this much down (!) because we're in the middle of a mild crisis here at work. At this time I need to devote all my remaining brain cells to the problem.

Provided that you are drawing a sufficient amount of quiescent current (not sure if you are running at 5A continuously ?), a choke input (LC) power supply would give you that kind of voltage reduction. As a side effect you would get near 100 % power factor correction (if the choke value is beyond the critical inductance) and therefore you might get away with using your current power transformer. The chokes would not be cheap though.

P.S. I have seen commercial chokes with dual windings that can be used either in parallel or in series connection to get different inductance values. If you run them in differential mode one choke for a bipolar power supply might be enough.
Are the chokes more expensive than the correct transformer?

I would say it is in the same ball park but you may be lucky and find cheaper parts. As always, it depends on the solution you choose and where you get the parts!

In this particular case you would need a new transformer of 700VA and more would be better. RS components have a 800VA toroid EUR 85 (my local price). With the current transformer you need to drop a high voltage so you need chokes of say 10mH or above at low DCR. Just as an example, a suitable pair of Corobar coils from Intertechnik would cost ca. 75 EUR here in Germany. For commercial PFC chokes I would try a number of my local suppliers and get a quote - I ordered chokes in the past but have no current prices.

P.S. Here is an example of commercial chokes with dual windings. This is a local supplier, all pages are in German, but there should be other suppliers elsewhere. No idea how much they would cost: