Hello.

I´m build a linear power supply 13.8V / 60A for a transceiver radio.
The common approach will be use common regulators like 7812 or LM317 and a lot of power driver transistors, a big heat sink, big capacitors and of course a big transformer.

I´m just think about if is there some advantage changing ONLY the common regulator for a switched mode design using the same large transformer and same large capacitors.

At this link http://focus.tij.co.jp/jp/lit/an/slva001d/slva001d.pdf on page 27 there´s a circuit that explain exactly what I´m trying to do. Of course, the driver transistor must be replaced for a compatible project amperage (60A).

Is there some advantage doing this? Less power transistors maybe, better regulation...

Thanks.

Hi there,

It sounds like you are asking about using a switch mode power scheme rather
than a linear.
The advantage of a switch mode power supply is efficiency, but only when
there is a certain input output voltage differential, otherwise a linear may be
just as efficient.
Most apps for switching power supplies however do have large input output
differential and so are well suited for the switching type supply.
If you have very large input output differential then a switcher is definitely
a good idea over the linear because a huge savings in power will result.

You should also use a switcher when you have a wide variation in input voltage.
The problem with the linear is that at high line there will be very low efficiency.
The switcher wont have this problem.

You do have to realize that switchers are a bit more complex to build than
regular linears, but it sounds like your app could benefit from a switcher so
perhaps this would be a good idea. I say this because even smaller power supplies
that are linear require fairly large heat sinks, while switchers will always have
smaller ones which means less space too.

Since it is quite likely that you will be using a switcher, perhaps you should go
after the MOSFET transistor type design. The MOSFETs have less loss overall
as compared to bipolar when they are driven correctly, and that's always a
good idea.

60A for a radio? I would have thought its a typo but you wrote it twice

Thanks for first replies.

I don´t know if I can explain exactly what I´m trying to do... After all living in south Brazil, English is not my natural language.

Sceadwian: Yes I´m a ham . I don´t really need 60A, I need 45A but until I now in this hobby a good amount of extra feeding power can solve a lot of problems (ripple, overheating...).

Well...

Doing this project using a typical linear approach we have:

A) A transformer from 220V AC to something like 25V/60A AC.
B) A rectifier to convert AC to DC.
C) Two huge filtering capacitors 2 x 60.000 uF.
D) A regulation stage using common ICs like LM78XX driving lots of power transistors.

What I´m asking is... Using all the same for A, B and C, there some advantage changing only part D to a switched regulation (13.8V) approach?
Can this give me a better regulation? Maybe less waste in heating energy. Maybe less power transistors are needed... I don´t know

If yes, I ´m thinking to use the circuit in page 27 http://focus.tij.co.jp/jp/lit/an/slva001d/slva001d.pdf and change only the power driver transistors and the 140uH inductor.

Thanks all.

Hi again,


If you are considering using a 25v winding to put out 14 volts, well
that's quite a waste of power. 14 times 25 is 630 watts out,
but with 25v in that's 1125 watts input meaning the regulator is
roughly 50 percent efficient (truely bad).

A switcher can give you 80 percent easy these days. With MOSFETs
even higher.

Contrary to the older designs, switchers can be built to put out very
very little ripple with the addition of a secondary filter stage. This
is a relatively new concept even though i am sure it has been known
for years. The secondary filter stage however is kept out of the
feedback loop for good stability.

Switchers are much harder to build and design however, and im not
sure how complex you want your power supply to be.

If you do go with a linear, do a few simulations so you can reduce
the transformers output voltage to a lower level and reduce wasted
power consumption.