multiple output flyback converter

[tech_savvy]

I wanted to design flyback converter.
How to determine transformer specifications...IC to be used...etc.
Vpri=5 V,Vsec=5V(8 secondaries),Isec=200mA each.

 

[John Larkin]

On 3 Jan 2005 11:06:26 -0800, "tech_savvy" <sanjay_td@rediffmail.com>
wrote:

I wanted to design flyback converter.
How to determine transformer specifications...IC to be used...etc.
Vpri=5 V,Vsec=5V(8 secondaries),Isec=200mA each.

You might as well ask how to build your own helicopter.

John

 

[Leon Heller]

"tech_savvy" <sanjay_td@rediffmail.com> wrote in message
news:1104779186.005487.9440@c13g2000cwb.googlegroups.com...

I wanted to design flyback converter.
How to determine transformer specifications...IC to be used...etc.
Vpri=5 V,Vsec=5V(8 secondaries),Isec=200mA each.

http://schmidt-walter.fbe.fh-darmstadt.de/

Leon

 

[Ken Smith]

In article <1104779186.005487.9440@c13g2000cwb.googlegroups.com>,
tech_savvy <sanjay_td@rediffmail.com> wrote:

I wanted to design flyback converter.
How to determine transformer specifications...IC to be used...etc.
Vpri=5 V,Vsec=5V(8 secondaries),Isec=200mA each.

5V * 200mA * 8 = 8W this is quite posible with many chips

The input side current will be a few amps, lets say 5. Look for a chip
that can handle that much.

Pretend that you have just one secondary with 1.6A of load and follow any
of the many app-notes for doing that design.

You need a low leakage inductance in the transformer. This should work
for you:

Your inductor will be a 1:1 so take 16 wires, form a wire rope, wind the
inductor and then use 8 in parallel as the primary. Try to spread the
primary windings evenly around in the wire rope and the 8 others as the
secondary.
--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <GFoCd.23143$rL3.9092@trnddc03>,
Harry Dellamano <harryd@tdsystems.org> wrote:
[...]

Hey Ken,
Since it is a 1:1 Flyback, might as well add the cap from drain to output
diode anode and gets the benefits of a SEPIC. Leakage inductance causes no
ringing, cleaner switching. Eight outputs, eight coupling caps, unless he
wants isolation which was not stated.

I take 8 outputs to imply 8 isolated outputs. If they are not isolated,
there is little reason to make 8 instead of one. For that matter, his
input and output voltages were equal so he could use 8 wires if isolation
was not needed. The 8 wires solution produces a lot less ringing than
even the SEPIC design would.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <pan.2005.01.03.22.44.00.41242@example.net>,
Rich Grise <richgrise@example.net> wrote:
[...]

I think that if they guy thinks flyback is appropriate for 1:1, he needs
to re-take the course.

Flyback designs work just fine at a 1:1 ratio. With a 1:1 transformer,
the switching waveform has equal transistor and diode conduction times.

It is about the only way that one inductive element can give you many
semi-regulated outputs. Current-fed, psudo-resonant and true resonant
designs generally need two inductors. Voltage fed forward converters need
N inductors for N outputs.
--
--
kensmith@rahul.net forging knowledge