Looking for a reference design for a DC-DC power converter.

D

Daniel Rudy

Guest
I'm looking for a reference design for a DC-DC power converter. The
goals of this little project of mine is to convert the power from a
24VDC source into a single fixed output voltage that ranges from 3VDC to
48VDC just by changing the transformer, diodes, and sense resistors.
Because the source on the 24V rail is from a battery, the input voltage
can vary widely depending on the battery's state of charge, so the
converter needs to have a minimum input voltage of 16V. Maximum output
power ranges between 5W and 50W depending on components. High efficency
(>80%) is a must because of the battery.

I *COULD* use a standard buck, boost, or flyback design, but I want a
break in the positive rail in case of component failure...as an added
margin of safety to the down-wire electronics. The input will also be
fused according to the power rating, with a SCR crowbar to protect the
load in case of over-voltage.

I plan on making a number of these devices with the same basic design
with variations of output power and voltage.

A few interesting numbers that I came up with when deciding transformer
ratios. Also are the resistor numbers for the voltage divider network
at a current of about 1mA and a 1.0 volt reference.

24v-8v 3:1 ratio at 5v input is 15v; Rsense 4K/1K
24v-6v 4:1 ratio at 3v input is 12v. Rsense 2K/1K
24v-72v 1:3 ratio at 48v input is 16v. Rsense 47K/1K

I have a conceptual drawing here:

http://home.pacbell.net/dcrudy/dc-dc_converter__concept_1_.jpg


Any ideas or suggestions?

Thanks.

--
Daniel Rudy

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At about the time of 12/3/2004 1:52 AM, GPG stated the following:

Daniel Rudy <5n6o7.8d9c0r1u2d3y4.5s6p7a8m9@0e1m2a3i4l5.6p7a8c9b0e1l2l3.4i5n6v7a8l9i0d1.2n3e4t5> wrote in message news:<Ccurd.27246$zx1.14031@newssvr13.news.prodigy.com>...

At about the time of 12/1/2004 2:37 PM, John Popelish stated the following:


Since the negative rail is common to input and output, why not use a
tapped coil as both primary and secondary and use only two diodes for
the output? Both these changes should potentially improve the
efficiency.


The two diode full wave rectifier is a better idea than the bridge
circuit that I considered using. I'm sure that an autotransformer would
work, but I need a break in the positive rail in case one of the
switching transistors short out. Looks like more pSpice work needs to
be done.

Thanks.

SEPIC?
Not quite, but it will be hard to get a 24v battery down to 12v or even
5 volts without damaging it to made a SEPIC design feasible.

--
Daniel Rudy

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Remove all numbers, then remove invalid, email, no, and spam to reply.
 

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