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

D

Daniel Rudy

Jan 1, 1970
0
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.
 
R

Rene Tschaggelar

Jan 1, 1970
0
Well, the manufacturers of these switch mode controller
tend to have a bunch of application notes together with
the datasheets.

Rene
 
G

Genome

Jan 1, 1970
0
"Daniel Rudy"
<5n6o7.8d9c0r1u2d3y4.5s6p7a8m9@0e1m2a3i4l5.6p7a8c9b0e1l2l3.4i5n6v7a8l9i0d1.2
n3e4t5> wrote in message
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

Email address has been encoded to reduce spam.
Remove all numbers, then remove invalid, email, no, and spam to reply.

Email address has been de-encoded for added spam

[email protected]

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J

John Popelish

Jan 1, 1970
0
Daniel said:
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?

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.
 
D

Daniel Rudy

Jan 1, 1970
0
At about the time of 12/1/2004 9:53 AM, Genome stated the following:
Email address has been de-encoded for added spam

[email protected]

Mortgage
Loan
Credit
Card
Insurance
Life
Equity
Pension
Car
House
Pet
Holiday
Villa
Visa
Home
Retirement
Pension
Disney
Loan
Education
Investment
Stock
Trade
Portfolio
CFD
Spread
Bet
Betting
Low
APR
Terms
Best
Offer
Porn
XXX

DNA

What is your problem?
 
D

Daniel Rudy

Jan 1, 1970
0
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.
 
J

John Popelish

Jan 1, 1970
0
Daniel said:
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.

As long as the center of the auto transformer is connected to the
negative rail, the rectifiers cannot put out a positive rail voltage
from a blown fet. The inductor just saturates and blows the input
fuse.
 
D

Daniel Rudy

Jan 1, 1970
0
At about the time of 12/1/2004 5:55 PM, John Popelish stated the following:
Daniel Rudy wrote:




As long as the center of the auto transformer is connected to the
negative rail, the rectifiers cannot put out a positive rail voltage
from a blown fet. The inductor just saturates and blows the input
fuse.

I like that idea, and it looks good on paper when I draw it out. I have
seen designs like this up to about 100 watts or so. I just thought of
something. The capacitor that sits across the coil primary, I wonder
what would happen if I replaced that with a diode, or even a syncronized
MOSFET...

Thanks for your help.
 
J

John Popelish

Jan 1, 1970
0
Daniel said:
At about the time of 12/1/2004 5:55 PM, John Popelish stated the following:


I like that idea, and it looks good on paper when I draw it out. I have
seen designs like this up to about 100 watts or so. I just thought of
something. The capacitor that sits across the coil primary, I wonder
what would happen if I replaced that with a diode, or even a syncronized
MOSFET...

I can't picture the capacitor you mention. Are you talking about a
resonant design, or some sort of snubber capacitor?
 
G

Genome

Jan 1, 1970
0
"Daniel Rudy"
<5n6o7.8d9c0r1u2d3y4.5s6p7a8m9@0e1m2a3i4l5.6p7a8c9b0e1l2l3.4i5n6v7a8l9i0d1.2
n3e4t5> wrote in message
At about the time of 12/1/2004 9:53 AM, Genome stated the following:


What is your problem?

--
Daniel Rudy

Email address has been encoded to reduce spam.
Remove all numbers, then remove invalid, email, no, and spam to reply.

I'm a sad lonely bastard and I think you are a troll.

DNA

[email protected]

Email address is not encoded, but it's a throwaway.

Sign up for yours now.

http://www.yahoo.com

Yes! I wish to subscribe to your FREE E-zine.
I only buy viagra in bulk.
 
B

Boris Mohar

Jan 1, 1970
0
Email address has been de-encoded for added spam
In the bar at the top of the Empire State Building there are two men sitting
together. Guy #1 says to Guy #2, "I bet you that I can jump out of that
window over there and come up those stairs in just 2 seconds."

Guy #2 doesn't believe him so he says, "I'd like to see you try!" Then Guy #1
jumps out the window and appears at the top of the stairs in just under 2
seconds. Guy #2 is flabbergasted.

Guy #1 then bets that he can jump out the window and come up the stairs with
a beautiful woman in his arms. Guy #2 says, "That's impossible!" .

Guy #1 says, "You just watch." He does it and Guy #2 is really impressed but
thinks: "Hey, this guy is really drunk so if he can do it, so can I."

He decides to try to show up this other guy and he jumps out the window. He
splats himself all over the sidewalk.

Guy #1 watches him plummet to his messy death, laughs to himself at his own
triumph, and walks back to the bar and resumes his seat. The bartender says,
"Superman, you're really a jerk when you're drunk!"
 
G

GPG

Jan 1, 1970
0
Daniel Rudy said:
At about the time of 12/1/2004 2:37 PM, John Popelish stated the following:


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?
 
D

Daniel Rudy

Jan 1, 1970
0
At about the time of 12/2/2004 4:16 PM, Genome stated the following:
"Daniel Rudy"

I'm a sad lonely bastard and I think you are a troll.

Whatever you say about your life is for you to say.

As for me being a troll, how can asking a legitimate, on-topic question
in here, complete with a conceptual design, using my real name, be a troll?
 
D

Daniel Rudy

Jan 1, 1970
0
At about the time of 12/3/2004 1:52 AM, GPG stated the following:

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.
 
D

Daniel Rudy

Jan 1, 1970
0
At about the time of 12/1/2004 6:56 PM, John Popelish stated the following:
I can't picture the capacitor you mention. Are you talking about a
resonant design, or some sort of snubber capacitor?

Resonant.

I'll try and draw it...

------------\_/--------+-------)||(--------|>|-----------
| | )||(
PWM | )||(
- )||(
- )||(
| )||(
GND +-)||(-+
|---+--|
|
GND
 
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