12V TO 12V SMPS circuit topology choices - diyAudio
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Old 10th November 2014, 01:56 AM   #1
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Question 12V TO 12V SMPS circuit topology choices

I'm in the process of beginning a build on a 12V to 12V SMPS to regulate a 12V Lead-Acid battery to a steady ~12V for devices that require a non-fluctuating 12V supply but powered from a 12V battery while charging (14.4V) or discharging (10-12.6V)

Not sure which topology will be the best for a DIY project, I'm looking for efficiency, ease of parts selection, and most important.....RELIABILITY

TO make dissipation simple, I'm building the project on a large heatsink as the chassis, so no need for a fan.

I have lots of salvaged MBR3045PT (30A,45V) and also MBR4045PT Schottky diodes, and several varied MOSFETS rated 50-75A and also some 30A,600V Rectifiers with a higher voltage drop (MUR3060PT)

Preferred 10V-15V input range or better, 12.2V regulated output goal on all loads. 50-70A output.

1. Should I go a PUSH-PULL into a ferrite transformer driven by MOSFETS, winding it for higher than 12V on the secondary, rectified by schottky diodes, then PWM the output voltage down using an output inductor........

2. Would a BUCK-BOOST with just a single inductor be better instead, using MOSFETS for switching.

My issues if not being sure what to do are because I assume I may need pretty high voltage schottky diodes for a push pull, but higher voltage parts drop more volts................However, a BUCK-BOOST loses power on two voltage drops, but uses less space and doesn't require a transformer.

Decisions, decisions.........
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Old 13th November 2014, 05:00 PM   #2
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12.2*70 = 854W on secondary side.
854*80% = 1100W on primary.

I would go fullbridge.
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Old 14th November 2014, 10:30 PM   #3
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by palstanturhin View Post
12.2*70 = 854W on secondary side.
854*80% = 1100W on primary.

I would go fullbridge.
I would get a BIG battery.

Just curious, what kind of circuit demands such precision in its power source?

How was it used before?

What PSU gave it
Quote:
non-fluctuating 12V
Is it really that critical?
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Old 25th December 2014, 10:27 PM   #4
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Quote:
Originally Posted by JMFahey View Post
I would get a BIG battery.

Just curious, what kind of circuit demands such precision in its power source?
How was it used before?
What PSU gave it
Is it really that critical?
Sorry I didn't reply back, life circumstances kept me offline , and my thread got buried in the midst............

Anyway......Yes, the 12V is very critical. High-Power-Computer use.....Even though ATX spec allows +/- 10% in reality, (10.8-13.2V) stability will be an issue, so I want much less than 5% fluctuation, or nearly none. This will also be used to power other digital 12V devices as well that need true regulated 12V, hence the high output rating as a run-all PSU.

Also the agenda is cleaner, better power than the regular Mains-Powered Computer PSU, with ease of repair and customization, being a DIY design, and I'll independently build the other 5V and 3.3V rails with their own buck converters.

My Batteries in my vehicle are TWO 115AH Deep-Cycle Marine Batteries, batteries are no issue, and I run a 1500W Power Inverter effortlessly. Using a direct 12V supply would net MUCH more efficiency than using the 120V power inverter to power the computer.
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Old 26th December 2014, 04:40 AM   #5
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Do you have multiple loads being powered from regulated 12V? Do you know the max current ratings of all those loads?

Do any of the 12V regulated loads have a substantial periodic load current, or are the loads static? Similarly, are there other loads on the battery that have substantial periodic load current (eg. an inverter)?

How were you going to avoid flattening the battery?
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Old 26th December 2014, 05:40 AM   #6
DUG is offline DUG  Canada
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Take a look at synchronous rectification...used to reduce rectifier losses...significantly.

Also take a look at multi-phase controllers.
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Old 29th December 2014, 12:36 AM   #7
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Powerstream has something similar to what I'm about to be building, just wish I could find one of their schematics to base a design off of...........

DC/DC DC input mini-redundant industrial ATX PC power supplies 12VDC input, 400 watts with hot swap capability for solar powered server farms
12V Input PC ATX computer Power Supplies, 12VDC Input, car computer power supply, 12 volt.

The idea, is reliable backup power so computer never shuts off similar to how a laptop uses the battery, but with a desktop.

I'm stuck between using buck-boost, or just a push-pull with a huge ferrite transformer and diode rectifiers. It appears with the wide voltage range of the powerstream supplies, that they use some type of boost topology for sure.
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Old 29th December 2014, 01:28 AM   #8
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You probably want at least real B+ isolation from the regulated bus, so a tranformer is necessary. Push pull would be the right topology there. Since this is a serious project in terms of power and complexity, you may as well go for fairly high efficiency as well, so choose a moderate switching frequency, big cores, and maybe think twice about using parts bin components. Ideally all your loads not served from USB or something would be isolated as well. Are you sure a collection of Powerstream or similar products isn't just what you need? If you're not looking for exceptional efficiency or something, whacking this up yourself probably wont be the "cheaper" way out, depending on how you value time.
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Old 30th December 2014, 06:18 PM   #9
infinia is offline infinia  United States
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hmm 2 deep cycle batteries in a car. how are you charging them?
what loads do you have and how long do you need to run them without the charger?
seems like RV forum would be a better place, they do this stuff all the time and will have practical solutions.

if it's just some simple mobile computing tasks, look into newer laptops or NUCs. then investigate mobile DC/DC 40-100W chargers. new Intel Baytrail should keep IPC ~ 7-10W and lower costs as well.

if it was for off grid type cabins with solar I would consider running multiple batts at 24V or higher, then usually you'll always have the need to run an inverter anyway.

EDIT always reduce the loads 1st! then hunt for eff. vs cost of new hardware.
if yer running older ATX hardware on mobile platforms then you have to re- examine that.
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Last edited by infinia; 30th December 2014 at 06:47 PM.
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Old 30th December 2014, 08:22 PM   #10
infinia is offline infinia  United States
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Quote:
Would a BUCK-BOOST with just a single inductor be better instead, using MOSFETS for switching
you need Boost-Buck
Simplest topology is a single MOSFET, two inductors and rectifiers. As used in one MPPT DC/DC controller that I know of. expensive stuff ! you don't really need galvanic isolation but full blown transformer gives more grounding choices should noise issues raise their head.
also DC range doesn't need to go below a flat battery ( really don't want run a SLA battery lower than 50% many times!) and reasonable drop. so 13.6 VDC nominal and range of 12.0-15.5 VDC would be better spec.
off grid stuff > if you used two batteries in series, then much simpler single Buck topology can be used.
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