dc voltage converter high amps - help

[1forgotten]

Hi. Could somebody point me in the right direction. Looking to build 12v dc drawing around 12 amps to around 5 volt dc converter. Needs to be efficent. I think they call it switch mode power supply.Any literature on subject/circuit diagrams or hints would be great. Thanks in advance

 

[Zephyr]

**broken link removed**

These?

This: Linear Technology - LTM4627 - 15A DC/DC

Looks interesting

 

[1forgotten]

dc/dc converter

Hi Thanks for info zepher. Is it possible to reduce voltage from 12v at 10 amps and reduced it to 5v with the current alot higher(30 amps) ? Can it be done.
Thanks

 

[Zephyr]

The best you'd get is 80% efficiency, and maybe 70% if you're unlucky. Using that, you can just replace the Switched-mode Supply with a transformer that's really, really, really inefficient and pump the numbers in.

VI = VI

 

[indulis]

The best you'd get is 80% efficiency, and maybe 70% if you're unlucky.

An efficiency of 80% for a buck converter at those power levels would be considered poor... low to mid 90's is about right.

 

[Zephyr]

The values from the datasheet will be far better than my guesstimate.

Basically, as long as the I/O voltage and amperes are within the limits, just do the math and work it out.

 

[1forgotten]

dc/dc converter

Hi Thanks to all replies. So a transformer is capable of doing say current doubling(or multiplying). So I can use a switch mode power supply to hold max current draw and then feed in to transformer. Is this transformer hand wound or can I use off the shelf item. If hand wound how do I work out 12volts down to 5 volts. Where can I find required info .Punch in numbers? How .Very new to this.Any reading to further knowledge would be great.
Thanks again

 

[Zephyr]

Transformers only work for AC supplies.

That switch mode power supply can drop your 12 volt DC supply to a 5 volts with decent efficiency.

Treat the switched mode power supply as a transformer. I've you've got 12 volts and 12 amps input, you can have 5 volts and 12*2/5 amps output. Ignoring inefficiencies.

 

[indulis]

Transformers only work for AC supplies.

No... transformers and coupled inductors (flyback transformers) are used in DC-DC converters all the time.


Reading this will help...

 

[ronv]

If you go all the way back to #3. The answer is no. You cannot get more power out than you put in so if you need 30 amps of +5 you need a bigger "bulk" supply to start with.

 

[Zephyr]

By transformers, I meant classical few loops on a wire transformers.

I tend to call DC-DC converters, but I understand where the misunderstanding may have come from.

 

[indulis]

Transformers used in DC-DC converters are no different than "regular" transformers... the core is a different material, it's a square wave and the frequency is a lot higher, but all the same "rules" apply.

 

[bountyhunter]

An efficiency of 80% for a buck converter at those power levels would be considered poor... low to mid 90's is about right.

Actually, low to mid 90's efficiency for a 5V @ 30A output buck converter would be outstanding and not that easy to do. It would require synchronous rectification with a lot of FETs in parallel

 

[bountyhunter]

If you go all the way back to #3. The answer is no. You cannot get more power out than you put in so if you need 30 amps of +5 you need a bigger "bulk" supply to start with.

CORRECT. And the design is 150W load power which is more than most simple "IC based" solutions are good for. When we built a supply in that range it would typically be an AC offline converter of some kind.

 

[indulis]

Actually, low to mid 90's efficiency for a 5V @ 30A output buck converter would be outstanding and not that easy to do. It would require synchronous rectification with a lot of FETs in parallel

I never suggested a "all-in-one" IC as a solution.

Some of the new offerings from TI are outstanding... I just replaced 4 powerpak secondary FET's in a current doubler (1.5V @ 30A) with 2, 3mm x 4mm (i believe that's the case size... don't have the data sheet at home) and got the same performance.

 

[bountyhunter]

I never suggested a "all-in-one" IC as a solution.

I never did either, but what I said stands: getting 90's per cent efficiency from a 5V/30A converter powered from 12V is actually quite difficult to do and will take a lot of silicon in parallel. Designing power supplies is what I did for a living. Do the math: with 150W of load power, 95% eff means you only have about 7.5W TOTAL POWER to give up in the rectifier FETs (top and bottom), FET drivers, inductors, and filter caps. At 30A, that's not easy to get.

 

[indulis]

Designing power supplies is what I did for a living.

As do I.
One of our POL offerings is a 2 phase buck wit 4 FET's total (12Vin, 5Vout @ 30A with 93% efficiency). I wouldn't call that really difficult or a lot of silicon in parallel (compared toVRM's). 12Vin, 5Vout @ 30A with 93% efficiency

 

[bountyhunter]

Interesting. Like to see the schematic and the specs for the FETs, inductor and output caps. If you are using only four FEts, they must have some serious silicon inside to get the ON resistance low enough. We also did some >25A designs and I remember we had to use the lowest ESR electrolytics commercially available (about ten in parallel) to keep the effective ESR low enough to minimize heating.

 

[indulis]

Sent you a PM

 

[bountyhunter]

I read the data sheet and it actually proves my point. The original poster was asking:

Looking to build....

The data sheet you supplied is for a ready made 1 MHz power converter which is clearly state of the art and does make 93% efficiency putting out 5V/30A, hence my original statement: that result is outstanding and I don't think any typical electronically oriented person would have a hope or prayer of matching it trying to build one themselves out of generally available parts.

The ready made converters always have high efficiency but are usually pretty pricey.