DC/DC Power Supply Help

Hi all, I am in need of a DC-DC Power supply schematic that outputs between 12.7 and 14.5VDC and an input that could be anywhere from 12VDC up to 36VDC. The crutch is this-I need it to put out at around 80 amps. Realistically, the supply will be running 80% of the time under 20amps, but there are occassions where it will need to draw upwards of 60amps continuous.

I found this schematic (attached), but it looks like it is only about 50% efficient assuming a 24v in and 12v out. Am I correct on this or should it be higher?

Does anyone know of any simple circuits for a supply that will work for me, or know of one that I can simply modify to get the power output needed? Any thoughts would be appreciated. To give you an idea of my experience level, I was an EE major for 2 years but never completed my schooling.

I don't need anything fancy, and really am trying to keep it as simple as possible and get 80% efficiency or better. Is this possible with BJT transistors, or will I need to use a switching supply or MOSFET design?

Thanks !

this is a link to the schematic I referenced: http://www.zen22142.zen.co.uk/Circuits/Power/3730.htm

 

Yes the circuit technically is an AC to DC power supply, but I simply used a 24V battery pack instead of an AC transformer. I will be a bit more clear for you as well. As far as input, I do not need it to accept 12VDC to 36VDC, I mean I can input 12, 24 or 36VDC since my power source is 12V batteries....

What I am powering is actually my Prius' 12V system. The system is currently powered by an internal DC/DC Converter within the prius that converts the main 1.3kw battery (220V nom) into 13.3 - 14.1 VDC. It has a rated output of 100A, however the system will only ever draw 80 amps max on rare occassions. Typically the load is about 15-30 amps.

I mean, I was even thinking of trying to find a simple circuit that can take my 24V battery setup and just output ~13-14V. Can I do something like this without transistors? Just an LM317 to regulate the voltage, and a capacitor to smooth it out?

Your advice is GREATLY appreciated!

 

Do you have an example of a high current DC to DC that would utilize FET's?

I have nothing against the schematic I posted, but I can not deal with the hassle of trying to cool hundreds of watts of power dissipation from the outboard transistors. And, with only 50% efficiency, I would need almost double the battery capacity to run the system.

 

Thanks for the links, but @ powerstream I would be looking at spending almost $1,000. My only option is to make my own. I work at an electronics supplier and we stock over 750,000 different parts obsolete and new, so my cost on parts would be essentially zero.

 

Sorry everyone I was not getting notifications on this thread. The NWH11 Prius is much different than the Gen II prius. I do not want to tap into the traction battery. I want to power the entire 12v system via an external power source i.e. batteries in either 24v or 36v configuration. Yes, the battery supplies 25amps at startuo and will show 2 amps once the car is started, but that 2 amps is not outgoing, it is 2 amps charging the battery. If you were to put your clamp meter on the converter output, you would see that the converter is supplying anywhere from 15 - 80 amps of 14v DC.

The problem with the Toyota system that I want to change, is the fact that currently the cars computers and accesories are powered via the traction battery. The Prius' DC/DC converter converts the 200v traction battery into 14v. During typical driving in the Gen II, the traction battery is providing a constant 600 watts. This is essentially half of the capacity of the traction battery being wasted every hour. My intention is to disconnect the converter, and power the 12v system using an external power supply which is the build in question here.

I hope this explains everything,