boost-buck 12v regulation for a PW-70a

greenwire · 02-11-2004, 05:34 AM

Hey there.. i've got a few questions about switching regulators for all you power nuts out there.

i'm using one of those retarded power supplies that doesn't regulate the 12v line and i'd like my carputer to be able to a) survive a crank and b) run off the alternator

what i'm looking for is a high-current (5.8a or more) boost-buck 12v regulator that has an input voltage range wide enough to accomodate the cranking drop and the alternator voltage, something like 6v-15v.. it only needs to be able to boost while cranking, the rest of the time it's going to be bucking from the alternator or just leaving the battery power alone. if anyone knows what i could do here i'd love to hear about it

none · 02-11-2004, 11:04 AM

My suggestion would be several TI PT5071's. These are only 1.5 amps, so you will need three or four, but it will still probably be the best solution. Search around here, several people are using these chips.

greenwire · 02-11-2004, 03:52 PM

okay, those look nice for regulating 1.5a but is it possible to link them together to increase the power output? i was thinking something more along the lines of a chip to drive a pair of mosfets like the max1858 (from maxim).. the problem with that chip is that it's only a buck controller so it won't let me survive cranking, but the power handling is right on the money.

none · 02-11-2004, 04:12 PM

Quote: Originally Posted by greenwire

okay, those look nice for regulating 1.5a but is it possible to link them together to increase the power output?

Yes.

binary.h4x · 02-11-2004, 04:12 PM

if you run the chips parallel to eachother you can use a larger current

greenwire · 02-12-2004, 04:29 PM

right on.. does anyone have any schematics for that or is it just a simple matter of hooking the outputs of a couple chips together in paralell?

greenwire · 02-21-2004, 04:11 PM

eh, just wanted to refresh my question about the schematics.. i'm just wondering about the filter caps on the input and output and whether or not it's possible to run all 4 chips with only 2 capacitors or if the paralell arrangement needs all 8 caps to ground.. also, what should pin 2 (UVadj) be connected to? i can't find that anywhere in the datasheet... one last question.. what about pin 3 (stby)? what's that mosfet doing there and do i need it?

(here's a link to the datasheet http://focus.ti.com/lit/ds/symlink/pt5071.pdf )

EBJUSTIN · 02-21-2004, 08:09 PM

Quote: Originally Posted by greenwire

eh, just wanted to refresh my question about the schematics.. i'm just wondering about the filter caps on the input and output and whether or not it's possible to run all 4 chips with only 2 capacitors or if the paralell arrangement needs all 8 caps to ground.. also, what should pin 2 (UVadj) be connected to? i can't find that anywhere in the datasheet... one last question.. what about pin 3 (stby)? what's that mosfet doing there and do i need it?

(here's a link to the datasheet http://focus.ti.com/lit/ds/symlink/pt5071.pdf )

I am using 4 PT5071's in parallel to supply my PW60. You'll need to isolate the outputs via schottkey diodes...it works very reliably.

EBJUSTIN · 02-21-2004, 10:20 PM

Quote: Originally Posted by EBJUSTIN

I am using 4 PT5071's in parallel to supply my PW60. You'll need to isolate the outputs via schottkey diodes...it works very reliably.

Here is a quick and dirty schematic. You can leave pins 1,2,3 & 14 unconnected.

PASware · 02-22-2004, 08:55 AM

schema for 3x pt5071 (want a 4th: not difficult, just add one, simple schema)

the diodes you need: 1n5401
I used 100uf 63v capicitors

This is mine:

EBJUSTIN · 02-22-2004, 02:05 PM

Quote: Originally Posted by EBJUSTIN

Here is a quick and dirty schematic. You can leave pins 1,2,3 & 14 unconnected.

Sorry, my schematic pic didn't load properly. Here is a pic of my supply...I am only using diodes on the outputs and 100uF caps on the input and output. Some of the diodes and caps are on the bottom side of the PCB

http://www.mp3car.com/vbulletin/show...bjustin+pt5071

greenwire · 02-22-2004, 07:29 PM

okay guys, i wasn't sure about the filter caps being necessary between all the chips so i drew up a quick schematic that i think might work.. i'll be using schottkey diodes to isolate the units from each other and a filter cap on the input and output.

aparantly the ESR of the caps must be less than 250microohms at 100kHz and they have to be able to handle at least 300mA (rms) of ripple.. do you guys know if this changes when more chips are added or should i just try and find a 100uF cap with the lowest ESR and highest ripple curent rating?

(in the schematic the bottom rail is ground, pin 2 on both connectors)