Variable power supply

[lilshawn]

I'm looking to buy/design/build/modify an existing device. anything really.

I have a brushless motor (6-12v DC 2.5 amps) i wish to vary the speed on and it must be done via voltage change. (no PWM, motor does not like it at all..and neither does the switcher FET.)

I would like to get a power supply to drive it that will vary from 6 volts DC to 12 volts DC at ~3 amps using a pot.

IE: all the way down outputs 6 volts DC, all the way up outputs 12 volts DC. Dropping under 6 volts DC results in the motor stopping all together which is bad. so it must stay above 6v.

i'm thinking an adjustable voltage regulator power supply of some description.

I have, at my disposal, various power supplies and i'll likely use a 24 volt supply so the voltage offset from whatever regulator and circuit won't be an issue.

iv'e been digging through ebay looking at power supplies and kits and whatnot, and havent found anything that i think would work.

Maybe i'm just looking at this the wrong way.

any thoughts?

[ed12]

lm317 in bosst strap mode

ed

[lilshawn]

I assume you mean in "boost strap"

as in using multiple lm317's? or is there a particular lm317 quirk at work to boost the output capability?

i could probably build one using a TO-3 lm317 (if i can find it) with a huge heatsink.

please, explain like i'm 5 

[ed12]

the output of the boost strap
is tied to the base of a high gain darlington t03 pkg
so in essence u adjust the 317 to the voltage and the t03 handle's the current
as a pass/amp unit
just set the upper/lower limt's for the pass through resisters.
on the 317 u have the voltage out as fixed via a resister pair
where 1 can be replaced with a pot >small resister 1-5k<
thus u can vari the output..which drive's the base of the darlington output
which is acting as a high gain pass transistor to handle the load >1-4amp<

ed

[lilshawn]

ahhhhh i see. okay. That make sense.

i'll see if i can find a schematic of that and i'll do up a simulation in livewire and see what i can come up with.

[ed12]

national
which did make the 317 has a neat little hand book on the exct thing.
in google or firefox u may need to refernce to lm317..and find what they call
the pass boot strap power supply..
if u cannot find it ?,ring my bell..
it should be listed under :linear:

ed

[Ken Layton]

How about something ready-made?

http://www.mcmelectronics.com/product/72-9630

[ed12]

i am not going to speak for shawn
but at a 100.00,i would build my own..
1 reason is i like to do it
the other reason is refer to #1
but u are right..congrad's on that 1

i went and found my linear hand book's tonight
for chit's and giggle's
could not believe i remered the it boost strap..built 1 40 year's ago
for dsc scale's in brantford ont..
when i first realy got into linear

ed

[lilshawn]

the ready made one would be nice for my bench, and it's not a bad price either... but i'm planning on integrating this supply into a computer case.

i'd also like to make it foolproof in the instance that I mentioned in an earlier post about the motor shutting off if the voltage drops below ~6 volts. so i'd be having the supply designed output 6 volts while the adjustment pot is turned all the way down and output 12 volts when turned all the way up. it'll take some creative resistor choices to accomplish this. thank goodness for circuit simulators...I won't have to try 10,000 resistor combinations to get it right.

[Ken Layton]

Vellaman makes some nice kits like this one:

http://www.vellemanusa.com/products/view/?id=350599

[lilshawn]

Vellaman makes some nice kits like this one:

http://www.vellemanusa.com/products/view/?id=350599

that look like it would actually work with a little modding.\

thanks, i'll have look into that one and see whats up..