Convert 0-30V 3A PSU to 5A or more

[audioguru2]

Thanks, Ante,
That looks wonderful.
I like your nice big filter cap, and especially the name on your schematic!

 

[ante1]

You are welcome! ;D The name, well it

 

[Kain]

I've been following this thread for quite a while since I built the original PSU 0-30V / 0-3A and still don't have any major problems. The reason I don't have problems though is due to the fact I never use it on its extremas. Now, I plan on modding it up to 5A with all the changes you guys suggested here. The most expensive parts however seem to be the OPA445AP. I didn't find them online any cheaper than 8$/piece. However, I found they are made by Texas Instruments. Therefore, if anybody is interested in building the modified version, just go and order samples from www.ti.com - you will save about $24. You can order up to 5 chips from each type with the limit of 8 different types. Oh, and you can order more than once ;D. I just did and wanted to share with you guys. The people from http://www.electronics-lab.com/forum/index.php?board=21;action=display;threadid=21 know exactly what I am talking about, right guys ? ;D

 

[ante1]

Kain,

An excellent suggestion. That

 

[Kain]

Thanks Ante. I was thinking to buy the chips but when I saw the price my mind was more like "HELL NO!!" However, when I saw the chip manufactor my mind changed to "wait a second.... " ;D I'm thinking to redo the PCB on Protel taking the rectifier and Q2 off the board. I am also planning to do some vertical resistor mounting since it saves space. However, this will happen after I get all my parts 8). By the way, does Q1 need a radiator as well or it can go without having one?

 

[audioguru2]

Hi Kain,
Do you also know of a power transformer manufacturer who gives away samples? ;D ;D
Q1 does not need a heatsink. It conducts only for a few seconds when you turn-off this project, to pull its output voltage immediately to 0V.

 

[MP1]

onsemi sends out samples through their online request form.

MP

 

[asciiwhite]

Can anyone source me a good place to get a
30VAC, 7.5A, 225VA transformer ?





Peace.
Dylan D.

 

[inferno]

ei! about the schematic ante posted, the Q1's emitter must be connected to 0V... ok?........

 

[audioguru2]

Hi Asciiwhite,
Newarkinone, or worldwide Farnell, has a nice Hammond 182H15 toroid with that rating. It has a 117/234V dual primary and 15/30V dual secondary. They also may have others.

Hi Inferno,
You are correct.

 

[asciiwhite]

Thanks heaps audioguru.
=---I found the Hammond 182H15 toroid on Newarkinone
but i couldnt find it on farnell online anyone got a direct link ?

 

[audioguru2]

Hi Asciiwhite,
Ask Hammond for a sample, but you offer to pay to ship the heavy thing. They are in Guelph, Ontario, Canada.
Once they gave me an expensive telco hybrid transformer.

 

[Kain]

Ok, I know this is not one of my smartest questions, but where the heck is the ground - 0V of this PSU? ;D

 

[ante1]

Kain,

If you refer to the schematic I made I have marked it

 

[Kain]

Yes, this is exactly what I ment. For a second I though that something is wrong with me too. I mean, I saw that somebody said that the emmiter of Q1 should be connected to ground and since it is already shown correctly on the schematic that you posted I wondered what the heck is wrong... ;D

 

[Kain]

I was just making some libraries for the PCB of this project when I saw the "small" power rating of R7 - "only" 15W. Now, I was checking on different manufactors about this type of resistors since they are not something that I can get here in some local store. This is what I saw in mouser electronics:

http://www.mouser.com/index.cfm?&handler=data.listcategory&terms=71-RH25-0.27&Ntt=*71RH250.27*&Ns=MfgrPartNumber%7c%7cSField&N=100+61300000&crc=true

I know this is 25W instead of 15W, but this seems to be one of the resistors that has R = 0.27. The thing I do not like about it is that it's low tolerance resistor which adds up to the price even more as you can see. What I like about it is that it is basically built into a heatsink ;D. I am just looking for appropriate resistor so I can finish the library and PCB. I was thinking also of more than one resistors in parallel, but I don't think this will save neither space or money. Any suggestions?

 

[ante1]

Kain,

If you want to save space try the Cool-Pak type resistor, just bolt it to the chassis.

View attachment 35945

 

[Kain]

It looks nice. Any idea where I can get it from and on what price? By the way is this 10W or 15W on the picture?

 

[ante1]

Well, I don

 

[Hilo90mhz]

Hello everyone

Im in the process of building this PS.. Using the updated SMARTER kit schematic posted in this thread... I know there has been tons of talk about using higher voltage OP amps and issues with under rated transformers.. Ive read both threads about 1.5 times... - alot of info to digest

Im building this with parts on hand.. which happen to be very close to those specified in the schematic. My OPamps are 44v OP177 types...
now believe me I know they should be rated for more, but im stubborn and want to try with these for now.. if they start smoking ill try something else

Now because im trying to get about 5A... basically the most I can (the actual output will be measured later). I know this entitles using a higher voltage rated transformer, because of all the drops incurred along the way.. I also know that lower VA transformers have bad voltage regulation.. and would float at a much higher voltage when not loaded.

So Im rewinding a microwave oven transformer.. Rated at about 600 - 800 W im guessing (still have to get out the scale to weigh all that iron). Ive removed the secondary and the primary looks real nice. Im going to determine the V/T ratio tomorrow with the original primary.

My first question is:
What do you think a good unloaded secondary voltage would be?
I think 26V AC is the max I can go and stilll keep below the 44v DC OP amp limit, because 26v * 1.5(because of AC RMS to near peak conversion)= 39v +5v(for - supply) = 44v ( ignore the extra .6v or else its over= I like to live dangerously ; )

Will 26v AC unloaded be enough to deliver 30v DC loaded on the output? Keep in mind the transformer core is rated for about 600W

I will be able to change the secondary turns/voltage without too much trouble later on... I just want a good starting point.


Thanks, Chester Lowrey

http://www.hot-streamer.com/hilo90mhz/