Problem with Maida regulator

[commstech]

I built a maida regulator for my tube preamp. Fired it up, and to my relief no smoking parts. Adjusted the voltage to 150Vdc. Vin before regulation is 350Vdc. ok, was happy that it worked. However, i realised when i decreased input voltage to 280Vdc, the regulated output dropped to 130Vdc!! schematic is in this link:

http://giaime.altervista.org/Maida_schem.GIF

i understand that the Vout is based on the following:

Vout = (1.25/R5) * (R5 + R6)

and hence independent on the Vin.

I tested it without connecting to the preamp.

Can someone possibly advise on the cause? i don't think my regulator is functioning correctly?

[HollowState]

For some reason the link doesn't work. It starts to go there, then switches to the home page.

[Mooly]

http://giaime.altervista.org/maida.html

You need to post some measurements. Always worth sticking a 'scope across anything like this just to make sure it's behaving itself.

[Giaime]

Hello commstech,

didn't you think to contact me, since I'm the author of the webpage?

What kind of mosfet did you use? Did you use proper insulated heat sinking for it?

Try to load the output a little bit, maybe 5-10mA or so, and see if it still looses its regulation.

[jackinnj]

Are you using 1uF for C2? C2 might not be getting a full charge under certain conditions so is acting like a "slow start". In the original article 1uF is used. Try disconnecting it and report back...

[commstech]

Originally posted by Giaime
Hello commstech,

didn't you think to contact me, since I'm the author of the webpage?

What kind of mosfet did you use? Did you use proper insulated heat sinking for it?

Try to load the output a little bit, maybe 5-10mA or so, and see if it still looses its regulation.

Hi Giaime, by posting here, i would think u would see it anyway and respond to me...

i used irf840 for the mosfet, and i am pretty sure it is properly insulated as i have specifically ensure that it is. all parts are used as suggested in your schematic.

will try to load it once the preamp cct is ready.

[commstech]

Originally posted by jackinnj
Are you using 1uF for C2? C2 might not be getting a full charge under certain conditions so is acting like a "slow start". In the original article 1uF is used. Try disconnecting it and report back...

hi jackinnj,

yes, i used 1uf for C2. all values of components are used as per schematics. ok, i will disconnect C2 and revert on the result.

[ErikdeBest]

I experienced the same problem with a (based on Morgan Jones) Maida I built some time ago: it would not handle large differences between in- an output, even at lowish currents. I don't even remember where I put it, but I will keep a look on this thread to see how I should tackle the next one!

Giaime, haven't seen you here in a long time!

Erik

[hemgjord]

Scope everything!
I had one per Morgan Jones design that constantly oscillated at a few MHz, barely visible on my old 20MHz scope.
It did not work as supposed
I never really found out what the cause was (probably a birds nest style beadboard).

/Olof

[Giaime]

Originally posted by ErikdeBest
Giaime, haven't seen you here in a long time!
Erik

/OT on

Hello Erik, nice to see you

I spent a lot of time away from diy hobbies to study, and finally I graduated this summer.

Btw I like your signature, I live in a very good cabernet zone

/OT off