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?
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?
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.
You need to post some measurements. Always worth sticking a 'scope across anything like this just to make sure it's behaving itself.
Giaime said: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.
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
Giaime, haven't seen you here in a long time!
Erik
Pity about that; Italy has so many great grapes that it does better than anyone, why grow something French? Whenever I taste an Italian cabernet, I think, "What a waste, this could have been Sangiovese (or Nebbiolo or Dolcetto or...) instead of another me-too wine."
In any case, I'm almost certain that this is an oscillation problem. Make C3 larger (30-50uF), and if that doesn't cure it, remove C1.
In any case, I'm almost certain that this is an oscillation problem. Make C3 larger (30-50uF), and if that doesn't cure it, remove C1.
and i have lost some sleep because of this.... perhaps i should forget about this and do with a simple CLC, be happy with it...
I've used dozens of Maida-style regs, generally with no (or very straightforward) issues. The performance is good enough that I'd advise not giving up yet. Make sure that the MOSFET and regulator are still intact. With power off and everything discharged, check for gate-to-source, gate-to-drain, and drain-to-source shorts, and check that the regulator chip isn't shorted input to output. When problems occur, solid state devices often transmute silicon to carbon.
Assuming no shorts, with power on, CAREFULLY measure the voltage from output to adjust pin and verify that it's 1.25V.
And the parts are cheap enough that I'd probably replace the MOSFET and 317 anyway.
Assuming no shorts, with power on, CAREFULLY measure the voltage from output to adjust pin and verify that it's 1.25V.
And the parts are cheap enough that I'd probably replace the MOSFET and 317 anyway.
One more thing- in Giame's design, the output-to-adjust resistor is 1k which is pretty high. That's probably to limit dissipation of the 180k set resistor. Unfortunately, the regulator will be unhappy if you're not drawing at least 5 and more likely 10mA. So be sure that you have a dummy load on the output that will pull at least 10mA.
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