hi,
few questions...
1-what op-amp you would recommend for 3.3v output?
i have a few lt6200 that work at low voltage, are they good?
what should i look for except voltage rating?
2-does open-loop gain of opmap determine the output impedance?
3-can i put in any bjt as pass transistor if it can sustain the heat? i was looking to use bc550c for my dac....
4-Should i buy Volume 4 to get all of the answers to my questions, or does it only give a "sneak peek"?
regards,
-pierre
few questions...
1-what op-amp you would recommend for 3.3v output?
i have a few lt6200 that work at low voltage, are they good?
what should i look for except voltage rating?
2-does open-loop gain of opmap determine the output impedance?
3-can i put in any bjt as pass transistor if it can sustain the heat? i was looking to use bc550c for my dac....
4-Should i buy Volume 4 to get all of the answers to my questions, or does it only give a "sneak peek"?
regards,
-pierre
And if it's for the DAC digital supply, would the super reg version preceded with the 317 be better as, if I recall correctly, those graphs Jack posted on page 2, showed a lower Z at higher frequencies? And higher Z at lower frequencies?
http://www.diyaudio.com/forums/diyaudio-store/247281-super-regulator-2.html#post3753662
Instead of a 371 one of those 5 pin regs recommended for their dynamic response, I can't find the number just now?
http://www.diyaudio.com/forums/diyaudio-store/247281-super-regulator-2.html#post3753662
Instead of a 371 one of those 5 pin regs recommended for their dynamic response, I can't find the number just now?
Last edited:
hi, Ian
I'm not sure how exactly a prereg would worsen the low frequency Out Z...
anyway, if you want a very good prereg (or simply a very good reg that can go down to 5V or so), i can personnally recommend the sigma11 (amb.org).
Or maybe two superreg in a row?
I'm not sure how exactly a prereg would worsen the low frequency Out Z...
anyway, if you want a very good prereg (or simply a very good reg that can go down to 5V or so), i can personnally recommend the sigma11 (amb.org).
Or maybe two superreg in a row?
Last edited:
if the opamp has to operate from the 3.3V rail then it must be specified for operating at that low voltage. There are some that go down to around 2.5V
It must also be specified for rail rial output. Unfortunately that compromises some performance, but you don't have many options.
It must also be specified for rail rial output. Unfortunately that compromises some performance, but you don't have many options.
Fully agree Andrew.
There is another option and that is to go back to supplying the opamp from the unregulated DC before the pass device. That can be made (much) higher than 3.3V giving you some additional leeway as to opamp selection.
Jan
Don't forget to check the common mode input behavior of the opamp. Could lead to startup surprises.
is it a matter of just connect the op-amp supply to the collector of the pass BJT and that's it , or it is just theoritical?
dangerous to try if i only have a multimeter?
Yes, you can do that as long as the incoming raw voltage is far less than the max rating of the opamp. "Normal" opamps can take 30-36 V but read the datasheet of the opamp first.
Ok I have a test load set up to the power and the sense connected to the return and return sense on both the neg and positive supplies separately and it works fine I get the 23v I want. When I connect the grounds of the pos and neg boards it turns the light bulb tester on. I am also using a center tap transformer and when I connect the center tap to the ground on the input of the boards it also shorts out.
I have noticed in the pictures posted the +/- rails are on separate transformer windings is this a necessity?
someone correct me if i'm wrong...
-center tap transfo is good for a positive and negative regulator for + and -
-seperate secondaries is necessary for two positive regulators joint by the output to make +and -
-center tap transfo is good for a positive and negative regulator for + and -
-seperate secondaries is necessary for two positive regulators joint by the output to make +and -
Why would it be dangerous? If your opamp is specced for total 30V supply and the collector of the pass is at, say 24, what can go wrong?
Jan
Yes. But separate secondaries are also a nice way to do + and - regs because you can put them together at the output so you can avoid a common ground loop through the CT.
Jan
i thought it maybe it could result in instability.
Pardon my ignorance, i lack electronic experience.
that was what i thought!
i was attempting to help Autotech 🙂
by the, way, i was about to P to P build a 3.3v reg with lt6200 op-amp( or maybe lmp7731), supplied with output 3.3V, and i was wondering what i could use as vref...
i thought about an LED, or 3 times 1n4004 in series, which would get me close to symetry in relation to 3.3V.
The is also the option of supplying the op-amp from before the pass transistor, but it would limit Vce voltage quite a bit.
I guess at that level, there is not may choice and i should just experiment...?
anyway...i will proceed and report....
Last edited:
A green LED+317 gives a good 3.3V regulator.
Fine adjustment using the out to adj resistor value.
Fine adjustment using the out to adj resistor value.
You can also buy 1.2V and 2.5V reference diodes. I don't know how LEDs perform noise wise compared to dedicated ref diodes though. Anyone know that?
Jan
Unfortunately 1.25V from the 317 plus either 1.2V, or 2.5V, don't arrive at 3.3V
2.05V + 1.25V = 3.3V
It is certainly not a "super regulator", more a good enough for most purposes.
From memory of some tests posted here, I thnk the lower voltage LEDs are quieter than the poorer voltage references. But I believe there are some that have lower noise than others.
2.05V + 1.25V = 3.3V
It is certainly not a "super regulator", more a good enough for most purposes.
From memory of some tests posted here, I thnk the lower voltage LEDs are quieter than the poorer voltage references. But I believe there are some that have lower noise than others.
Last edited: