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Old 13th June 2004, 01:04 AM   #1
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Default OPA548 Supply?

Today I learned about the OPA548 & OPA549 and then I remembered Kevin Gilmore's power supply in his Class A headphone amp design on Headwize (here). This is a great chip: great regulation for not too much money and simple to implement too, no need to go using lots of transistors and the likes to get super precise preregulation.

Now, Gilmore's design can deliver up to 1.5A, because of the LM317s. I'm going to design a similar circuit for my preamp (which won't be made anytime soon I'm afraid ), but I want the power supply to be able to deliver at least 2A (I want to have the option of using wide bandwidth mode on all the BUF634's that going to be in the circuit). I guess the best option is just to parallel 2 LM317's right? Or should I do it another way?

Second question. Gilmore's using a REF02, I'm going to use a REF3130, but anyway that' not the problem. As you can see, Gilmore connects the inverting input of the opamp delivering the negative voltage to the output of the opamp that delivers the positive voltage. But you could also connect it to the output of the reference voltage. What's best? Gilmore's way of doing it or connecting the inverting input of the 2nd opamp to the reference voltage?

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Old 13th June 2004, 01:21 PM   #2
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No one knows?
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Old 13th June 2004, 02:14 PM   #3
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the problem with using only one reference -- at least as you have configured it -- is that the "-" supply is going to track the fluctuations of the "+" supply with a lag -- this could cause some problems.

the OPA548 is a very nice high power op-amp, who wouldexpect less from Burr-Brown? however, its noise is specified at 90nV (Hz^1/2) -- one of the regulator designs using the LM329DZ reference, AD825 error amp and the D44 and D45 transistors. check the super-regulator threads. The OPA548 lists for $10 in the US, and the sum of the active parts in the super-reg is less $.

ditto the LM317, LM337's, first off unless you are using the HV versions you will blow the regulators as the max input is 40V, they have to be derated for the input-output differential, they they are noisy.
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Old 13th June 2004, 02:27 PM   #4
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Well, what you see there isn't my design, it's Kevin Gilmore's. I'm only going to need a max. of +15v & -15v, so there won't be a problem with the LM317s.

So, you're saying it's better to connect the output of the reference directly to the non-inverting input of the 1st & the inverting input of the 2nd opamp, right?

Oh, this is going to be used to power opamps etc, no discrete stuff. Is it still necesarry to have a super-precise regulator then? I'll check the super-regulator thread.

Another thing, which hasn't got to do much with this, but I'll ask it anyway. Why would someone use a LM337? You might as well use an LM317 and use the output as ground and the ground as -V, right?
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Old 13th June 2004, 02:41 PM   #5
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Quote:
Originally posted by Devil_H@ck
Another thing, which hasn't got to do much with this, but I'll ask it anyway. Why would someone use a LM337? You might as well use an LM317 and use the output as ground and the ground as -V, right?
If you're using a centre-tapped transformer that won't work; the ground needs to be common between the two. With two independent secondaries, however, what you describe would work (but that's not how the Gilmore circuit is wired).
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Old 13th June 2004, 02:47 PM   #6
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I just searched for the Super-regulator thread, but there's like 100 of them . What's the one jackinnj is refering too?
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