OPA637 - BUF634 power supply?

[AudioGeek]

I am thinking of building a circuit with a OPA637 connected to paralleled BUF634s.

I do not know if I should do regulated power supplies or just do a real simple non regulated power supply. Of course both op amps will have decoupled power supplies.

regulated or not?

Thanks!

[Bigun]

my vote: Not

[jcx]

engineering/technical answer: It Depends - on system operating conditions and performance requirements not stated

as one example of a possible consideration: the chips have limited Vmax allowed on the supply pins - by hiding the ripple with regulators between the chips and the raw supply you can run at higher op amp supply V since you don't have to allow extra margin for ripple, xfmr load regulation, line variability

[AudioGeek]

well as a reply it will be a small op amp based power amplifier. OPA637 as input op amp. coupled to paralleled output stage buffer.

Have been looking at +- 18vdc as a power supply voltage.

so for output buffer stage 3A or so is probably max current. And 12 BUF634 in parallel.

I see that the BUF634 at 200-300mA has a 4-5v drop for max output... will that really be a problem or will that just limit max output voltage?

Are there better output stage buffers i can use?

I really want to stick to op amps.

Are there any other issues that could come up?

thanks!

[AndrewT]

a 2pair output stage will be simpler and easier to wire up than 12 paralleled buffers.
You might be able to get a circuit that uses just 1pair of discrete devices as a buffer.

[satoru]

The absolute maximum power supply for OPA637 is +/-18V. If you plan to apply that much voltage to the little opamp, then it is safer to regulate it.

If you really have to stick to opamp for output, then look into power opamps, for example PA10 from Apex (oh, it's now part of Cirrus Logic, seems like).

As others suggested, wiring up 4 transistors (plus a transistor or two for temperature compensation) would be easier than mounting 12 BUF634 on heat sinks and wiring them.

So, my suggestion is to put a simple Darlington emitter follower (2 stage would be OK but 3 stage would result in lower THD and less stress to OPA637, of course), give it un-regulated power lane (>+/-20V), and design a simple series/shunt regulator (+/-18V) for OPA637. This will maximize the output voltage swing. You need a decent heat sink for 3A output, though. This is essentially what Andrew suggested.

Have fun!
Satoru