LM3886 (or similar) as voltage regulator - diyAudio
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Old 12th January 2005, 04:41 AM   #1
mirlo is offline mirlo  United States
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Default LM3886 (or similar) as voltage regulator

What would be the downside of using a LM3886 or other chip amp as a voltage regulator, say for preamp power or low power amplifier power?

With a good low noise reference and appropriate feedback, it might have some interesting properties, since the class-AB output would allow it to respond to some interesting loads pretty well.

The PSRR looks pretty good ...

-- mirlo
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Old 12th January 2005, 05:07 AM   #2
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It may work but remember that the gain must be more than 10!
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Old 12th January 2005, 07:09 AM   #3
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It can't drive large capacitors or reactive loads. Without large bypass capacitors, it makes a poor power supply.
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Old 13th January 2005, 02:34 AM   #4
mirlo is offline mirlo  United States
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Default nature of load presented by amplifier to power supply

General ideas I have about regulated power supply design for amplifiers:

A class A amplifier or preamplifier, will present a high impedance load to its power supply, much like a current source.

By making any capacitors on the regulated output very large, it should be possible to reduce the frequency of the output pole to the point where it becomes dominant. If this does not work, it might be possible to still use fairly large output capacitors but include extra "artificial" ESR by adding series resistance, to help keep the phase of the closed loop controlled.

I guess I'll have to try it and see ...

Are there other chip amps that have better stability characteristics than the LM3886?

We have used an OPA548 in a circuit to measure PSRR of some voltage regulators, but this was often a stability problem, and I have seen other reports of similar stability issues with OPA548 on head-fi.

-- mirlo
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Old 13th January 2005, 03:25 AM   #5
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first, the GBW of the LM3886 is quite low compared to an AD825 or AD797 and a bjt transistor (Peranders, error amps are run at very high gain at low frequencies), secondly, the LM3886 is not low noise, and third it is rather expensive compared to a discrete regulator and a associated components. Not a good idea.
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