I've got an analogue circuit with a gain of a few thousand. I note thatthe 78M05 and 79M05 regulators providing the +/-5V rails have a coupleof mV ripple at a few kHz (the input signal being amplified, causingincreased drain in IC's down the line) and I'm concerned it will coupleinto other, more sensitive parts of the circuit. I've tried LM317 /LM337 regs but they don't seem any better, despite a 10uF decoupler ontheir ref pins, perhaps because their ripple rejection is intended formains frequencies rather than kHz. I've noticed that there are someexpensive regulators touted as "fast transient response" around, dopeople find these significantly reduce supply ripple, i.e. couplingbetween IC's in analogue circuits?

Regulators have an inductive output characteristic, which wants to resonate with the output capacitor. That can cause some nasty noise peaks in the 5-100 kHz range, depending on the size of the output capacitor and the amount of current being drawn.A low-ohm resistor in series with the output will de-Q the resonance, and can sometimes help a lot.For sensitive circuitry you're often much better off using a capacitance multiplier. Op amps have practically infinite CMR at low frequencies, where the cap multiplier's vague idea of an output voltage occurs, but are really horrible up in the tens to hundreds of kHz, where a good cap multiplier is like a brick wall.CheersPhil Hobbs-- Dr Philip C D HobbsPrincipalElectroOptical Innovations55 Orchard RdBriarcliff Manor NY 10510845-480-2058email: hobbs (atsign) electrooptical (period) net

Are fast transient response regulators worth using?

Feb 02, 2011 43 Replies

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Rich Grise 15 years ago

He's just starved for attention, and crowing about how somebody is stalking him gives him a feeling of self-importance. I got tired of his sniveling, so have filtered him.

Cheers! Rich

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John Larkin 15 years ago

Seems easier to plonk both of them. Or all six of them. Whatever.

John

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Jamie 15 years ago

Paranoia.. It makes the world go around!

Jamie

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John Larkin 15 years ago

Which means, obviously, that it's not working.

John

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