5V to 5V regulators

feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

A sepic switcher would do it. Or boost up to 6 volts or so and then use a linear LDO.

feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

What does "...not very well regulated" mean? Does it mean poor stability of output voltage value; or does it mean that ripple and noise is getting thru the regulator?

And what is the headroom for the existing 5V regulator? Maybe just replace it with a modern unit? ...Jim Thompson

ike to feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order f or the LDO to do its thing.... does anyone know a good way to do this?

If he can afford a diode drop, then a capacitor multiplier will clean up the noise. (Assuming not too much current draw.)

Yup cascading regulators seems a bit silly.

George H.

I kinda gathered that the one he has may dip below 5V -- but, I'm not looking at his meter.

It's not uncommon to use a switcher into an LDO to get a really clean supply.

But cascading regulators when you could just rip one out and replace wouldn't make much sense.

OK, that makes sense.

Though I'm not sure I'd call the output from some LDO's 'really clean'.

I made this 'low noise' power supply that's an LDO regulator followed by a cap multiplier. (Sorta ~2-3nV/rtHz at moderate currents (100mA) (Noise almost all from the LDO.) I later needed a higher current (low noise) power supply for the same project (~0.4A). So I used a voltage reference into an opamp->transistor pass element-

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feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

ke to feed into a LDO regulator to clean it up a bit.... but I'm not sure h ow I can do this since I would have to be consistently above 5V in order fo r the LDO to do its thing.... does anyone know a good way to do this?

I can't touch the first regulator, it's regulation can be off by 8%, I can only add something to it's output, the cap option sounds interesting I'm go ing to look into that

thanks!

to feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

add something to it's output, the cap option sounds interesting I'm going to look into that

Schematic showing input voltage characteristics? ...Jim Thompson

Regulate raw voltage into about the same clean voltage is pretty common problem. Neat solution to that is one inductor convertor with switches on both sides of the inductor. So it could work in buck or boost mode depending on the input/output voltage relation. The only IC of this kind that I know is LTC3789; expensive and requires many extra components. I wonder why this good idea is not used very widely.

Vladimir Vassilevsky DSP and Mixed Signal Consultant

ke to feed into a LDO regulator to clean it up a bit.... but I'm not sure h ow I can do this since I would have to be consistently above 5V in order fo r the LDO to do its thing.... does anyone know a good way to do this?

If I'm able to get my first regulator up to 5.5V is that good enough for an LDO to clean it up to 5V or am I too close to 5V? My load is pretty light ... 13mA or so... I've found some LDOs that have a dropout voltage of less than 100mV

I'm thinking this part lp2950

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maybe one of the numerous boost converters meant for LiPo batteries something like a tps62100, add a diode or two to keep the Vin under the needed Vout

-Lasse

like to feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

n only add something to it's output, the cap option sounds interesting I'm going to look into that

panfilero, Is your problem that the 5V is not constant, it droops under load? Or is it the noise on the 5V line? The cap multiplier will do nothing for the droop.. in fact it might make it worse. (Higher output impedance.)

George H.

Easiest might be John's 2nd suggestion. A simple boost conversion that adds 20% or so to the voltage, then a linear regulator to make a clean

You mights as well suggest he improve the stabilzation control algorithm of SpaceX.

SpaceX.

C'mon, this ain't no rocket science :-)

to feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

LDO to clean it up to 5V or am I too close to 5V? My load is pretty light...

Not long ago you said you couldn't touch the first regulator. Where is this 5.5V coming from? What is it's tolerance?

I Haven't looked but I'm sure you can find regulators that are specified to work with less than 0.5V headroom.

If you're looking for a solution where the input voltage can go either side of 5V, then I can only suggest you look at SEPIC converters.

to feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

to clean it up to 5V or am I too close to 5V? My load is pretty light... 13mA or so... I've found some LDOs that have a dropout voltage of less than 100mV

to feed into a LDO regulator to clean it up a bit.... but I'm not sure how I can do this since I would have to be consistently above 5V in order for the LDO to do its thing.... does anyone know a good way to do this?

LDO to clean it up to 5V or am I too close to 5V? My load is pretty light...

The problem I can see in the spec of the LP2950 is that the datasheet gives a dropout voltage of 150mV at 100uA and 600mV at 100mA. The OP's last post suggest he may have 500mV headroom and a load of 13mA, the datasheet doesn't guarantee this performance. It depends if this a one-off product or large-scale production. If the latter I would avoid the LP2950.

I'm not following what you are describing. Can you explain in a little more detail? I guess I'm not getting how you use a cap multiplier... oh! I guess you are saying a cap multiplier rather than a cap *voltage* multiplier! Is it that difficult to just use a large cap rather than a cap multiplier? Or do I completely not understand what you are saying?

Rick